WO2014104443A1 - 극저온 인성이 우수하고 저항복비 특성을 갖는 고강도 강판 및 그의 제조방법 - Google Patents
극저온 인성이 우수하고 저항복비 특성을 갖는 고강도 강판 및 그의 제조방법 Download PDFInfo
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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
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/001—Heat treatment of ferrous alloys containing Ni
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- 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
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- 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
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- 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
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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
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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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
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- 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
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- 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
- C21D2211/008—Martensite
Definitions
- the present invention relates to a high-strength steel sheet suitable for application to steel for gas tanks used for storage of gas due to its resistance to wear properties and excellent cryogenic toughness and a method of manufacturing the same.
- the steel for gas tank can withstand high pressure and external shock. High strength properties are required so that they have sufficient toughness even at low gas temperatures.
- steels used in gas tanks are required to have excellent low-temperature toughness even at temperatures below -75 ° C, depending on the class.
- the removal of the weld of the weld portion is an important part.
- Patent Documents 1 and 2 are techniques for improving strength and toughness due to the refinement of grains.
- Patent Documents 3 to 7 are techniques for refining ferrites due to unrecrystallized steel rolling. Among them, Patent Document 3 discloses a reduction ratio in the austenite unrecrystallized steel temperature range during heating after low carbon steel is heated.
- Patent Document 4 proposes a method to refine the ferrite through compression processing of more than%, and accelerated cooling, Patent Document 4, the first heat treatment of general carbon steel to martensite structure and then reheat it to the ferrite stable silver range 50% reduction per pass
- Patent Documents 5 and 6 the austenite grain size is limited to a certain size by static recrystallization, and the method of realizing fine ferrite by rolling at a reduction ratio of 303 ⁇ 4> or more per pass in the austenite uncrystallized region is limited.
- Patent Literature 7 proposes a method of refining ferrite by reducing the reheated low carbon steel to a total pressure reduction rate of 75% or more through a single pass or a multistage pass near an Ar3 temperature and limiting the holding time between rolling passes to 1 second or less.
- the above-described techniques are techniques that suggest considerably difficult manufacturing conditions because they must be subjected to a large pressure drop per pass in the rolling process, which is the main process for manufacturing steel, and limit the time between passes. This requires the installation of extra-large rolling equipment and control systems, making it almost impossible to implement with existing equipment.
- the above techniques are all related to the improvement of strength and toughness due to the refinement of grains. Accordingly, when the refinement of ferrite grains is realized, the yield strength increases simultaneously with the increase in tensile strength. .
- Patent Document 1 Japanese Patent Application Publication No. 199 No. 296253
- Patent Document 2 Japanese Laid-Open Patent Publication No. 1997-316534
- Patent Document 3 Korean Patent Publication No. 1999-0029986
- Patent Document 4 Korean Patent Publication No. 1999-0029987
- Patent Document 6 Korean Patent Publication No. 2004-0p59579
- Patent Document 5 Korean Patent Publication No. 2004-0059581
- Patent Document 7 US Patent No. 4466842
- An aspect of the present invention is to provide a high strength steel sheet having a resistance ratio ratio as well as improving strength and toughness and a method of manufacturing the same ''
- the microstructure comprises 70-90) ultrafine ferrite and 10-30% MA (martensite / austenite) tissue in area fraction and provides a high strength steel sheet having a yield ratio (YS / TS) of 0.8 or less.
- MA martensite / austenite
- Another aspect of the invention the step of heating the slab having the above composition; Co-rolling the heated slab to control the austenite average grain size below 40 ym;
- a high strength steel sheet having a yield ratio (YS / TS) of 0.8 or less including the step of forming the fine MA (martensite / austenite) having an average particle diameter of 5 ⁇ or less in an area fraction in the ultrafine ferrite matrix after the holding. It provides a method of manufacturing.
- a high strength steel sheet having a toughness value of 150 J or more at -75 ° C., having a high tensile strength of 530 MPa or more, and achieving a resistance ratio of 0.8 or less, and having excellent toughness can be provided.
- Figure 1 shows the results of observing the ultrafine ferrite type : phase of the invention material B-1 under a microscope.
- Figure 2 shows the results of microscopic observation of the shape of the ultrafine MA phase (martensite / austenite mixed tissue) after Lapella etching 3 ⁇ 4 the invention material B-1.
- Figure 3 is a schematic of the process of forming the MA phase, (a) is a conventional steel, (b) relates to the invention steel according to the present invention.
- the present invention has a high strength and high toughness and a resistance ratio while controlling the microstructure of steel composition and applying rolling conditions using SDT (Strain Induces Dynamic Transformat ion), which is one of the grain refinement methods. It relates to a steel sheet and a method of manufacturing the same.
- SDT Stress Induces Dynamic Transformat ion
- High strength steel sheet which is an aspect of the present invention, in weight%, carbon (C): 0.02-0.12%, manganese (Mn): 0.5-2.0%, silicon (Si): 0.05-0.5%, nickel (Ni): 0.05- 1.0%, Titanium (Ti): 0,005-0.1%, aluminum (Al): 0.005-0.5%, phosphorus (P): 0.015% or less, sulfur (S): 0.015% or less, remaining Fe and other unavoidable impurities.
- Carbon (C) is an element that needs to be contained in an appropriate amount in order to effectively strengthen the steel, in the present invention to form a MA phase (martensite / austenite mixed structure), and to determine the out-size fraction of the MA phase formed Since it is the most important element, it needs to be contained in an appropriate range.
- the content of C exceeds 0.12%, low-temperature toughness is lowered, and since too many MA phases are formed, the fraction exceeds 3, which is not preferable.
- the C content is less than 0.0, it is not preferable because the MA phase is formed too small and the fraction is less than 10%, leading to a decrease in yield and a decrease in yield ratio. Therefore, in the present invention, it is preferable to limit the content of C to 0.020.1.
- Manganese (Mn) contributes to the refinement of ferrite and is a useful element for improving strength by solid solution strengthening. Therefore, in order to obtain the effect of Mn, it needs to be added at 0.5% or more. However, if the content exceeds 2.0% It is not preferable because the hardenability is excessively increased and the toughness of the weld portion is greatly reduced. Therefore, in the present invention, it is preferable to limit the content of Mn to 0.5 ⁇ 2.0%. Si: 0.05-0.5%
- Silicon (Si) has the effect of strengthening the strength by the solid solution effect, and is an element that is also useful as a deoxidizer in the steelmaking process.
- the content of Si exceeds 0.5%, the low-temperature toughness decreases and the weldability deteriorates. Therefore, the content of Si should be limited to 0.5% or less. However, if the content is less than 0.05%, the deoxidation effect is insufficient, and strength improvement effect is not obtained, which is not preferable.
- Si increases the stability of the MA (martensite / austenite mixed structure), it is possible to form a large fraction of the MA phase even with a low content of C, which helps in improving the strength and the resistance ratio. However, if the MA phase is formed too excessively, the toughness is rather deteriorated, so that the preferable Si content range is limited to 0.1-0.4) in consideration of this point.
- Nickel (Ni) is almost the only element that can simultaneously improve the strength and toughness of the base material, and in order to obtain the above-mentioned effect, it is necessary to add Ni to 0.05% or more. However, such Ni is an expensive element, when the content exceeds 1.03 ⁇ 4, there is a problem that the economic efficiency is lowered.
- Titanium (Ti) forms oxides and nitrides in the steel, thereby suppressing the growth of crystal grains upon reheating and greatly improving low-temperature toughness. Therefore, in order to obtain such an effect, it is necessary to add Ti to 0.005% or more. However, if the content exceeds 0.13 ⁇ 4, there is a problem that the low-temperature toughness decreases due to clogging of the playing nozzle or crystallization of the center part, and therefore, the content of Ti is preferably limited to 0.005 to 0.13 ⁇ 4>.
- Aluminum (A1) is a useful element for deoxidizing molten steel, which needs to be added at 0.005% or more. However, if the content exceeds 0.5% it is not preferable because it causes nozzle clogging during continuous casting.
- A1 promotes the formation of MA phase (martensite / austenite complex), it can form a large number of MA phases even with a small amount of C, thereby improving strength and implementing resistance recovery.
- the preferred content range of A1 is limited to 0.01 ⁇ 0.05%.
- Phosphorus (P) is an element that causes grain boundary segregation in the base metal and the welded portion, which causes a problem of embrittlement of steel, and thus it is necessary to actively reduce it.
- Phosphorus (P) is an element that causes grain boundary segregation in the base metal and the welded portion, which causes a problem of embrittlement of steel, and thus it is necessary to actively reduce it.
- Sulfur (S) is an element which causes MlS and the like to greatly inhibit the layer toughness by forming MnS, etc., and is preferably controlled as low as possible. Therefore, the content is limited to 0.015% or less.
- the steel having the advantageous composition of the present invention described above can obtain a sufficient effect only by including the alloying element in the content range described above, but to further improve properties such as the strength and toughness of the steel, the toughness and weldability of the weld heat affected zone, and the like.
- the following alloying elements are preferably added within an appropriate range.
- Ytt 1 the following alloy element stones may be added in one kind or may be added together in two or more kinds.
- Copper (Cu) is an element capable of increasing the strength while minimizing the decrease in toughness of the base metal, and it is necessary to add Cu to 0.01% or more in order to obtain such an effect. However, excessive addition of Cu greatly inhibits the product surface quality, and therefore, the content is preferably limited to 0.5% or less. Nb: 0.005-0.1%
- Niobium (Nb) precipitates in the form of NbC or NbCN to greatly improve the strength of the base metal and the welded portion.
- Nb dissolved in reheating at a high temperature suppresses the recrystallization of austenite and suppresses the transformation of ferrite or bainite, thereby making it possible to refine the structure.
- the austenite stability is greatly increased even after cooling after the final rolling, and also plays a role of promoting the formation of the MA phase (martensite / austenite mixed structure) even at the time of low speed wetting. Therefore, in order to obtain such an effect, it is necessary to add Nb to 0.00 or more, but if the content is excessively excessively more than 0.13 ⁇ 4, the possibility of causing brittle cracks in the corners of the steel is not preferable.
- Molybdenum (Mo) is a useful element because its utilization can be greatly improved by greatly improving the hardenability even with a small amount of addition. In order to obtain the above-mentioned effect, it is necessary to add Mo to 0.005% or more. However, Mo is an expensive element and when it is added in excess of 0.5%, there is a problem of excessively increasing the hardness of the welded portion and inhibiting toughness. Preference is given to adding up to 3 ⁇ 4.
- the microstructure of the steel provided by the present invention includes an ultrafine ferrite having a grain size of ⁇ or less in an area fraction of 70 to 90%, and an average particle diameter of 5 ⁇ or less.
- the ultrafine ferrite when the ultrafine ferrite is formed at an area ratio of 70% or more as a microstructure, it is advantageous to secure toughness at cryogenic temperatures due to a low interlaminar transition temperature together with an increase in strength due to grain refinement.
- the fine ⁇ phase (martensite / austenite mixed structure) is evenly distributed at an area ratio of 10% or more, continuous yielding behavior appears due to the operating potential formed at the interface between the ⁇ phase and the ferrite structure, thereby increasing the work hardening rate. Can achieve a resistance ratio.
- the yield strength is lowered, but also contributes to an increase in the tensile strength, it is more advantageous for the implementation of high strength resistance ratio.
- manufacturing conditions must be controlled, and in particular, optimization of rolling conditions, that is, rolling pass conditions and angle angle conditions is important.
- the manufacturing process of the steel according to the present invention may be made of a slab reheating-rough rolling-finish rolling ⁇ cooling, detailed conditions for each process are as follows. Slab reheating temperature: 1000-1200 ° C
- the present invention was intended to implement the initial austenite grain refining by optimizing the conditions during rough rolling. As the initial austenite grain size becomes finer, the fraction of austenite grains acting as a ferrite nucleation site increases, thereby facilitating ferrite nucleation, lowering the grain boundary strain required for SIDT generation, and shifting the ferrite transformation temperature to a high temperature.
- Finish rolling after the rough rolling is the most important technical element in the present invention together with the rough rolling.
- it is intended to form ultrafine ferra art by SIDT by optimizing the conditions during finish rolling.
- the critical deformation amount for generating the SIDT is different for each steel type, but if the effective rolling reduction is more than the threshold value, the SIDT may be generated. Therefore, in the present invention, in order to give the critical deformation amount, the finish rolling silver is limited to Ar3 + 30t Ar3 + 100 ° C. If the finish rolling silver exceeds Ar3 + 100 ° C, ultrafine ferrite by SIDT cannot be obtained, whereas at less than Ar3 + 30 ° C, coarse cornerstone ferrite is formed along the austenite grains during rolling, which causes abnormal reverse rolling. In this case, it is not preferable because it may cause a decrease in strength and laminar toughness.
- the cumulative reduction ratio may be 60% or more while maintaining the reduction ratio per rolling pass during the final rolling at the above-described finishing rolling temperature. If the rolling reduction per rolling pass is less than 10% during finish rolling, it is impossible to give enough critical strain to generate SIDT, so ultrafine ferrite cannot be obtained.In addition, if the cumulative rolling reduction is less than 60%, the ultrafine ferrite fraction by SIDT is reduced. It may not be possible to obtain enough, making tissue refinement impossible. Therefore, it is preferable to perform finish rolling as proposed in the present invention. When the rolling is controlled in this way, ultrafine ferrite having a grain size of ⁇ or less can be obtained. Cooling condition after rolling: After holding 30-90 seconds at the end of finishing rolling, angle up to 300 ⁇ 500 ° C with an angular velocity of 10 ° C / s or more
- the rolled steel as described above is then subjected to cooling, preferably maintained at the finish rolling end temperature for about 30-90 seconds before cooling.
- the MA-phase (martensite / austenite heunhap organization) there is generated when naenggik "in which the employment element high concentration layer region, in the case of the existing steel material With reference to Figure 3 nyaenggak immediately after being formed a ferrite for rough rolling
- the distance that the employment elements in the grains move to the grain boundary increases and it is difficult to form a highly concentrated region due to the lack of time to move the grains.
- by providing a step of maintaining a predetermined time at the finish rolling finish temperature by providing a time to move the employment elements sufficiently, by forming a large amount of high concentration of the concentration of the employment element around the grain boundary it is possible to form a large amount of the MA during cooling.
- nyaeng yellowfin cooling rate is 10 ° C / s or higher A and nyaenggak end to control the temperature to 300 ⁇ 500 ° C, if the cooling rate is 10 ° C / s less than the pearlite coarse in second phase is formed, and the cause of inhibiting the impact toughness, in particular to obtain the MA onto
- it is impossible to implement the resistance ratio and if the cooling end temperature exceeds 500 ° C., the fine-grained ferrite may coarsen, which may also degrade the laminar toughness.
- the MA phase formed by is coarsened, and its fraction cannot be sufficiently secured, thus making it impossible to implement a resistance ratio.
- the end of each angle is less than 300 ° C martensite phase is formed in the second phase may reduce the toughness of the steel, it is preferable in the present invention to limit the cooling end temperature to 300 ⁇ 500 ° C. .
- the M ⁇ phase having an average particle diameter of 5 ⁇ or less as the second phase in the ultrafine ferrite matrix is distributed in an area fraction of 10-303 ⁇ 4>.
- the steel sheet manufactured by completing the above cooling may have a thickness of 8t to 50t.
- each slab is reheated at 1000 ⁇ 1200 ° C and at 15T or more reduction rate per pass at 1200T Tnr, cumulative reduction rate more than 30%
- finish rolling and cooling were performed under the respective rolling and cooling conditions to prepare steel sheets.
- the ferrite grain size (FGS) and the MA phase (martensite / austenite mixed structure) fractions were measured for each manufactured steel sheet, and the tensile strength and yield strength of the steel sheet were measured to evaluate the material properties of the steel sheet. Low temperature impact toughness was measured, and the results are shown in Table 3 below.
- the ferrite grain size (FGS) is obtained by mirror-polishing test specimens from l / 4t part of the steel sheet, and then etched with FGS corrosion solution and observed 500 times using an optical microscope, and then determined the grain size and size by image analysis. It measured and calculated
- the fraction of MA phase was obtained by mirror-polishing test specimens from l / 4t part of steel sheet, which was corroded using lapela corrosion solution, observed 500 times using optical microscope, and the fraction of MA phase was determined by image analysis.
- Tensile strength was measured by taking a JIS No. 4 specimen in a direction perpendicular to the rolling direction from the l / 4t portion of the steel sheet and performing a tensile test at room temperature.
- the low temperature laminar toughness was taken from the l / 4t region of the steel sheet to prepare a V ⁇ notch test specimen, and then the Charpy lamella test was conducted five times at -75 ° C to obtain the average.
- the invention materials satisfying the composition and manufacturing conditions proposed by the present invention not only have high strength and high toughness, but also have a yield ratio of 0.8 or less. It can be confirmed that it is steel.
- the ultrafine ferrite shape is observed as shown in Figure 1
- MA phase martensite / austenite as shown in Figure 2
- the mixed tissue is formed in the ferrite matrix.
- the composition and the production conditions proposed in the present invention do not satisfy all of the comparative materials E-4 to E-8 ferrite grain size is too coarse, it is difficult to ensure a sufficient MA phase of high strength It could not be secured, and thus could not achieve a resistance ratio.
- the ferrite grain size was too coarse, and the MA phase was formed too excessively to secure low-temperature toughness.
- the composition of the composition satisfies the present invention
- the production conditions do not satisfy the present invention A-4 to A-8, B-4 to B-8, C-4 to C-8 and 1 to D
- the ferrite grain size was too coarse, or the MA phase was not formed at all, so that it was impossible to achieve a resistance ratio or secure low temperature toughness.
- the MA phase is used in the case of comparative materials E— 1 to E-4 ′ F-1 to F-4 and G-1 to G— 4, in which the manufacturing conditions satisfy the present invention but the composition does not satisfy the present invention. Insufficient fractions or too much formation resulted in failure to achieve resistance ratios or securing low temperature toughness.
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Abstract
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Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA2896531A CA2896531C (en) | 2012-12-27 | 2012-12-28 | High strength steel sheet having excellent cryogenic temperature toughness and low yield ratio properties, and method for manufacturing same |
CN201280078067.6A CN104884656B (zh) | 2012-12-27 | 2012-12-28 | 极低温韧性优异且具有低屈服特性的高强度钢板及其制备方法 |
EP12891147.6A EP2940172B1 (en) | 2012-12-27 | 2012-12-28 | High strength steel sheet having excellent cryogenic temperature toughness and low yield ratio properties, and method for manufacturing same |
US14/654,649 US10689735B2 (en) | 2012-12-27 | 2012-12-28 | High strength steel sheet having excellent cryogenic temperature toughness and low yield ratio properties, and method for manufacturing same |
JP2015551044A JP6219405B2 (ja) | 2012-12-27 | 2012-12-28 | 極低温靱性に優れ低降伏比特性を有する高強度鋼板及びその製造方法 |
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KR101917451B1 (ko) * | 2016-12-21 | 2018-11-09 | 주식회사 포스코 | 저온인성이 우수한 저항복비 강판 및 그 제조방법 |
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CN113814269B (zh) * | 2021-07-12 | 2022-07-19 | 燕山大学 | 细化低碳贝氏体钢中m-a组元的轧制工艺 |
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US20150315682A1 (en) | 2015-11-05 |
KR20140085068A (ko) | 2014-07-07 |
CN104884656B (zh) | 2017-03-08 |
JP2016507649A (ja) | 2016-03-10 |
EP2940172B1 (en) | 2017-03-01 |
EP2940172A4 (en) | 2016-01-06 |
US10689735B2 (en) | 2020-06-23 |
CA2896531C (en) | 2019-07-16 |
CA2896531A1 (en) | 2014-07-03 |
KR101482359B1 (ko) | 2015-01-13 |
EP2940172A1 (en) | 2015-11-04 |
JP6219405B2 (ja) | 2017-10-25 |
CN104884656A (zh) | 2015-09-02 |
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