Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
• • 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
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • 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
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0236—Cold 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
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0242—Flattening; Dressing; Flexing
• • 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
• • 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
  • 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
  • C21D8/0273—Final recrystallisation annealing
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/18—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
  • 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
  • C21D2211/001—Austenite

Definitions

• the present invention relates to austenitic stainless steel and a method for manufacturing the same, and more particularly, to a low-cost austenitic stainless steel having high strength and high formability and a method for manufacturing the same.
• the trend of the automobile market is changing from the existing automobile industry centered on internal combustion engines to the battery oriented eco-friendly automobile market. That is, the conventional internal combustion engine vehicle market favoring medium or large vehicles is changing to a battery-centered driving engine market favoring small or light vehicles.
• the structural material that protects the battery protects the battery from external shocks from the risk of safety accidents such as explosions, requires high strength characteristics to take responsibility for the safety of passengers, and has to be light in order not to increase the weight of a small or light vehicle.
• structural materials that protect batteries but also general structural materials are being made lighter and stronger. Accordingly, it is necessary to develop high-strength, high-molding materials with excellent productivity and excellent stability so that they can be applied throughout the industry.
• Stainless steel is a material that can be applied throughout the industry due to its excellent corrosion resistance.
• austenitic stainless steel since the elongation rate is excellent, there is no problem in making a complex shape according to the various needs of customers, and it has the advantage of a beautiful appearance.
• austenitic stainless steel is inferior in yield strength compared to general carbon steel, and there is an economic problem of using expensive alloying elements. Therefore, it is required to develop stainless steel for structural materials that can secure a high level of yield strength and appropriate tensile strength while maintaining high formability.
• the alloy component constituting the austenitic stainless steel is expensive compared to most carbon steels.
• Ni contained in austenitic stainless steel is not only unstable in raw material supply and demand due to extreme fluctuations in material price, but also difficult to secure supply price stability, and at the same time, there is a problem in price competitiveness because the material itself is high. Therefore, it is required to develop a low-cost austenitic stainless steel in which the content of expensive alloying elements such as Ni is reduced as much as possible.
• the present invention is to provide a low-cost austenitic stainless steel of high strength and high formability.
• the high-strength, high-molding, low-cost austenitic stainless steel according to an example of the present invention is, by weight, C: more than 0% 0.08% or less, N: 0.2 to 0.25%, Si: 0.8 to 1.5%, Mn: 8.0 to 9.5%, Cr: 15.0 to 16.5%, Ni: more than 0% and 1.0% or less, Cu: 0.8 to 1.8%, the balance Fe and other unavoidable impurities, and the following formula (1) to (4) may be satisfied.
• C, N, Si, Mn, Cr, Ni, and Cu mean the content (% by weight) of each element.
• Each high-strength, high-molding, low-cost austenitic stainless steel of the present invention may have a yield strength of 400 MPa or more of the cold-rolled annealed material.
• Each high-strength, high-molding, low-cost austenitic stainless steel of the present invention may have an elongation of 55% or more of the cold-rolled annealed material.
• Each high-strength, high-molding, low-cost austenitic stainless steel of the present invention may have a yield strength of 800 MPa or more of the temper rolled material.
• Each high-strength, high-molding, low-cost austenitic stainless steel of the present invention may have an elongation of 25% or more of the temper rolling material.
• the method for producing a high-strength, high-molding, low-cost austenitic stainless steel according to an example of the present invention is, by weight, C: more than 0% 0.08% or less, N: 0.2 to 0.25%, Si: 0.8 to 1.5%, Mn: 8.0 to 9.5%, Cr: 15.0 to 16.5%, Ni: more than 0% and 1.0% or less, Cu: 0.8 to 1.8%, balance Fe and other unavoidable impurities, Preparing a slab satisfying the following formulas (1) to (4), preparing a hot-rolled material by hot rolling the slab, and then annealing to prepare a hot-rolled annealed material, cold-rolling the hot-rolled annealed material to cold-rolled It may include the steps of preparing a cold-rolled annealing material by annealing at a temperature of 1050° C. or higher and then performing temper rolling to prepare a temper-rolled material.
• C, N, Si, Mn, Cr, Ni, and Cu mean the content (% by weight) of each element.
• the step of temper rolling may be performed at a reduction ratio of 20% or more.
• the slab may have a reduction in cross section of 50% or more at a high temperature of 800° C. or more.
• the cold-rolled annealed material which is cold-rolled and then annealed at 1050° C. or higher, exhibits excellent yield strength, and austenitic stainless steel capable of securing sufficient elongation required for molding even after temper rolling to secure additional strength.
• austenitic stainless steel capable of securing sufficient elongation required for molding even after temper rolling to secure additional strength.
• the high-strength, high-molding, low-cost austenitic stainless steel according to an embodiment of the present invention is, by weight, C: more than 0% and 0.08% or less, N: 0.2 to 0.25%, Si: 0.8 to 1.5%, Mn: 8.0 to 9.5%, Cr: 15.0 to 16.5%, Ni: more than 0% and 1.0% or less, Cu: 0.8 to 1.8%, the balance Fe and other unavoidable impurities, and the following formulas (1) to (4) may be satisfied.
• C, N, Si, Mn, Cr, Ni, and Cu mean the content (% by weight) of each element.
• the high-strength, high-molding, low-cost austenitic stainless steel according to an embodiment of the present invention is, by weight, C: more than 0% and 0.08% or less, N: 0.2 to 0.25%, Si: 0.8 to 1.5%, Mn: 8.0 to 9.5%, Cr: 15.0 to 16.5%, Ni: more than 0% and not more than 1.0%, Cu: 0.8 to 1.8%, balance Fe and other unavoidable impurities.
• Carbon (C) is an effective element for stabilizing the austenite phase, and may be added to secure the yield strength of the austenitic stainless steel.
• the content is excessive, cold workability is reduced due to the solid solution strengthening effect, and ductility, toughness, corrosion resistance, etc. may be reduced by inducing grain boundary precipitation of Cr carbide, and welding properties between materials may be deteriorated. Accordingly, the upper limit of the C content in the present invention may be limited to 0.08% by weight.
• Nitrogen (N) is one of the most important elements in the present invention. Nitrogen is a powerful austenite phase stabilizing element, and is an effective element for improving the corrosion resistance and yield strength of austenitic stainless steels. However, when the content is excessive, defects such as nitrogen pores may occur during production of the cast slab, and cold workability may be deteriorated due to the solid solution strengthening effect. Accordingly, the upper limit of the N content in the present invention may be limited to 0.25% by weight.
• Si acts as a deoxidizer during the steelmaking process and is an effective element for improving corrosion resistance.
• Si is an effective element for improving the yield strength of steel among substitution-type elements.
• Si may be added in an amount of 0.8 wt% or more.
• Si as a ferrite phase stabilizing element, promotes the formation of delta ( ⁇ ) ferrite in the cast slab when excessively added, thereby reducing hot workability and adversely affecting the ductility and impact properties of the material. Accordingly, the upper limit of the Si content in the present invention may be limited to 1.5% by weight.
• Manganese (Mn) is an austenite phase stabilizing element added to replace nickel (Ni) in the present invention, and may be added in an amount of 8.0 wt % or more to suppress the formation of processing-induced martensite to improve cold workability.
• MnS S-based inclusions
• Mn fumes are generated during the steelmaking process, which accompanies manufacturing risks.
• the addition of an excessive amount of Mn sharply deteriorates the corrosion resistance of the product. Accordingly, the upper limit of the Mn content in the present invention may be limited to 9.5% by weight.
• Chromium (Cr) is a ferrite stabilizing element, but is effective in suppressing martensite phase formation, and is a basic element for securing corrosion resistance required for stainless steel, and may be added in an amount of 15.0 wt % or more. However, if the content is excessive, a large amount of delta ( ⁇ ) ferrite in the slab is formed as a ferrite stabilizing element, which may adversely affect hot workability and material properties. Accordingly, the upper limit of the Cr content in the present invention may be limited to 16.5% by weight.
• Nickel (Ni) is a strong austenite phase stabilizing element, and is added to ensure good hot workability and cold workability. However, since Ni is an expensive element, it causes an increase in raw material cost when added in a large amount. In the present invention, the upper limit of the Ni content may be limited to 1.0% by weight in consideration of both the cost and efficiency of the steel.
• Copper (Cu) is an austenite phase stabilizing element, and is added to replace nickel (Ni) in the present invention.
• Cu is an element that improves the corrosion resistance of the steel in a reducing environment, it can be added 0.8% by weight or more.
• the upper limit of the Cu content may be limited to 1.8% by weight in consideration of the cost, efficiency, and material properties of the steel.
• the remaining component of the present invention is iron (Fe).
• Fe iron
• the impurities are known to any person skilled in the art of a conventional manufacturing process, all details thereof are not specifically mentioned in the present specification.
• impurities that are unavoidably incorporated include phosphorus (P) and sulfur (S), and the content thereof may include at least one of P: 0.035 wt% or less, S: 0.01 wt% or less, according to an example of the present invention. .
• Phosphorus (P) is an impurity that is unavoidably contained in steel and is an element that causes intergranular corrosion of steel or inhibits hot workability, so it is preferable to control its content as low as possible.
• the upper limit of the P content may be limited to 0.035% by weight or less.
• S is an impurity that is unavoidably contained in steel, and is an element that segregates at grain boundaries of steel and is a major cause of impairing hot workability, so it is preferable to control its content as low as possible.
• the upper limit of the S content may be limited to 0.01% by weight or less.
• the alloy composition may be further limited according to the following formulas (1) to (4).
• the formula (1) regarding the austenite phase fraction was derived to secure excellent elongation of the cold rolled annealed material prepared by cold rolling and then annealing.
• Mn, Ni, and N mean the content (% by weight) of each element.
• Equation (1) The lower the value of Equation (1), the lower the fraction of the austenite phase after annealing.
• the value of Equation (1) is less than 7.5, the austenitic stainless steel contains 5% or more of delta ferrite or the martensitic phase during cold rolling. A phase transformation will occur.
• the lower limit of the value of Equation (1) may be limited to 7.5 in order to secure a sufficient elongation of the steel material.
• Equation (2) was derived in consideration of the improvement of the yield strength by the stress field of the steel material in order to secure the high yield strength of the austenitic stainless steel.
• C, N, Si, Mn, Cr, Ni, and Cu mean the content (% by weight) of each element.
• Equation (2) As the value of Equation (2) is higher, the stress field between the lattices increases due to the atomic size difference between the alloying elements, and the limit to withstand plastic deformation against external stress increases. When the value of Equation (2) is less than 12, it is difficult to secure the yield strength required in the present invention. Accordingly, in the present invention, the lower limit of the value of Equation (2) may be limited to 12 for high strength characteristics.
• Equation (3) was derived in consideration of the phase transformation due to deformation of the austenitic stainless steel.
• C, N, Si, Mn, Cr, Ni, and Cu mean the content (% by weight) of each element.
• Equation (3) As the value of Equation (3) is higher, the austenite phase is easily transformed into martensite by external stress. Specifically, when the value of Equation (3) exceeds 70, the austenitic stainless steel exhibits abrupt work-induced martensitic transformation behavior with respect to deformation, and non-uniform plastic working occurs. As a result, there is a problem in that the elongation of the austenitic stainless steel is inferior, so the upper limit of the value of Equation (3) may be limited to 70.
• Equation (4) was derived by considering the dislocation slip behavior of the steel due to the deformation of the austenitic stainless steel.
• C, N, Si, Mn, Cr, Ni, and Cu mean the content (% by weight) of each element.
• Equation (4) The lower the value of Equation (4), the more difficult the cross-slip expression of the austenite phase due to external stress.
• the value of Equation (4) is less than 11, the austenitic stainless steel shows only planar slip behavior with respect to deformation, and the accumulation of dislocations occurs rapidly due to external stress.
• the elongation of the austenitic stainless steel is inferior, it is difficult to perform temper rolling, and hot rolling defects such as edge cracks occur during hot deformation at high temperature, which may cause a problem of productivity decrease.
• the lower limit of the value of Equation (4) may be limited to 11.
• Equation (4) when the value of Equation (4) is increased, there is a problem in that the plasticity non-uniformity increases due to the occurrence of frequent cross-slip, which increases the stress concentration in the weak part of the steel. As the strength of the steel increases, the tendency of such brittleness and plasticity non-uniformity increases, so that in the case of high-strength steel as in the present invention, a decrease in the elongation of the steel is likely to occur. In consideration of this, the upper limit of Equation (4) in the present invention may be limited to 17.
• the slab having the above-described alloy composition may have a reduction in cross-section of 50% or more at a high temperature of 800° C. or more.
• the yield strength of the cold-rolled annealed material may be 400 MPa or more.
• the elongation of the cold-rolled annealing material may be 55% or more.
• cold-rolled annealing material means a steel material prepared by hot-rolling-annealing-cold rolling-annealing of a slab.
• the yield strength of the temper rolled material may be 800 MPa or more.
• the yield strength may be 800 MPa or more, and the elongation may be 25% or more.
• "passage-rolled material” means a steel material prepared by temper rolling the above-described cold-rolled annealed material.
• the method for manufacturing high-strength, high-molding, low-cost austenitic stainless steel according to an embodiment of the present invention is, in weight %, C: more than 0% and 0.08% or less, N: 0.2 to 0.25%, Si: 0.8 to 1.5%, Mn: 8.0 to 9.5%, Cr: 15.0 to 16.5%, Ni: more than 0% and 1.0% or less, Cu: 0.8 to 1.8%, the balance Fe and other unavoidable impurities, and the cast steel that satisfies formulas (1) to (4) preparing a hot-rolled material by hot rolling the slab, then annealing to prepare a hot-rolled annealed material, cold rolling the hot-rolled annealed material to prepare a cold-rolled material, and then annealing at a temperature of 1050 ° C. or higher to cold-rolled It may include the step of providing a blunt material and a step of temper rolling to provide a temper rolled material.
• the cast steel having the above-described alloy composition may be prepared as a hot-rolled material by hot rolling at a temperature of 1000 to 1300 °C, and then annealing at a temperature range of 1000 to 1100 °C to manufacture a hot-rolled annealing material. At this time, the annealing heat treatment may be performed for 10 seconds to 10 minutes.
• the hot-rolled annealing material may be cold-rolled to prepare a cold-rolled material, and then annealed to produce a cold-rolled annealed material.
• cold rolling was performed as a method for improving the yield strength of austenitic stainless steel, and then low temperature annealing heat treatment was performed in a low temperature range of 1000° C. or less.
• Low-temperature annealing heat treatment does not complete recrystallization, but is a method of increasing strength by using the energy accumulated in the steel during cold rolling.
• the austenitic stainless steel that has been subjected to the low-temperature annealing heat treatment as described above has the disadvantage that not only there is a possibility that the material may appear non-uniform, but also fine pickling occurs in the pickling process, which is a subsequent process, or the surface shape is not beautiful.
• the hot-rolled annealed material may be cold-rolled to prepare a cold-rolled material, and then annealed at a temperature of 1050° C. or higher to manufacture a cold-rolled annealed material.
• the annealing heat treatment may be performed for 10 seconds to 10 minutes.
• excellent elongation can be secured by not performing low-temperature annealing after cold rolling, and yield strength can also be secured at an appropriate level or more through alloy composition design.
• the cold-rolled annealed material according to an embodiment of the present invention may have a yield strength of 400 MPa or more.
• the cold-rolled annealed material according to an embodiment of the present invention may have an elongation of 55% or more.
• the present invention it is possible to secure excellent yield strength through control of alloy composition and subsequent temper rolling even without performing low-temperature annealing after cold rolling.
• the yield strength of the temper rolled material may be 800 MPa or more.
• the temper rolling may be performed at a reduction ratio of 20% or more.
• strength can be increased by using a phenomenon in which high work hardening occurs as an austenite phase transforms into a work-induced martensite phase during cold deformation, or by using dislocation accumulation of steel.
• high work hardening occurs as an austenite phase transforms into a work-induced martensite phase during cold deformation
• dislocation accumulation of steel there is a fear that the elongation of the steel material is rapidly reduced.
• the present invention by designing the alloy composition as described above, it is possible to appropriately control the phase transformation and dislocation behavior of the steel, thereby preventing the elongation of the steel from rapidly decreasing due to the temper rolling.
• the yield strength of the temper rolled material is 800 MPa or more, and the high strength, high formability and low cost austenitic stainless steel with an elongation of 25% or more and high forming characteristics are simultaneously satisfied.
• a steel material having an alloy composition shown in Table 1 was prepared as a slab through ingot melting, heated at 1250° C. for 2 hours, and then hot rolled to prepare a hot rolled material. Thereafter, annealing heat treatment was performed at 1100° C. for 90 seconds to prepare a hot-rolled annealed material. Then, cold rolling was performed at a reduction ratio of 70% to prepare a cold rolled material, and then annealed heat treatment was performed at 1100° C. for 10 seconds to prepare a cold rolled annealed material.
• Table 1 shows the values of Equations (1) to (4) derived by substituting the alloy composition and alloying element content for each Inventive Example and Comparative Example.
• the yield strength, tensile strength, and elongation of the cold-rolled annealed materials of each invention example and comparative example were measured.
• the yield strength, tensile strength, and elongation of the temper-rolled material prepared by 20% temper rolling of the cold-rolled annealed material of each invention example and comparative example were measured.
• Yield strength, tensile strength, and elongation were measured according to ASTM standards, and yield strength (YS), MPa), tensile strength (Tensile Strength (TS), MPa) and elongation (Elongation ( EL), %) are shown in Table 2 below.
• Yield strength, tensile strength, and elongation were measured according to ASTM standards, and yield strength (YS), MPa), tensile strength (Tensile Strength (TS), MPa) and elongation (Elongation ( EL), %) are shown in Table 2 below.
• yield strength (YS), MPa), tensile strength (Tensile Strength (TS), MPa) and elongation (Elongation ( EL), %) are shown in Table 2 below.
• the occurrence of cracks during the 180° adhesion bending test of the annealed material is also described in Table 2 below.
• the cold-rolled annealed material can secure a yield strength of 400 MPa or more and an elongation of 55% or more.
• the temper rolling materials of Inventive Examples 1 to 4 have a yield strength of 800 MPa or more and a sufficient elongation of 25% or more even when the temper rolling is performed.
• Inventive Examples 1 to 4 have a relatively low Ni content of 1.0% by weight or less, thereby securing price competitiveness.
• Comparative Example 1 was a commercially produced standard austenitic stainless steel, and did not satisfy the composition and formulas (2), (3), and (4) of the present invention, and thus the yield strength was low.
• the commercial austenitic stainless steel of Comparative Example 1 had a Ni content of 8.1% by weight and was inferior in price competitiveness due to excessive Ni addition compared to the present invention.
• Comparative Example 2 did not satisfy Equation (1), so the initial delta ferrite remained substantially inside the steel after cold rolling and then annealing. Since the phase interface between the delta ferrite phase and the austenite phase is prone to cracking due to the phase difference during the forming process such as bending of steel, a low value of Equation (1) accompanies cracking during bending. As a result, Comparative Example 2 had a high Si content, so the yield strength was high, and the elongation was also observed, but bending cracks occurred due to the remaining delta ferrite, so that the formability including the bending properties was inferior.
• Comparative Examples 3 to 5 are steel grades that do not satisfy Formulas (1) to (4) in common. After cold rolling because they do not satisfy Formula (1), a significant portion of the initial delta ferrite remains inside the steel after annealing and bending Formability including properties was inferior, and Equation (2) was not satisfied, resulting in low yield strength. In addition, since the value of Equation (3) was 100 or more, Equation (3) was not satisfied, and plasticity non-uniformity due to the phase transformation to processing induced martensite easily occurred during deformation. In addition, since the value of Equation (4) was low, Equation (4) was not satisfied, and the accumulation of dislocations occurred extremely due to the influence of planar slip. As a result, the elongation was inferior. In particular, Comparative Examples 3 to 5 do not satisfy the formulas (3) and (4), so that the inferior elongation is further lowered after the temper rolling, so that they do not have suitable physical properties for use as a temper rolling material.
• Comparative Example 6 did not satisfy Equation (1) and was cold-rolled, and then a significant portion of initial delta ferrite remained inside the steel after annealing, resulting in inferior formability including bending properties. In addition, Comparative Example 6 showed a high Si content and excellent yield strength by Equation (2), but did not secure sufficient elongation due to the influence of Equations (3) and (4).
• Comparative Example 7 did not satisfy Equation (1) and was cold-rolled, and then a significant portion of initial delta ferrite remained inside the steel after annealing, resulting in inferior formability including bending properties. Also, in Comparative Example 7, the value of Equation (3) was 100 or more, which did not satisfy Equation (3), so that plasticity non-uniformity due to the phase transformation into processing-induced martensite easily occurred during deformation. For this reason, the elongation of the cold rolled annealed material and the temper rolled material was inferior.
• Comparative Example 8 satisfies the composition of alloy elements except Cu and Equations (1) to (4). For this reason, it showed excellent yield strength and elongation when cold-rolled annealed material. However, Comparative Example 8 had poor hot workability due to excessive Cu content. A detailed evaluation thereof will be described later with reference to Table 3 below.
• Comparative Examples 9 to 10 had excessive hot workability due to excessive Si and Cu contents. A detailed evaluation thereof will be described later with reference to Table 3 below.
• Comparative Examples 11 and 12 did not satisfy Equation (1), so after cold rolling, a significant portion of initial delta ferrite remained inside the steel after annealing, resulting in inferior formability including bending properties.
• the value of Equation (4) was excessive, and the plasticity non-uniformity in which the stress concentration in the weak part of the steel increased due to the frequent cross-slip expression was increased. As a result, the elongation of the cold rolled annealed material and the temper rolled material was inferior.
• the austenitic stainless steel according to the present invention has excellent hot workability, and thus has high productivity and high error rate, and thus has excellent price competitiveness.
• the reduction of area at each temperature of the slabs of several comparative examples and invention examples having excellent elongation was measured.
• the reduction in area was measured through a high-temperature tensile test based on ASTM standards, and the results are shown in Table 3.
• Comparative Example 1 is a commercially produced standard austenitic stainless steel, and exhibits excellent hot workability due to small amounts of Cu and N added to reduce Si or Ni required for the expression of high strength characteristics. However, since such commercial 300 series austenitic stainless steel contains a large amount of expensive Ni element, price competitiveness is quite low. In addition, as evaluated in Table 2, the component composition and formulas (2), (3) and (4) of the present invention were not satisfied, so the yield strength was low.
• Comparative Examples 2, 6, 9, and 10 an excessive amount of Si was added to improve the yield strength of the cold-rolled annealed material, and Cu was excessively added to replace Ni for price competitiveness. In Comparative Examples 2, 6, 9, and 10, the amount of Si and Cu added was excessive, and thus the hot workability was inferior.
• Comparative Example 8 the amount of Cu added was excessively outside the range limited by the present invention.
• the excessively added Cu segregated on the edge or surface of the slab to induce liquid embrittlement, etc., thereby inferior to the hot workability of Comparative Example 8.
• due to poor hot workability there is a fear that a decrease in the error rate due to edge cracks and an increase in correction cost after hot working occurs, or additional equipment investment for reducing edge cracks may be required.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Heat Treatment Of Steel (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=78269451

Family Applications (1)

Country Status (6)

Citations (5)

Family Cites Families (10)

• 2020
  • 2020-04-22 KR KR1020200048614A patent/KR102385472B1/ko active IP Right Grant
• 2021
  • 2021-02-02 WO PCT/KR2021/001345 patent/WO2021215630A1/ko unknown
  • 2021-02-02 JP JP2022564367A patent/JP7395769B2/ja active Active
  • 2021-02-02 US US17/918,014 patent/US20230142021A1/en active Pending
  • 2021-02-02 CN CN202180028609.8A patent/CN115398022B/zh active Active
  • 2021-02-02 EP EP21793437.1A patent/EP4119693A4/en active Pending

Patent Citations (5)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events