WO2019078538A1 - 표면품질이 우수한 저온용 고 망간강재 및 제조방법 - Google Patents
표면품질이 우수한 저온용 고 망간강재 및 제조방법 Download PDFInfo
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- 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
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- 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
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
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- 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
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- 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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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
- C22C38/06—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
- C22C38/18—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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
Definitions
- the present invention relates to a low-temperature steel which can be used at a wide temperature range from a low temperature to a room temperature such as a liquefied gas storage tank and a transportation facility, and more particularly, to a low-temperature high- .
- Low-temperature tanks are made of materials with excellent mechanical properties such as strength and toughness at low temperatures. Typical examples are aluminum alloys, austenitic stainless steels, 35% invar steel, and 9% Ni steels.
- one of the methods for producing a material having a high low temperature toughness is to have a stable austenite structure at a low temperature.
- the slab Since the phase transformation does not occur, the slab has a coarse cast structure. As a result, when the slab is hot-rolled, surface-boundary cracking occurs. In addition, the slabs not accompanied by the phase transformation have a coarse casting structure, and thus the high temperature ductility is not good.
- Patent Document 1 Korean Published Patent Application No. 2011-0009792
- a low-temperature high manganese steel having excellent yield strength and impact toughness as well as excellent surface quality.
- a method for manufacturing a low-temperature high manganese steel material which is excellent in yield strength and impact toughness and can be manufactured at low cost for a low-temperature high manganese steel material excellent in surface quality .
- a low temperature high manganese steel comprises 0.3 to 0.8 wt% of C, 18 to 26 wt% of Mn, 0.01 to 1 wt% of Si, 0.01 to 0.5 wt% of Al, 0.1 to 0.1 wt% of Ti, % or less (excluding 0%), Cr: 1 ⁇ 4.5 wt%, Cu: 0.1 ⁇ 0.9 wt%, S: 0.03 (excluding 0%) wt% or less, P: 0.3% or less (excluding 0%), N 0.001 to 0.03% by weight, B: 0.004% by weight or less (excluding 0%), the balance Fe and other unavoidable impurities, the microstructure is austenite single phase structure, the average grain size of the austenite structure is 50 ⁇ or less , The number of austenite grains having a size of 50 ⁇ or more may be less than 1 per cm 2 .
- the high manganese steel may contain not more than 1% by volume of precipitates (including 0%).
- the high manganese steel may have an impact energy in the rolling direction at -196 DEG C of 100 J or more and the high manganese steel has a material anisotropy index which is the ratio of the thickness direction impact energy at -196 DEG C to the rolling direction impact energy at -196 DEG C. Can be 0.6 or more.
- the yield strength of the high manganese steel may be 400 MPa or more.
- the high manganese steel is produced by a method comprising the steps of preparing a slab having the above composition, reheating the slab and hot rolling the reheated slab, wherein the surface of the slab before reheating has a size of 150 m or more And a number of grains having a grain size of less than 1 per cm < 2 > may be formed.
- the average grain size of the surface layer portion of the slab before reheating may be 100 ⁇ or less.
- the slab before reheating may have a section reduction of at least 60% at 1100 ° C.
- a method of manufacturing a high-temperature high-manganese steel comprises the steps of: 0.3 to 0.8 wt% of C, 18 to 26 wt% of Mn, 0.01 to 1 wt% of Si, 0.01 to 0.5 wt% , Ti: 0.1 wt% or less (excluding 0%), P: 0.3 wt% or less (excluding 0%), N: 0.001 to 0.03 wt%, B: 0.1 to 0.9 wt%, S: 0.004 wt% or less (excluding 0%), the balance Fe and other unavoidable impurities; A deforming step of deforming the slab so that a fine recrystallized structure is formed in a surface layer portion of the slab; Air-cooling the slab having a fine recrystallized structure to the surface layer at room temperature as described above; A reheating step of heating the air-cooled slab to a temperature of 1100 to 1250 ° C; A hot rolling step of finishing rolling the reheated
- the deforming step is performed so that a recrystallized structure having a number of grains having a size of 150 mu m or more and less than 1 per cm < 2 > is formed.
- the average grain size of the surface layer portion of the slab after the deformation imparting step may be 100 ⁇ or less.
- the deformation imparting step may be carried out by rough rolling under a reduced pressure condition at 1000 to 1200 ° C.
- the deformation-imparting step may be carried out by a high-temperature forging treatment at 1000 to 1200 ° C.
- the average grain size of the surface layer portion of the slab after the high-temperature forging treatment may be 100 ⁇ or less.
- the deforming step may be performed so as to have a thickness reduction ratio of 15 to 50% with respect to the initial slab.
- the finish rolling temperature can be controlled according to the final steel material thickness during hot rolling in the hot rolling step.
- the final pass rolling temperature in the hot rolling step is 18t [t: steel material thickness (mm)] or more
- the final pass rolling temperature is set to be 850 DEG C or more and less than 900 DEG C and the final steel material thickness is 18t [t: steel material thickness )]
- the final pass rolling temperature of the hot finish rolling may be 900 ° C or higher and 950 ° C or lower.
- a low-temperature high manganese steel having excellent yield strength and impact toughness as well as excellent surface quality can be provided at low cost.
- Figs. 1 and 2 show the microstructure of the slab before and after the forging operation.
- Fig. 1 shows the slab microstructure before the forging operation
- Fig. 2 shows the slab microstructure after the forging operation.
- FIG. 3 and 4 show microstructure of a conventional steel material and a steel material consistent with the present invention.
- Fig. 3 shows the microstructure of a conventional steel material (comparative example (2)) in which an austenitic grains are formed, Shows a uniform austenite structure of a steel material (embodiment (3)) to which a slab forging operation is applied according to the present invention.
- Fig. 5 and Fig. 6 are photographs showing an example of a result of evaluating whether or not surface irregularities of the steel material occur, Fig. 5 shows an example where surface irregularity occurs, and Fig. 6 shows an example where irregularity does not occur.
- FIG. 7 is a graph showing the change in high temperature ductility of the slab according to the grain size of the microstructure of the slab surface layer microstructure.
- the present invention relates to a high-temperature high-manganese steel having excellent surface quality and a method of manufacturing the same, and the preferred embodiments of the present invention will be described below.
- the embodiments of the present invention can be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below.
- the embodiments are provided to explain the present invention to a person having ordinary skill in the art to which the present invention belongs.
- the present invention can be suitably applied to materials for use in low-temperature parts such as fuel tanks for storing and transporting liquefied petroleum gas and liquefied natural gas at low temperature, storage tanks, marine membranes, transport pipes, etc. .
- austenite single phase from the slab state to the product that is, a property that phase transformation does not occur, appears.
- the slab Since the phase transformation does not occur, the slab has a coarse cast structure. As a result, when the slab is hot-rolled, surface-boundary cracking occurs.
- the surface quality of the steel is made dull and the thickness irregularity of the final structure is caused .
- the slabs not accompanied by the phase transformation have a coarse casting structure, and thus the high temperature ductility is not good.
- the present inventors have conducted research and experiments to obtain a high-temperature-high manganese steel having a high yield strength and excellent impact toughness and an excellent surface quality, and as a result, the present invention has been completed.
- the main concept of the present invention is as follows.
- the size of the microstructure of the steel and the number of coarse grains are appropriately controlled. This can improve the surface quality of the steel.
- Cooling conditions of hot-rolled steel are properly controlled. This can inhibit carbide formation at grain boundaries. Impact toughness can be improved by suppressing the formation of carbide in the grain boundary.
- the slab Before the hot rolling of the slab, the slab is subjected to deformation so as to form a fine recrystallized structure on the surface layer of the slab.
- Examples of the treatment for applying the strain include rough rolling under a reduced pressure or hot forging.
- a fine recrystallization structure is formed in the surface layer of the slab by subjecting the slab to a deformation treatment, for example, a rough rolling treatment under a reduced pressure condition or a forging treatment, before the hot rolling of the slab, And the surface quality of the steel can be improved. Further, since a fine recrystallized structure is formed in the surface layer portion of the slab, the high temperature ductility of the slab can be improved.
- the hot rolling condition is controlled appropriately. In particular, it controls the finishing rolling temperature according to the final steel material thickness during hot rolling. As a result, a high strength can be secured.
- the low-temperature high-manganese steel according to one embodiment of the present invention comprises 0.3 to 0.8 wt% of C, 18 to 26 wt% of Mn, 0.01 to 1 wt% of Si, 0.01 to 0.5 wt% of Al, 0.1 wt% of Ti, (Excluding 0%), P: not more than 0.3% (excluding 0%), N: not more than 0% (excluding 0%) , Cr: 1 to 4.5% 0.001 to 0.03% by weight, B: 0.004% by weight or less (excluding 0%), the balance Fe and other unavoidable impurities, the microstructure is austenite single phase structure, the average grain size of the austenite structure is 50 ⁇ or less, The number of austenite grains having a grain size of 50 mu m or more may be less than one per cm < 2 >.
- C carbon
- austenite stability is insufficient and ferrite or martensite is formed and the low-temperature toughness is lowered.
- carbides are formed to cause surface defects. Therefore, the content thereof is preferably limited to 0.3 to 0.8% by weight.
- Mn manganese
- Mn manganese
- the content of Mn is preferably limited to 18 to 26% by weight.
- Si silicon is an element which improves the casting of molten steel and, particularly when added to austenite steel, is solidified in the steel to increase the strength effectively.
- the toughness may be lowered while lowering the austenite stability. Therefore, the upper limit of the Si content is preferably limited to 1% by weight.
- Al is an element that stabilizes austenite in the appropriate amount range and affects the activity of carbon in steel, effectively inhibiting carbide formation and increasing toughness.
- the upper limit of the Al content is preferably limited to 0.5% by weight.
- Ti (titanium) is an element that increases the strength and toughness by forming precipitates alone or in combination to refine the austenite grains. In addition, when sufficient precipitate-forming sites are present in the austenite grains, fine precipitates are formed in the grains to increase strength through precipitation hardening. However, when it is added in an amount exceeding 0.1% by weight, a large amount of oxides are produced in the steelmaking process, thereby causing problems such as process and casting during continuous casting, or deterioration of elongation, toughness and surface quality of the steel by coarsening of the carbonitride.
- the content of Ti (titanium) is preferably limited to 0.1% by weight or less.
- Cr chromium
- Cr is superior to strength enhancement through strengthening of the austenite structure. It has an effect of improving the surface quality effectively at high temperature oxidation since it has a corrosion resistance effect.
- Cr is preferably added in an amount of 1% by weight or more.
- the content of Cr is preferably limited to 1 to 4.5% by weight.
- Cu is an element which improves low-temperature toughness while stabilizing austenite with manganese and carbon.
- the solubility in carbide is very low and the diffusion in austenite is slow, so that it is concentrated in the austenite and nucleated carbide interface, thereby inhibiting carbon diffusion, effectively slowing carbide growth and inhibiting carbide formation Cr is preferably used.
- Cu is preferably added in an amount of 0.1 wt% or more.
- the content of Cu is preferably limited to 0.1 to 0.9% by weight.
- S sulfur
- S (sulfur) needs to be controlled to 0.03 wt% or less for the control of inclusions.
- P phosphorus
- the content thereof should be controlled to 0.3 wt% or less. If the content of P exceeds 0.3 wt%, the main composition may deteriorate, so that the upper limit of the content is preferably limited to 0.3 wt%.
- N nitrogen
- the upper limit of the N content is preferably limited to 0.03% by weight.
- the effect is insignificant, so that the lower limit of the N content is preferably limited to 0.001% by weight.
- B boron
- the microstructure of the low temperature high manganese steel product for use according to the embodiment of the invention is not more than the average grain size of the austenite 50 ⁇ m, the number of the austenite crystal grains having at least 1 per 2 cm size 50 ⁇ m ≪ / RTI >
- the average crystal grain size of the austenite structure exceeds 50 ⁇ , uneven deformation occurs in the structure due to the high density of the coarse grains, which may deteriorate the surface quality after processing,
- the average crystal grain size is limited to 50 mu m or less.
- the average crystal grain size of the austenite structure becomes smaller, the strength of the steel becomes higher accordingly.
- the grain boundary carbide can be easily precipitated by grain refinement and the low temperature toughness can be damped at the opposite part due to the increase in strength,
- the average crystal grain size of the austenite structure is limited to 20 mu m or more. Accordingly, the average grain size of the austenite structure is preferably 20 to 50 mu m, and more preferably, the average grain size of the austenite structure is 20 to 30 mu m.
- the number of austenite grains having a size of 50 mu m or more in the austenite structure is one or more per cm < 2 & gt ;
- the surface density may deteriorate after processing into a structure due to high density of coarse grains. Therefore, the number of austenite grains having a size of 50 mu m or more is preferably limited to less than 1 per cm < 2 & gt ; . More preferably, the number of austenite grains having a size of 30 ⁇ or more may be less than 1 per cm 2 .
- the high manganese steel may contain not more than 1% by volume of precipitates (including 0%). If the content of the precipitate exceeds 1 vol%, the low-temperature toughness may decrease . Therefore, it is preferable to suppress the content of the precipitate to 1 vol% or less (including 0%).
- the thickness of the high manganese steel may be 8.0 mm or more, and preferably 8.0 to 40 mm.
- the low-temperature high-manganese steel according to one embodiment of the present invention may have a Charpy impact absorption energy of 100 J or more in the rolling direction (RD, direction) at -196 ⁇ .
- the material anisotropy index of the steel means the ratio of the Charpy impact absorption energy (TD) of the steel in the thickness direction (TD) to the Charpy impact absorption energy in the rolling direction (RD) of the steel.
- the material anisotropy index of steel means a value obtained by dividing the Charpy impact absorption energy in the steel thickness direction (TD) at -196 DEG C by the Charpy impact absorption energy in the steel material rolling direction (RD) at -196 DEG C do.
- the low-temperature high-manganese steel according to an embodiment of the present invention restricts the material anisotropy index to a certain level or higher, thereby effectively preventing the Charpy impact absorption energy from being unevenly distributed in the direction of the material in the final product .
- the lower limit of the material anisotropy index to prevent unevenness of the physical properties of the final product depending on the direction of the material may be 0.6, and the lower limit of the preferable material anisotropy index may be 0.8.
- a method for manufacturing a high-temperature high-manganese steel material comprising the steps of: 0.3 to 0.8 wt% of C, 18 to 26 wt% of Mn, 0.01 to 1 wt% of Si, 0.01 to 0.5 wt% Ti: 0.1 wt% or less (excluding 0%), P: 0.3 wt% or less (excluding 0%), N: 0.001 to 0.03 wt%, B: 0.1 to 0.9 wt%, S: 0.004 wt% or less (excluding 0%), the balance Fe and other unavoidable impurities; A deforming step of deforming the slab so that a fine recrystallized structure is formed in a surface layer portion of the slab; Air-cooling the slab having a fine recrystallized structure to the surface layer at room temperature as described above; A reheating step of heating the air-cooled slab to a temperature of 1100 to 1250 ° C; A hot rolling step of finishing
- a deformation-imparting step of deforming the slab so as to form a fine recrystallized structure on the surface layer of the slab may be performed, followed by air cooling to room temperature.
- the slab surface layer means a region from the surface to a depth of 2 mm from the surface in the thickness direction of the slab.
- the slab is composed of coarse casting structure, cracks are easily generated during hot rolling and the ductility at high temperature is not good.
- the slab is deformed so as to form a fine recrystallized structure in the surface layer portion of the slab, thereby preventing cracking during hot rolling and improving the high temperature ductility.
- a fine recrystallized structure can be formed in regions other than the surface layer portion.
- the deforming step is performed so that a recrystallized structure having a number of grains having a size of 150 mu m or more and less than 1 per cm < 2 > is formed.
- a recrystallized structure having a number of grains having a size of 150 mu m or more and less than 1 per cm < 2 > is formed.
- the hot slab is heated and heated in a reheating furnace, Generation and propagation of the product may adversely affect the surface quality of the product.
- the average grain size of the surface layer portion of the slab after the deformation imparting step may be 100 ⁇ or less.
- the process for carrying out the deformation-imparting step is not particularly limited, and any process can be used as long as the deformation can be imparted to the slab before reheating the slab to form a fine recrystallized structure on the surface layer of the slab.
- One example of the process for performing the deformation-imparting step is a rough rolling treatment under a reduced pressure condition at 1000 to 1200 ° C. If the temperature for rough rolling under the reduced pressure condition is less than 1000 ⁇ ⁇ , the processing temperature is too low to secure a fine recrystallized structure, and there is a problem that the deformation resistance becomes large during the rough rolling process.
- the advantage of the recrystallized structure is advantageous, however, the partial melting and depth calculation at the segregation zone in the casting structure may be deepened, and the surface quality deterioration may occur.
- recrystallization may occur at least in the surface layer portion of the slab, and a fine recrystallized structure may be formed in the surface layer portion of the slab.
- Another example of the processing for performing the deformation-imparting step is a high-temperature forging treatment at 1000 to 1200 ° C.
- the processing temperature is too low to secure a fine recrystallized structure. Further, there is a problem that the deformation resistance increases during forging.
- the forging temperature exceeds 1200 ° C., However, the depth of partial melting and ingress calculations in the segregation bed in the casting structure may be deepened, and surface quality deterioration may occur.
- the deformation-imparting step is performed such that the number of austenite grains having a grain size of 150 mu m or more in the slab surface layer portion is less than 1 per cm < 2 & gt ;.
- the average grain size of the surface layer portion of the slab after the deformation imparting step may be 100 ⁇ or less.
- the deforming step may be carried out to have a thickness reduction ratio of at least 15% with respect to the initial slab.
- the thickness reduction rate is too small, it is difficult to ensure sufficient deformation, and it is difficult to secure the surface layer recrystallized structure.
- the thickness reduction ratio at the deformation imparting step is excessive, the microstructure of the final steel may become excessively fine, and the low temperature toughness may be deteriorated, so that the slab thickness reduction rate at the deformation imparting step may be limited to less than 50%.
- the thickness reduction rate may be between 15 and 50%.
- a slab having a fine recrystallized structure formed in its surface layer may have a sectional reduction rate (high temperature ductility) of at least 60% at 1100 ° C.
- Another example of the processing for performing the deforming step is a shot blasting method.
- the air-cooled slab is reheated at a temperature of 1100 to 1250 ° C. If the slab reheating temperature is too low, the rolling load may be excessive during hot rolling, so that the heating temperature is preferably set to 1100 DEG C or higher. The higher the heating temperature, the easier the hot rolling is. However, since the steel having a high Mn content as in the present steels has a problem that the internal quality of the steel is badly calculated at the time of heating at high temperature, the surface quality is deteriorated. desirable.
- the reheated slab is hot-rolled at a temperature of 850 to 950 ° C to obtain a hot-rolled steel material.
- the thickness of the hot-rolled steel may be 8 mm or more, preferably 8 to 40 mm.
- the hot finish rolling temperature is too low, the load becomes large during rolling, and therefore, it is preferable that the hot finish rolling is performed at 850 ⁇ or higher.
- the finish rolling temperature can be controlled according to the final steel material thickness during hot rolling in the hot rolling step. In this case, the strength can be further improved.
- the final pass rolling temperature of the hot finish rolling may be 900 ° C or higher and 950 ° C or lower.
- the final steel material thickness is 18t [t: steel material thickness (mm)] or more and the final pass rolling temperature of the hot finish rolling is 900C or higher, it may be difficult to secure sufficient strength.
- the final steel material thickness is less than 18t [t: steel material thickness (mm)]
- the final pass rolling temperature is less than 900 deg. C, the strength is greatly increased and low temperature impact toughness may be lowered.
- the carbide may be precipitated because the temperature is lower than the carbide forming temperature, and the low temperature impact toughness Can bring about a decline.
- the final steel material thickness is less than 18t [t: steel material thickness (mm)] if the final pass rolling temperature exceeds 950 deg. C, it may be difficult to secure the temperature because a lot of rolling proceeds in a short time.
- the hot rolling is carried out such that the reduction rate is 40% or more of the total reduction rate at a temperature lower than the non-recrystallization temperature (Tnr) when the steel material thickness is 18t [t: steel material thickness (mm)] or more.
- Tnr non-recrystallization temperature
- the hot-rolled steel is accelerated and cooled to an accelerated cooling end temperature of 600 DEG C or less at a cooling rate of 10 DEG C / sec or more. Since the hot-rolled steel has a Cr content of 1 to 4.5% by weight and contains C, accelerated cooling is indispensable for suppressing the precipitation of carbide which causes deterioration of low-temperature toughness.
- the accelerated cooling rate is less than 10 ° C / sec, carbide may be precipitated in the grain boundary, and the impact toughness may be weakened.
- the cooling rate may be 10 to 40 DEG C / sec.
- the accelerated cooling end temperature exceeds 600 ⁇
- the carbide precipitates at the grain boundaries due to the above-mentioned causes, and the impact toughness may be thereby weakened.
- the accelerated cooling end temperature may be from room temperature to 600 ° C, and preferably from 300 to 400 ° C.
- the steel material produced as described above is austenitic single-phase structure
- the average grain size of the austenite structure may be 20 to 50 ⁇
- the average grain size of the austenite structure may be more preferably 20 to 30 ⁇ .
- the steel material produced as described above may have a microstructure in which the number of austenite grains having a grain size of 50 mu m or more is less than 1 per cm < 2 & gt ;, more preferably the number of austenite grains having a grain size of 30 mu m or more cm < 2 >.
- the steel material produced as described above may have a shock absorption energy of 100 J or more in the rolling direction (RD) at -196 ° C. and -196 ° C. to the impact absorption energy in the rolling direction (RD) at -196 ° C.
- the material anisotropy index which is the ratio of the shock absorption energy in the thickness direction (TD), may be 0.6 or more, and more preferably, the material anisotropy index may be 0.8 or more.
- the yield strength of the steel material produced as described above may be 400 MPa or more.
- the slabs having the steel compositions shown in the following Table 1 were forged according to the conditions shown in Table 2, air-cooled to room temperature, and then subjected to reheating, hot rolling and cooling under the conditions shown in Table 2 below to produce hot rolled steels having the thicknesses shown in Table 2 below.
- the number of austenite grains (g / cm 2 ), average grain size, precipitate fraction (volume%) and yield strength, which have a grain size of 50 ⁇ m or more and a grain size of 30 ⁇ m or more, Charpy impact toughness and occurrence of surface unevenness were investigated.
- the results are shown in Table 3 below.
- the Charpy impact toughness was measured with respect to the rolling direction (RD, Rolling Direction) and the thickness direction (TD, Thickness Direction) of the hot-rolled steel, The ratio of the Charpy impact absorption energy at -196 ⁇ was calculated to calculate the material anisotropy index.
- Fig. Fig. 1 shows slab microstructure before forging
- Fig. 2 shows slab microstructure after forging.
- Specimen Type 50 ⁇ m or more of coarse grains of steel (pieces / cm 2 ) The number of coarse grains of steel of 30 ⁇ m or more (pieces / cm 2 ) Average grain size of steel ( ⁇ m) The precipitate fraction (volume%) Yield strength (MPa) -196 ° C Impact Toughness (J, RD) -196 DEG C Impact Toughness (J, TD) Material Anisotropy Index Surface unevenness Remarks One 4 6 55 Less than 1% 384 100 57 0.57 Occur Comparative Example 1 2 3 5 52 Less than 1% 410 151 85 0.56 Occur Comparative Example 2 3 0.02 0.03 18 4% 565 49 43 0.87 Not occurring Comparative Example 3 4 0.1 0.1 24 Less than 1% 465 146 122 0.84 Not occurring Inventory 1 5 0.1 0.5 29 Less than 1% 356 103 91 0.88 Not occurring Inventory 2 6 0.1 0.1 27 Less than 1% 410 130 119 0.92 Not occurring Inventory 3 7 0.1
- the number of coarse peelings (pieces / cm 2 ) And the average grain size of the steel material is 50 ⁇ or less, and the number of coarse grains (number / cm 2 ) of 50 ⁇ or more and 30 ⁇ or more is less than 1.
- the yield strength and the impact toughness are excellent as well as the surface unevenness does not occur.
- the yield strength is low, the impact toughness is excellent and surface irregularity does not occur.
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Abstract
Description
강종 | 강 조성(중량%) | ||||||||||
C | Mn | Si | Al | Ti | Cr | Cu | S | P | N | B | |
1 | 0.45 | 24.5 | 0.3 | 0.0271 | 0.031 | 3.7 | 0.50 | 0.0022 | 0.0178 | 0.0112 | 0.0029 |
2 | 0,45 | 24.5 | 0.3 | 0.0377 | 0.031 | 3.8 | 0.50 | 0.0012 | 0.0252 | 0.0134 | 0.0025 |
3 | 0.45 | 24.5 | 0.3 | 0.0362 | 0.032 | 3.7 | 0.48 | 0.0014 | 0.0239 | 0.0152 | 0.0026 |
4 | 0.45 | 24.5 | 0.3 | 0.0371 | 0.021 | 3.5 | 0.48 | 0.0007 | 0.027 | 0.0136 | 0.0025 |
5 | 0.45 | 24.5 | 0.3 | 0.0334 | 0.002 | 3.3 | 0.41 | 0.0013 | 0.0135 | 0.0201 | 0.0025 |
6 | 0.45 | 24.5 | 0.3 | 0.0278 | 0.029 | 3.6 | 0.53 | 0.0029 | 0.0192 | 0.0161 | 0.0018 |
7 | 0.45 | 24.5 | 0.3 | 0.0451 | 0.003 | 3.3 | 0.41 | 0.0010 | 0.0166 | 0.0172 | 0.0025 |
8 | 0.45 | 24.5 | 0.3 | 0.0266 | 0.029 | 3.3 | 0.42 | 0.0011 | 0.0164 | 0.0151 | 0.0028 |
강종 | 단조온도(1100℃) | 단조두께감소율(%) | 슬라브표층부150㎛ 이상조대립수 (개/cm2) | 슬라브고온연성(%) | 재가열온도(℃) | 마무리압연온도(℃) | Tnr이하압하율 (%) | 냉각속도(℃/sec) | 냉각종료온도(℃) | 강판두께(mm) | 비고 |
1 | 미적용 | - | 10 | 24 | 1200 | 930 | 35 | 25 | 380 | 21 | 비교예1 |
2 | 미적용 | - | 5 | 35 | 1180 | 920 | 46 | 33.5 | 400 | 15 | 비교예2 |
3 | 적용 | 52 | 0.03 | 80 | 1180 | 800 | 45 | 8 | 400 | 20 | 비교예3 |
4 | 적용 | 28 | 0.1 | 89 | 1180 | 930 | 55 | 33.5 | 380 | 15 | 발명예1 |
5 | 적용 | 28 | 0.1 | 90 | 1200 | 930 | 30 | 23.9 | 372 | 27 | 발명예2 |
6 | 적용 | 28 | 0.1 | 87 | 1200 | 862 | 45 | 23.9 | 364 | 27 | 발명예3 |
7 | 적용 | 28 | 0.1 | 85 | 1220 | 860 | 55 | 23.9 | 391 | 27 | 발명예4 |
8 | 적용 | 28 | 0.1 | 80 | 1220 | 850 | 50 | 15 | 350 | 36 | 발명예5 |
시편종류 | 강재의50㎛ 이상 조대립 수(개/cm2) | 강재의30㎛ 이상 조대립 수(개/cm2) | 강재의 평균 결정립 크기(㎛) | 석출물분율(부피%) | 항복강도 (MPa) | -196℃ 충격인성 (J, RD) | -196℃ 충격인성(J, TD) | 재질이방성지수 | 표면불균일 | 비고 |
1 | 4 | 6 | 55 | 1%미만 | 384 | 100 | 57 | 0.57 | 발생 | 비교예1 |
2 | 3 | 5 | 52 | 1%미만 | 410 | 151 | 85 | 0.56 | 발생 | 비교예2 |
3 | 0.02 | 0.03 | 18 | 4% | 565 | 49 | 43 | 0.87 | 미발생 | 비교예3 |
4 | 0.1 | 0.1 | 24 | 1%미만 | 465 | 146 | 122 | 0.84 | 미발생 | 발명예1 |
5 | 0.1 | 0.5 | 29 | 1%미만 | 356 | 103 | 91 | 0.88 | 미발생 | 발명예2 |
6 | 0.1 | 0.1 | 27 | 1%미만 | 410 | 130 | 119 | 0.92 | 미발생 | 발명예3 |
7 | 0.1 | 0.1 | 26 | 1%미만 | 462 | 110 | 97 | 0.88 | 미발생 | 발명예4 |
8 | 0.1 | 0.1 | 26 | 1%미만 | 433 | 100 | 101 | 1.01 | 미발생 | 발명예5 |
Claims (20)
- C: 0.3~0.8 중량%, Mn: 18~26 중량%, Si: 0.01~1 중량%, Al: 0.01~0.5 중량%, Ti: 0.1 중량% 이하(0% 제외), Cr: 1~4.5 중량%, Cu: 0.1~0.9 중량%, S: 0.03 중량% 이하(0% 제외), P: 0.3 중량% 이하(0% 제외), N: 0.001 ~ 0.03 중량%, B: 0.004 중량% 이하(0% 제외), 잔부 Fe 및 기타 불가피한 불순물을 포함하고, 미세조직이 오스테나이트 단상 조직이고, 오스테나이트 조직의 평균 결정립 크기가 50㎛이하이고, 50㎛ 이상의 크기를 갖는 오스테나이트 결정립의 수가 cm2당 1개 미만인 저온용 고 망간 강재.
- 제1항에 있어서, 상기 고 망간 강재는 1 부피% 이하(0% 포함)의 석출물을 포함하는 것을 특징으로 하는 저온용 고망간 강재.
- 제1항에 있어서, 상기 오스테나이트 조직의 평균 결정립 크기가 20~30㎛인 것을 특징으로 하는 저온용 고망간 강재.
- 제1항에 있어서, 상기 오스테나이트 조직 중 30㎛ 이상의 크기를 갖는 오스테나이트 결정립의 수가 cm2당 1개 미만인 것을 특징으로 하는 저온용 고망간 강재.
- 제1항에 있어서, 상기 고 망간 강재는 -196℃에서의 압연방향 충격에너지가 100J 이상인 것을 특징으로 하는 저온용 고망간 강재.
- 제1항에 있어서, 상기 고 망간 강재는 -196℃에서의 압연방향 충격에너지에 대한 -196℃에서의 두께방향 충격에너지의 비인 재질이방성 지수가 0.6 이상인 것을 특징으로 하는 저온용 고망간 강재.
- 제1항에 있어서, 상기 고 망간 강재는 400MPa 이상의 항복강도를 갖는 것을 특징으로 하는 저온용 고망간 강재.
- 제1항에 있어서, 상기 고 망간 강재는 제1항의 조성을 갖는 슬라브를 준비하는 공정, 슬라브를 재가열하는 공정과 재가열된 슬라브를 열간압연하는 공정을 포함하는 제조방법으로 제조되는 것으로, 상기 재가열 전의 슬라브의 표층부(여기서, 슬라브 표층부는 표면에서, 슬라브 두께 방향으로 표면으로부터 2mm 깊이까지의 영역을 의미함)에는 150㎛ 이상의 크기를 갖는 결정립 수가 단위 cm2당 1개 미만인 재결정 조직이 형성되어 있는 것을 특징으로 하는 저온용 고망간 강재.
- 제8항에 있어서, 상기 재가열 전의 슬라브의 표층부의 평균 결정립 크기가 100㎛이하인 것을 특징으로 하는 저온용 고망간 강재.
- 제8항 또는 제9항에 있어서, 상기 재가열 전의 슬라브는 1100℃에서 60% 이상의 단면 감소율을 갖는 것을 특징으로 하는 저온용 고망간 강재.
- 제1항에 있어서, 상기 고 망간 강재는 8.0~40mm의 두께를 갖는 것을 특징으로 하는 저온용 고망간 강재.
- C: 0.3~0.8 중량%, Mn: 18~26 중량%, Si: 0.01~1 중량%, Al: 0.01~0.5 중량%, Ti: 0.1 중량% 이하(0% 제외), Cr: 1~4.5 중량%, Cu: 0.1~0.9 중량%, S: 0.03 중량% 이하(0% 제외), P: 0.3 중량% 이하(0% 제외), N: 0.001 ~ 0.03 중량%, B: 0.004 중량% 이하(0% 제외), 잔부 Fe 및 기타 불가피한 불순물을 포함하는 슬라브를 준비하는 단계;상기 슬라브의 표층부에 미세한 재결정 조직이 형성되도록 슬라브에 변형을 가하는 변형부여단계;상기와 같이 표층부에 미세한 재결정 조직이 형성된 슬라브를 상온까지 공냉하는 단계;상기와 같이 공냉된 슬라브를 1100~1250℃의 온도로 가열하는 재가열 단계;상기와 같이 재가열된 슬라브를 850~950℃의 온도에서 마무리 압연하여 열연강재를 얻는 열간압연 단계; 및상기 열연강재를 10℃/sec 이상의 냉각속도로 600℃ 이하의 가속냉각종료온도까지 가속냉각하는 가속냉각단계를 포함하는 저온용 고 망간 강재의 제조방법.
- 제12항에 있어서, 상기 변형부여단계는 1000~1200℃에서 강압하 조건의 조압연처리에 의해 실시되는 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
- 제12항에 있어서, 상기 변형부여단계는 1000~1200℃의 고온 단조처리에 의해 실시되는 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
- 제12항에 있어서, 상기 변형부여단계는 상기 슬라브의 표층부(여기서, 슬라브 표층부는 표면에서, 슬라브 두께 방향으로 표면으로부터 2mm 깊이까지의 영역을 의미함)에, 150㎛ 이상의 크기를 갖는 결정립 수가 단위 cm2당 1개 미만인 재결정 조직이 형성되도록 실시되는 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
- 제12항 내지 제15항 중 어느 한 항에 있어서, 상기 변형부여단계 후의 슬라브의 표층부의 평균결정립 크기가 100㎛ 이하인 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
- 제12항 내지 제15항 중 어느 한 항에 있어서, 상기 변형부여단계는 초기 슬라브에 대해 15~50%의 두께 감소율을 갖도록 실시되는 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
- 제12항에 있어서, 상기 열간압연단계에서 열간압연 시 최종 강재 두께가 18t[t: 강재두께(mm)] 이상일 때에는 열간 마무리 압연 마지막 패스 압연온도가 850℃ 이상 900℃ 미만이고, 최종 강재 두께가 18t[t: 강재두께(mm)] 미만일 때에는 열간 마무리 압연 마지막 패스 압연온도가 900℃ 이상 950℃ 이하인 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
- 제12항에 있어서, 상기 열간압연단계에서 열간압연 시 강재 두께가 18t[t: 강재두께(mm)] 이상 일 경우 미재결정온도(Tnr) 이하의 온도에서의 압하율이 전체 압하율의 40% 이상인 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
- 제12항에 있어서, 상기 열연강재는 8~40mm의 두께를 갖는 것을 특징으로 하는 저온용 고 망간 강재의 제조방법.
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EP21193240.5A EP3974556A1 (en) | 2017-10-18 | 2018-10-11 | High manganese steel for low temperature, having excellent surface quality |
CN201880067461.7A CN111225992B (zh) | 2017-10-18 | 2018-10-11 | 具有优异的表面品质的用于低温的高锰钢及其制造方法 |
JP2020521408A JP6947922B2 (ja) | 2017-10-18 | 2018-10-11 | 表面品質に優れた低温用高マンガン鋼材及びその製造方法 |
EP18868100.1A EP3699313B1 (en) | 2017-10-18 | 2018-10-11 | High manganese steel for low temperature, having excellent surface quality, and manufacturing method therefor |
US16/649,739 US11584970B2 (en) | 2017-10-18 | 2018-10-11 | High manganese steel for low temperature applications having excellent surface quality and a manufacturing method thereof |
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