WO2020135437A1 - 一种耐海水腐蚀钢及其制造方法 - Google Patents

一种耐海水腐蚀钢及其制造方法 Download PDF

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WO2020135437A1
WO2020135437A1 PCT/CN2019/128004 CN2019128004W WO2020135437A1 WO 2020135437 A1 WO2020135437 A1 WO 2020135437A1 CN 2019128004 W CN2019128004 W CN 2019128004W WO 2020135437 A1 WO2020135437 A1 WO 2020135437A1
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steel
seawater corrosion
resistant steel
seawater
corrosion
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PCT/CN2019/128004
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English (en)
French (fr)
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温东辉
宋凤明
杨阿娜
王炜
李自刚
周庆军
缪乐德
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宝山钢铁股份有限公司
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Priority to MYPI2021003173A priority Critical patent/MY197608A/en
Priority to JP2021535749A priority patent/JP7217353B2/ja
Priority to US17/417,259 priority patent/US20220064768A1/en
Publication of WO2020135437A1 publication Critical patent/WO2020135437A1/zh
Priority to PH12021551343A priority patent/PH12021551343A1/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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the invention relates to a steel type and a manufacturing method thereof, in particular to a corrosion-resistant steel type and a manufacturing method thereof.
  • Corrosion-resistant steel is based on ordinary carbon steel by selectively adding appropriate Cu, P, Cr, Ni, Mo, Al, Ca, Mg, Sb and other alloy elements to improve its corrosion resistance. According to the use environment, it can be divided into atmospheric corrosion-resistant steel, seawater corrosion-resistant steel and acid-resistant steel, among which atmospheric corrosion-resistant steel is also called weather-resistant steel. Corrosion-resistant steel can effectively extend the service life of the steel structure, thereby reducing the cost of use and the pressure on the environment, so it is widely used in many fields.
  • corrosion-resistant steel is mainly focused on atmospheric corrosion resistance, and there is little about seawater corrosion-resistant steel.
  • the existing seawater corrosion-resistant steel also has certain defects, such as its low strength, which cannot meet the production needs for high-strength weight loss, and for example, more Ni, P, S are added to the composition system of seawater corrosion-resistant steel And other alloys, making its manufacturing cost higher, and poor plasticity, toughness and welding performance.
  • the publication number is CN101029372 and the publication date is September 5, 2007.
  • the Chinese patent document titled "A Seawater Corrosion Resistant Steel” discloses a seawater corrosion resistant steel and its production method. In the technical scheme disclosed in this patent document, its component system is combined with Cu-Cr-Mo to achieve a certain seawater corrosion resistance. However, its yield strength is below 450 MPa, and it is difficult to meet the current high-strength weight loss design requirements.
  • the publication number is CN105256233A and the publication date is January 20, 2016.
  • the Chinese patent document entitled "Corrosion Resistant Steel for Marine Applications” discloses a corrosion resistant steel for marine applications.
  • the technical solution disclosed in this patent document involves the use of Cr-Al to achieve seawater corrosion resistance.
  • the highest yield strength level involved in this technical solution is only 390 MPa.
  • seawater corrosion-resistant steel which is mainly applied to steel structural parts such as steel sheet piles in a marine environment, and the seawater corrosion-resistant steel has high strength and good corrosion resistance.
  • One of the objects of the present invention is to provide a seawater corrosion-resistant steel, which not only has good seawater corrosion resistance, but also has high strength and excellent toughness and welding performance, which is very conducive to the realization of marine steel structures The need for high-strength weight loss.
  • the present invention proposes a seawater corrosion-resistant steel, whose chemical element mass percentage is:
  • C In the seawater corrosion-resistant steel described in the present invention, C can be incorporated into the steel matrix to play the role of solid solution strengthening. In addition, C can form fine carbide precipitation particles, which in turn play a role in precipitation strengthening. Therefore, in order to ensure the implementation effect, the mass percentage of C in the steel grades involved in the present invention is not less than 0.03. However, on the other hand, C exceeding the upper limit of the range value in this case will be detrimental to steel plate welding, toughness and plasticity. In addition, the inventor of the present invention also considered that the mass percentage of C will affect the limitation of the formation of pearlite structure and other carbides.
  • the mass percentage of C in the seawater corrosion-resistant steel according to the present invention is controlled at 0.03-0.05%.
  • Si is a deoxidizing element and does not form carbides.
  • Si replaces Fe atoms in the steel type according to the present invention in a substitutional manner to hinder the movement of dislocations, thereby achieving solid solution strengthening.
  • the inventors of the present invention found that Si has a higher solid solubility in steel, which can increase the volume fraction of ferrite in the steel and refine the grains. Therefore, the addition of Si can significantly improve the toughness of the steel grades involved in this case.
  • the effect of Si on improving strength is less than C, and the addition of Si will increase the work hardening rate during cold working, and to some extent reduce the toughness and plasticity of the steel grades involved in this case.
  • the inventor of the present case considered that excessively high content of Si will promote the graphitization of C, which is not good for toughness, but also bad for the surface quality and welding performance. Based on the above considerations, the inventor of the present application controlled the mass percentage of Si in the seawater corrosion-resistant steel according to the present invention to 0.04-0.08%.
  • Mn is a strengthening element in steel and is also an essential element for deoxidation in steelmaking.
  • Mn can promote the transformation of the medium and low temperature structure, refine the microstructure of the seawater resistant steel described in the present invention, and can also play a role in suppressing the formation of network cementite , which is more beneficial to the improvement of toughness of the steel grades involved in this case.
  • the mass percentage of Mn exceeds the upper limit defined in this case, it is easy to cause segregation, thereby worsening the matrix structure, and forming larger MnS inclusions, thereby deteriorating the weldability of the steel plate of the steel grade involved in the present invention And toughness of welding heat affected zone.
  • excessive Mn will also reduce the thermal conductivity of the steel grades involved in this case, reduce the cooling rate, and produce coarse crystals, which is very detrimental to the toughness and fatigue performance of the steel grades. Therefore, in the seawater-resistant steel according to the present invention, the mass percentage of Mn is controlled at 0.8-1.2%.
  • Cu has a solid solution strengthening effect.
  • the mass percentage of Cu exceeds the lower limit defined in this case, it can be tempered at an appropriate temperature and has a secondary hardening effect, thereby improving the present invention.
  • Cu is also one of the elements that can improve the corrosion resistance. Because the electrochemical potential of Cu is higher than Fe, it can be beneficial to promote the densification of the rust layer on the steel surface and the formation of a stable rust layer.
  • the inventors of the present invention found that when Cu and Ni are properly mixed, the atmospheric corrosion resistance of the steel grades involved in the present invention can be significantly improved.
  • the mass percentage of Cu exceeds the upper limit defined in this case, it may be detrimental to welding, and mesh cracking may easily occur during hot rolling. Therefore, in the seawater-resistant steel according to the present invention, the mass percentage of Cu is controlled to 0.1-0.2%.
  • Cr is a corrosion-resistant element of the steel type according to the present invention, and has a significant effect on improving the passivation ability of the steel.
  • Cr can also promote the formation of a dense passivation film or protective rust layer on the steel surface, and its enrichment in the rust layer can effectively improve the selective permeability of the rust layer to corrosive media.
  • the inventors of the present invention found that the addition of Cr can effectively improve the self-corrosion potential of steel and suppress the occurrence of corrosion.
  • Cr can form a continuous solid solution with Fe in the steel grades involved in the present invention, thereby playing the role of solid solution strengthening, and forms various types of carbides such as M 3 C, M 7 C 3 and M 23 with C C 6 , which in turn produces a secondary strengthening effect.
  • the inventor of the present case found that Cr has a "reverse" effect on the improvement of the seawater corrosion resistance of the steel grades involved in the present invention, which is mainly caused by pitting corrosion. Therefore, the inventor of the present case added an appropriate amount of Mo to suppress the "reverse" of Cr "The effect occurs.
  • Cr exceeding the upper limit defined in this case increases the manufacturing cost of the steel plate on the one hand, but is also disadvantageous for welding and toughness.
  • the seawater corrosion resistant steel described in the present invention controls the mass percentage of Cr to 2.5-5.5%, preferably, the mass percentage of Cr can be further controlled to 3.0-4.5%.
  • Ni is an important element for improving the corrosion resistance of steel, which can promote the stability of the rust layer.
  • Ni can also improve the hot work brittleness caused by Cu.
  • Ni can improve the strength of the steel grades involved in the present invention, improve its toughness, and improve the hardenability, and effectively prevent the network cracks caused by the hot brittleness of Cu.
  • Ni is a precious metal element, adding too much is not conducive to saving the manufacturing cost, and too high content of Ni will improve the adhesion of the scale, and pressing into the steel will cause hot rolling defects on the surface. Therefore, in the seawater corrosion-resistant steel described in the present invention, the mass percentage of Ni is controlled at 0.05-0.15%.
  • Mo exists in the steel in the form of carbides and solid solutions, thereby improving the hardenability of the steel grades involved in the present invention and suppressing polygonal ferrite and pearlite Formation, and can also play a role in promoting the formation of martensite structure.
  • Mo can also play a role of phase transformation strengthening and dislocation strengthening.
  • Mo when Mo coexists with Cr and Mn, it can reduce the temper brittleness caused by other elements and improve the low temperature impact toughness of the steel sheet.
  • seawater corrosion resistant steel according to the present invention can automatically add Mo in seawater corrosive environments Cl - void formed by the steel pitting corrosion (chloride ions), so as to form a dense protective layer, to prevent pitting corrosion depth development, Therefore, adding Mo to the Cr-containing corrosion-resistant steel can further improve the corrosion resistance. Therefore, Mo is added to the steel grade according to the present invention.
  • a higher mass percentage of Mo will be detrimental to welding performance and will cause higher manufacturing costs. Based on the above comprehensive considerations, in the seawater corrosion-resistant steel described in the present invention, the mass percentage of Mo is controlled to 0.15-0.35%.
  • Al is a ferrite-forming element, which is added to the steel as a deoxidizer during steelmaking, and a small amount of Al forms fine AlN precipitation during steelmaking, which is then cooled In the process, it has the function of refining austenite grains and improving the strength and toughness of steel.
  • Al is also used as a fixing agent for N, and Al has good oxidation resistance, and a corrosion-resistant oxide layer can be formed on the surface when exposed to air. Therefore, an appropriate amount Adding Al can improve the atmospheric corrosion resistance of steel.
  • Al and O oxygen
  • the corrosion potential of steel increases, and at the same time, Al and O (oxygen) can form a dense Al 2 O 3 film on the surface layer, which contains phases with good corrosion resistance ⁇ -Al 2 O 3 , AlFeO 3 , AlFe 3 substance, which is conducive to the improvement of corrosion resistance.
  • the addition of Al and Cr can significantly improve the corrosion resistance of the steel grades involved in the present case.
  • Al exceeding the upper limit defined in this case will increase the brittleness of ferrite in the steel, which in turn leads to a decrease in the toughness of the steel.
  • the mass percentage of Al is controlled at 1.5-3.5% , Preferably, the mass percentage of Al can be further controlled at 1.5-2.2%.
  • the mass percentage of Al and Cr can be controlled so that Cr/Al is 0.8-4 and Cr+Al ⁇ 7.0%. In this way, on the one hand, the cost of the alloy is controlled, and at the same time, the cooperation between Al and Cr in corrosion resistance is better played to ensure that the steel grade has excellent corrosion resistance in the marine environment.
  • Ti is a strong ferrite forming element and a carbonitride forming element, and its compound has a high melting point, which hinders the growth of austenite during heating.
  • the inventors of the present invention found that the precipitated carbonitrides can nail the grain boundaries to refine the austenite grains, and at the same time prevent the growth of the grains in the welding heat affected zone, which is conducive to improving the welding performance of the steel plates of the steel grades involved in this case. .
  • controlling the mass percentage of Ti to 0.01-0.02% can suppress the growth of austenite grains during the reheating of the slab, while controlling the recrystallization During the rolling process, the growth of ferrite grains is suppressed, and the toughness of the steel is improved.
  • the addition of a small amount of Ti to the steel grades involved in this case containing Al can significantly reduce the corrosion rate.
  • Ti can be preferentially combined with N in steel to reduce the amount of AlN in steel.
  • the mass percentage of Ti exceeds the upper limit defined in the present case, the titanium nitride particles tend to grow and agglomerate at high temperatures, thereby impairing the plasticity and toughness of the steel grade involved in the present invention.
  • the addition of Ca to the steel grades involved in this case can change the shape of the sulfide, suppress the hot brittleness of S, and improve the toughness.
  • the Ca added to the steel exists in the state of compounds (CaS, CaO or other composites), and the weak alkaline environment of the micro-region can be produced through the hydrolysis reaction, which is conducive to the formation of the protective oxide ⁇ -FeOOH, and on the other hand, Micro-Ca treatment can improve the morphology and distribution of inclusions, and improve the isotropy of toughness and mechanical properties.
  • the mass percentage of Ca should not be lower than the lower limit defined in this case, however, at the same time, once the mass percentage of Ca exceeds the upper limit defined in this case, it is easy to reduce the purity of steel and deteriorate the welding heat effect Zone resilience. Therefore, in the seawater corrosion-resistant steel described in the present invention, the mass percentage of Ca is controlled at 0.0015-0.003%, and in some embodiments, the mass percentage of Ca can also satisfy Ca/S ⁇ 0.65, thereby ensuring a sufficient amount of Ca combines with S to avoid excess S remaining in the steel and adversely affecting plasticity and toughness.
  • the technical solution described in the present invention uses less expensive Cr and Al as the main corrosion resistance elements, and achieves the improvement of seawater corrosion resistance through the appropriate ratio of the two, and the improvement by the addition of Mo Suppress pitting performance.
  • the inventors of the present invention also found that the precipitates of Ti are beneficial to the precipitation strengthening of the matrix, and the Ca treatment is beneficial to the improvement of the toughness of the matrix and the welding performance.
  • the seawater corrosion-resistant steel has a bainite + ferrite matrix structure, which not only has good seawater corrosion resistance, but also has high strength and excellent toughness and welding performance, which is conducive to the high strength reduction of marine steel structures. weight.
  • the mass percentages of Cr element and Al element also satisfy: the range of Cr/Al is 0.8-4, and Cr+Al ⁇ 7.0%.
  • the mass percentage of Cr is 3.0-4.5%, and/or the mass percentage of Al is 1.5-2.2%.
  • the mass percentage content of P, S and N elements satisfies at least one of the following items: P ⁇ 0.015%, S ⁇ 0.004%, N ⁇ 0.005%.
  • S easily forms plastic inclusion manganese sulfide with Mn during solidification, which is detrimental to plasticity and toughness; at the same time, S easily oxidizes to form SO 2 gas during welding, resulting in welding porosity and loose defects. Moreover, S is also the main element that produces hot brittleness during hot rolling. Therefore, in the technical solution described in the present invention, the lower the mass percentage of S, the better, but considering the cost factors, the seawater resistance described in the present invention Corrosion steel controls the mass percentage of S to S ⁇ 0.004%;
  • P can promote the formation of the surface protective rust layer of the steel grades involved in the present invention, which can effectively improve the atmospheric corrosion resistance, but P easily segregates at the grain boundaries, reducing the grain boundary binding energy and the toughness and plasticity of the steel.
  • the coexistence of P and Mn will increase the temper brittleness of the steel.
  • the segregated P makes the steel plate prone to intergranular fracture, reducing the impact toughness of the seawater-resistant steel according to the present invention.
  • P is detrimental to the welding performance. Therefore, in the technical solution described in the present invention, P is a harmful element, that is, an impurity, and its mass percentage needs to be controlled to P ⁇ 0.015%.
  • N also needs to control its mass percentage to N ⁇ 0.005%.
  • seawater corrosion resistant steel according to the present invention, it also satisfies: Ca/S ⁇ 0.65.
  • the microstructure is bainite + ferrite.
  • seawater-resistant steel in the seawater-resistant steel according to the present invention, its yield strength ⁇ 450 MPa, tensile strength ⁇ 550 MPa, and its annual average corrosion rate under seawater full immersion conditions is below 0.1 mm/a.
  • another object of the present invention is to provide a method for manufacturing the seawater corrosion resistant steel described above.
  • the seawater corrosion resistant steel obtained by the manufacturing method not only has good seawater corrosion resistance, but also has high strength and Excellent toughness and welding performance, very suitable for marine steel structures.
  • the present invention proposes a method for manufacturing the above seawater resistant steel, which includes the steps of:
  • step (2) the reheating of the slab is controlled at 1200°C-1260°C because the seawater resistance obtained by the manufacturing method described in the present invention
  • Corrosion steel contains more Cr and Mo alloy elements, so the use of higher heating temperature is conducive to the full solid solution and homogenization of alloy elements, which is conducive to improving the uniformity of the slab material and the subsequent improvement of steel plate performance Therefore, the inventor of the present application controlled the reheating temperature of the slab in the range of 1200°C-1260°C.
  • step (3) the temperature at the end of rough rolling is controlled at 950°C to 1150°C.
  • the cumulative deformation in the rough rolling stage is controlled to ⁇ 80%, while in some embodiments, when the thickness of the steel plate exceeds 12 mm, the cumulative deformation in the rough rolling stage can be controlled to ⁇ 70% ,
  • step (4) the temperature at which the finish rolling is finished is controlled to be not less than 800°C.
  • the deformation ratio of the finishing rolling stage is controlled to ⁇ 5
  • the control deformation ratio of the finishing rolling stage can be controlled to ⁇ 3.5.
  • step (5) the steel sheet after finish rolling is water-cooled to 550-650° C. for coiling.
  • seawater corrosion-resistant steel and its manufacturing method described in the present invention have the following advantages and beneficial effects:
  • the seawater corrosion-resistant steel according to the present invention not only has good seawater corrosion resistance, but also has high strength, excellent toughness, and welding performance, and is very suitable for marine steel structures.
  • the seawater corrosion-resistant steel described in the present invention adopts the Cr-Al-Mo composition system design, through the addition of Cr and Al alloy elements to achieve the improvement of seawater corrosion resistance, and by adding Mo to suppress the occurrence of pitting corrosion and eliminate the content Higher Cr inhibits the “reverse” effect of corrosion in seawater environments, thereby further improving seawater corrosion resistance.
  • seawater corrosion resistant steel according to the present invention has excellent formability, satisfies the subsequent cold working requirements of the steel plate, is easy to weld, and meets the requirement of no preheating welding above 0°C.
  • the manufacturing method of the present invention also has the above advantages and beneficial effects.
  • the manufacturing method of the present invention adopts a controlled rolling and controlled cooling production process. Therefore, it does not require heat treatment after rolling and can be supplied directly in the state of hot rolling. , Which effectively shortened the supply cycle and reduced production costs.
  • FIG. 1 shows the microstructure of the seawater-resistant steel of Example 1.
  • Table 1 lists the mass percentage (mass%) of each chemical element in the seawater corrosion-resistant steel of Examples 1-6.
  • the examples in this case do not use the Cu-Cr-Mo composition system in the prior art, nor do they have higher contents of P, S, C, and Si.
  • Adopt Cr-Al-Mo composition system design through the addition of Cr and Al alloy elements to achieve the improvement of seawater corrosion resistance, and by adding Mo to suppress the occurrence of pitting corrosion, eliminate the higher content of Cr in the seawater environment to inhibit corrosion "Reverse" effect to further improve seawater corrosion resistance.
  • the manufacturing method of the seawater corrosion-resistant steel of Example 1-6 is obtained by the following steps:
  • Rough rolling The temperature at the end of rough rolling is controlled at 950°C-1150°C. When the thickness of the steel plate does not exceed 12mm, the cumulative deformation during the rough rolling phase is controlled to ⁇ 80%, and when the thickness of the steel plate exceeds 12mm, the cumulative deformation during the rough rolling phase is controlled Amount ⁇ 70%.
  • Finishing rolling control the temperature at the end of finishing rolling not less than 800°C, when the thickness of the steel sheet does not exceed 12mm, control the deformation ratio of the finishing rolling stage ⁇ 5, when the thickness of the steel sheet exceeds 12mm, control the deformation ratio of the finishing rolling stage ⁇ 3.5.
  • Table 2 lists the specific process parameters involved in the manufacturing method of the seawater corrosion-resistant steel of Examples 1-6.
  • the mechanical properties of seawater corrosion-resistant steel in the examples of this case are excellent, and the test steel was tested according to GB/T 228.1-2010 "Metal Material Tensile Test Part 1: Tensile Test Method at Room Temperature" Tensile properties, its yield strength is 450MPa ⁇ 600MPa, tensile strength is 550Mpa ⁇ 700MPa.
  • the low-temperature toughness and elongation of the seawater corrosion-resistant steels of the embodiments also perform well, and the elongation can reach 21.5 to 28.5%, and the impact energy at -40°C is ⁇ 76J.
  • the seawater corrosion resistance test adopts the full immersion testing machine manufactured by China Shipbuilding Group 725, and the corrosion resistance under the seawater full immersion condition is tested in the laboratory with reference to JB/T7901-1999 standard.
  • the sample size is 100 ⁇ 30 ⁇ 3mm
  • the surface roughness is in accordance with GB1031
  • the maximum allowable value of Ra is 3.2 ⁇ m
  • take three parallel samples use a degreasing agent to remove the oil on the surface of the sample before the test, and clean the sample with anhydrous alcohol , Blow dry with a blower, measure the sample size and weigh the original weight.
  • the test medium is 3.5% NaCl solution.
  • the moving speed of the sample in the corrosive medium is 1m/sec, the test temperature is 30°C, and the test time is 30 days.
  • the corrosion rate is calculated as follows:
  • Table 4 lists the corrosion rates and relative weight loss rates of the seawater corrosion-resistant steels of Examples 1-4 and Comparative Examples 1 and 2.
  • the relative weight loss rate is calculated by calculating the relative ratio of the corrosion rate (Cr, mm/a) obtained by the corrosion weight loss of each sample to the corrosion rate of Comparative Example 1.
  • Example 1 Numbering Corrosion rate (mm/a) Relative weightlessness rate (%) Comparative Example 1 0.187 100 Comparative Example 2 0.135 72.4
  • Example 1 0.068 36.63
  • Example 2 0.07 37.64
  • Example 3 0.068 36.34
  • Example 4 0.071 38.22
  • Example 5 0.070 37.41
  • Example 6 0.069 36.79
  • each example of the present case has better seawater corrosion resistance than Comparative Example 1-2, and its average annual corrosion thickness is below 0.1 mm/a.
  • FIG. 1 shows the microstructure of the seawater-resistant steel of Example 1.
  • FIG. 1 shows the microstructure of the seawater corrosion-resistant steel of Example 1.
  • the microstructure of the seawater corrosion-resistant steel of Example 1 is bainite + ferrite.
  • seawater corrosion-resistant steel and its manufacturing method described in the present invention have the following advantages and beneficial effects:
  • the seawater corrosion-resistant steel described in the present invention not only has good seawater corrosion resistance, but also has high strength, excellent toughness, and welding performance, and is very suitable for marine steel structures.
  • the seawater corrosion-resistant steel described in the present invention adopts the Cr-Al-Mo composition system design, through the addition of Cr and Al alloy elements to achieve the improvement of seawater corrosion resistance, and by adding Mo to suppress the occurrence of pitting corrosion and eliminate the content Higher Cr inhibits the “reverse” effect of corrosion in seawater environments, thereby further improving seawater corrosion resistance.
  • seawater corrosion resistant steel according to the present invention has excellent formability, satisfies the subsequent cold working requirements of the steel plate, is easy to weld, and meets the requirement of no preheating welding above 0°C.
  • the manufacturing method of the present invention also has the above advantages and beneficial effects.
  • the manufacturing method of the present invention adopts a controlled rolling and controlled cooling production process. Therefore, it does not require heat treatment after rolling and can be supplied directly in the state of hot rolling , Which effectively shortened the supply cycle and reduced production costs.

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Abstract

一种耐海水腐蚀钢，其化学元素质量百分配比为：C：0.03-0.05％，Si：0.04-0.08％，Mn:0.8-1.2％，Cu：0.1-0.2％，Cr：2.5-5.5％，Ni：0.05-0.15％，Mo：0.15-0.35％，Al:1.5-3.5％，Ti：0.01-0.02％，Ca：0.0015-0.003％，余量为Fe和其他不可避免的杂质。该海水耐腐蚀钢制造方法，包括：(1)冶炼和浇铸；(2)再加热：铸坯被再加热到1200℃-1260℃；(3)粗轧；(4)精轧；(5)卷取；(6)冷却至室温。该耐海水腐蚀钢具有良好的耐海水腐蚀性能以及优良的力学性能。

Description

一种耐海水腐蚀钢及其制造方法 技术领域
本发明涉及一种钢种及其制造方法，尤其涉及一种耐腐蚀钢种及其制造方法。
背景技术
耐腐蚀钢是在普碳钢的基础上通过选择性添加适当的Cu、P、Cr、Ni、Mo、Al、Ca、Mg、Sb等合金元素而提高其耐腐蚀性能。根据使用环境可分为耐大气腐蚀钢、耐海水腐蚀钢和耐酸钢等，其中耐大气腐蚀钢也叫耐候钢。耐腐蚀钢能够有效延长钢结构的使用寿命，从而降低使用成本及对环境的压力，所以在众多的领域获得广泛应用。
然而，在现有技术中，耐腐蚀钢主要集中在耐大气腐蚀方面，鲜有关于耐海水腐蚀钢。此外，现有的耐海水腐蚀钢也存在一定缺陷，例如其强度不高，无法满足生产对于高强减重的需求，又例如耐海水腐蚀钢的成分体系中添加了较多的Ni、P、S等合金，使得其制造成本较高，且塑性、韧性和焊接性能不佳。
公开号为CN101029372，公开日为2007年9月5日，名称为“一种耐海水腐蚀钢”的中国专利文献公开了一种耐海水腐蚀钢及其生产方法。在该专利文献所公开的技术方案中，其成分体系上通过Cu-Cr-Mo的配合，实现一定的耐海水腐蚀性能，然而其屈服强度在450MPa以下，难以满足目前高强减重的设计要求。
公开号为CN105154789A，公开日为2015年12月16日，名称为“一种深海用高性能隔水管钢及生产方法”的中国专利文献公开了一种深海用高性能隔水管钢。在该专利文献所公开的技术方案中，其成分体系上属于Cu-Ni-Cr-Mo体系，其中Ni含量0.7-1.5％，使得其成本较高。
公开号为CN105256233A，公开日为2016年1月20日，名称为“用于海洋应用的耐蚀钢”的中国专利文献公开了一种用于海洋应用的耐蚀钢。在该专 利文献所公开的技术方案中，其涉及采用Cr-Al的配合实现耐海水腐蚀性能，然而，该技术方案所涉及的屈服强度等级最高仅为390MPa。
基于此，期望获得一种耐海水腐蚀钢，其主要应用于海洋环境下的钢结构部件例如钢板桩上，并且该耐海水腐蚀钢强度高耐蚀性佳。
发明内容
本发明的目的之一在于提供一种耐海水腐蚀钢，该耐海水腐蚀钢不仅具有良好的耐海水腐蚀性能，而且还具有高的强度和优良的韧性、焊接性能，非常有利于实现海洋钢结构的高强减重的需要。
为了实现上述目的，本发明提出了一种耐海水腐蚀钢，其化学元素质量百分配比为：
C：0.03-0.05％，Si：0.04-0.08％，Mn:0.8-1.2％，Cu：0.1-0.2％，Cr：2.5-5.5％，Ni：0.05-0.15％，Mo：0.15-0.35％，Al:1.5-3.5％，Ti：0.01-0.02％，Ca：0.0015-0.003％，余量为Fe和其他不可避免的杂质。
在本发明所述的耐海水腐蚀钢中，各化学元素的设计原理如下：
C：在本发明所述的耐海水腐蚀钢中，C可以融入钢基体中，从而起到固溶强化的作用。此外，C可以形成细小的碳化物析出粒子，进而起到析出强化作用。因此，为了保证实施效果，在本发明所涉及的钢种中C的质量百分比不低于0.03。然而，另一方面，超过本案范围值上限的C会对钢板焊接、韧性及塑性不利。此外，本案发明人还考虑到C的质量百分比会对于限制珠光体组织及其它碳化物的形成造成影响，为了保证本发明所涉及的钢种的显微结构为均相组织，同时避免异相之间的电位差所引起的原电池腐蚀，以提高本案所涉及的钢种的耐蚀性能，因而，将本发明所述的耐海水腐蚀钢的C的质量百分比控制在0.03-0.05％。
Si：在本发明所述的技术方案中，Si为脱氧元素，不形成碳化物。此外，Si在本发明所涉及的钢种中以置换的方式替代Fe原子，阻碍位错运动，从而实现固溶强化。另外，本案发明人发现Si在钢中具有较高的固溶度，可以增加钢中铁素体体积分数，细化晶粒，因而，添加Si可以显著有利于提高本案所涉及的钢种的韧性。然而，Si对强度的提高效果小于C，并且添加Si会提高冷加工时的加工硬化率，在一定程度上降低本案所涉及的钢种的韧性和塑 性。此外，本案发明人考虑到含量过高的Si会促进C的石墨化，对韧性不利，也会对表面质量及焊接性能不利。基于上述考虑，本案发明人将本发明所述的耐海水腐蚀钢中Si的质量百分比控制在0.04-0.08％。
Mn：对于本发明所述的耐海水腐蚀钢而言，Mn是钢中的强化元素，也是炼钢脱氧的必要元素。此外，在本发明所述的技术方案中，Mn可以促进中低温组织转变，细化本发明所述的耐海水腐蚀钢的显微组织，还可以起到抑制网状渗碳体的形成的作用，从而对本案所涉及的钢种的韧性的提高较为有利。然而，另一方面，当Mn的质量百分比超过本案所限定的上限时，则易导致偏析，进而恶化基体组织，并且形成较大的MnS夹杂，从而恶化本发明所涉及的钢种的钢板可焊性和焊接热影响区韧性。此外，过量的Mn还会降低本案所涉及的钢种的导热系数，降低冷却速度，产生粗晶，对钢种的韧性和疲劳性能十分不利。因此，在本发明所述的耐海水腐蚀钢中将Mn的质量百分比控制在0.8-1.2％。
Cu：在本发明所述的技术方案中，Cu有固溶强化作用。此外，在本发明所述的耐海水腐蚀钢中，当Cu的质量百分比超过本案所限定的下限值时，其可以在适当温度下回火有二次硬化效应，从而提高本发明所涉及的钢种的强度。同时，Cu也是可以提高耐腐蚀性能的元素之一，由于Cu的电化学电位高于Fe，因而，其可以有利于促进钢表面锈层致密化及稳定锈层的形成。此外，本案发明人发现当Cu与Ni适当配比，可以显著地提高本发明所涉及的钢种的耐大气腐蚀性能。然而，另一方面，Cu的质量百分比超过本案所限定的上限时，可能对焊接不利，并且在热轧时容易发生网裂。因此，在本发明所述的耐海水腐蚀钢中将Cu的质量百分比控制在0.1-0.2％。
Cr：对于本发明所述的耐海水腐蚀钢而言，Cr是本发明所涉及的钢种的耐蚀元素，对改善钢的钝化能力具有显著的效果。此外，Cr还可以促进钢表面形成致密的钝化膜或保护性锈层，其在锈层内的富集能有效提高锈层对腐蚀性介质的选择性透过特性。另外，本案发明人发现Cr的加入可以有效提高钢的自腐蚀电位，抑制腐蚀的发生。此外，Cr在本发明所涉及的钢种中可以与Fe形成连续固溶体，从而起到固溶强化的作用，并与C形成多种类型的碳化物例如M 3C、M 7C 3和M 23C 6，进而产生二次强化效应。然而，本案发明人发现Cr对本发明所涉及的钢种耐海水腐蚀性能的改善有“逆反”效应，这主要是由于点 蚀引发的，因而，本案发明人加入适量Mo，从而抑制Cr的“逆反”效应的发生。然而，超过本案所限定的上限的Cr一方面提高了钢板的制造成本，另一方面也对焊接及韧性不利。基于此，在本发明所述的耐海水腐蚀钢将Cr的质量百分比控制在2.5-5.5％，优选地，可以将Cr的质量百分比进一步控制在3.0-4.5％。
Ni：在本发明所述的技术方案中，Ni是提高钢耐腐蚀性能的重要元素，其可以促进锈层的稳定。此外，Ni还可以改善Cu引起的热加工脆性问题。另外，Ni可以提高本发明所涉及的钢种强度的同时，改善其韧性，并提高淬透性，有效阻止Cu的热脆引起的网裂。然而，由于Ni为贵重金属元素，添加过多不利于节约制造成本，而且含量过高的Ni会提高氧化皮的粘附性，压入钢中会在表面形成热轧缺陷。因此，在本发明所述的耐海水腐蚀钢中将Ni的质量百分比控制在0.05-0.15％。
Mo：在本发明所述的耐海水腐蚀钢中，Mo以碳化物和固溶的形式存在于钢中，从而提高本发明所涉及的钢种的淬透性，抑制多边形铁素体和珠光体的形成，并且还可以起到促进马氏体组织的形成的作用。另外，在本发明所述的技术方案中，Mo还可以起到相变强化和位错强化的作用。此外，Mo与Cr和Mn并存时可以降低其它元素导致的回火脆性，改善钢板的低温冲击韧性。并且，在本发明所述的耐海水腐蚀钢中加入Mo在海水腐蚀环境下可以自动补充Cl -(氯离子)对钢材点腐蚀形成的空隙，从而形成致密保护层，阻止点腐蚀向纵深发展，所以在含Cr耐腐蚀钢中加入Mo可以进一步提高耐腐蚀性能。因而，在本发明所涉及的钢种中加入Mo。然而，另一方面，质量百分比较高的Mo会对焊接性能不利，并且会造成制造成本较高。基于上述综合考量，在本发明所述的耐海水腐蚀钢中，将Mo的质量百分比控制在0.15-0.35％。
Al：在本发明所述的技术方案中，Al为铁素体形成元素，在炼钢过程中作为脱氧剂在钢中添加，微量的Al在炼钢时形成细小的AlN析出，在随后的冷却过程中有细化奥氏体晶粒的作用，改善钢材的强韧性能。此外，在本发明所涉及的钢种中，Al也作为N的固定剂使用，并且Al具有良好的抗氧化性，暴露在空气中即可在表面生成一种耐腐蚀的氧化层，因此，适量添加Al可以提高钢的耐大气腐蚀性能。此外，添加Al后，钢的腐蚀电位提高，同时Al与O(氧)能够在表层形成致密的Al 2O 3薄膜，薄膜内含有耐蚀性能好的物相α -Al 2O 3，AlFeO 3，AlFe 3物质，从而有利于耐腐蚀性能的提高。特别是，在本发明所述的耐海水腐蚀钢中，Al与Cr配合添加可以显著提高本案所涉及的钢种的耐腐蚀性能。然而，超过本案所限定的上限值的Al会使得钢中铁素体脆性增加，进而导致钢韧性的降低，因此，在本发明所述的技术方案中，控制Al的质量百分比在1.5-3.5％，优选地，可以进一步控制Al的质量百分比在1.5-2.2％。另外考虑到Al与Cr的配合添加，因而，在一些优选的实施方式中，可以控制Al与Cr的质量百分比满足Cr/Al在0.8-4，Cr+Al≤7.0％。这样一方面控制了合金成本，同时更好的发挥Al与Cr在耐腐蚀性能方面的配合作用，保障钢种在海洋环境下具有优良的耐腐蚀性能。
Ti：在本发明所述的技术方案中，Ti是强铁素体形成元素及碳氮化物形成元素，其化合物熔点高，在加热时对奥氏体长大有阻碍作用。此外，本案发明人发现析出的碳氮化物可以钉轧晶界从而细化奥氏体晶粒，同时阻止焊接热影响区晶粒长大，有利于提高本案所涉及的钢种的钢板的焊接性能。因此，在本发明所述的耐海水腐蚀钢中，控制Ti的质量百分比在0.01-0.02％，其一方面可以抑制板坯再热过程中的奥氏体晶粒长大，同时在再结晶控轧过程中抑制铁素体晶粒长大，提高钢的韧性，并且，另一方面，在含Al的本案所涉及的钢种中同时加入微量Ti可以明显降低腐蚀速率。此外，在本发明所述的技术方案中，Ti可以优先与钢中的N结合，减少钢中AlN的数量。然而，若Ti的质量百分比超过本案所限定的上限时，在高温下氮化钛颗粒容易长大并团聚，进而损害本发明所涉及的钢种的塑性及韧性。
Ca：在本发明所述的技术方案中，Ca加入本案所涉及的钢种中可以改变硫化物形状，抑制S的热脆性，改善韧性。此外，加入钢中的Ca以化合物(CaS、CaO或其他复合物)状态存在，通过水解反应可以生产微区的弱碱环境，有利于保护性氧化物α-FeOOH的形成，并且另一方面，微Ca处理可以改善夹杂物的形态和分布，有利提高韧性及力学性能的各向同性。为了保证实施效果，Ca的质量百分比不应低于本案所限定的下限值，然而，同时Ca的质量百分比一旦超过本案所限定的上限值，又容易降低钢质纯净度，恶化焊接热影响区韧性。因此，在本发明所述的耐海水腐蚀钢中控制Ca的质量百分比在0.0015-0.003％，并且在一些实施方式中，Ca的质量百分比还可以满足Ca/S≥0.65，从而保证有足够数量的Ca与S结合，避免有多余的S残留在钢中对塑性、韧性等产生不 利影响。
综上所述可以看出，本发明所述的技术方案以较廉价的Cr和Al为主要的耐蚀元素，通过二者的合适配比实现耐海水腐蚀性能的提高，并通过Mo的添加提高抑制点蚀性能。此外，本案发明人还发现Ti的析出物有利于基体的析出强化，而Ca处理有利于基体韧性和焊接性能的提高，因此，本案发明人设计了上述的元素成分范围，从而使得本发明所述的耐海水腐蚀钢具有贝氏体+铁素体基体组织，使其可以不仅具有良好的耐海水腐蚀性能，同时兼具高的强度和优良的韧性、焊接性能，有利于海洋钢结构的高强减重。
进一步地，在本发明所述的耐海水腐蚀钢中，Cr元素和Al元素的质量百分含量还满足：Cr/Al的范围为0.8-4，Cr+Al≤7.0％。
进一步地，在本发明所述的耐海水腐蚀钢中，Cr质量百分含量为3.0-4.5％，并且/或者Al质量百分含量为1.5-2.2％。
进一步地，在本发明所述的耐海水腐蚀钢中，在其他不可避免的杂质中，P、S和N元素的质量百分含量满足下述各项的至少其中之一：P≤0.015％，S≤0.004％，N≤0.005％。
S易在凝固过程中与Mn形成塑性夹杂物硫化锰，对塑性及韧性不利；同时S在焊接时易氧化形成SO 2气体，导致焊接气孔及疏松缺陷。而且S也是热轧过程中产生热脆性的主要元素，因此，在本发明所述的技术方案中，S的质量百分比越低越好，但是考虑到成本因素，因而，本发明所述的耐海水腐蚀钢将S的质量百分比控制在S≤0.004％；
P可以促进本发明所涉及的钢种的表面保护性锈层的形成，可以有效提高耐大气腐蚀性能，但P易在晶界处产生偏析，降低晶界结合能及钢的韧性及塑性。此外，P与Mn共存将加剧钢的回火脆性，偏聚的P使得钢板易发生沿晶断裂，降低本发明所述的耐海水腐蚀钢的冲击韧性。另外，P对焊接性能不利，因此，在本发明所述的技术方案中，P为有害元素，即杂质，需要将其质量百分比控制在为P≤0.015％。另外N作为有害元素，也需要将其质量百分比控制在N≤0.005％。
进一步地，在本发明所述的耐海水腐蚀钢中，还满足：Ca/S≥0.65。
进一步地，在本发明所述的耐海水腐蚀钢中，其微观组织为贝氏体+铁素体。
需要说明的是，上述公式的Cr、Al、Ca以及分别表示其各自的质量百分比，并且代入上述公式的数值为百分号前的数值，例如Ca的质量百分比为0.0022％、S的质量百分比为0.0032％，则代入上述公式Ca/S＝0.0022/0.0032＝0.69。
进一步地，在本发明所述的耐海水腐蚀钢中，其屈服强度≥450MPa，抗拉强度≥550Mpa，且其在海水全浸条件下的年均腐蚀速率在0.1mm/a以下。
相应地，本发明的另一目的在于提供一种上述的耐海水腐蚀钢的制造方法，通过该制造方法所获得的耐海水腐蚀钢不仅具有良好的耐海水腐蚀性能，而且还具有高的强度和优良的韧性、焊接性能，非常适用于海洋钢结构。
为了实现上述目的，本发明提出了一种上述的耐海水腐蚀钢的制造方法，包括步骤：
(1)冶炼和浇铸；
(2)再加热：铸坯被再加热到1200℃-1260℃；
(3)粗轧；
(4)精轧；
(5)卷取；
(6)冷却至室温。
需要特别指出的是，在本发明所述的制造方法中，在步骤(2)中，控制铸坯在1200℃-1260℃再加热是因为，通过本发明所述的制造方法所获得的耐海水腐蚀钢由于中含有较多的Cr、Mo合金元素，因而，采用更高的加热温度有利于合金元素的充分固溶及均匀化，进而有利于改善铸坯材质的均匀性及后续钢板性能的提高，因此，本案发明人将铸坯的再加热温度控制在1200℃-1260℃范围内。
进一步地，在本发明所述的制造方法中，在步骤(3)中，粗轧结束温度控制在950℃-1150℃。在一些实施方式中，当钢板厚度不超过12mm时，控制粗轧阶段累计变形量≥80％，而在一些实施方式中，当钢板厚度超过12mm时，可以控制粗轧阶段累计变形量≥70％，
进一步地，在本发明所述的制造方法中，在步骤(4)中，控制精轧结束的温度不低于800℃。此外，在一些实施方式中，当钢板厚度不超过12mm时，控制精轧阶段的变形比≥5，而在一些实施方式中，当钢板厚度超过12mm时， 可以控制精轧阶段的控制变形比≥3.5。
进一步地，在本发明所述的制造方法中，在步骤(5)中，将精轧后的钢板水冷至550-650℃进行卷取。
相较于现有技术，本发明所述的耐海水腐蚀钢及其制造方法具有如下的优点以及有益效果：
本发明所述的耐海水腐蚀钢不仅具有良好的耐海水腐蚀性能，而且还具有高的强度和优良的韧性、焊接性能，非常适用于海洋钢结构。
此外，本发明所述的耐海水腐蚀钢采用Cr-Al-Mo成分体系设计，通过Cr、Al合金元素的配合加入实现耐海水腐蚀性能的提高，并通过加入Mo抑制点蚀的发生，消除含量较高的Cr在海水环境下抑制腐蚀的“逆反”效应，从而进一步改善耐海水腐蚀性能。
另外，本发明所述的耐海水腐蚀钢具有优良的成形性能，满足钢板后续的冷加工要求，并易于焊接，满足0℃以上无预热焊接要求。
本发明所述的制造方法同样也具有上述优点以及有益效果，此外，本发明所述的制造方法采用控轧控冷生产工艺，因而，轧后不需要进行热处理，可以直接热轧状态进行供货，从而有效缩短了供货周期，降低了生产成本。
附图说明
图1显示了实施例1的耐海水腐蚀钢的微观组织。
具体实施方式
下面将结合具体的实施例以及说明书附图对本发明所述的耐海水腐蚀钢及其制造方法做进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
实施例1-6
表1列出了实施例1-6的耐海水腐蚀钢中各化学元素的质量百分比(mass％)。
表1.(mass％，余量为Fe以及除了P、S以及N以外其他不可避免的杂质元素)
Figure PCTCN2019128004-appb-000001
Figure PCTCN2019128004-appb-000002
由表1可以看出，相较于现有技术，本案各实施例并不采用现有技术中的Cu-Cr-Mo成分体系，也没有含量较高的P、S、C以及Si，本案实际采用Cr-Al-Mo成分体系设计，通过Cr、Al合金元素的配合加入实现耐海水腐蚀性能的提高，并通过加入Mo抑制点蚀的发生，消除含量较高的Cr在海水环境下抑制腐蚀的“逆反”效应，从而进一步改善耐海水腐蚀性能。
实施例1-6的耐海水腐蚀钢的制造方法采用以下步骤制得：
(1)冶炼和浇铸：按照表1所示的化学元素成分，在500kg真空感应炉上冶炼，浇铸得到铸坯。
(2)再加热：铸坯被再加热到1200℃-1260℃。
(3)粗轧：粗轧结束温度控制在950℃-1150℃，当钢板厚度不超过12mm时，控制粗轧阶段累计变形量≥80％，当钢板厚度超过12mm时，控制粗轧阶段累计变形量≥70％，。
(4)精轧：控制精轧结束的温度不低于800℃，当钢板厚度不超过12mm时，控制精轧阶段的变形比≥5，当钢板厚度超过12mm时，控制精轧阶段的变形比≥3.5。
(5)卷取：将精轧后的钢板水冷至550-650℃进行卷取。
(6)冷却至室温。
表2列出了实施例1-6的耐海水腐蚀钢的制造方法中所涉及的具体工艺参数。
表2.
Figure PCTCN2019128004-appb-000003
Figure PCTCN2019128004-appb-000004
对实施例1-6的耐海水腐蚀钢进行各项性能测试，测试结果列于表3。
表3.
Figure PCTCN2019128004-appb-000005
由表3可以看出，本案各实施例的耐海水腐蚀钢的力学性能表现优良，根据GB/T 228.1-2010“金属材料拉伸试验第1部分：室温拉伸试验方法”测试了试验钢的拉伸性能，其屈服强度为450MPa～600MPa，抗拉强度为550Mpa～700MPa。此外，各实施例的耐海水腐蚀钢的低温韧性以及延伸率也表现良好，延伸率可以达到21.5-28.5％，在-40℃条件下的冲击功≥76J。
此外，将本案实施例1-4的耐海水腐蚀钢与现有技术中的对比例1以及对比例2进行了耐海水腐蚀试验的对比，其中对比例1采用的是Q345B、对比例2采用的是Q345C-NHY3。
耐海水腐蚀试验采用中国船舶集团725所制造的全浸试验机，参照 JB/T7901-1999标准在实验室测试了在海水全浸条件下的耐腐蚀性能。试样尺寸为100×30×3mm，表面粗糙度按照GB1031进行，Ra最大允许值为3.2μm，取平行样品数目3个，试验前采用脱脂剂除去试样表面油污，用无水酒精清洗试样，用吹风机吹干，测量试样尺寸并称原始重量。
试验介质为3.5％NaCl溶液。试样在腐蚀介质中的运动速度为1m/秒，试验温度为30℃，试验时间为30天。腐蚀速率的计算如下：
Figure PCTCN2019128004-appb-000006
式中:Cr为平均年腐蚀速率，量纲为mm/a；Δm为实验前后试样失重量，量纲为g；S为试样总表面积，量纲为cm 2；ρ为试样密度，ρ＝7.85g/cm 3；t为腐蚀时间，量纲为h。
表4列出了实施例1-4的耐海水腐蚀钢与对比例1以及对比例2的腐蚀速率以及相对失重率。所述相对失重率通过计算各个试样的腐蚀失重得到腐蚀速率(Cr，mm/a)与对比例1的腐蚀速率相对比值计算获得。
表4.
编号 腐蚀速率(mm/a) 相对失重率(％)
对比例1 0.187 100
对比例2 0.135 72.4
实施例1 0.068 36.63
实施例2 0.07 37.64
实施例3 0.068 36.34
实施例4 0.071 38.22
实施例5 0.070 37.41
实施例6 0.069 36.79
由表4可以看出，本案的各个实施例具有比对比例1-2更好的耐海水腐蚀性能，其年均腐蚀厚度在0.1mm/a以下。
图1显示了实施例1的耐海水腐蚀钢的微观组织。如图1所示，实施例1的耐海水腐蚀钢的微观组织为贝氏体+铁素体。
相较于现有技术，本发明所述的耐海水腐蚀钢及其制造方法具有如下的优点以及有益效果：
本发明所述的耐海水腐蚀钢不仅具有良好的耐海水腐蚀性能，而且还具有 高的强度和优良的韧性、焊接性能，非常适用于海洋钢结构。
此外，本发明所述的耐海水腐蚀钢采用Cr-Al-Mo成分体系设计，通过Cr、Al合金元素的配合加入实现耐海水腐蚀性能的提高，并通过加入Mo抑制点蚀的发生，消除含量较高的Cr在海水环境下抑制腐蚀的“逆反”效应，从而进一步改善耐海水腐蚀性能。
另外，本发明所述的耐海水腐蚀钢具有优良的成形性能，满足钢板后续的冷加工要求，并易于焊接，满足0℃以上无预热焊接要求。
本发明所述的制造方法同样也具有上述优点以及有益效果，此外，本发明所述的制造方法采用控轧控冷生产工艺，因而，轧后不需要进行热处理，可以直接热轧状态进行供货，从而有效缩短了供货周期，降低了生产成本。
需要说明的是，本发明的保护范围中现有技术部分并不局限于本申请文件所给出的实施例，所有不与本发明的方案相矛盾的现有技术，包括但不局限于在先专利文献、在先公开出版物，在先公开使用等等，都可纳入本发明的保护范围。
此外，本案中各技术特征的组合方式并不限本案权利要求中所记载的组合方式或是具体实施例所记载的组合方式，本案记载的所有技术特征可以以任何方式进行自由组合或结合，除非相互之间产生矛盾。
还需要注意的是，以上所列举的实施例仅为本发明的具体实施例。显然本发明不局限于以上实施例，随之做出的类似变化或变形是本领域技术人员能从本发明公开的内容直接得出或者很容易便联想到的，均应属于本发明的保护范围。

Claims (11)

  1. 一种耐海水腐蚀钢，其特征在于，其化学元素质量百分配比为：
    C：0.03-0.05％，Si：0.04-0.08％，Mn:0.8-1.2％，Cu：0.1-0.2％，Cr：2.5-5.5％，Ni：0.05-0.15％，Mo：0.15-0.35％，Al:1.5-3.5％，Ti：0.01-0.02％，Ca：0.0015-0.003％，余量为Fe和其他不可避免的杂质。
  2. 如权利要求1所述的耐海水腐蚀钢，其特征在于，Cr元素和Al元素的质量百分含量还满足：Cr/Al的范围为0.8-4，Cr+Al≤7.0％。
  3. 如权利要求1所述的耐海水腐蚀钢，其特征在于，Cr质量百分含量为3.0-4.5％，并且/或者Al质量百分含量为1.5-2.2％。
  4. 如权利要求1所述的耐海水腐蚀钢，其特征在于，在其他不可避免的杂质中，P、S和N元素的质量百分含量满足下述各项的至少其中之一：P≤0.015％，S≤0.004％，N≤0.005％。
  5. 如权利要求4所述的耐海水腐蚀钢，其特征在于，还满足：Ca/S≥0.65。
  6. 如权利要求1所述的耐海水腐蚀钢，其特征在于，其微观组织为贝氏体+铁素体。
  7. 如权利要求1-6中任意一项所述的耐海水腐蚀钢，其特征在于，其屈服强度≥450MPa，抗拉强度≥550Mpa，且其在海水全浸条件下的年均腐蚀速率在0.1mm/a以下。
  8. 如权利要求1-7中任意一项所述的耐海水腐蚀钢的制造方法，其特征在于，包括步骤：
    (1)冶炼和浇铸；
    (2)再加热：铸坯被再加热到1200℃-1260℃；
    (3)粗轧；
    (4)精轧；
    (5)卷取；
    (6)冷却至室温。
  9. 如权利要求8所述的制造方法，其特征在于，在步骤(3)中，粗轧结束温度控制在950℃-1150℃范围内；当钢板的厚度不超过12mm时，控制粗轧阶段累计变形量≥80％；当钢板厚度超过12mm时，控制粗轧阶段 累计变形量≥70％。
  10. 如权利要求8所述的制造方法，其特征在于，在步骤(4)中，控制精轧结束的温度不低于800℃，当钢板的厚度不超过12mm时，控制精轧阶段的变形比≥5，当钢板厚度超过12mm时，控制精轧阶段的变形比≥3.5。
  11. 如权利要求8所述的制造方法，其特征在于，在步骤(5)中，将精轧后的钢板水冷至550-650℃进行卷取。
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