WO2008004684A1 - Stainless steel with low chromium content excellent in the corrosion resistance of repeatedly heat-affected zones and process for production thereof - Google Patents

Stainless steel with low chromium content excellent in the corrosion resistance of repeatedly heat-affected zones and process for production thereof Download PDF

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Publication number
WO2008004684A1
WO2008004684A1 PCT/JP2007/063622 JP2007063622W WO2008004684A1 WO 2008004684 A1 WO2008004684 A1 WO 2008004684A1 JP 2007063622 W JP2007063622 W JP 2007063622W WO 2008004684 A1 WO2008004684 A1 WO 2008004684A1
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Prior art keywords
corrosion resistance
stainless steel
weld
heat
affected zone
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PCT/JP2007/063622
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French (fr)
Japanese (ja)
Inventor
Masuhiro Fukaya
Akihiko Takahashi
Shinichi Teraoka
Shunji Sakamoto
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Nippon Steel & Sumikin Stainless Steel Corporation
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Priority claimed from JP2007168307A external-priority patent/JP5225620B2/en
Application filed by Nippon Steel & Sumikin Stainless Steel Corporation filed Critical Nippon Steel & Sumikin Stainless Steel Corporation
Priority to BRPI0706042-4A priority Critical patent/BRPI0706042B1/en
Priority to US12/084,182 priority patent/US7883663B2/en
Priority to AU2007270326A priority patent/AU2007270326B2/en
Publication of WO2008004684A1 publication Critical patent/WO2008004684A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Definitions

  • the present invention improves the intergranular corrosion resistance in the heat-affected zone in the vicinity of the weld when multiple welding is performed (multi-pass), and further avoids preferential corrosion that occurs in the vicinity of the fusion line in the weld. It relates to a low chromium-containing stainless steel with excellent corrosion resistance of welds that can be used for a long period of time in applications where the corrosive environment is severe as structural steel. Background art
  • Chromium-containing stainless steel with low chromium content and low nickel content is extremely advantageous in terms of price compared to austenitic stainless steel such as SUS304 steel. It is suitable for applications that are used in large quantities.
  • Such a chromium-containing steel has a ferrite structure or a martensite structure according to its composition.
  • fillite or martensite stainless steels are inferior in the low temperature toughness or corrosion resistance of welds.
  • the C content is as high as about 0.1 nias s%, so the weld toughness is poor and the weldability is inferior. Therefore, the welding workability is also inferior, so that problems remain in the application to parts that require welding.
  • JP-B-51-13463 proposes Cr: 10-18%, Ni: 0.1-3.4%, Si: 1.0% or less, and Mn: 4.0% This is a method of generating a mashite martensite structure in the heat affected zone of the weld with a steel component reduced to C: 0.030% or less and N: 0.020% or less.
  • Japanese Patent Laid-Open No. 2002-32725 1 discloses intergranular corrosion resistance of welds of chromium-containing steel using martensite transformation by adding appropriate amounts of carbon and nitrogen stabilizing elements Nb and Ti.
  • chromium-containing steels that are excellent in low temperature toughness are disclosed.
  • Japanese Patent No. 2002-32725 1 discloses intergranular corrosion resistance of welds of chromium-containing steel using martensite transformation by adding appropriate amounts of carbon and nitrogen stabilizing elements Nb and Ti.
  • chromium-containing steels that are excellent in low temperature toughness are disclosed.
  • 349 1625 discloses a Fe—Cr alloy that has improved the corrosion resistance of welds by adding carbonitride-forming elements Ti, Nb, Ta, and Zr. .
  • this patent contains Co, V and W. It is essential to improve the initial rust resistance.
  • the intergranular corrosion resistance of the weld heat-affected zone is improved, but the part along the interface between the weld zone and the mash martensite structure, which is the heat-affected zone closest to it (fusion fusion zone)
  • the present inventor has newly found that there is a problem that preferential corrosion occurs in the vicinity.
  • This phenomenon is called a knife line attack found in welds of SUS321 and SUS347 stable austenitic stainless steels as disclosed in Journal of the Japan Welding Society, Vol. 44, 1975, No. 8, page 679.
  • This phenomenon is similar to the phenomenon, and the interface (fusion line) between the weld and heat-affected zone preferentially progresses in corrosion and the corrosion area expands, so this is an issue to be improved.
  • the cause of knife line attack is that when C is fixed with 1 ⁇ (nya ⁇ (: and stainless steel is welded, Ti C and NbC are dissolved in the region where the thermal history is raised to about 1200 or more.
  • Cr carbide precipitates at the grain boundaries and the corrosion resistance decreases, but in the case of low chromium-containing stainless steel, what are the causes? Whether or not preferential corrosion occurs in Japan has not been fully examined and no measures have been taken.
  • the low-chromium stainless steel added with the C and N fixing elements described above is a component system with improved intergranular corrosion resistance in the weld zone, but the corrosion resistance of the heat-affected zone after multiple welds. However, it has been reported that corrosion may occur in the heat affected zone.
  • Welding structure From the viewpoint of expanding the degree of freedom in construction design and improving the level of weld repair, a low-chromium stainless steel capable of multi-pass welding with excellent corrosion resistance in the heat-affected zone even after multiple welding has been awaited.
  • edge cracks during hot rolling are likely to occur in the production of low chromium-containing stainless steel. This is thought to be due to the fact that the phase stability of the austenite and Del Yuferai cocoon in the hot working temperature range is directly affected by the balance change of the contained elements. Therefore, there are issues to be solved from the viewpoint of optimizing the manufacturing process, and improvements were desired.
  • the present invention prevents deterioration of corrosion resistance at the welded part when multi-pass low-chromium stainless steel using martensite transformation is used, and it is difficult to use railway wagons of coal and iron ore. Even in a corrosive environment, the multi-pass welds have excellent intergranular corrosion resistance, and at the same time, there is no preferential corrosion that occurs near the weld fusion line.
  • the first issue is to provide stainless steel. If necessary, the second is to provide high-strength, low-chromium stainless steel with an excellent balance of strength and ductility. Let it be an issue.
  • r P (%) 420x C% + 470 xN% + 23xNi% + 9 xCu
  • the metal structure can be appropriately tempered into a two-phase structure of Ferai and martensite. It was found that high-strength chromium-containing stainless steel with an excellent balance of strength and ductility can be produced. In particular, it is effective and practical in the case of a component that appropriately contains Nb and Ni and has increased temper softening resistance. Practically, for example, the heat treatment temperature is 600 to 800, the holding time is 2 to 30 hours, and an appropriate temperature is set. Thus, a desired metal structure can be obtained.
  • the present invention has been completed based on such findings, and the gist thereof is as follows.
  • r P (%) 420 x C% + 470 XN% + 23xNi% + 9 XCu%
  • Multipass as described in (1) or (2) characterized by containing one or two of Nb: 0.01 to 0.5% and ⁇ : 0.01 to 0.5% in mass%
  • Nb 0.01 to 0.5%
  • ⁇ 0.01 to 0.5%
  • Stainless steel composed of the components described in any one of (1) to (3), wherein the metal structure is a two-phase structure of a ferrite phase and a martensite phase. ⁇ 110 ⁇
  • the half-width broadening B defined by the following formula (C) of the diffraction line is 0.1 to 1.0, and has an excellent balance of strength and ductility, and the grain boundary of the heat-affected zone of the multipass welding
  • Figure 1 shows an example of the relationship between annealing temperature and hardness.
  • Figure 3 shows the cross-sectional metallographic structure of the heat affected zone after the improved Strauss test.
  • Fig. 4 shows an example of the relationship between annealing conditions, strength, and ductility.
  • N precipitates as a nitride and deteriorates the intergranular corrosion resistance due to the formation of a Cr-deficient phase, so the upper limit of its content is 0.02 mass% or less.
  • the upper limit of its content is 0.02 mass% or less.
  • the lower limit of the content is 0.004. It was set as mass%.
  • Si is an element usually used as a deoxidizing material, but if the content is 0.2% by mass or less, a sufficient deoxidizing effect cannot be obtained. In addition, it may be positively added for the purpose of improving oxidation resistance. However, if its content exceeds 1% by mass, the manufacturability of the material deteriorates, so the content is 0.2 to 1% by mass. %.
  • Mn is an austenite phase (a phase) stabilizing element, and effectively contributes to the improvement of weld toughness by making the weld heat-affected zone structure a martensite structure.
  • Mn is also useful as a deoxidizer, as is the case with Si, so it should be contained in a range of more than 1.5 mass%.
  • Si silicon
  • its content is limited to 2.5% by mass or less. More preferably, it is 2.0 mass% or less.
  • P is an element that segregates at the grain boundaries and is not only detrimental to hot workability, formability, and toughness, but is also harmful to corrosion resistance.
  • the content exceeds 0.04 mass%, the effect becomes significant. Therefore, the P content is limited to 0.04 mass% or less. More preferably, it is 0.025% or less.
  • S is an element that forms sulfide inclusions and degrades the corrosion resistance of steel.
  • the upper limit of its content must be 0.03 mass%. The smaller the S content, the better the corrosion resistance, but the desulfurization load for reducing S is increased, so the lower limit is preferably set to 0.003 mass%.
  • Cr is an element effective for improving corrosion resistance, but if it is less than 10% by mass, it is difficult to ensure sufficient corrosion resistance.
  • Cr is an element that stabilizes the ferrite phase ( ⁇ phase). Addition of more than 15% by mass not only causes a decrease in workability, The stability of the austenite phase (a phase) decreases, and a sufficient amount of martensite phase cannot be secured during welding, leading to a decrease in weld strength and toughness. Therefore, in the present invention, Cr is contained in the range of 10 mass% or more and 15 mass% or less. A particularly preferable range for combining weather resistance, workability, and weldability is 11.0 to 13.0% by mass. Furthermore, not only the intergranular corrosion resistance of the heat-affected zone of multi-pass welding, but also to prevent the occurrence of preferential corrosion in the vicinity of the welded part fusion line. .
  • Ni is an indispensable element for improving the corrosion resistance and for forming martensite in the weld and improving the toughness of the weld. Its content must be at least 0.2% by mass. Become. However, if the content exceeds 3.0% by mass, the amount of martensite generated in the welded portion will increase significantly, so the content should be 0.2 to 3.0% by mass. In addition, Ni has the effect of increasing the temper softening resistance of the martensite structure of the hot-rolled sheet. Therefore, when manufacturing a high-strength material with a good balance of strength and ductility, it can be applied during tempering and annealing of the hot-rolled sheet. The range can be widened.
  • Ti is an essential element for preventing intergranular corrosion resistance in welds.
  • the T i content must be at least four times the sum of the C and N contents.
  • the lower limit of Ti content is set to 4 X (C mass% + N mass%) in terms of corrosion resistance
  • the upper limit is set to 0.35 mass% in terms of surface properties.
  • a 1 is an effective additive as a deoxidizer, but if it is contained in a large amount, the surface quality of the steel deteriorates and the weldability also deteriorates, so its content is in the range of 0.005 to 0.1% by mass. And Preferably, from 0.005 to 0.03 mass% is there.
  • the component concentration is specified so that the following equation (A) is satisfied. With this rule, it is possible to obtain a chromium-containing steel with excellent weld toughness and intergranular corrosion.
  • ⁇ P (%) 420 x C + 470xN% + 23xNi% + 9 xCu%
  • the ferrite average particle size is preferably 6 or more in terms of ferrite particle size number according to JIS G 0522.
  • the ferrite grain size number refers to that in the final product. Since the chromium-containing steel of the present invention is required to have a low cost as a structural material, the final product is exclusively a hot-rolled annealing material.
  • the component concentration is defined so as to satisfy the following equation (B).
  • Such regulations can prevent surface flaws on the hot rolled sheet. If the content of Ti and N is not satisfied and (B) is not satisfied, the molten steel will solidify, and a large number of coarse TiN will crystallize at the liquidus temperature, causing surface defects during hot rolling. As mentioned above, the final product is a hot-rolled annealed material and is often descaled and used as pickled skin. Therefore, it is necessary to regulate the components from the viewpoint of preventing surface wrinkles.
  • the low chromium content stainless steel described above is excellent in weld toughness and intergranular corrosion resistance, but in order to improve the corrosion resistance in low pH solutions, addition of Mo or Cu to the steel Works effectively.
  • Cu loading is effective for low pH dilute sulfuric acid environment with coal leachate when loading coal.
  • both Mo and Mo In order to improve the corrosion resistance of both Mo and Mo, it is necessary to add at least 0.05% by mass, respectively. However, if Mo exceeds 3% by mass and Cu exceeds 3% by mass, the effect of improving corrosion resistance is saturated. In addition, the upper limit is 3 mass% for Mo and 3 mass% for Cu. Preferably, both Mo and Cu are 0.1 to 1.5% by mass. Since it is an austenite stable element next to N and Ni, it is also an effective element for controlling the phase stability calculated from a in Eq. (A). Also, Cu is a solid solution strengthening element, so it is a useful element for increasing strength.
  • Nb and V are carbonitride forming elements and can be selectively added.
  • Nb In order to fix C and N, Nb requires a content of 0.01% by mass, but even if added over 0.5% by mass, the improvement effect of intergranular corrosion resistance is saturated. However, it may cause deterioration of other characteristics such as workability. Therefore, Nb is in the range of 0.01 to 0.5 mass%. Preferably, it is 0.03 to 0.3% by mass.
  • V is also in the range of 0.01 to 0.5 mass%. Preferably, it is 0.03 to 0.3 mass%.
  • Nb is the hot rolled sheet metal.
  • High-strength materials with a tempered balance of strength and ductility have a resistance of 450 MPa or more and an elongation of 15% or more. It is desirable to have a resistance of 450MPa and an elongation of 20% or more.More preferably, it has a yield strength of 500MPa or more and an elongation of 20% or more. Is not a fully annealed ferrite single-phase structure, but a two-phase structure consisting of a Ferai phase and a martensite phase. It is a metal structure in the temper softening process of the martensite phase structure of hot-rolled sheets.
  • a metal structure in which the precipitated austenite phase (reverse transformation, r phase) is transformed into a martensite phase transformed during cooling may be used.
  • the present invention as a method for measuring the degree of recovery of dislocations in the tempering process of the martensite structure, that is, the degree of recovery of the disorder of the crystal structure, the following (C ) Applying the half-value spread ⁇ defined by did. ⁇ ⁇ ⁇ ⁇ ⁇ and ⁇ «2 peaks were separated, and the half width of the ⁇ ⁇ ⁇ line was measured to obtain ⁇ .
  • Cu is used as the X-ray source, but other X-ray sources may be used.
  • This method is based on the Japan Iron and Steel Institute, Material and Structure Properties Subcommittee, Stainless Steel Formability and Utilization Technology Voluntary Forum, “Strengthening and Utilization Technology of Stainless Steel” September 29, 1998, p. 49 As disclosed in, is a general purpose evaluation method for evaluating the tempering behavior of steel.
  • the half width corresponds to the dislocation density.
  • the definition of the half-value width is the width of the diffraction angle corresponding to the intensity of 1 2 of the peak intensity from the diffractive surface.
  • the larger the half width the greater the amount of strain (disturbance of the crystal structure) of the material.
  • B 0 means an annealed structure from which strain has been removed (tempered structure and ferrite single phase). In the present invention, B was less than 0.1. In the martensitic structure of hot-rolled steel sheets, the B value is approximately 2.0.
  • the B value is 0.1 to 1.0. It is preferably 0.3 to 0.8. If the B value is more than 1.0 and less than 2.0, tempering does not proceed and ductility is insufficient.
  • the molten steel adjusted to the above preferred component composition is melted in a commonly known melting furnace such as a converter or an electric furnace, and then vacuum degassing (RH method)
  • the steel material is scoured by a known scouring method such as VOD method or AOD method, and then forged into a slab or the like by a continuous forging method or an ingot one-piece method.
  • the steel material is then heated and made into a hot-rolled steel sheet by a hot rolling process. At that time, the selection of the heating temperature in the hot rolling process is very important from the viewpoint of avoiding edge cracks in the hot rolled sheet.
  • the heating temperature in the hot rolling step of ⁇ is austenite phase in the case of heating in either the upper limit temperature Ac below 4 austenite single phase deposition minutes determined in ⁇ , or Ac 4 than Good hot workability can be obtained by selecting a temperature at which the amount of ferrite is greater than 50%.
  • the temperature of Ac 4 can be determined from the component values of the steel by phase diagram calculation using the integrated thermodynamic calculation system Thermo-C a 1 c (distributor: CRC Solutions).
  • CRC Solutions integrated thermodynamic calculation system Thermo-C a 1 c
  • the heating temperature is preferably 1300 or less. .
  • the hot rolling finishing temperature is 800: or more and 1000 or less.
  • the coiling temperature is 800 or less, preferably 650 to 750 when tempering annealing is performed.
  • the hot rolling finishing temperature should be 900 or less and the coiling temperature should be 650 or less. Therefore, it is desirable to accumulate work strain and improve the temper softening resistance in order to widen the annealing condition range.
  • the hot rolling After the hot rolling is finished, it is preferable to subject the hardened structure to a martensite phase by hot-rolled sheet annealing to soften the martensite phase by tempering.
  • the tempering temperature should be as high as possible in the ferrite temperature range. Although the transformation point, which is the upper limit temperature of the ferrite single phase, varies depending on the amount of Ni, etc., it is often adjusted to about 650-700 for practical steels, and annealing below this temperature is desirable. Therefore, in this hot-rolled sheet annealing, it is preferable to set the annealing temperature: 650 to 750 t and the holding time: 2 to 20 h from the viewpoint of improving workability and ensuring ductility.
  • the temperature range between 600 and 750 is annealed at a cooling rate of 50 and Zh or less after hot-rolled sheet annealing.
  • the temper softening process of the martensite phase structure of the hot-rolled sheet rather than the fully annealed ferrite phase structure Therefore, it is necessary to control the two-phase structure of the ferrite phase and martensite phase.
  • the heat treatment temperature of the hot-rolled sheet is set to 550 t: to 850.
  • the holding time There is no particular restriction on the holding time, but it is desirable to set the heat treatment time considering practicality. Therefore, it is preferable that the heat treatment temperature is 600 to 800 t: and the holding time is 2 to 30 h.
  • the cooling rate is usually controlled to 50t: Zh or less.
  • Heat treatment temperature is ( ⁇ or less The above may be Ac, or the following.
  • the metal structure obtained by the following heat treatment it is a metal structure in which the precipitated austenite phase (reverse transformation phase) is combined with the martensite phase transformed during cooling.
  • the holding time in this case is not particularly limited, but is practically 2 to 30 hours, preferably 2 to 15 hours.
  • the steel sheets after hot rolling or after hot rolling annealing were adjusted to the desired surface properties with the scale removed by shot blasting, pickling, etc. as necessary, or by polishing, skin pass, etc. Later, it may be a product plate.
  • the component steel according to the present invention can be applied to various steel materials that can be used as structural steels in fields such as thick steel plates, shaped steels manufactured by hot rolling, and bar steels.
  • Tables 1 and 2 show invention examples and comparative examples related to the first problem.
  • Table 1 shows the components in steel of the invention steel and comparative steel in mass%.
  • Steel Nos. 1 to 20 are invention steels, and Steel Nos. 2 to 26 are comparative steels.
  • the pieces of the ingredients shown in Table 1 were melted into a 40 kg or 35 kg flat ingot by vacuum melting. After cleaning these steel surfaces, the ingots were heated for 1 hour at 1 1 50 to 1 250 to perform hot rough rolling consisting of multiple passes followed by hot finish rolling. Hot rolled The end temperature was 800 to 950. The hot-rolled sheet was air-cooled, held at a coiling temperature of 700 ° C for 1 hour, and then air-cooled and subjected to a simulated winding heat treatment to obtain a hot-rolled sheet with a thickness of 4 mm. Subsequently, in order to determine the annealing temperature of the hot-rolled sheet, the hot-rolled sheet of each component value was subjected to 600 to 775 for 5 hours, and then air-cooled heat treatment. The temperature at which it becomes the softest was the annealing temperature.
  • Figure 1 shows an example of the relationship between heat treatment temperature and hardness. As hot-rolled, it has high hardness but is softened by heat treatment. In this example, it becomes softest at 675 to 700. If heat treatment is performed at a higher temperature, the austenite phase precipitates and transforms into martensite during cooling, so it hardens.
  • the Vickers hardness (Hv) of the L section was measured and evaluated at the center of the plate thickness with a load of 1 kg.
  • Table 2 shows the evaluation results of various characteristics of the inventive examples and comparative examples. Case Nos. 1 to 20 are examples of the present invention, and Case Nos. 2 to 27 are comparative examples.
  • the steel of the present invention not only has excellent weld corrosion resistance without occurrence of intergranular corrosion of multiple welds and preferential corrosion near the weld fusion line, but also has excellent impact characteristics of the welds. . Furthermore, the material of strength and ductility is also good, and it is possible to drastically improve sulfuric acid resistance by selectively adding elements. In addition, by designing the components of the steel material and devising the manufacturing conditions, it is possible to obtain a steel material with excellent manufacturability that is free from edge cracks and surface defects in the hot rolled sheet.
  • Comparative Example No. 21 is inferior in corrosion resistance of the heat affected zone because the soot content and T i / (C + N) are out of the scope of the present invention.
  • Comparative Example No. 22 since T i ⁇ N was outside the scope of the present invention, surface flaws occurred during hot rolling.
  • Comparative Example No. 23 T i deviated from the upper limit of the range of the present invention, so T i ⁇ N deviated from the range of the present invention, and surface flaws occurred due to hot rolling.
  • Comparative example In case No. 24, the impact characteristics of the weld heat-affected zone are inferior because a is outside the scope of the present invention.
  • Comparative Example No. 26 is inferior in sulfuric acid resistance and corrosion resistance of the heat affected zone because Cr is outside the lower limit of the range of the present invention.
  • edge cracking occurred because the amount of ⁇ at the hot rolling heating temperature was out of the range of the present invention.
  • the components were analyzed by sampling test pieces from steel plates.
  • Gas analysis method for C, S and N (N is an inert gas melting and thermal conductivity measurement method, C and S are combustion and infrared absorption method in oxygen stream), and X-ray fluorescence analyzer for other elements ( SH I MADZU, MXF-2 1 00).
  • Judgment of the occurrence of cracks in the hot-rolled sheet was made based on the appearance observation. ⁇ indicates no crack, ⁇ indicates that there is no crack from the front surface to the back surface with a crack, and X indicates that there is a crack and the crack penetrates from the front surface to the back surface.
  • the sulfuric acid immersion test method is shown below.
  • a 2 mm x 25 mm x 25 mm corrosion test piece was prepared from the hot rolled annealed pickling plate.
  • the liquid volume was 50 OmL per test piece.
  • the test temperature was 30.
  • the corrosion rate is 3 g Zm 2 / h or less, ⁇ , especially 2 g Zm 2 Zh or less is indicated by ⁇ , and when it is more than 3 g Zm 2 Zh Is indicated by X.
  • Fig. 2 shows the effect of Cu and Cr on the corrosion rate when 0.25% by mass of steel is used and the pH is 2, as a result of the sulfuric acid immersion test.
  • Cu is added, the corrosion rate decreases.
  • the addition of 0.3 to 0.5% by mass results in the lowest corrosion rate.
  • Increasing the amount of Cu added further saturates the Cu effect. Even if Cr is increased, the corrosion rate can be reduced.
  • TIG welding was performed with tanning, welding speed ZOOcmZmiiK welding current 110 A, and the sealing gas was argon. MIG welding was performed by the following method.
  • Welding material is 309 LSi (C: 0.017%, Si: 0 ⁇ 74%, Mn: 1.55%, P: 0.024%, S: 0.001%, Ni: 13.68%, Cr: 23.22%), voltage 25 ⁇ 30V, current: 230 to 250A, shielding gas: 98% Ar + 2% ⁇ 2
  • the welding machine used Daihen turbo-pulse. The test was conducted under sufficient conditions to penetrate the 4 mm plate thickness and reverse the wave. In the case of a butt weld joint, the root face is 2 mm (gap 0) at a 90 ° V groove, the heat input Q is about 12500 J Zcm, and in the case of cross welding, the seam weld is left about 1 mm thick. After deletion, welding was performed, and the Q was about 5600 J cm.
  • the intergranular corrosion test is basically copper sulfate monosulfate standardized by IIS.
  • the test (G0575) (Strauss test) is generally used, and this test is appropriate for high chromium-containing stainless steels such as SUS304.
  • stainless steel with a low chromium content in the steel (.about 12% low chromium stainless steel) is too corrosive, so tests were conducted using an evaluation method suitable for low chromium stainless steel. .
  • Figure 3 shows the cross-sectional metallographic structure of the weld heat-affected zone after the modified Strauss test.
  • A) to d) are a) Comparative Steel No. 21
  • the heat-affected zone adjacent to the weld metal is 1, the heat-affected zone next to it—2 and the heat-affected zone—3. 1 and 2 are martensite and the base metal and metal structure are different.
  • the heat affected zone 13 is affected by the heat of welding, but no martensite is formed.
  • corrosion mainly consisting of intergranular corrosion has occurred in all the heat-affected zones 1 to 3 of several hundred meters from the surface.
  • the corroded area is black near the surface Contrast part.
  • the white deposit on top of it is a deposit of copper, corresponding to the occurrence of corrosion.
  • the figure on the right is an enlarged view of the surface layer of the figure on the left.
  • no corrosion has occurred.
  • Impact characteristics were measured by Charpy test.
  • a JIS4 2 mmV notch subsize (thickness 4 mm) test piece conforming to the HS standard was taken from the MIG weld and an impact test was performed at 20.
  • the V-notch was inserted in the BOND part where the weld metal and base metal part were 1/2 each.
  • the impact value is 30 J Zcm 2 or more, it is indicated as ⁇ .
  • the impact value is less than 30 J Zcni 2, X is indicated.
  • Tables 3 and 4 show invention examples and comparative examples related to the second problem.
  • Table 3 shows the mass% of components in the steel of the present invention steel (steel materials No. 27 to 35).
  • the pieces of the ingredients shown in Table 3 were melted into 40 kg or 35 kg flat ingots by vacuum melting. After cleaning the surface of these steels, the ingot was heated at 1150 for 1 hour, followed by hot rough rolling consisting of multiple passes followed by hot finish rolling.
  • the hot rolling end temperature was 800 to 900.
  • the hot-rolled sheet was air-cooled, held at a coiling temperature of 500 for 1 hour, and then air-cooled and subjected to a simulated coiling heat treatment to obtain a hot-rolled sheet with a thickness of 4 mm.
  • the hot-rolled sheet of each component value is held at 575: -850 at 5-50 hours, and then the batch heat treatment cooling process is simulated at 20 Controlled cooling with Zh and at 100 removed from the furnace.
  • Figure 4 shows an example of the relationship between heat treatment conditions, strength, and ductility.
  • steel No. 33 was held for 5 hours, it was softened by heat treatment with high strength and low elongation as it was hot rolled.
  • the elongation is 15% or more with a proof stress of 450 MPa or more in a wide temperature range of 675 or more and 800 or less.
  • Table 4 shows the heat treatment conditions and various evaluation results of the inventive examples and comparative examples.
  • Case Nos. 28 to 41 are examples of the present invention
  • Case Nos. 42 to 50 are comparative examples.
  • a metal structure corresponding to claim 4 of the present invention a high-strength, low-chromium-containing stainless steel having an elongation of 15% or more or 20% or more and a high strength and ductility balance of 450 MPa or more is obtained. It is possible.
  • the B value of case No. 36 is 0.36, 0.2% resistance to 538 MPa, elongation 2 1.5 %.
  • These steels also have excellent intergranular corrosion resistance in the heat-affected zone of multi-pass welding and preferential corrosion resistance in the vicinity of the weld fusion line.
  • Comparative Examples No.42 to 46, 49 and 50 are not suitable because the heat treatment conditions are low temperature or short time, and because the metal structure is outside the scope of the present invention, the elongation is less than 15% and the strength-ductility balance is inferior. .
  • Comparative Examples No. 47 and 48 the heat treatment takes a long time and is not suitable, so the metal structure deviated from the scope of the present invention. Therefore, the yield strength was less than 450 MPa, and the strength ductility balance was inferior.
  • the evaluation test was carried out by the following method. Except for the following, the determination of the metal structure in accordance with Example 1 was evaluated by the half-width broadening B of the Cu—Kal ⁇ 110 ⁇ diffraction line in X-ray diffraction. A B value of 0.1 to 1.0 is indicated by ⁇ , and a value of less than 0.1 and exceeding 1.0 is indicated by X.
  • 0.2% proof stress is 450MPa or more is indicated by ⁇ , and less than 450MPa is indicated by X.
  • 0.2% proof stress is 500 MPa or more is indicated by ⁇ .
  • Elongation of 15% or more is indicated by ⁇ , and less than 15% is indicated by X.
  • the present invention does not contain an unnecessarily expensive element, can be used as a structural steel even in severe corrosion environments, does not cause preferential corrosion in the vicinity of the welded fusion line, and is resistant to grains in multipass welds. It is an industrially extremely valuable invention that can provide a low chromium-containing stainless steel having excellent corrosion resistance and can be provided as a high-strength material if necessary.

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Abstract

A stainless steel with low chromium content which is little lowered in the corrosion resistance of a weld formed by repeated welding and is excellent in the intergranular corrosion resistance of a weld even under severe corrosive atmosphere and which is freed from preferential corrosion in the heat affected zone near a weld fusion line and is excellent in productivity. The stainless steel contains by mass C: 0.03% or below, N: 0.004 to 0.02%, Si: 0.2 to 1%, Mn: more than 1.5% to 2.5%, P: 0.04% or below, S: 0.03% or below, Cr: 10 to 15%, Ni: 0.2 to 3.0%, Al: 0.005 to 0.1%, and Ti: 4 × (C% + N%) to 0.35% with the balance consisting of Fe and unavoidable impurities and satisfies the requirements: γp(%) of 80 or above as represented by a prescribed numerical formula and Ti% × N% < 0.004.

Description

明 細 書 複数回溶接熱影響部の耐食性に優れた低クロム含有ステンレス鋼お よびその製造方法 技術分野  Description Low-chromium stainless steel with excellent corrosion resistance in heat-affected zone of multiple times and its manufacturing method Technical Field
本発明は、 複数回溶接した場合 （マルチパス） の溶接部近傍の熱 影響部における耐粒界腐食性を向上させ、 さ らに溶接隣接部フュー ジョ ンライ ン近傍に発生する優先腐食を回避し、 構造用鋼等として 腐食環境の厳しい用途で長期間に亘つて使用できる、 溶接部の耐食 性に優れた低クロム含有ステンレス鋼に関する。 背景技術  The present invention improves the intergranular corrosion resistance in the heat-affected zone in the vicinity of the weld when multiple welding is performed (multi-pass), and further avoids preferential corrosion that occurs in the vicinity of the fusion line in the weld. It relates to a low chromium-containing stainless steel with excellent corrosion resistance of welds that can be used for a long period of time in applications where the corrosive environment is severe as structural steel. Background art
クロム含有量が低く、 かつニッケル含有量が低いクロム含有ステ ンレス鋼は、 SUS304鋼のようなオーステナイ ト系ステンレス鋼と比 較して、 価格的に極めて有利であることから、 構造用鋼のように大 量に使用される用途に適している。 このようなクロム含有鋼は、 そ の成分組成に応じたフェライ ト組織あるいはマルテンサイ ト組織を 有する。 一般的に、 フィ ライ ト系あるいはマルテンサイ ト系ステン レス鋼は、 溶接部の低温靭性あるいは耐食性に劣る。 例えば、 SUS4 10に代表されるマルテンサイ ト系ステンレス鋼の場合は、 C含有量 が 0. l nias s %程度と高いため、 溶接部靭性ゃ溶接部の加工性に劣り 、 加えて溶接に際しては予熱を必要とし、 溶接作業性にも劣ること から、 溶接が必要な部材への適用には問題を残していた。  Chromium-containing stainless steel with low chromium content and low nickel content is extremely advantageous in terms of price compared to austenitic stainless steel such as SUS304 steel. It is suitable for applications that are used in large quantities. Such a chromium-containing steel has a ferrite structure or a martensite structure according to its composition. Generally, fillite or martensite stainless steels are inferior in the low temperature toughness or corrosion resistance of welds. For example, in the case of martensitic stainless steel represented by SUS4 10, the C content is as high as about 0.1 nias s%, so the weld toughness is poor and the weldability is inferior. Therefore, the welding workability is also inferior, so that problems remain in the application to parts that require welding.
このような溶接部の特性劣化を防止する手段として、 特公昭 5 1— 13463号公報および特公昭 6 1— 23259号公報に記載されているような 、 溶接部で形成されるマルテンサイ ト組織を用いて、 耐食性および 低温靭性の低下を防止する方法が開示されている。 特公昭 5 1— 1346 3号公報が提案するのは、 C r ： 10〜 18 %、 N i ： 0. 1〜3. 4 %、 S i ： 1. 0 %以下および Mn ： 4. 0 %以下を含有し、 さ らに C ： 0. 030 %以下、 N ： 0. 020 %以下に低減した鋼成分とし、 溶接熱影響部にマツシブマ ルテンサイ ト組織を生成させる方法であり、 これによつて溶接部の 性能を向上させた溶接構造用マルテンサイ ト系ステンレス鋼を提案 している。 As a means for preventing such deterioration of the properties of the welded portion, a martensite structure formed by the welded portion as described in Japanese Patent Publication No. 51-13463 and Japanese Patent Publication No. 61-23259 is used. Corrosion resistance and A method for preventing a decrease in low temperature toughness is disclosed. JP-B-51-13463 proposes Cr: 10-18%, Ni: 0.1-3.4%, Si: 1.0% or less, and Mn: 4.0% This is a method of generating a mashite martensite structure in the heat affected zone of the weld with a steel component reduced to C: 0.030% or less and N: 0.020% or less. We are proposing welded martensitic stainless steel with improved weld performance.
このような溶接部でのマルテンサイ ト変態を用いた低クロム含有 ステンレス鋼は、 実際に海上コンテナーの骨材として使用されてお り、 今まで溶接部における耐食性あるいは低温靭性が問題となった 例はない。 しかしながら、 厳しい腐食環境 （鋼材の濡れ時間が長い 、 塩化物濃度が高い、 高温、 pHが低い等） の下で使用された場合に は、 溶接部における耐食性が不十分である場合が生じることが分か つてきた。 例えば、 石炭や鉄鉱石を運搬する鉄道貨車の荷台等で使 用された場合には、 溶接熱影響部で粒界腐食が発生する場合が報告 されている。  Low chromium-containing stainless steel using martensite transformation in such welds is actually used as an aggregate in marine containers, and examples of corrosion resistance or low-temperature toughness in welds have been problems until now. Absent. However, when used in severe corrosive environments (long steel wetting time, high chloride concentration, high temperature, low pH, etc.), the corrosion resistance of welds may be insufficient. I've come to understand. For example, it has been reported that intergranular corrosion occurs in the heat-affected zone when used in the platform of a railway freight car that carries coal or iron ore.
低クロム含有ステンレス鋼の溶接熱影響部の耐食性や溶接部靱性 を改善する方法として、 上記の高純度化、 さ らにはそれに加えて炭 素や窒素を炭化物や窒化物として固定するための元素の添加が有効 であることから、 このような手段によって製造した種々の鋼が開示 されている。 例えば、 特開 2002— 32725 1号公報には、 炭素 · 窒素安 定化元素である Nbや T iを適量添加することによって、 マルテンサイ ト変態を用いたクロム含有鋼の溶接部の耐粒界腐食性劣化を防止す るとともに、 低温靭性に優れるクロム含有鋼が開示されている。 特 許第 349 1625号公報にも同様に、 炭窒化物形成元素である T i , Nb , T aや Z rを添加し、 溶接部の耐食性を向上した Fe— C r合金が開示され ている。 しかしながら、 この特許は、 Co , Vおよび Wを含有するこ とが必須であり、 耐初期発銹性の向上を目的としている。 As a method to improve the corrosion resistance and weld toughness of the weld heat-affected zone of low chromium-containing stainless steel, the above-mentioned high purity, and in addition, elements for fixing carbon and nitrogen as carbides and nitrides Various steels produced by such means are disclosed because the addition of is effective. For example, Japanese Patent Laid-Open No. 2002-32725 1 discloses intergranular corrosion resistance of welds of chromium-containing steel using martensite transformation by adding appropriate amounts of carbon and nitrogen stabilizing elements Nb and Ti. In addition, chromium-containing steels that are excellent in low temperature toughness are disclosed. Similarly, Japanese Patent No. 349 1625 discloses a Fe—Cr alloy that has improved the corrosion resistance of welds by adding carbonitride-forming elements Ti, Nb, Ta, and Zr. . However, this patent contains Co, V and W. It is essential to improve the initial rust resistance.
以上の背景より、 近年、 内陸で採掘し沿岸まで鉄道輸送される石 炭や鉄鉱石の鉄道貨車用荷台等の使用される環境では、 溶接熱影響 部の粒界腐食対策として、 特開 2002— 32725 1号公報および特許第 34 9 1625号公報の開示と同様の T iを添加した低クロム含有ステンレス 鋼が適用されている例がある。  Based on the above background, in recent years, as a countermeasure against intergranular corrosion in the weld heat affected zone, in the environment where coal and iron ore used for railway freight carriages are mined inland and transported to the coast by railway, There is an example in which low chromium-containing stainless steel added with Ti similar to the disclosure of Japanese Patent No. 327251 and Japanese Patent No. 34 9 1625 is applied.
しかし、 この例では溶接熱影響部の耐粒界腐食性は向上するもの の、 溶接部とそれに最隣接する熱影響部であるマツシブマルテンサ イ ト組織との界面に沿った部位 （フュージョ ンライ ン） 近傍で優先 腐食が発生する問題があることを、 本発明者は新たに知見した。 こ の現象は、 溶接学会誌、 第 44巻、 1975、 第 8号、 679頁に開示され ているように SUS32 1や SUS347の安定系オーステナイ ト系ステンレス 鋼の溶接部で見られるナイフライ ンアタックと呼ばれる現象に類似 しており、 溶接部と熱影響部の界面 （フュージョ ンライ ン） が優先 的に腐食進展し、 腐食領域が拡大していく ことから、 改善すべき課 題である。  However, in this example, the intergranular corrosion resistance of the weld heat-affected zone is improved, but the part along the interface between the weld zone and the mash martensite structure, which is the heat-affected zone closest to it (fusion fusion zone) The present inventor has newly found that there is a problem that preferential corrosion occurs in the vicinity. This phenomenon is called a knife line attack found in welds of SUS321 and SUS347 stable austenitic stainless steels as disclosed in Journal of the Japan Welding Society, Vol. 44, 1975, No. 8, page 679. This phenomenon is similar to the phenomenon, and the interface (fusion line) between the weld and heat-affected zone preferentially progresses in corrosion and the corrosion area expands, so this is an issue to be improved.
ナイフライ ンアタックの原因は、 1^ (ゃ^(：で Cを固定し ステン レス鋼を溶接した際、 その熱履歴が約 1200で以上に昇温された領域 で T i Cや NbCが固溶し、 その後の冷却過程で鋭敏化温度域を通過する 際に結晶粒界に C r炭化物が析出して耐食性が低下することにある。 しかしながら、 低クロム含有ステンレス鋼の場合に、 どのような原 因で優先腐食が生じるのか、 十分な検討は行われておらず、 対策も 講じられていない。  The cause of knife line attack is that when C is fixed with 1 ^ (nya ^ (: and stainless steel is welded, Ti C and NbC are dissolved in the region where the thermal history is raised to about 1200 or more. However, when passing through the sensitization temperature range in the subsequent cooling process, Cr carbide precipitates at the grain boundaries and the corrosion resistance decreases, but in the case of low chromium-containing stainless steel, what are the causes? Whether or not preferential corrosion occurs in Japan has not been fully examined and no measures have been taken.
また、 前述の C , Nの固定化元素を添加した低クロム含有ステン レス鋼は、 溶接部の耐粒界腐食性を向上した成分系ではあるけれど も、 複数回溶接後の熱影響部の耐食性は十分とは言い難く、 溶接熱 影響部で腐食が発生する場合があることが報告されている。 溶接構 造設計の自由度拡大や溶接補修のしゃすさ向上の観点より、 複数回 溶接後も熱影響部の耐食性に優れたマルチパス溶接可能な低クロム ステンレス鋼が待ち望まれていた。 In addition, the low-chromium stainless steel added with the C and N fixing elements described above is a component system with improved intergranular corrosion resistance in the weld zone, but the corrosion resistance of the heat-affected zone after multiple welds. However, it has been reported that corrosion may occur in the heat affected zone. Welding structure From the viewpoint of expanding the degree of freedom in construction design and improving the level of weld repair, a low-chromium stainless steel capable of multi-pass welding with excellent corrosion resistance in the heat-affected zone even after multiple welding has been awaited.
一方、 低クロム含有ステンレス鋼の製造においては、 熱延時のェ ッジ割れ （耳割れ） が発生しやすいことが知られている。 含有元素 のバランス変化によって、 熱間加工温度域におけるオーステナイ ト とデル夕フェライ 卜の相安定性が直接的に影響を受けることに起因 すると考えられる。 よって、 製造プロセスの最適化の観点からも解 決すべき課題が存在しており、 その改善が望まれていた。  On the other hand, it is known that edge cracks during hot rolling are likely to occur in the production of low chromium-containing stainless steel. This is thought to be due to the fact that the phase stability of the austenite and Del Yuferai cocoon in the hot working temperature range is directly affected by the balance change of the contained elements. Therefore, there are issues to be solved from the viewpoint of optimizing the manufacturing process, and improvements were desired.
さ らに、 石炭や鉄鉱石の鉄道貨車用荷台等の使用される場合には 、 積載量を増加することによる輸送効率の向上や軽量化による燃料 費低減等が切望されている。 鉄道貨車の総重量は決まっているので 、 積載量を上げるためにはステンレス鋼板を薄手化することが必須 である。 これを実現するためには低クロム含有ステンレス鋼板の高 強度化が不可欠であるが、 加工性も考慮した強度延性バランスに優 れた低クロム含有ステンレス鋼板は未だ開発されておらず、 その出 現が期待されていた。 発明の開示  In addition, when coal or iron ore railcar freight trucks are used, it is desired to improve transportation efficiency by increasing the loading capacity and to reduce fuel costs by reducing weight. Since the total weight of railway wagons is fixed, it is essential to make the stainless steel sheet thinner in order to increase the loading capacity. In order to achieve this, it is indispensable to increase the strength of low chromium-containing stainless steel sheets, but no low chromium-containing stainless steel sheets with excellent balance of strength and ductility considering workability have yet been developed. Was expected. Disclosure of the invention
本発明は、 マルテンサイ 卜変態を用いた低クロム含有ステンレス 鋼を複数回溶接した場合 （マルチパス） の溶接部での耐食性劣化を 防止し、 石炭や鉄鉱石の鉄道貨車が使用されるような厳しい腐食環 境においてもマルチパス溶接部の耐粒界腐食性に優れ、 同時に溶接 部フュージョ ンライ ン近傍に発生する優先腐食を生じることがなく 、 さ らには製造性にも優れた最適な低クロム含有ステンレス鋼を提 供することを第一の課題とする。 必要に応じ、 強度延性バランスに 優れた高強度の低クロム含有ステンレス鋼を提供することを第二の 課題とする。 The present invention prevents deterioration of corrosion resistance at the welded part when multi-pass low-chromium stainless steel using martensite transformation is used, and it is difficult to use railway wagons of coal and iron ore. Even in a corrosive environment, the multi-pass welds have excellent intergranular corrosion resistance, and at the same time, there is no preferential corrosion that occurs near the weld fusion line. The first issue is to provide stainless steel. If necessary, the second is to provide high-strength, low-chromium stainless steel with an excellent balance of strength and ductility. Let it be an issue.
本発明者らは、 上記第一の課題を解決すべく鋭意検討した結果、 複数回溶接した場合 （マルチパス） の溶接部およびその近傍での粒 界腐食の発生を防止するには、 粒界腐食の発生原因となる炭素およ び窒素を安定化する Tiおよび Nbを添加することによって達成するこ とができるが、 一方、 Tiおよび Nbの添加では、 溶接部フュージョ ン ライ ン近傍の優先腐食発生防止には効果が無いことを知見した。 そこで、 溶接部に隣接する熱影響部の優先腐食を防止すべく検討 した結果、 溶接部隣接のマツシブマルテンサイ 卜が形成される熱影 響部は非常に高温に曝されるため、 溶接方法によっては、 この部位 に限りスケールが厚く形成され、 スケール直下の Cr濃度が低下して 、 いわゆる Cr欠乏層が形成され、 その結果、 現象的にはナイフライ ンアタックに類似の優先腐食が生じることを見出した。 また、 マル チパス溶接熱影響部の耐粒界腐食性に効果のある Tiの含有量が増加 すると、 TiNの晶出により表面欠陥の原因となるので、 Tiと Nの濃 度積を 0.004以下に制御する必要があることを明らかにした。 さ ら に溶接熱影響部の耐食性向上に加えて、 溶接部靭性の低下を防止す ベく検討した結果、 オーステナイ ト安定度を記述する下記 （A) 式 を満足すべく成分設計し相安定性を適正化することによって、 目的 を達成しうることを見出した。  As a result of intensive studies to solve the above first problem, the present inventors have found that in order to prevent the occurrence of intergranular corrosion at and near the welded part when multiple welding is performed (multipass), This can be achieved by adding Ti and Nb, which stabilize the carbon and nitrogen that cause corrosion, while Ti and Nb add preferential corrosion near the weld fusion line. It was found that there is no effect in preventing the occurrence. Therefore, as a result of examining to prevent preferential corrosion of the heat affected zone adjacent to the weld zone, the heat affected zone where the mash martensite adjacent to the weld zone is exposed to very high temperature, Found that the scale is formed thick only in this part, the Cr concentration just below the scale is reduced, so-called Cr-deficient layer is formed, and as a result, the phenomenon of preferential corrosion similar to knife line attack occurs. . In addition, if the Ti content, which has an effect on the intergranular corrosion resistance of the multipass weld heat-affected zone, increases, it causes surface defects due to TiN crystallization. Clarified that there is a need to control. Furthermore, in addition to improving the corrosion resistance of the weld heat-affected zone, as a result of careful study to prevent a decrease in weld toughness, a component design was made to satisfy the following formula (A) describing the austenite stability, and the phase stability It was found that the objective can be achieved by optimizing.
r P (%) = 420x C % + 470 xN % + 23xNi% + 9 xCu r P (%) = 420x C% + 470 xN% + 23xNi% + 9 xCu
+ 7 XMn% - 11.5XCr% - 11.5xSi% - 12xMo% -23xV % -47xNb% -49xTi% - 52XA1% + 189≥80 · · · · (A) r P (ガンマポテンシャル） は、 オーステナイ トの安定度を評価 する指標であり、 同時にマルテンサイ 卜の形成のしゃすさを表す指 標である。  + 7 XMn%-11.5XCr%-11.5xSi%-12xMo% -23xV% -47xNb% -49xTi%-52XA1% + 189≥80 (A) r P (gamma potential) It is an index that evaluates the degree, and at the same time, it is an index that represents the speed of formation of martensi cocoons.
さ らに加えて、 成分設計したステンレス鋼を製造するにあたり、 铸片の熱間圧延工程における加熱温度を、 オーステナイ ト単相域か あるいはデル夕フェライ ト量が 50 %超となる温度に制御した場合に エッジ割れの生じない低クロム含有ステンレス鋼を製造可能である ことを見出した。 In addition, in producing stainless steel with component design, It is possible to produce low-chromium stainless steel that does not cause edge cracking when the heating temperature in the hot rolling process of the slab is controlled to the austenite single-phase region or to a temperature at which the Dell evening ferrite amount exceeds 50%. I found it.
また、 本発明者らは、 上記第二の課題を解決すべく鋭意検討した 結果、 低クロム含有フェライ ト系ステンレス鋼においては、 焼鈍し たフェライ ト組織のままでは十分な高強度化は実現できないことを 知見した。  In addition, as a result of intensive studies to solve the above second problem, the present inventors have not been able to achieve a sufficiently high strength with an annealed ferrite structure in a low chromium-containing ferritic stainless steel. I found out.
そこで、 低クロム含有フェライ 卜系ステンレス鋼を高強度化すべ く検討したところ、 溶接部隣接熱影響部の耐食性を向上すべく成分 設計したステンレス鋼を製造するにあたり、 熱延板の熱処理工程に おける熱処理温度と保持時間を適切に選択することにより、 マルテ ンサイ ト組織である熱延板の焼き戻し軟化熱処理過程において、 金 属組織をフェライ 卜とマルテンサイ 卜の 2相組織に適切に調質でき 、 強度延性バランスに優れた高強度のクロム含有ステンレス鋼を製 造可能であることを見出した。 特に Nbや N iを適切に含有する焼き戻 し軟化抵抗を高めた成分の場合に効果的かつ実用的である。 熱処理 条件は、 実用的には例えば熱処理温度を 600〜800で、 保持時間を 2 〜30時間、 で適切な温度を設定すると所望の金属組織を得ることが できる。  Therefore, we studied to increase the strength of ferritic stainless steel with low chromium content. As a result, in the production of stainless steel with components designed to improve the corrosion resistance of the heat-affected zone adjacent to the weld, By appropriately selecting the heat treatment temperature and holding time, in the temper softening heat treatment process of the hot-rolled sheet, which is a martensite structure, the metal structure can be appropriately tempered into a two-phase structure of Ferai and martensite. It was found that high-strength chromium-containing stainless steel with an excellent balance of strength and ductility can be produced. In particular, it is effective and practical in the case of a component that appropriately contains Nb and Ni and has increased temper softening resistance. Practically, for example, the heat treatment temperature is 600 to 800, the holding time is 2 to 30 hours, and an appropriate temperature is set. Thus, a desired metal structure can be obtained.
本発明は、 かかる知見に基づいて完成されたものであって、 その 要旨とするところは以下の通りである。  The present invention has been completed based on such findings, and the gist thereof is as follows.
( 1 ) 質量％で、 C ： 0. 03 %以下、 N ： 0. 004〜0. 02 %、 S i ： 0. 2 〜 1 %、 Mn ： 1. 5超〜 2. 5 %、 P ： 0. 04 %以下、 S ： 0. 03 %以下、 C r ： 10〜 15 %、 N i ： 0. 2〜3. 0 %、 A 1 ： 0. 005〜0. 1 %を含有し、 さ らに 、 T i ： 4 X ( C % + N % ) 以上、 0. 35 %以下を含有し、 残部が Feお よび不可避不純物からなり、 かつ、 各元素の含有量が下記 （A ) 式 および （ B ) 式を満足することを特徴とするマルチパス溶接熱影響 部の耐粒界腐食性および溶接部フュージョ ンライ ン近傍の耐優先腐 食性に優れた低クロム含有ステンレス鋼。 (1) By mass%, C: 0.03% or less, N: 0.004 to 0.02%, Si: 0.2 to 1%, Mn: more than 1.5 to 2.5%, P: 0.04% or less, S: 0.03% or less, Cr: 10 to 15%, Ni: 0.2 to 3.0%, A1: 0.005 to 0.1%, In addition, Ti: 4 X (C% + N%) or more and 0.35% or less, the balance is Fe and inevitable impurities, and the content of each element is expressed by the following formula (A) And a low-chromium stainless steel with excellent intergranular corrosion resistance in the heat-affected zone of the multipass weld and excellent corrosion resistance near the weld fusion line, characterized by satisfying the formula (B).
r P ( % ) = 420 x C % + 470 XN % + 23xNi% + 9 XCu% r P (%) = 420 x C% + 470 XN% + 23xNi% + 9 XCu%
+ 7 XMn% - 11.5xCr% - 11.5xSi% - 12xMo% - 23xV % -47xNb% -49xTi% -52xAl% + 189≥80 - · . - (A) Ti% X N % < 0.004 · · · · ( B )  + 7 XMn%-11.5xCr%-11.5xSi%-12xMo%-23xV% -47xNb% -49xTi% -52xAl% + 189≥80-... (A) Ti% XN% <0.004 )
( 2 ) 質量％でさ らに、 Mo : 0.05〜 3 %、 Cu ： 0· 05〜 3 %の 1種 または 2種を含有することを特徴とする （ 1 ) に記載のマルチパス 溶接熱影響部の耐粒界腐食性および溶接部フユ一ジョ ンライ ン近傍 の耐優先腐食性に優れた低クロム含有ステンレス鋼。  (2) The multipass welding heat effect according to (1), characterized by containing one or two of Mo: 0.05 to 3% and Cu: 0 · 05 to 3% in mass% A low chromium-containing stainless steel with excellent intergranular corrosion resistance in the weld zone and superior corrosion resistance in the vicinity of the welded fusion line.
( 3 ) 質量％でさ らに、 Nb : 0.01〜0.5%、 ¥ : 0.01〜0.5%の 1 種または 2種を含有することを特徴とする （ 1 ) または （ 2 ) に記 載のマルチパス溶接熱影響部の耐粒界腐食性および溶接部フュージ ヨ ンライ ン近傍の耐優先腐食性に優れた低クロム含有ステンレス鋼  (3) Multipass as described in (1) or (2), characterized by containing one or two of Nb: 0.01 to 0.5% and ¥: 0.01 to 0.5% in mass% Low chromium stainless steel with excellent intergranular corrosion resistance in weld heat affected zone and preferential corrosion resistance in the vicinity of weld zone fusion joint line
( 4 ) ( 1 ) 〜 （ 3 ) のいずれかに記載の成分からなるステンレ ス鋼であって、 金属組織が、 フェライ ト相とマルテンサイ ト相の 2 相組織であり、 X線回折における Kひ { 110} 回折線の下記 （ C ) 式で定義される半価幅広がり Bが 0. 1〜 1.0であることを特徴とする 強度延性バランスに優れ、 かつマルチパス溶接熱影響部の耐粒界腐 食性および溶接部フユ一ジョ ンライ ン近傍の耐優先腐食性に優れた 低クロム含有ステンレス鋼。 (4) Stainless steel composed of the components described in any one of (1) to (3), wherein the metal structure is a two-phase structure of a ferrite phase and a martensite phase. {110} The half-width broadening B defined by the following formula (C) of the diffraction line is 0.1 to 1.0, and has an excellent balance of strength and ductility, and the grain boundary of the heat-affected zone of the multipass welding A low-chromium stainless steel with excellent corrosion resistance and preferential corrosion resistance in the vicinity of the welded fusion line.
B = (W - Wo) /Wo · · · · ( C )  B = (W-Wo) / Wo · · · · (C)
Wo : 内部歪み無しの半価幅 （deg) Wo: Half width without internal distortion (deg)
W ： 半価幅 （deg) W: Half width (deg)
( 5 ) ( 1 ) 〜 （ 3 ) のいずれかに記載の成分からなる铸片の熱 間圧延工程における加熱温度は、 铸片の成分から決定されるオース テナイ ト単相の上限温度 Ac4未満であるか、 あるいは Ac4超で加熱す る場合にはオーステナイ ト相中のデル夕フェライ ト量が 50%超とな る温度とすることを特徴とするマルチパス溶接熱影響部の耐粒界腐 食性および溶接部フュージョ ンライン近傍の耐優先腐食性に優れた 低クロム含有ステンレス鋼の製造方法。 図面の簡単な説明 (5) Heat of the flakes comprising the component according to any one of (1) to (3) The heating temperature in the hot rolling process is lower than the upper limit temperature Ac 4 of the austenite single phase determined from the components of the flakes, or in the case of heating above Ac 4 Production of low chromium-containing stainless steel with excellent intergranular corrosion resistance in heat-affected zone of multipass welding and preferential corrosion resistance in the vicinity of welded fusion line Method. Brief Description of Drawings
図 1 は、 焼鈍温度と硬さの関係の一例を示す図である。  Figure 1 shows an example of the relationship between annealing temperature and hardness.
図 2は、 硫酸浸漬試験結果で、 0.25質量％Tiの鋼材でかつ pH= 2 の場合の腐食速度に及ぼす Cuと Crの影響を示す図である。  Fig. 2 shows the effect of Cu and Cr on the corrosion rate of a steel material of 0.25 mass% Ti and pH = 2 as a result of the sulfuric acid immersion test.
図 3は、 改良ス トラウス試験後の溶接熱影響部の断面金属組織を 示す図である。 a ) 比較鋼 No.21 (Ti無添加） の MIG溶接熱影響部の 断面組織 b ) 発明鋼 No. 1 の TIG溶接熱影響部の断面組織 c ) 発明鋼 No. 1 の MIG溶接熱影響部の断面組織 d ) 発明鋼 No.11の MIG溶接熱影 響部の断面組織図である。 （なお、 図 3において、 1， 2， 3は溶 接熱影響部一 1 , 2 , 3を示す。 ）  Figure 3 shows the cross-sectional metallographic structure of the heat affected zone after the improved Strauss test. a) Cross-sectional structure of MIG welding heat-affected zone of comparative steel No. 21 (without addition of Ti) b) Cross-sectional structure of TIG welding heat-affected zone of invention steel No. 1 c) MIG welding heat-affected zone of invention steel No. 1 D) Cross sectional structure of MIG welding heat affected zone of invention steel No. 11. (In Fig. 3, 1, 2 and 3 indicate the weld heat affected zone 1, 2 and 3)
図 4は、 焼鈍条件と強度、 延性の関係の一例を示す図である。 発明を実施するための最良の形態  Fig. 4 shows an example of the relationship between annealing conditions, strength, and ductility. BEST MODE FOR CARRYING OUT THE INVENTION
本発明についてさ らに詳細に説明する。 先ず、 成分の限定理由を 説明する。  The present invention will be described in further detail. First, the reasons for limiting the ingredients will be explained.
Cは、 溶接部のマルテンサイ ト組織の靭性を低下すると共に、 耐 粒界腐食性の低下原因となるため、 その含有量は 0.03質量％以下と する。  C lowers the toughness of the martensitic structure of the weld and reduces the intergranular corrosion resistance. Therefore, its content is set to 0.03% by mass or less.
Nは、 窒化物として析出し Cr欠乏相の生成により、 耐粒界腐食性 を劣化させるため、 その含有量の上限を 0.02質量％以下とする。 た だし、 本発明の組成範囲において、 過度の N低減は精鍊負荷を増大 させるだけでなく、 軟質化することにより、 構造材としての所望の 材質が得られなくなるので、 含有量の下限を 0. 004質量％とした。 N precipitates as a nitride and deteriorates the intergranular corrosion resistance due to the formation of a Cr-deficient phase, so the upper limit of its content is 0.02 mass% or less. The However, in the composition range of the present invention, excessive N reduction not only increases the fertility load, but also softens, so that the desired material as a structural material cannot be obtained, so the lower limit of the content is 0.004. It was set as mass%.
S iは、 通常は脱酸材として用いられる元素であるが、 含有量が 0. 2質量％以下では十分な脱酸効果が得られない。 また、 耐酸化性を 向上させる目的で積極的に添加される場合もあるが、 その含有量が 1質量％を超えると材料の製造性を劣化させるため、 その含有量は 0. 2〜 1質量％に限定した。  Si is an element usually used as a deoxidizing material, but if the content is 0.2% by mass or less, a sufficient deoxidizing effect cannot be obtained. In addition, it may be positively added for the purpose of improving oxidation resistance. However, if its content exceeds 1% by mass, the manufacturability of the material deteriorates, so the content is 0.2 to 1% by mass. %.
Mnは、 オーステナイ ト相 （ァ相） 安定化元素であり、 溶接熱影響 部組織をマルテンサイ ト組織にして溶接部靭性の改善に有効に寄与 する。 また、 Mnは、 S iと同様、 脱酸剤としても有用なので、 1. 5質 量％超の範囲で含有させるものとした。 しかしながら、 過剰に添加 すると、 鋼材の耐食性を劣化させる硫化物系介在物を形成し、 材料 の耐食性を劣化させるので、 その含有量は 2. 5質量％以下に限定し た。 より好ましくは、 2. 0質量％以下でぁる。  Mn is an austenite phase (a phase) stabilizing element, and effectively contributes to the improvement of weld toughness by making the weld heat-affected zone structure a martensite structure. Mn is also useful as a deoxidizer, as is the case with Si, so it should be contained in a range of more than 1.5 mass%. However, if added excessively, sulfide inclusions that deteriorate the corrosion resistance of the steel material are formed, and the corrosion resistance of the material is deteriorated. Therefore, its content is limited to 2.5% by mass or less. More preferably, it is 2.0 mass% or less.
Pは、 粒界偏析しゃすい元素であり、 熱間加工性や成形性、 靭性 を低下させるだけでなく、 耐食性に対しても有害な元素である。 特 に含有量が 0. 04質量％超になるとその影響が顕著になるので、 Pの 含有は 0. 04質量％以下に抑制するものとした。 より好ましくは 0. 02 5 %以下である。  P is an element that segregates at the grain boundaries and is not only detrimental to hot workability, formability, and toughness, but is also harmful to corrosion resistance. In particular, when the content exceeds 0.04 mass%, the effect becomes significant. Therefore, the P content is limited to 0.04 mass% or less. More preferably, it is 0.025% or less.
Sは、 硫化物系介在物を形成し、 鋼材の耐食性を劣化させる元素 であり、 その含有量の上限は 0. 03質量％にする必要がある。 Sの含 有量は少ないほど耐食性は良好となるが、 低 S化のための脱硫負荷 を増大させるので、 下限を 0. 003質量％とするのが好ましい。  S is an element that forms sulfide inclusions and degrades the corrosion resistance of steel. The upper limit of its content must be 0.03 mass%. The smaller the S content, the better the corrosion resistance, but the desulfurization load for reducing S is increased, so the lower limit is preferably set to 0.003 mass%.
C rは、 耐食性の改善に有効な元素であるが 10質量％未満では十分 な耐食性の確保が難しい。 また、 C rはフェライ ト相 （ α相） 安定化 元素であり、 15質量％超の添加は加工性の低下を招くだけでなく、 オーステナイ ト相 （ァ相） の安定性が低下し、 溶接時に十分な量の マルテンサイ ト相を確保できなくなり、 溶接部の強度および靭性の 低下を招く。 従って、 本発明では、 C rは 10質量％以上、 15質量％以 下の範囲で含有させるものとした。 なお、 耐鑌性や加工性、 溶接性 を兼備する上で特に好ましい範囲は 1 1. 0〜 13. 0質量％である。 さ ら に、 マルチパス溶接熱影響部の耐粒界腐食性のみならず、 溶接部フ ユ ージョ ンライ ン近傍の優先腐食発生を防止するには 1 1. 4質量％以 上とするのが好ましい。 Cr is an element effective for improving corrosion resistance, but if it is less than 10% by mass, it is difficult to ensure sufficient corrosion resistance. Cr is an element that stabilizes the ferrite phase (α phase). Addition of more than 15% by mass not only causes a decrease in workability, The stability of the austenite phase (a phase) decreases, and a sufficient amount of martensite phase cannot be secured during welding, leading to a decrease in weld strength and toughness. Therefore, in the present invention, Cr is contained in the range of 10 mass% or more and 15 mass% or less. A particularly preferable range for combining weather resistance, workability, and weldability is 11.0 to 13.0% by mass. Furthermore, not only the intergranular corrosion resistance of the heat-affected zone of multi-pass welding, but also to prevent the occurrence of preferential corrosion in the vicinity of the welded part fusion line. .
N iは、 耐食性の向上のため、 および溶接部にマルテンサイ トを形 成し、 溶接部靱性を向上させるために不可欠な元素であり、 その含 有量は少なく とも 0. 2質量％以上必要となる。 ただし、 その含有量 が 3. 0質量％を超えると溶接部でのマルテンサイ 卜の生成量が著し く増加するため、 0. 2〜 3. 0質量％の含有とする。 また、 N iは熱延板 のマルテンサイ ト組織の焼き戻し軟化抵抗を高める作用があるため 、 強度延性バランスに優れた高強度材を製造する場合には、 熱延板 の焼き戻し焼鈍時の適用範囲を広くすることができる。  Ni is an indispensable element for improving the corrosion resistance and for forming martensite in the weld and improving the toughness of the weld. Its content must be at least 0.2% by mass. Become. However, if the content exceeds 3.0% by mass, the amount of martensite generated in the welded portion will increase significantly, so the content should be 0.2 to 3.0% by mass. In addition, Ni has the effect of increasing the temper softening resistance of the martensite structure of the hot-rolled sheet. Therefore, when manufacturing a high-strength material with a good balance of strength and ductility, it can be applied during tempering and annealing of the hot-rolled sheet. The range can be widened.
T iは、 溶接部での耐粒界腐食性の防止に不可欠な元素である。 T i の含有量は、 Cと Nの含有量の和に対して、 少なく とも 4倍の含有 量が必要となるが、 一方で 0. 35質量％を超えて添加しても耐粒界腐 食性の改善効果は飽和し、 後述するようにクラスター状介在物の生 成により熱間圧延時の表面疵の発生や加工性の低下など他の特性を 劣化させる原因になる。 したがって、 耐食性の面から T i含有量の下 限は 4 X ( C質量％ + N質量％) とし、 表面性状の面から上限を 0. 35質量％とした。  Ti is an essential element for preventing intergranular corrosion resistance in welds. The T i content must be at least four times the sum of the C and N contents. On the other hand, even if it exceeds 0.35% by mass, it is resistant to intergranular corrosion. The effect of improving the food texture is saturated, and as will be described later, the formation of cluster inclusions causes other properties such as surface flaws during hot rolling and deterioration of workability. Therefore, the lower limit of Ti content is set to 4 X (C mass% + N mass%) in terms of corrosion resistance, and the upper limit is set to 0.35 mass% in terms of surface properties.
A 1は脱酸剤として効果的な添加成分であるが、 多量に含有すると 鋼材の表面品質が劣化し、 溶接性も悪くなるため、 その含有量は 0. 005〜 0. 1質量％の範囲とする。 好ましく は、 0. 005〜 0. 03質量％で ある。 A 1 is an effective additive as a deoxidizer, but if it is contained in a large amount, the surface quality of the steel deteriorates and the weldability also deteriorates, so its content is in the range of 0.005 to 0.1% by mass. And Preferably, from 0.005 to 0.03 mass% is there.
さ らに、 以上の成分濃度範囲に加えて下記 （A) 式を満足するよ うに成分濃度を規定する。 かかる規定によって溶接部の靭性、 粒界 腐食とも優れたクロム含有鋼を得ることができる。  In addition to the above component concentration range, the component concentration is specified so that the following equation (A) is satisfied. With this rule, it is possible to obtain a chromium-containing steel with excellent weld toughness and intergranular corrosion.
質量％で、  % By mass
Ύ P (%) =420 x C + 470xN % +23xNi% + 9 xCu%  Ύ P (%) = 420 x C + 470xN% + 23xNi% + 9 xCu%
+ 7 XMn% - 11.5XCr% - 11.5XSi% - 12xMo% -23xV % -47XNb% -49xTi% - 52xAl% + 189≥80 - ， · · （A) (A) 式の r pはステンレス鋼における、 オーステナイ トの安定 度を示す指標であり、 同時にマルテンサイ ト形成のしゃすさを表す 指標でもある。 ァ pが 80%以上の場合には、 溶接熱影響部が冷却時 に高温のオーステナイ ト単相域を経由して完全変態し、 溶接熱影響 部に十分なマルテンサイ ト組織を形成する。 一方、 80%未満の場合 には、 オーステナイ トが不安定になり、 マルテンサイ 卜相形成が不 十分となる。 同時に、 熱間圧延中にァ単相を経て完全変態させ、 熱 延ままで細粒組織を得るためにも （A) 式を満足することが必要で ある。 -- '  + 7 XMn%-11.5XCr%-11.5XSi%-12xMo% -23xV% -47XNb% -49xTi%-52xAl% + 189≥80-, · · · · · · · · · · · It is an index that shows the stability of the site, and at the same time, an index that shows the speed of martensite formation. When the ap is 80% or more, the weld heat affected zone undergoes complete transformation via the high-temperature austenite single phase during cooling, and a sufficient martensite structure is formed in the weld heat affected zone. On the other hand, if it is less than 80%, the austenite becomes unstable and the formation of the martensite phase is insufficient. At the same time, it is necessary to satisfy the formula (A) in order to obtain a fine grain structure as it is while being rolled by complete transformation through a single phase during hot rolling. -'
また、 フェライ トの結晶粒径も微細な方が、 粒界面積を増加させ ることによる耐粒界腐食性の向上ならびに低温靭性の向上にも有利 である。 従ってフェライ ト平均粒径は、 JIS G 0522に準拠したフエ ライ ト粒度番号で 6番以上とすることが好ましい。 なお、 このフエ ライ ト粒度番号は最終製品におけるものを指すが、 本発明のクロム 含有鋼は構造材料として低コス トであることが求められるため、 最 終製品は専ら熱延焼鈍材である。  A finer ferrite grain size is also advantageous in improving intergranular corrosion resistance and low temperature toughness by increasing the interfacial area. Therefore, the ferrite average particle size is preferably 6 or more in terms of ferrite particle size number according to JIS G 0522. The ferrite grain size number refers to that in the final product. Since the chromium-containing steel of the present invention is required to have a low cost as a structural material, the final product is exclusively a hot-rolled annealing material.
さ らに、 以上の成分濃度範囲および上記 （A) 式に加え、 下記 （ B ) 式を満足するように成分濃度を規定する。 かかる規定によって 熱延板の表面疵の発生を防止することができる。 ( B ) 式を満足せず T iと Nの含有量が多いと、 溶鋼が凝固すると き、 液相線温度において、 粗大な T iNが多数晶出し、 熱延時に表面 疵の原因となる。 前述のように、 最終製品は熱延焼鈍材であり、 デ スケールして酸洗肌として使用されることが多いので、 表面疵防止 の観点からも成分の規制が必要である。 In addition to the above component concentration range and the above equation (A), the component concentration is defined so as to satisfy the following equation (B). Such regulations can prevent surface flaws on the hot rolled sheet. If the content of Ti and N is not satisfied and (B) is not satisfied, the molten steel will solidify, and a large number of coarse TiN will crystallize at the liquidus temperature, causing surface defects during hot rolling. As mentioned above, the final product is a hot-rolled annealed material and is often descaled and used as pickled skin. Therefore, it is necessary to regulate the components from the viewpoint of preventing surface wrinkles.
T i % X N %く 0. 004 · · · · ( B )  T i% X N% 0.0.004 (B)
以上説明した低クロム含有ステンレス鋼は、 溶接部の靭性および 耐粒界腐食性に優れるが、 さ らに pHの低い溶液中での耐食性を向上 させるには、 鋼中への Moあるいは Cuの添加が有効に働く。 特に石炭 を積載する場合の、 石炭浸出液による低 pHの希硫酸環境に対しては Cu添加が有効である。  The low chromium content stainless steel described above is excellent in weld toughness and intergranular corrosion resistance, but in order to improve the corrosion resistance in low pH solutions, addition of Mo or Cu to the steel Works effectively. In particular, Cu loading is effective for low pH dilute sulfuric acid environment with coal leachate when loading coal.
Mo、 とも耐食性を向上させるには、 少なく ともそれぞれ 0. 05質 量％以上添加する必要があるが、 Moは 3質量％、 Cuは 3質量％を超 えて添加すると、 耐食性の向上効果が飽和するとともに加工性など を劣化させる原因となることから、 Moは 3質量％、 Cuは 3質量％を その上限とする。 好ましく は、 Mo、 Cuとも 0. 1〜 1. 5質量％である。 また はじ， N , N iに次ぐオーステナイ ト安定元素であることから 、 ( A ) 式のァ pから算出される相安定性を制御するためにも有効 な元素である。 また、 Cuは固溶強化元素でもあるため、 高強度化す る場合には有用な元素である。  In order to improve the corrosion resistance of both Mo and Mo, it is necessary to add at least 0.05% by mass, respectively. However, if Mo exceeds 3% by mass and Cu exceeds 3% by mass, the effect of improving corrosion resistance is saturated. In addition, the upper limit is 3 mass% for Mo and 3 mass% for Cu. Preferably, both Mo and Cu are 0.1 to 1.5% by mass. Since it is an austenite stable element next to N and Ni, it is also an effective element for controlling the phase stability calculated from a in Eq. (A). Also, Cu is a solid solution strengthening element, so it is a useful element for increasing strength.
Nbと Vは炭窒化物形成元素であり、 選択的に添加することができ る。 Cと Nの固定化のためには、 Nbでは 0. 0 1質量％の含有量が必要 となるが、 0. 5質量％を超えて添加しても耐粒界腐食性の改善効果 は飽和し、 加工性など他の特性を劣化させる原因になる。 したがつ て、 Nbは 0. 01〜0. 5質量％の範囲とする。 好ましく は、 0. 03〜0. 3質 量％である。 Vも同様の理由により、 0. 01〜0. 5質量％の範囲とす る。 好ましく は、 0. 03〜0. 3質量％である。 また、 Nbは熱延板のマ ルテンサイ ト組織の焼き戻し軟化抵抗を高める作用があるため、 強 度延性バランスに優れた高強度材を製造する場合には、 熱延板の焼 き戻し焼鈍時の適用範囲を広くすることができる。 Nb and V are carbonitride forming elements and can be selectively added. In order to fix C and N, Nb requires a content of 0.01% by mass, but even if added over 0.5% by mass, the improvement effect of intergranular corrosion resistance is saturated. However, it may cause deterioration of other characteristics such as workability. Therefore, Nb is in the range of 0.01 to 0.5 mass%. Preferably, it is 0.03 to 0.3% by mass. For the same reason, V is also in the range of 0.01 to 0.5 mass%. Preferably, it is 0.03 to 0.3 mass%. Nb is the hot rolled sheet metal. Since it has the effect of increasing the temper softening resistance of the rutensite structure, when manufacturing high-strength materials with an excellent balance of strength and ductility, the range of application during tempering and annealing of hot-rolled sheets can be widened. .
強度延性バランスを調質した高強度材は、 耐カ 450MP a以上で伸び は 15 %以上である。 耐カ 450MPaで、 伸び 20 %以上であることが望ま しい さ らに望ましくは、 耐力 500MP a以上で、 伸び 20 %以上である 強度延性バランスに優れた高強度の低クロム含有ステンレス鋼の 金属組織は、 完全焼鈍したフエライ ト単相組織ではなく、 フェライ 卜相とマルテンサイ ト相の 2相組織に制御されたものである。 熱延 板のマルテンサイ ト相組織の焼き戻し軟化過程にある金属組織であ High-strength materials with a tempered balance of strength and ductility have a resistance of 450 MPa or more and an elongation of 15% or more. It is desirable to have a resistance of 450MPa and an elongation of 20% or more.More preferably, it has a yield strength of 500MPa or more and an elongation of 20% or more. Is not a fully annealed ferrite single-phase structure, but a two-phase structure consisting of a Ferai phase and a martensite phase. It is a metal structure in the temper softening process of the martensite phase structure of hot-rolled sheets.
Ό 、 マルテンサイ 卜相の高強度と焼き戻しによる延性を具備したも のである 。 また、 上記の金属組織に、 析出したオーステナイ ト相 （ 逆変能、 r相） が冷却時に変態したマルテンサイ ト相を複合した金属 組織でち良い。 、 マ ル テ ン テ ン し た し た 具備 具備 具備 具備 し た し た 高 高 高 し た 高 し た し た し た し た. Also, a metal structure in which the precipitated austenite phase (reverse transformation, r phase) is transformed into a martensite phase transformed during cooling may be used.
上記の焼き戻しによるマルテンサイ 卜の軟化進展の程度と強度、 延性には相関関係があるため、 マルテンサイ ト相とフェライ ト相の 分率を制御することが、 強度や延性等の材質設計するうえで重要で ある。 しかしながら、 金属組織中のフェライ ト相とマルテンサイ ト 相を区別して体積率を求めることは一般的には困難である。 両相と も同じ結晶構造であるため、 X線回折での回折角度が殆ど同じであ り区別することが難しく、 また両相ともに強磁性体であるために磁 性の有無により区別することも難しい。  Since the degree of softening of martensite cocoon due to tempering and the strength and ductility are correlated, controlling the fraction of martensite phase and ferrite phase is important in designing materials such as strength and ductility. is important. However, it is generally difficult to obtain the volume fraction by distinguishing between ferrite phase and martensite phase in the metal structure. Since both phases have the same crystal structure, the diffraction angles in X-ray diffraction are almost the same and are difficult to distinguish, and because both phases are ferromagnetic, they can be distinguished by the presence or absence of magnetic properties. difficult.
そこで、 本発明においては、 マルテンサイ ト組織の焼き戻し過程 における転位の回復程度すなわち結晶構造の乱れの復旧程度を計測 できる方法として、 X線回折プロファイルにおける Κ α { 1 10 } 回 折線の下記 （ C ) 式で定義される半価幅広がり Βを適用することに した。 Κ α ΐ , Κ « 2のピークの分離を行って、 Κ α ΐ線の半価幅 を測定して Βを求めた。 Therefore, in the present invention, as a method for measuring the degree of recovery of dislocations in the tempering process of the martensite structure, that is, the degree of recovery of the disorder of the crystal structure, the following (C ) Applying the half-value spread Β defined by did.ピ ー ク α ΐ and Κ «2 peaks were separated, and the half width of the Κ α ΐ line was measured to obtain Β.
Β = (W— Wo) /Wo—— —— （C )  Β = (W— Wo) / Wo—— —— (C)
Wo : 内部歪み無しの半価幅 （deg)  Wo: Half width without internal distortion (deg)
W ： 半価幅 （deg)  W: Half width (deg)
本発明においては、 X線源として Cuを用いたが、 他の X線源であ つてもよい。 また、 11質量％Crフェライ ト系ステンレス鋼 （後述の 実施例表 1 の鋼材 No. 1 ) の値 （Wo= 0.089deg) を用いて Bを評価 した。  In the present invention, Cu is used as the X-ray source, but other X-ray sources may be used. In addition, B was evaluated using the value (Wo = 0.089 deg) of 11 mass% Cr ferritic stainless steel (steel material No. 1 in Example Table 1 described later).
本手法は （社） 日本鉄鋼協会、 材料と組織の特性部会、 ステンレ ス鋼の成形性と利用技術自主フォーラム、 「ステンレス鋼の高強度 化と利用技術」 平成 10年 9 月 29日、 49頁、 に開示されているように 、 鋼の焼戻挙動を評価するための汎用的な評価手法である。  This method is based on the Japan Iron and Steel Institute, Material and Structure Properties Subcommittee, Stainless Steel Formability and Utilization Technology Voluntary Forum, “Strengthening and Utilization Technology of Stainless Steel” September 29, 1998, p. 49 As disclosed in, is a general purpose evaluation method for evaluating the tempering behavior of steel.
半価幅は転位密度に相当する。 半価幅の定義は、 回折面からのピ ーク強度の 1 2 の強度に対応する回折角の幅である。 半価幅が大 きいほど材料のひずみ量 （結晶構造の乱れ） が大きく、 焼き戻しが 進行し転位が回復して歪み量が小さくなると半価幅は小さくなる。 B = 0 は歪みを除去した焼鈍組織 （焼戻組織でフェライ ト単相） を 意味しており、 本発明においては、 Bは 0. 1未満であった。 熱延ま まの鋼板のマルテンサイ ト組織では B値はおよそ 2.0である。 焼き 戻し過程でマルテンサイ ト相とフェライ 卜相の 2相組織に制御し、 強度延性に優れた高強度材とするには、 B値は 0. 1〜 1.0である。 好 ましく は 0.3〜0.8である。 B値が 1.0超〜 2.0未満では、 焼き戻しが 進まず延性が不足する。  The half width corresponds to the dislocation density. The definition of the half-value width is the width of the diffraction angle corresponding to the intensity of 1 2 of the peak intensity from the diffractive surface. The larger the half width, the greater the amount of strain (disturbance of the crystal structure) of the material. As the tempering progresses and the dislocation recovers and the strain amount decreases, the half width decreases. B = 0 means an annealed structure from which strain has been removed (tempered structure and ferrite single phase). In the present invention, B was less than 0.1. In the martensitic structure of hot-rolled steel sheets, the B value is approximately 2.0. In order to obtain a high-strength material with excellent strength ductility by controlling the martensite phase and ferri-phase to a two-phase structure during the tempering process, the B value is 0.1 to 1.0. It is preferably 0.3 to 0.8. If the B value is more than 1.0 and less than 2.0, tempering does not proceed and ductility is insufficient.
次に、 低クロム含有ステンレス鋼の好適な製造方法について説明 する。 まず、 上記の好適成分組成に調整した溶鋼を、 転炉または電 気炉等の通常公知の溶製炉にて溶製したのち、 真空脱ガス （RH法） 、 VOD法、 AOD法等の公知の精練方法で精練し、 ついで連続铸造法あ るいは造塊一分塊法でスラブ等に铸造して、 鋼素材とする。 鋼素材 は、 ついで加熱され、 熱間圧延工程により熱延鋼板とされる。 その 際、 熱間圧延工程における加熱温度の選択は、 熱延板のエッジ割れ 回避の観点より非常に重要である。 オーステナイ ト系ステンレス鋼 の場合、 熱間加工の段階でデル夕フェライ トが 50 %未満、 特に 10〜 30 %含有する相状態では、 オーステナイ ト、 デル夕フェライ ト両相 の変形抵抗の差異により、 軟質なデル夕フェライ ト相に歪みが集中 し、 両相界面にクラックを生じ、 面割れや特にエッジ割れなどの欠 陥が発生しやすいので、 工程、 歩留、 品質上種々の問題が生じる。 本発明者は、 低クロム含有ステンレス鋼の熱間加工温度域において も同様であることを見出した。 Next, a preferred method for producing a low chromium-containing stainless steel will be described. First, the molten steel adjusted to the above preferred component composition is melted in a commonly known melting furnace such as a converter or an electric furnace, and then vacuum degassing (RH method) The steel material is scoured by a known scouring method such as VOD method or AOD method, and then forged into a slab or the like by a continuous forging method or an ingot one-piece method. The steel material is then heated and made into a hot-rolled steel sheet by a hot rolling process. At that time, the selection of the heating temperature in the hot rolling process is very important from the viewpoint of avoiding edge cracks in the hot rolled sheet. In the case of austenitic stainless steel, during the hot working stage, in the phase state containing less than 50% of Dell evening ferrite, especially 10-30%, due to the difference in deformation resistance between both austenite and Dell evening ferrite, Distortion concentrates on the soft Dell evening ferrite phase, causing cracks at the interface between the two phases, and defects such as surface cracks and especially edge cracks are likely to occur, resulting in various problems in process, yield, and quality. The present inventor has found that the same applies to the hot working temperature range of the low chromium-containing stainless steel.
したがって、 铸片の熱間圧延工程における加熱温度は、 铸片の成 分から決定されるオーステナイ ト単相の上限温度 Ac4未満であるか 、 あるいは Ac4超で加熱する場合にはオーステナイ ト相中のデル夕 フェライ ト量が 50 %超となる温度を選択すると、 良好な熱間加工性 を得られる。 Ac4の温度は、 統合型熱力学計算システムの The rmo - C a 1 c (販売元 ： CRCソ リューショ ンズ） による状態図計算により、 鋼 材の成分値から決定することができる。 加熱温度が高いとデルタフ ェライ ト量の増加に伴い変形能も向上するが、 デル夕フェライ ト主 体の相状態の場合、 加熱温度が高すぎると結晶粒の粗大化を招き、 熱間加工時に熱延板エッジ部に粗大結晶粒に起因するしわ状の欠陥 が発生し、 エッジ割れと同様に工程、 歩留、 品質上の問題となるの で、 加熱温度は 1300で以下とするのが好ましい。 Therefore, the heating temperature in the hot rolling step of铸片is austenite phase in the case of heating in either the upper limit temperature Ac below 4 austenite single phase deposition minutes determined in铸片, or Ac 4 than Good hot workability can be obtained by selecting a temperature at which the amount of ferrite is greater than 50%. The temperature of Ac 4 can be determined from the component values of the steel by phase diagram calculation using the integrated thermodynamic calculation system Thermo-C a 1 c (distributor: CRC Solutions). When the heating temperature is high, the deformability is improved as the amount of delta ferrite increases, but in the case of the Dell State ferrite main phase, if the heating temperature is too high, the crystal grains become coarse and during hot working. Wrinkle-like defects due to coarse crystal grains occur at the edge of the hot-rolled sheet, which causes problems in process, yield, and quality as with edge cracking. Therefore, the heating temperature is preferably 1300 or less. .
また、 熱間圧延工程では所望の板厚の熱延鋼板とすることができ ればよく、 熱間圧延条件は特に限定されないが、 熱間圧延の仕上げ 温度は 800 :以上、 1000で以下とすることが、 強度、 加工性や延性 を確保する点から好ましい。 また、 巻き取り温度は、 焼戻し焼鈍を する場合には 800 以下、 好ましくは 650で〜 750 である。 Moreover, in the hot rolling process, it is only necessary to obtain a hot rolled steel sheet having a desired thickness, and the hot rolling conditions are not particularly limited, but the hot rolling finishing temperature is 800: or more and 1000 or less. Can be strength, workability and ductility It is preferable from the viewpoint of ensuring. The coiling temperature is 800 or less, preferably 650 to 750 when tempering annealing is performed.
なお、 後述の焼き戻し過程のフェライ ト相とマルテンサイ ト相の 2相組織にて高強度化する場合には、 熱間圧延の仕上げ温度を 900 で以下、 巻き取り温度を 650で以下とすることにより、 加工歪みを 蓄積し焼き戻し軟化抵抗を向上することが、 焼鈍条件範囲を広くす る上で望ましい。  In addition, when increasing the strength of the two-phase structure of the ferrite phase and martensite phase, which will be described later, the hot rolling finishing temperature should be 900 or less and the coiling temperature should be 650 or less. Therefore, it is desirable to accumulate work strain and improve the temper softening resistance in order to widen the annealing condition range.
熱間圧延終了後、 組織がマルテンサイ ト相となり硬質なものにつ いては、 マルテンサイ ト相の焼戻しによる軟質化のために熱延板焼 鈍を施すのが好ましい。 焼き戻し温度はフェライ ト温度域で出来る だけ高い温度が望ましい。 フェライ ト単相の上限温度である 変態 点は N i等の添加量によって異なるが、 実用鋼では概ね 650〜 700 :に 調整することが多く、 この温度以下での焼鈍が望ましい。 したがつ て、 この熱延板焼鈍は、 焼鈍温度 ： 650〜 750t 、 保持時間 ： 2〜20 h とするのが軟質化のみならず、 加工性の改善、 延性の確保の観点 から好ましい。  After the hot rolling is finished, it is preferable to subject the hardened structure to a martensite phase by hot-rolled sheet annealing to soften the martensite phase by tempering. The tempering temperature should be as high as possible in the ferrite temperature range. Although the transformation point, which is the upper limit temperature of the ferrite single phase, varies depending on the amount of Ni, etc., it is often adjusted to about 650-700 for practical steels, and annealing below this temperature is desirable. Therefore, in this hot-rolled sheet annealing, it is preferable to set the annealing temperature: 650 to 750 t and the holding time: 2 to 20 h from the viewpoint of improving workability and ensuring ductility.
なお、 熱延板焼鈍後、 600〜750での温度範囲を冷却速度が 50で Z h以下の徐冷とするのが、 軟質化の面でより好ましい。  In addition, it is more preferable in terms of softening that the temperature range between 600 and 750 is annealed at a cooling rate of 50 and Zh or less after hot-rolled sheet annealing.
必要に応じ、 強度延性バランスに優れた高強度の低クロム含有ス テンレス鋼を提供する場合には、 完全焼鈍したフェライ ト相組織で はなく、 熱延板のマルテンサイ ト相組織の焼き戻し軟化過程にある フェライ ト相とマルテンサイ ト相の 2相組織に制御することが必要 である。 このため、 熱延板の熱処理温度を 550t：〜 850でとする。 保 持時間には特に制約は無いが、 実用性を考慮した熱処理時間とする ことが望ましい。 よって、 好ましく は熱処理温度 600〜 800t：、 保持 時間を 2〜 30 hとすることが望ましい。 バッチ熱処理の場合には、 通常、 冷却速度は 50t: Z h以下に制御される。 熱処理温度は (^以 上であっても Ac ,以下であっても良い。 If necessary, when providing a high-strength, low-chromium stainless steel with an excellent balance of strength and ductility, the temper softening process of the martensite phase structure of the hot-rolled sheet rather than the fully annealed ferrite phase structure Therefore, it is necessary to control the two-phase structure of the ferrite phase and martensite phase. For this reason, the heat treatment temperature of the hot-rolled sheet is set to 550 t: to 850. There is no particular restriction on the holding time, but it is desirable to set the heat treatment time considering practicality. Therefore, it is preferable that the heat treatment temperature is 600 to 800 t: and the holding time is 2 to 30 h. In the case of batch heat treatment, the cooling rate is usually controlled to 50t: Zh or less. Heat treatment temperature is (^ or less The above may be Ac, or the following.
Ac ,以下の場合には、 マルテンサイ ト相の焼き戻し軟化過程にあ る金属組織であり、 保持時間は完全焼鈍したフェライ ト単相組織と なるより も短時間の保持時間とする必要がある。 この熱処理条件は 、 鋼の個別の成分組成について、 熱延板組織の温度一時間マップを 作成することにより求めることができる。  Ac, in the following cases, is a metal structure in the temper softening process of the martensite phase, and the retention time needs to be shorter than that of a fully annealed ferrite single phase structure. This heat treatment condition can be obtained by creating a one-hour temperature map of the hot-rolled sheet structure for each individual component composition of steel.
Ac ,以上の場合には、 以下の熱処理で得られる金属組織に加え て、 析出したオーステナイ ト相 （逆変態ァ相） が冷却時に変態した マルテンサイ ト相を複合した金属組織である。 この場合の保持時間 は特に限定されないが、 実用的には 2 〜30時間であり、 好ましくは 2 〜 1 5時間である。  In the above case, in addition to the metal structure obtained by the following heat treatment, it is a metal structure in which the precipitated austenite phase (reverse transformation phase) is combined with the martensite phase transformed during cooling. The holding time in this case is not particularly limited, but is practically 2 to 30 hours, preferably 2 to 15 hours.
また、 熱延後、 あるいは熱延焼鈍後の鋼板は、 必要に応じショ ッ トブラス ト、 酸洗等によりスケールを除去した状態で、 あるいはさ らに研磨、 スキンパス等により所望の表面性状に調整したのち、 製 品板としてもよい。 また、 本発明による成分鋼は、 厚鋼板や熱間圧 延により製造する形鋼、 さ らには棒鋼といった分野で、 構造用鋼と して利用できる種々の鋼材への適用が可能である。 実施例  In addition, the steel sheets after hot rolling or after hot rolling annealing were adjusted to the desired surface properties with the scale removed by shot blasting, pickling, etc. as necessary, or by polishing, skin pass, etc. Later, it may be a product plate. Further, the component steel according to the present invention can be applied to various steel materials that can be used as structural steels in fields such as thick steel plates, shaped steels manufactured by hot rolling, and bar steels. Example
(実施例 1 )  (Example 1)
表 1 および表 2 に第一の課題に関する発明例と比較例を示す。 表 1 は、 本発明鋼及び比較鋼の鋼中成分を質量％で示す。 鋼材 No . 1 〜20は本発明鋼であり、 鋼材 No. 2 1〜26は比較鋼である。  Tables 1 and 2 show invention examples and comparative examples related to the first problem. Table 1 shows the components in steel of the invention steel and comparative steel in mass%. Steel Nos. 1 to 20 are invention steels, and Steel Nos. 2 to 26 are comparative steels.
真空溶解法により、 表 1 に示す成分の铸片を、 40 kgあるいは 35 kg の偏平イ ンゴッ トに溶製した。 これらの鋼の表面を手入れした後、 1 1 50 〜1 250 でィ ンゴッ トを 1 時間加熱し、 複数パスからなる熱 間粗圧延およびそれに続く熱間仕上げ圧延を実施した。 熱延圧延終 了温度は 800で〜 950でであった。 熱延板は空冷の後、 巻き取り温度 700°Cで 1 時間保持し、 その後空冷して巻き取り模擬熱処理を実施 し、 板厚 4 mmの熱延板とした。 続いて、 熱延板の焼鈍温度を決定す るために、 各成分値の熱延板を 600で〜 775 で 5時間、 その後空冷 の熱処理を実施した。 最も軟質となる温度を焼鈍温度とした。 The pieces of the ingredients shown in Table 1 were melted into a 40 kg or 35 kg flat ingot by vacuum melting. After cleaning these steel surfaces, the ingots were heated for 1 hour at 1 1 50 to 1 250 to perform hot rough rolling consisting of multiple passes followed by hot finish rolling. Hot rolled The end temperature was 800 to 950. The hot-rolled sheet was air-cooled, held at a coiling temperature of 700 ° C for 1 hour, and then air-cooled and subjected to a simulated winding heat treatment to obtain a hot-rolled sheet with a thickness of 4 mm. Subsequently, in order to determine the annealing temperature of the hot-rolled sheet, the hot-rolled sheet of each component value was subjected to 600 to 775 for 5 hours, and then air-cooled heat treatment. The temperature at which it becomes the softest was the annealing temperature.
図 1 は、 熱処理温度と硬さの関係を示した一例である。 熱延まま では、 高硬度であるが、 熱処理することによって軟質化している。 この例では 675〜700でで最も軟質化する。 それ以上の高温で熱処理 すると、 オーステナイ ト相が析出し冷却時にマルテンサイ 卜に変態 するので、 逆に硬質化する。 なお、 L断面のビッカース硬さ （Hv) は、 荷重 1 kgで板厚中央部にて測定し評価した。  Figure 1 shows an example of the relationship between heat treatment temperature and hardness. As hot-rolled, it has high hardness but is softened by heat treatment. In this example, it becomes softest at 675 to 700. If heat treatment is performed at a higher temperature, the austenite phase precipitates and transforms into martensite during cooling, so it hardens. The Vickers hardness (Hv) of the L section was measured and evaluated at the center of the plate thickness with a load of 1 kg.
最後にショ ッ トおよび酸洗によるデスケーリ ングを実施し、 熱延 焼鈍板を製造した。  Finally, descaling by shot and pickling was performed to produce hot-rolled annealed sheets.
表 2 に本発明例および比較例の各種特性の評価結果を示す。 事例 No. 1 〜20は本発明例であり、 事例 No. 2 1〜27は比較例である。  Table 2 shows the evaluation results of various characteristics of the inventive examples and comparative examples. Case Nos. 1 to 20 are examples of the present invention, and Case Nos. 2 to 27 are comparative examples.
本発明鋼は複数溶接部の粒界腐食や溶接部フュージョ ンライ ン近 傍の優先腐食の発生の無い優れた溶接部耐食性を有しているのみな らず、 溶接部の衝撃特性も優れている。 さらに、 強度、 延性の材質 も良好で、 選択的に添加する元素によって耐硫酸性を飛躍的に向上 することも可能である。 さ らに、 鋼材の成分設計や製造条件の工夫 により、 熱延板のエッジ割れや表面欠陥のない、 製造性に優れた鋼 材とすることができる。  The steel of the present invention not only has excellent weld corrosion resistance without occurrence of intergranular corrosion of multiple welds and preferential corrosion near the weld fusion line, but also has excellent impact characteristics of the welds. . Furthermore, the material of strength and ductility is also good, and it is possible to drastically improve sulfuric acid resistance by selectively adding elements. In addition, by designing the components of the steel material and devising the manufacturing conditions, it is possible to obtain a steel material with excellent manufacturability that is free from edge cracks and surface defects in the hot rolled sheet.
比較例の事例 No. 2 1は Π含有量および T i / ( C + N ) が本発明範 囲を外れたために、 溶接熱影響部の耐食性に劣る。 比較例の事例 No . 22は T i · Nが本発明範囲を外れたために、 熱延にて表面疵が発生 した。 比較例の事例 No. 23は T iが本発明範囲の上限を外れたために 、 T i · Nが本発明範囲を外れ、 熱延にて表面疵が発生した。 比較例 の事例 No. 24はァ pが本願発明範囲を外れたため、 溶接熱影響部の 衝撃特性が劣る。 比較例の事例 No. 25は C rが本発明範囲の上限を外 れたために、 ァ pが本願発明範囲を外れ、 溶接熱影響部の衝撃特性 が劣る。 また、 本願はァ単相の温度域が存在しないので Ac ,を定義 できない。 比較例の事例 No. 26は C rが本発明範囲の下限を外れたた めに、 耐硫酸性および溶接熱影響部の耐食性が劣る。 比較例の事例 No. 27は、 熱延加熱温度での δ量が本発明範囲を外れたために、 ェ ッジ割れが発生した。 Comparative Example No. 21 is inferior in corrosion resistance of the heat affected zone because the soot content and T i / (C + N) are out of the scope of the present invention. In Comparative Example No. 22, since T i · N was outside the scope of the present invention, surface flaws occurred during hot rolling. In Comparative Example No. 23, T i deviated from the upper limit of the range of the present invention, so T i · N deviated from the range of the present invention, and surface flaws occurred due to hot rolling. Comparative example In case No. 24, the impact characteristics of the weld heat-affected zone are inferior because a is outside the scope of the present invention. In Comparative Example No. 25, Cr deviated from the upper limit of the scope of the present invention, so that p deviated from the scope of the present invention, and the impact characteristics of the weld heat affected zone were inferior. In addition, Ac, cannot be defined because there is no single-phase temperature range in this application. Comparative Example No. 26 is inferior in sulfuric acid resistance and corrosion resistance of the heat affected zone because Cr is outside the lower limit of the range of the present invention. In Comparative Example No. 27, edge cracking occurred because the amount of δ at the hot rolling heating temperature was out of the range of the present invention.
以下に、 各種特性の評価試験方法について説明する。  The following describes the evaluation test methods for various characteristics.
成分は鋼板から試験片をサンプリ ングして成分分析を行った。 C , S， Nについてはガス分析法 （Nは不活性ガス溶融一熱伝導測定 法で、 C , Sは酸素気流中燃焼一赤外線吸収法） で、 その他の元素 については蛍光 X線分析装置 （SH I MADZU , MXF-2 1 00 ) で実施した。 熱延板の耳割れ発生有無の判断は、 熱延板のエッジ部のクラック 有無を外観観察から判断した。 割れ無しを〇、 クラック有りで表面 から裏面へクラックが貫通していない場合を△、 クラック有りで、 表面から裏面へクラックが貫通している場合を Xとした。 なお、 熱 延加熱温度が、 科学技術計算ソフ ト ： サーモカルクを用いて各成分 値から計算される Ac4 (オーステナイ ト単相の上限温度） より も低 い温度であるか、 あるいは高い場合にはデル夕フェライ ト量が 50 % 超の温度である場合に限り、 耳割れ発生が生じなかった。 The components were analyzed by sampling test pieces from steel plates. Gas analysis method for C, S and N (N is an inert gas melting and thermal conductivity measurement method, C and S are combustion and infrared absorption method in oxygen stream), and X-ray fluorescence analyzer for other elements ( SH I MADZU, MXF-2 1 00). Judgment of the occurrence of cracks in the hot-rolled sheet was made based on the appearance observation. ◯ indicates no crack, △ indicates that there is no crack from the front surface to the back surface with a crack, and X indicates that there is a crack and the crack penetrates from the front surface to the back surface. In addition, when the hot rolling heating temperature is lower or higher than Ac 4 (the upper limit temperature of the austenite single phase) calculated from each component value using the scientific calculation software: Thermocalc. Ear cracking did not occur only when the amount of Dell evening ferrite was above 50%.
熱延板の表面欠陥の一つであるへゲ疵の発生有無の判断は、 熱延 板表面の疵有無を外観観察から判断した。 表面欠陥無しを〇、 有り を Xとした。  Judgment on the occurrence of wrinkles, which is one of the surface defects of hot-rolled sheets, was made by visual observation of the presence or absence of wrinkles on the hot-rolled sheet surface. “No” indicates surface defects and “X” indicates presence.
0. 2 %耐カおよび伸びは、 熱延焼鈍板から； H S Z 220 1の 13B号試験 片を作製し、 J I S Z 224 1の試験方法でイ ンス トロン型引張試験機を 用いて試験した。 L方向 （圧延方向に平行） のデータを n = 2で測 定した。 表中の〇xは 0.2%耐力が 320MPa以上を〇で示し、 320MPa 未満を Xで示した。 また、 伸びが 20%以上を〇で示し、 20%未満を Xで示した。 ' 0.2% resistance and elongation were determined from hot-rolled annealed plates; HSZ 2201 No. 13B test pieces were prepared and tested using an Instron type tensile tester according to the JISZ2241 test method. Measure the data in the L direction (parallel to the rolling direction) at n = 2. Set. ○ x in the table indicates 0.2% proof stress of 320MPa or more with ○, and less than 320MPa with X. Elongation of 20% or more is indicated by ○, and less than 20% is indicated by X. '
硫酸浸漬試験方法を以下に示す。 熱延焼鈍酸洗板から、 2匪 X 25 mmX25mmの腐食試験片を作製した。 腐食液は 0.1， 0.01， 0.001N - 硫酸溶液 （pH= 1 , 2， 3 ) とした。 液量は、 試験片 1枚当たり 50 OmLとした。 試験温度は 30 とした。  The sulfuric acid immersion test method is shown below. A 2 mm x 25 mm x 25 mm corrosion test piece was prepared from the hot rolled annealed pickling plate. The corrosive solution was 0.1, 0.01, 0.001N-sulfuric acid solution (pH = 1, 2, 3). The liquid volume was 50 OmL per test piece. The test temperature was 30.
代表例として pH= 2の場合で、 腐食速度が 3 g Zm2/h以下の場 合を〇で、 そのうち特に 2 g Zm2Zh以下の場合を◎で示し、 3 g Zm2Zh超の場合を Xで示した。 図 2は、 硫酸浸漬試験結果で、 0. 25質量％Πの鋼材でかつ pH= 2の場合の腐食速度に及ぼす Cuと Crの 影響を示す図である。 Cuを添加すると腐食速度は低下する。 0.3〜0 .5質量％の添加で腐食速度が最も低下する。 それ以上 Cu添加量を増 加しても、 Cuの効果は飽和する。 Crを増加しても、 腐食速度を低減 することができる。 As a typical example, when pH = 2, the corrosion rate is 3 g Zm 2 / h or less, ◯, especially 2 g Zm 2 Zh or less is indicated by ◎, and when it is more than 3 g Zm 2 Zh Is indicated by X. Fig. 2 shows the effect of Cu and Cr on the corrosion rate when 0.25% by mass of steel is used and the pH is 2, as a result of the sulfuric acid immersion test. When Cu is added, the corrosion rate decreases. The addition of 0.3 to 0.5% by mass results in the lowest corrosion rate. Increasing the amount of Cu added further saturates the Cu effect. Even if Cr is increased, the corrosion rate can be reduced.
TIG溶接は、 なめづけで実施し、 溶接速度 ZOOcmZmiiK 溶接電流 1 10A、 シールガスはアルゴンとした。 MIG溶接は以下の方法で実施 した。  TIG welding was performed with tanning, welding speed ZOOcmZmiiK welding current 110 A, and the sealing gas was argon. MIG welding was performed by the following method.
溶接材料は 309 LSi ( C ： 0.017%、 Si ： 0· 74%、 Mn： 1.55%、 P ： 0.024% , S ： 0.001%、 Ni ： 13.68%、 Cr： 23.22 % ) を用い、 電 圧 25〜30V、 電流 ： 230〜 250A、 シールドガス ： 98% Ar+ 2 %〇2 の条件で行った。 溶接機はダイヘン turbo-pulseを使用した。 4 mm 板厚を貫通、 裏波出し十分条件で実施した。 突き合わせ溶接継ぎ手 の場合には、 90 ° V開先でルートフェイス 2 mm (ギャップ 0 ) とし 、 入熱量 Qは約 12500 J Zcm、 クロス溶接の場合には、 シーム溶接 部は 1 mm厚程度残して削除後溶接し、 Qは約 5600 Jノ cmとした。 Welding material is 309 LSi (C: 0.017%, Si: 0 · 74%, Mn: 1.55%, P: 0.024%, S: 0.001%, Ni: 13.68%, Cr: 23.22%), voltage 25 ~ 30V, current: 230 to 250A, shielding gas: 98% Ar + 2% ○ 2 The welding machine used Daihen turbo-pulse. The test was conducted under sufficient conditions to penetrate the 4 mm plate thickness and reverse the wave. In the case of a butt weld joint, the root face is 2 mm (gap 0) at a 90 ° V groove, the heat input Q is about 12500 J Zcm, and in the case of cross welding, the seam weld is left about 1 mm thick. After deletion, welding was performed, and the Q was about 5600 J cm.
粒界腐食試験としては、 基本的に IISに規格された硫酸一硫酸銅 試験 （G0575) (ス トラウス試験） を用いることが一般的で、 SUS30 4等の高クロム含有ステンレス鋼に対しては適切な試験である。 し かしながら、 鋼中のクロム含有量が低いステンレス鋼 （.12%程度の 低クロムステンレス鋼） については腐食性が厳しすぎるため、 低ク ロムステンレス鋼に適した評価方法で試験を実施した。 すなわち、 硫酸濃度を 0.5%まで低減した溶液中 （沸騰） で 24時間の浸漬試験The intergranular corrosion test is basically copper sulfate monosulfate standardized by IIS. The test (G0575) (Strauss test) is generally used, and this test is appropriate for high chromium-containing stainless steels such as SUS304. However, stainless steel with a low chromium content in the steel (.about 12% low chromium stainless steel) is too corrosive, so tests were conducted using an evaluation method suitable for low chromium stainless steel. . In other words, a 24-hour immersion test in a solution (boiling) with a sulfuric acid concentration reduced to 0.5%
(改良ス トラウス試験） を行った。 硫酸濃度を低減した以外は、 JI Sに準拠して試験を行い、 断面の金属組織の観察より粒界腐食発生 有無の判断をした。 溶接熱影響部を観察し、 粒界腐食の発生無しの 場合を〇、 発生した場合を Xで示した。 また、 溶接部最隣接熱影響 部に優先腐食が全く発生なしの場合は◎で、 複数観察部位のうち一 部発生が認められた場合には〇で、 複数観察部位すべてに優先腐食 の発生有りの場合には Xで示した。 なお、 観察部位は 7箇所である 図 3は、 改良ス トラウス試験後の溶接熱影響部の断面金属組織を 示す図であり、 a ) 〜 d ) はそれぞれ、 a ) 比較鋼鋼材 No.21 (Ti 無添加） の MIG溶接熱影響部の断面組織、 b ) 発明鋼鋼材 No. 1の TI G溶接熱影響部の断面組織、 c ) 発明鋼鋼材 No. 1の MIG溶接熱影響 部の断面組織、 d ) 発明鋼鋼材 No.11の MIG溶接熱影響部の断面組織 を示す。 (Improved Strauss test) was conducted. Except for reducing the sulfuric acid concentration, tests were conducted in accordance with JIS, and the presence or absence of intergranular corrosion was determined by observing the metal structure of the cross section. The weld heat-affected zone was observed, and the case where no intergranular corrosion occurred was marked with ◯, and the case where it occurred was marked with X. In addition, ◎ indicates that no preferential corrosion has occurred in the heat-affected zone closest to the weld, and ◯ indicates that some of the multiple observation sites have been observed. Preferential corrosion has occurred in all of the multiple observation sites. In the case of, it is indicated by X. Figure 3 shows the cross-sectional metallographic structure of the weld heat-affected zone after the modified Strauss test. A) to d) are a) Comparative Steel No. 21 ( B) Cross-sectional structure of the TIG welding heat-affected zone of the invention steel No. 1; c) Cross-sectional structure of the MIG welding heat-affected zone of the invented steel No. 1 D) The cross-sectional structure of the heat-affected zone of MIG welded steel of invention steel No. 11 is shown.
溶接部は、 盛り上がった溶接金属部の他、 3種類の異なった熱影 響部が形成されている。 溶接金属に隣接する熱影響部一 1、 その隣 の熱影響部— 2そして熱影響部— 3である。 1 と 2はマルテンサイ 卜が形成され母材と金属組織が異なっている。 熱影響部一 3は溶接 の熱の影響は受けているがマルテンサイ トは形成されていない。 図 3 a ) では表面から数百 m程度の熱影響部 1〜 3全ての部位で粒 界腐食を主体とする腐食が発生している。 腐食部は表面近傍の黒い コントラス ト部である。 またその上の白色の付着物は、 銅の析出し たもので、 腐食の発生に対応している。 右の図は左の図の表層部の 拡大図である。 図 3 b ) では腐食は全く発生していない。 In the weld zone, there are three different types of heat affected zone in addition to the raised weld metal zone. The heat-affected zone adjacent to the weld metal is 1, the heat-affected zone next to it—2 and the heat-affected zone—3. 1 and 2 are martensite and the base metal and metal structure are different. The heat affected zone 13 is affected by the heat of welding, but no martensite is formed. In Fig. 3 a), corrosion mainly consisting of intergranular corrosion has occurred in all the heat-affected zones 1 to 3 of several hundred meters from the surface. The corroded area is black near the surface Contrast part. The white deposit on top of it is a deposit of copper, corresponding to the occurrence of corrosion. The figure on the right is an enlarged view of the surface layer of the figure on the left. In Fig. 3 b), no corrosion has occurred.
なお、 本実施例においては、 TIG溶接はなめづけ溶接で実施して いるので、 MIG溶接とは異なり溶接金属部は存在していない。 よつ て、 熱影響部は溶接金属部との界面が存在しないので、 優先腐食も 生じ難い。 図 3 c ) では熱影響部 2 と 3の腐食は発生していないが 、 溶接金属に隣接する熱影響部一 1 には、 フュージョ ンラインに沿 つた楔状の腐食の形成が観察される。 図 3 d ) では、 熱影響部の腐 食は全く発生していない。  In this example, since TIG welding is performed by tanning welding, unlike MIG welding, there is no weld metal part. Therefore, since the heat affected zone does not have an interface with the weld metal, preferential corrosion is unlikely to occur. In Fig. 3c), no corrosion of the heat affected zone 2 and 3 occurred, but the formation of wedge-shaped corrosion along the fusion line is observed in the heat affected zone 1 adjacent to the weld metal. In Fig. 3d), no corrosion occurred in the heat affected zone.
衝撃特性はシャルピー試験で実施した。 HS規格に準拠した JIS4 号 2 mmVノッチサブサイズ （厚み 4mm) 試験片を MIG溶接部より採 取し、 20でで衝撃試験を行った。 Vノッチは溶接金属と母材部がそ れぞれ 1 / 2 となる BOND部に入れた。 衝撃値が 30 J Zcm2以上の場 合は〇で、 30 J Zcni2未満の場合には Xで示した。 Impact characteristics were measured by Charpy test. A JIS4 2 mmV notch subsize (thickness 4 mm) test piece conforming to the HS standard was taken from the MIG weld and an impact test was performed at 20. The V-notch was inserted in the BOND part where the weld metal and base metal part were 1/2 each. When the impact value is 30 J Zcm 2 or more, it is indicated as ◯. When the impact value is less than 30 J Zcni 2, X is indicated.
表 1 table 1
Figure imgf000025_0001
Figure imgf000025_0001
r P (%) =420 [C] +470 [N] +23 [Ni] +9 [Cu] +7 [Mn]-ll.5 [Cr] -11.5 [Si] -12 [Mo] -23 [V] -47 [Nb] -49 [Ti] -52 [Al] +189  r P (%) = 420 [C] +470 [N] +23 [Ni] +9 [Cu] +7 [Mn] -ll.5 [Cr] -11.5 [Si] -12 [Mo] -23 [ V] -47 [Nb] -49 [Ti] -52 [Al] +189
—： 本発明範囲を外れることを示す —: Indicates that it is outside the scope of the present invention.
表 2 Table 2
Figure imgf000026_0001
Figure imgf000026_0001
(実施例 2 ) (Example 2)
表 3および表 4に第二の課題に関する発明例と比較例を示す。 表 3 は、 本発明鋼 （鋼材 No. 27〜35) の鋼中成分の質量％を示す 。 真空溶解法により、 表 3 に示す成分の铸片を、 40kgあるいは 35kg の偏平イ ンゴッ 卜に溶製した。 これらの鋼の表面を手入れした後、 1 150ででイ ンゴッ トを 1 時間加熱し、 複数パスからなる熱間粗圧延 およびそれに続く熱間仕上げ圧延を実施した。 熱延圧延終了温度は 800で〜 900でであった。 熱延板は空冷の後、 巻き取り温度 500 で 1 時間保持し、 その後空冷して巻き取り模擬熱処理を実施し、 板厚 4 mmの熱延板とした。 続いて、 熱延板の焼鈍温度を決定するために 、 各成分値の熱延板を 575 ：〜 850でで 5〜50時間まで保定し、 その 後バッチ熱処理の冷却過程を模擬して 20で Z hで制御冷却し 100で 以下で炉から取り出した。  Tables 3 and 4 show invention examples and comparative examples related to the second problem. Table 3 shows the mass% of components in the steel of the present invention steel (steel materials No. 27 to 35). The pieces of the ingredients shown in Table 3 were melted into 40 kg or 35 kg flat ingots by vacuum melting. After cleaning the surface of these steels, the ingot was heated at 1150 for 1 hour, followed by hot rough rolling consisting of multiple passes followed by hot finish rolling. The hot rolling end temperature was 800 to 900. The hot-rolled sheet was air-cooled, held at a coiling temperature of 500 for 1 hour, and then air-cooled and subjected to a simulated coiling heat treatment to obtain a hot-rolled sheet with a thickness of 4 mm. Subsequently, in order to determine the annealing temperature of the hot-rolled sheet, the hot-rolled sheet of each component value is held at 575: -850 at 5-50 hours, and then the batch heat treatment cooling process is simulated at 20 Controlled cooling with Zh and at 100 removed from the furnace.
図 4は、 熱処理条件と強度、 延性の関係を示した一例である。 鋼 材 No. 33を 5時間保定した場合、 熱延ままでは、 高強度低伸びであ る力 、 熱処理することによって軟質化している。 この例では 675で 以上 800で以下の広い温度範囲で、 450MPa以上の耐力で伸び 15 %以 上となる条件が存在する。  Figure 4 shows an example of the relationship between heat treatment conditions, strength, and ductility. When steel No. 33 was held for 5 hours, it was softened by heat treatment with high strength and low elongation as it was hot rolled. In this example, there is a condition that the elongation is 15% or more with a proof stress of 450 MPa or more in a wide temperature range of 675 or more and 800 or less.
最後にショ ッ トおよび酸洗によるデスケーリ ングを実施し、 熱延 焼鈍板を製造した。  Finally, descaling by shot and pickling was performed to produce hot-rolled annealed sheets.
表 4に本発明例および比較例の熱処理条件および各種特性の評価 結果を示す。 事例 No. 28〜41は本発明例であり、 事例 No. 42〜50は比 較例である。 本発明の請求の範囲 4に対応する金属組織の場合には 、 伸びが 15 %以上あるいは 20 %以上で、 かつ耐カ 450MPa以上の強度 延性バランスに優れた高強度の低クロム含有ステンレス鋼が得られ る。  Table 4 shows the heat treatment conditions and various evaluation results of the inventive examples and comparative examples. Case Nos. 28 to 41 are examples of the present invention, and Case Nos. 42 to 50 are comparative examples. In the case of a metal structure corresponding to claim 4 of the present invention, a high-strength, low-chromium-containing stainless steel having an elongation of 15% or more or 20% or more and a high strength and ductility balance of 450 MPa or more is obtained. It is possible.
例えば、 事例 No. 36の B値は 0. 36で、 0. 2 %耐カ 538MPa、 伸び 2 1. 5 %である。 For example, the B value of case No. 36 is 0.36, 0.2% resistance to 538 MPa, elongation 2 1.5 %.
これら鋼はマルチパス溶接熱影響部の耐粒界腐食性および溶接部 フュージョ ンライン近傍の耐優先腐食性にも優れている。  These steels also have excellent intergranular corrosion resistance in the heat-affected zone of multi-pass welding and preferential corrosion resistance in the vicinity of the weld fusion line.
比較例の事例 No.42〜46, 49および 50は熱処理条件が低温または 短時間であり適切でないので金属組織が本発明範囲を外れたために 、 伸びが 15 %未満であり、 強度延性バランスに劣る。 比較例の事例 No.47および 48は熱処理が長時間であり適切でないので金属組織が 本発明範囲を外れたために、 耐力が 450MPa未満であり、 強度延性バ ランスに劣る。  Comparative Examples No.42 to 46, 49 and 50 are not suitable because the heat treatment conditions are low temperature or short time, and because the metal structure is outside the scope of the present invention, the elongation is less than 15% and the strength-ductility balance is inferior. . In Comparative Examples No. 47 and 48, the heat treatment takes a long time and is not suitable, so the metal structure deviated from the scope of the present invention. Therefore, the yield strength was less than 450 MPa, and the strength ductility balance was inferior.
評価試験は下記の方法で実施した。 下記以外は実施例 1 に準じた 金属組織の判定を X線回折における Cu— K a l { 110} 回折線の 半価幅広がり Bで評価した。 B値が 0. 1〜1.0を〇、 0. 1未満と 1.0超 を Xで示す。  The evaluation test was carried out by the following method. Except for the following, the determination of the metal structure in accordance with Example 1 was evaluated by the half-width broadening B of the Cu—Kal {110} diffraction line in X-ray diffraction. A B value of 0.1 to 1.0 is indicated by ◯, and a value of less than 0.1 and exceeding 1.0 is indicated by X.
0.2%耐カおよび伸びの測定方法は実施例 1 と同様であるが、 評 価は以下のようにした。 0.2%耐力が 450MPa以上を〇で示し、 450MP a未満を Xで示した。 特に 0.2%耐力が 500MPa以上の場合を◎で示し た。 また、 伸びが 15%以上を〇で示し、 15%未満を Xで示した。 特 に伸びが 20 %以上の場合を◎で示した。 The measurement methods of 0.2% resistance and elongation were the same as in Example 1, but the evaluation was as follows. 0.2% proof stress is 450MPa or more is indicated by ○, and less than 450MPa is indicated by X. In particular, the case where the 0.2% proof stress is 500 MPa or more is indicated by ◎. Elongation of 15% or more is indicated by ○, and less than 15% is indicated by X. In particular, the case where the elongation is 20% or more is indicated by ◎.
表 3 Table 3
Figure imgf000029_0001
Figure imgf000029_0001
r P (%) =420 [C] +470 [N] +23 [Ni] +9 [Cu] +7 [Mn] -11.5 [Cr] -11.5 [Si] -12 [Mo] -23 [V] -47 [Nb] -49 [Ti] -52 [Al] +189 r P (%) = 420 [C] +470 [N] +23 [Ni] +9 [Cu] +7 [Mn] -11.5 [Cr] -11.5 [Si] -12 [Mo] -23 [V] -47 [Nb] -49 [Ti] -52 [Al] +189
表 4 Table 4
Figure imgf000030_0001
Figure imgf000030_0001
産業上の利用可能性 Industrial applicability
本発明は必要以上に高価元素を含有することなく、 厳しい腐食環 境においても構造用鋼として使用できる、 溶接隣接部フュージョ ン ライ ン近傍に優先腐食発生の無い、 そしてマルチパス溶接部の耐粒 界腐食性に優れた低クロム含有ステンレス鋼を提供でき、 かつ必要 に応じ高強度材として提供することも可能であり、 産業上極めて価 値の高い発明である。  The present invention does not contain an unnecessarily expensive element, can be used as a structural steel even in severe corrosion environments, does not cause preferential corrosion in the vicinity of the welded fusion line, and is resistant to grains in multipass welds. It is an industrially extremely valuable invention that can provide a low chromium-containing stainless steel having excellent corrosion resistance and can be provided as a high-strength material if necessary.

Claims

請 求 の 範 囲 The scope of the claims
1 . 質量％で、 1. In mass%,
C ： 0.03%以下、  C: 0.03% or less,
N ： 0.004〜0.02%  N: 0.004 to 0.02%
Si ： 0.2〜 1 %、  Si: 0.2-1%,
Mn ： 1.5超〜 2.5%、  Mn: more than 1.5 to 2.5%,
P ： 0.04%以下、  P: 0.04% or less,
S ： 0.03%以下、  S: 0.03% or less,
Cr ： 10〜 15%、  Cr: 10 to 15%,
Ni ： 0.2〜3.0%、  Ni: 0.2-3.0%,
A1 ： 0.005〜0. 1%を含有し、 さ らに、  A1: 0.005 to 0.1% is contained, and
Ti : 4 X ( C % + N %) 以上、 0.35%以下を含有し、 残部が Feお よび不可避不純物からなり、 かつ、  Ti: 4 X (C% + N%) or more and 0.35% or less, with the balance being Fe and inevitable impurities, and
各元素の含有量が下記 （A) 式および （B ) 式を満足することを 特徴とするマルチパス溶接熱影響部の耐粒界腐食性および溶接部フ ュ一ジョ ンライ ン近傍の耐優先腐食性に優れた低クロム含有ステン レス鋼。  The intergranular corrosion resistance of the heat-affected zone of multipass welding and the preferential corrosion resistance in the vicinity of the welded fusion line, characterized in that the content of each element satisfies the following formulas (A) and (B) Low chromium content stainless steel with excellent properties.
r P ( % ) = 420 x C % + 470 XN % + 23XNi% + 9 XCu% r P (%) = 420 x C% + 470 XN% + 23XNi% + 9 XCu%
+ 7 XMn% - 11.5xCr% - 11.5xSi% - 12xMo% - 23xV % -47XNb% -49XTi% - 52XA1% + 189≥80 · · · · (A) Ti% X N % <0.004 · · · · ( B )  + 7 XMn%-11.5xCr%-11.5xSi%-12xMo%-23xV% -47XNb% -49XTi%-52XA1% + 189≥80 (A) Ti% XN% <0.004 )
2. 質量％で、 さ らに、  2. In mass%,
Mo ： 0.05〜 3 %、  Mo: 0.05-3%,
Cu ： 0.05〜 3 %の 1種または 2種を含有することを特徴とする請 求の範囲 1 に記載のマルチパス溶接熱影響部の耐粒界腐食性および 溶接部フュージョ ンライ ン近傍の耐優先腐食性に優れた低クロム含 有ステンレス鋼。 Cu: Intergranular corrosion resistance of the multipass weld heat-affected zone described in Claim 1 characterized by containing 0.05 to 3% of 1 type or 2 type, and priority for resistance in the vicinity of the welded fusion line Low chromium content with excellent corrosivity Stainless steel.
3. 質量％で、 さ らに、  3. In mass%,
Nb： 0.01〜0.5%、  Nb: 0.01-0.5%
V ： 0.01〜0.5%の 1種または 2種を含有することを特徴とする 請求の範囲 1 または請求の範囲 2 に記載のマルチパス溶接熱影響部 の耐粒界腐食性および溶接部フュージョ ンライ ン近傍の耐優先腐食 性に優れた低クロム含有ステンレス鋼。  V: 0.01-0.5% of 1 type or 2 types, characterized by intergranular corrosion resistance of multipass weld heat affected zone and weld zone fusion line according to claim 1 or claim 2 Low chromium-containing stainless steel with excellent preferential corrosion resistance nearby.
4. 請求の範囲 1 〜請求の範囲 3 のいずれかに記載の成分からな るステンレス鋼であって、 金属組織が、 フェライ ト相とマルテンサ イ ト相の 2相組織であり、 X線回折における Κ α { 110} 回折線の 下記 （ C) 式で定義される半価幅広がり Βが 0. 〜 1.0であることを 特徴とする強度延性バランスに優れ、 かつマルチパス溶接熱影響部 の耐粒界腐食性および溶接部フュージョ ンライ ン近傍の耐優先腐食 性に優れた低ク ロム含有ステンレス鋼。  4. Stainless steel comprising the component according to any one of claims 1 to 3, wherein the metal structure is a two-phase structure of a ferrite phase and a martensite phase, and in X-ray diffraction半 α {110} diffraction line half-width broadening で defined by the following formula (C) Β is 0 to 1.0 and has excellent strength-ductility balance and grain resistance in the heat-affected zone of multi-pass welding A low chromium-containing stainless steel with excellent interfacial corrosion resistance and preferential corrosion resistance in the vicinity of the weld fusion line.
Β = (W- Wo) /Wo ( C )  Β = (W- Wo) / Wo (C)
Wo ： 内部歪み無しの半価幅 （deg)  Wo: Half width without internal distortion (deg)
W ： 半価幅 （deg) W: Half width (deg)
5. 請求の範囲 1〜請求の範囲 3のいずれかに記載の成分からな る铸片の熱間圧延工程における加熱温度は、 铸片の成分から決定さ れるオーステナイ ト単相の上限温度 Ac4未満であるか、 あるいは Ac4 超で加熱する場合にはオーステナイ ト相中のデル夕フェライ ト量が 50%超となる温度とすることを特徴とするマルチパス溶接熱影響部 の耐粒界腐食性および溶接部フュージョ ンライ ン近傍の耐優先腐食 性に優れた低クロム含有ステンレス鋼の製造方法。 5. The heating temperature in the hot rolling process of the flakes comprising the components according to any one of claims 1 to 3 is the upper limit temperature of the austenite single phase determined from the flake components Ac 4 The intergranular corrosion resistance of the heat-affected zone in multi-pass welding is characterized by a temperature at which the amount of Dell ferrite in the austenite phase exceeds 50% when heating with Ac 4 or more. Of low-chromium stainless steel with excellent corrosion resistance and preferential corrosion resistance in the vicinity of the weld line.
PCT/JP2007/063622 2006-07-04 2007-07-03 Stainless steel with low chromium content excellent in the corrosion resistance of repeatedly heat-affected zones and process for production thereof WO2008004684A1 (en)

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JP2009280850A (en) * 2008-05-21 2009-12-03 Jfe Steel Corp Stainless steel sheet for structure having excellent weld zone corrosion resistance, and weld structure
JP2011127142A (en) * 2009-12-15 2011-06-30 Jfe Steel Corp Stainless steel sheet for welded structure having excellent slipperiness, method for producing the same, and welded structure

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