CN113430456A - 2000 MPa-grade delay-cracking-resistant hot forming steel and production method thereof - Google Patents

2000 MPa-grade delay-cracking-resistant hot forming steel and production method thereof Download PDF

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CN113430456A
CN113430456A CN202110598881.1A CN202110598881A CN113430456A CN 113430456 A CN113430456 A CN 113430456A CN 202110598881 A CN202110598881 A CN 202110598881A CN 113430456 A CN113430456 A CN 113430456A
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陈勇
赵广威
郎丰军
胡宽辉
何嘉
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Wuhan Iron and Steel Co Ltd
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Wuhan Iron and Steel Co Ltd
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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
    • 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
    • C21D8/0247—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
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

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Abstract

The invention relates to 2000MPa grade delayed cracking resistant hot forming steel, C: 0.20-0.40%, Si: 0.20-0.80%, Mn: 0.5-1.5%, P is less than or equal to O.O06%, S is less than or equal to 0.004%, Als: 0.050% -0.085%, Cr: 1.0% -1.5%, Ni: 0.50-0.80%, Ti: 0.020-0.050%, Nb 0.020-0.050%, Cu: 0.20 to 0.40 percent; b: 0.002% -0.005% and the balance of Fe and inevitable impurities. The invention has the tensile strength of 2000MPa, greatly improves the extensibility of the material, has good product of strength and elongation, and better resistance to delayed cracking.

Description

2000 MPa-grade delay-cracking-resistant hot forming steel and production method thereof
Technical Field
The invention relates to the field of high-strength steel production in metallurgical industry, in particular to 2000 MPa-grade delay cracking resistant hot forming steel and a production method thereof.
Background
With the rapid development of the automobile industry, light weight and safety become the main direction of the development of the automobile industry. The use of the hot formed steel is the most effective measure for improving the automobile collision safety at present and is also an important way for light weight. At present, the most applied steel plates are low-carbon Mn-B series steel plates, the structure of the steel plates is uniform martensite after quenching, the tensile strength is 1300-1800 MPa, 2000 MPa-level hot forming steel is developed by some enterprises and is mainly applied to parts such as A columns, B columns, front and rear bumpers, hinge reinforcing plates, door anti-collision beams, middle channels and the like.
However, as strength increases, the problem of delayed cracking of the steel also arises. Delayed cracking is a phenomenon in which a material undergoes a brittle failure suddenly after a certain time under the action of a static stress, which is the result of the interaction between the material and the environment and the stress. Research has proved that the delayed cracking of steel is caused by hydrogen in the material and the service environment of the material, and is a form of material deterioration caused by hydrogen, and particularly the delayed cracking phenomenon is very obvious after the tensile strength reaches 2000 MPa. Delayed cracking, which often occurs suddenly when the level of applied stress experienced by the material is significantly lower than its yield strength, is unpredictable, often results in more severe damage and consequences, and becomes a bottleneck that restricts the application and development of ultra-high strength steel.
The hydrogen trap has great influence on the delayed cracking of the steel, and researches show that the uniform dispersion irreversible hydrogen trap can effectively disperse the hydrogen in the steel, reduce the diffusion of the hydrogen and relieve the delayed cracking of the material to a certain extent. Many studies show that precipitated phases in steel are good irreversible hydrogen traps, and micro-alloy elements such as Nb, Ti and V are added into the steel, so that nano-sized carbonitride precipitates generated in the steel can effectively capture hydrogen to form irreversible hydrogen so as to inhibit the movement of the hydrogen in the steel, thereby obtaining good delayed fracture resistance.
The prior invention patent CN201710030911.2 discloses a method for preparing hot forming steel with tensile strength more than or equal to 2000MPa, which comprises the following chemical components in percentage by mass:
c: 0.3% -0.5%, Si: 1.2% -1.7%, Mn: 1.4% -2.0%, Al: 0.01 to 0.07 percent, less than or equal to 1.5 percent of Cr, less than or equal to 0.008 percent of P, less than or equal to 0.005 percent of S, B: 0.001-0.01%, Ti: 0.05 to 0.1 percent, Nb: 0.01 to 0.08 percent of the total weight of the alloy, and the balance of Fe and inevitable impurity elements;
the hot formed steel is obtained by adopting smelting, hot rolling, cold rolling and cover annealing, and after austenitizing and quenching, the yield strength R isp0.21000 to 1200MPa, tensile strength RmNot less than 2000MPa, elongation A508 to 9 percent; the cover-type annealing process is adopted to reduce the strength of the base material before hot forming to 424-588 MPa of yield strength, 616-760 MPa of tensile strength and A of elongation50The temperature is increased to 17.3 to 20.4 percent.
The invention patent CN201910549621.8 discloses that the components of 1800MPa class hot forming steel and the manufacturing method thereof are as follows according to the weight percentage:
0.31-0.52% of C, Si: 0.30-0.40%, Mn: 1.4-2.1%, p is less than or equal to 0.010%, S is less than or equal to 0.010%, Cr: 0.31% -0.51%, Nb: 0.08-0.11%, Mo: 0.11% -0.21%, RE: 0.02% -0.1%, Ni: less than or equal to 2.0 percent, and the balance of Fe and inevitable impurities. The manufacturing method comprises smelting, continuous casting, hot continuous rolling, acid cleaning, cold rolling, annealing and hot forming; the tensile strength of the hot forming steel obtained by the method is more than 1800MPa, and the elongation is more than 8 percent; the microstructure is martensite and ferrite, wherein the volume fraction content of the martensite is 94-96%, and the steel has the characteristics of high strength and high elongation.
The invention patent CN201610713644.4 discloses a hot forming steel with tensile strength more than or equal to 2100MPa directly rolled by a medium-thin slab, which comprises the following components in percentage by weight:
0.41-0.50% of C, Si: 0.45-0.65%, Mn: 1.6-2.0%, P is less than or equal to 0.006%, S is less than or equal to 0.004%, Als: 0.015% -0.060%, Cr: 0.55 to 0.65 percent of Ti: 0.046% -0.060% or Nb: 0.046% -0.060% or V: 0.046-0.060% or a combination of two or more of them, B: 0.004-0.005%, Mo: 0.46% -0.60%, Ni: 0.25 to 0.40 percent of the total weight of the alloy, and less than or equal to 0.004 percent of the total weight of the alloy. The production steps are as follows: desulfurizing molten iron; smelting and refining in an electric furnace or a converter; continuous casting; descaling before entering a soaking pit; soaking; heating; descaling by high-pressure water before entering a rolling mill; rolling; cooling; coiling; austenitizing; stamping and forming by using a die; and (6) quenching. None of the above documents concerns the danger of delayed cracking when the strength reaches 2000MPa, nor does it suggest a countermeasure, nor how to reduce the susceptibility to delayed cracking.
The invention patent 101275200A discloses that "a hot-formed martensitic steel" addresses the delayed cracking problem of martensitic steels by proposing that the delayed cracking property of steel can be improved by properly containing a certain amount of austenite in hot-formed steel. However, this document develops a steel for thin-thickness parts, and the results of the tensile test using a round bar sample, rather than using a thin sheet sample, are greatly different from the practical application.
Patent documents "a 1500MPa grade low hydrogen induced delayed cracking sensitive hot forming steel and a production method" publication No. CN110079743A and "a 1300MPa grade low hydrogen induced delayed cracking sensitive hot forming steel and a production method" publication No. CN110157864A respectively introduce two kinds of low delayed cracking sensitive hot forming steel, but the component design and the manufacturing process can not meet the requirement of 2000MPa strength grade, when the strength is improved to 2000MPa, the delayed cracking sensitivity is obviously improved, and more hydrogen resistant elements are required to be added in the component design and the manufacturing process.
The invention patent CN202010173441.7 'niobium vanadium composite microalloyed hot forming steel and production and hot stamping forming method thereof' uses niobium vanadium composite microalloyed hot forming steel, and the chemical components have the following weight percentages: c: 0.23 to 0.29 percent; si: 0.2% -1.0%; mn: 1.0% -2.5%; p is less than or equal to 0.020%; s is less than or equal to 0.010 percent; al: 0.02% -0.06%; cr: 0.2% -1.0%; b: 0.001% -0.003%; ti: 0.01 to 0.03 percent; nb and V are both 0.03% -0.08%; n is less than or equal to 30ppm, and the balance is Fe and other inevitable impurities. The preparation process flow of the steel plate comprises the working procedures of steel making, casting, hot rolling, acid washing and cold rolling. The matrix of the part obtained by the steel plate after hot stamping forming has the characteristics of ultrafine grains, strong plasticity, impact toughness, bending resistance, fracture resistance and excellent hydrogen-induced delayed fracture resistance, the collision intrusion resistance and the energy absorption performance of a hot forming part product can be obviously improved, the hydrogen-induced delayed fracture risk is reduced, but the strength grade of the steel is only 1500MPa, Nb and V are compounded, the requirement on the manufacturing process is very high, the performance stability of the steel is not high, and the yield and the manufacturing cost are seriously influenced.
Disclosure of Invention
The invention aims to solve the technical problem of providing 2000 MPa-grade delayed cracking resistant hot forming steel and a production method thereof, so as to overcome the defects in the prior art.
The technical scheme for solving the technical problems is as follows: 2000 MPa-grade delayed cracking resistant hot forming steel comprises the following components in percentage by weight:
c: 0.20-0.40%, Si: 0.20-0.80%, Mn: 0.5-1.5%, P is less than or equal to O.O06%, S is less than or equal to 0.004%, Als: 0.050% -0.085%, Cr: 1.0% -1.5%, Ni: 0.50-0.80%, Ti: 0.020-0.050%, Nb 0.020-0.050%, Cu: 0.20 to 0.40 percent; b: 0.002% -0.005% and the balance of Fe and inevitable impurities.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, yield strength R of 2000MPa grade delayed cracking resistant hot forming steelpO.21200MPa to 1400MPa, tensile strength RmNot less than 2000MPa, elongation A50mmNot less than 6 percent and hydrogen embrittlement sensitivity Iε≤50％。
A production method of 2000 MPa-grade delayed cracking resistant hot-formed steel comprises the following steps:
desulfurizing molten iron and smelting in a converter, wherein the tapping temperature is 1700-1780 ℃;
smelting in a converter and casting into a slab with the thickness of 200-250 mm;
slowly cooling the casting blank, exhausting gas in steel, heating the casting blank to 1200-1250 ℃ in the hot rolling process, controlling the heating rate to 350-400 ℃/h for rough rolling, and controlling the outlet temperature of rough rolling to 1080-1120 ℃; then, fine rolling is carried out, and the finish rolling temperature of the fine rolling is controlled to be 850-900 ℃; then carrying out laminar cooling at the cooling speed of 20-30 ℃/second, carrying out hot rolling and coiling, and controlling the coiling temperature at 600-650 ℃;
in the cold rolling process, conventional pickling and cold rolling are firstly carried out, and the total cold rolling reduction is controlled to be 55-65%; then annealing is carried out, the annealing temperature is controlled to be 780-840 ℃, and the temperature drop speed is controlled to be 8-10 ℃/s;
leveling, wherein the leveling elongation is controlled to be 1.1% -1.5%;
carrying out dehydrogenation treatment, heating to 200-250 ℃ in a dehydrogenation heating furnace, keeping the temperature for 100-150 minutes under the protection of nitrogen in the whole process, and slowly cooling;
performing conventional finishing and shearing, and blanking the sheared material on a cold stamping die;
heating the sample wafer in the protective atmosphere of nitrogen at the temperature of 830-880 ℃, and keeping the temperature for 5-7 minutes;
stamping and quenching are carried out at the temperature of 800-820 ℃, and the cooling speed is controlled at 50-80 ℃/s.
C: carbon is a strong solid solution strengthening element and plays a decisive role in obtaining ultrahigh strength, the strength of the steel is difficult to ensure due to too low carbon content, the content is too high, a large amount of pearlite, bainite and martensite are easily formed in the cooling process after finish rolling, the higher the content is, the higher the strength is, the plasticity is reduced, the welding performance is reduced due to too high carbon content, and the delayed cracking sensitivity is improved, wherein the content in the steel is limited to 0.20-0.40%.
Si: silicon can improve the hardenability of steel, has the function of reducing the volume change when austenite is transformed into martensite, thereby effectively controlling the generation of quenching cracks, can obstruct the diffusion of carbon when being tempered at low temperature, delays the speed of martensite decomposition and carbide aggregation growth, leads the hardness of the steel to be reduced slowly when being tempered, obviously improves the tempering stability and the strength of the steel, and influences the surface quality of the steel when the silicon content is too high, and combines the factors to determine that the silicon content in the steel of the invention is 0.20-0.80%.
Mn: manganese plays a role in solid solution strengthening, can make up the yield strength lost due to the reduction of carbon content, obviously improves the quality of steel, has relatively small influence on plasticity, is an austenite forming element, can reduce the phase transformation driving force, expands an austenite phase region, can reduce the Ms point of the steel, can ensure that martensite is obtained at a proper cooling speed, but can cause central segregation and anisotropy due to overhigh manganese content, can generate MnS with S in the steel and is unfavorable for delaying cracking due to overhigh manganese content, and therefore, the Mn content in the steel is determined to be 0.50-1.50 percent.
P is a harmful element in steel, is easy to cause central segregation of a casting blank, is easy to deviate to a grain boundary in the subsequent hot continuous rolling heating process, obviously increases the brittleness of the steel, and simultaneously controls the content of the P to be less than 0.006 percent based on the cost consideration without influencing the performance of the steel.
S is a very harmful element, sulfur in steel often exists in the form of manganese sulfide, the sulfide inclusion can deteriorate the toughness of the steel and cause performance anisotropy, meanwhile, the manganese sulfide has strong capturing capacity on hydrogen, but belongs to harmful hydrogen traps and causes the delayed cracking resistance to be reduced, the lower the sulfur content in the steel is, the better the sulfur content in the steel is, and the sulfur content in the steel is controlled to be below 0.004% based on the consideration of the manufacturing cost.
Cr: chromium increases the hardenability of steel and has a secondary hardening effect, the hardness and wear resistance of carbon steel can be improved without making the steel brittle, Cr can improve the strength and hardness of the steel in a rolled state, the elongation and the reduction of area are reduced, Cr can improve the hardenability, the steel has better comprehensive mechanical properties after quenching and tempering, in addition, chromium can improve the tempering stability of the steel, and carbide of Cr has the hydrogen adsorption effect and can inhibit the diffusion of hydrogen, so that the Cr content is required to be 1.0-1.50%.
B, boron is an element for strongly improving the hardenability, and the hardenability of the steel can be obviously improved by adding trace boron into the steel. However, the content thereof is less than 0.002% or more than 0.005% and the effect of improving hardenability is not significant, so that the content thereof is limited to 0.002% to 0.005% in the steel of the present invention in view of practical production and hardenability effects.
Al: aluminum plays a role in deoxidation in steel, in order to balance the oxygen content in the steel, certain acid-soluble aluminum needs to be kept, otherwise the effect cannot be exerted, meanwhile, a proper amount of aluminum is added into the steel, the adverse effect of nitrogen and oxygen atoms in the steel on the performance can be eliminated, the aluminum can also refine grains in the steel, so that the impact toughness of the steel is obviously improved, the cold-brittleness tendency and the aging tendency are reduced, the diffusion coefficient of hydrogen in the steel can also be reduced by adding Al, the hydrogen aggregation can be controlled, and therefore, the Als content is limited to 0.050% -O.085%.
Ti, Ti is a strong C, N compound forming element, and is added into steel for two main purposes, one is to protect B in the steel and improve the hardenability of the steel, and the other is to precipitate and strengthen the strength and the toughness of the steel. Ti added into the steel can be combined with C to generate stable TiC, and TiC particles have the function of preventing crystal grains from growing, can refine the crystal grains and improve the strength and the toughness. The carbon and the nitride of the titanium are good hydrogen traps, can effectively inhibit the diffusion of hydrogen in the steel, and are beneficial to improving the delayed cracking resistance of the steel, and the content of the carbon and the nitride of the titanium is limited to 0.020-0.050 percent in the steel.
Nb: niobium is also a strong C, N compound forming element and can play a role in refining austenite grains, and a small amount of niobium is added into steel to form a certain amount of niobium carbon and nitride, so that the austenite grains are prevented from growing, therefore, the quenched martensite lath has a small size, and the strength of the steel is greatly improved; in addition, niobium carbon and nitride are good hydrogen traps, hydrogen diffusion in steel can be effectively inhibited, and the delayed cracking resistance of the steel is favorably improved, however, the content of Nb is noble alloy, and the generation cost is increased due to overhigh content of Nb, so that the content of Nb is controlled to be 0.020-0.050%.
Ni: the nickel can improve the hardenability of the steel and the toughness of the steel, in addition, the nickel can improve the corrosion resistance of the steel, can resist acid and corrosion of alkali and atmosphere so as to reduce the risk of environmental fracture, and simultaneously the nickel can effectively pin hydrogen atoms so as to reduce the diffusion rate of the hydrogen in the steel and prevent hydrogen from gathering, and the content of the Ni in the steel is controlled to be 0.50-0.80 percent.
Cu: the copper in the steel has the outstanding effect of improving the corrosion performance of the low alloy steel, so that the absorption of hydrogen from the environment of the steel in a service process is inhibited, and the Cu has the effect of repelling the hydrogen, so that the hydrogen is difficult to enrich at a grain boundary when the copper element is in the grain boundary, but the copper content is too high to generate hot brittleness, so that the copper content in the steel is controlled to be 0.20-0.40%.
Compared with the prior art, the invention has the advantages that the tensile strength is more than 2000MPa, and the product has higher extensibility and lower delayed cracking sensitivity, so that the product is applied to the upper automobile body and the lower automobile body of the automobile to manufacture structural members and safety members, the weight of the automobile body can be reduced, and the safety of drivers and passengers can be effectively protected.
The invention has the advantages that: the technology optimizes the components and the process to manufacture the hot forming steel, has the tensile strength of 2000MPa, greatly improves the extensibility of the material, has good product of strength and elongation, has better performance of resisting delayed cracking, is suitable for producing the hot forming steel by adopting the common cold rolling process, and has better application prospect and economic benefit.
Drawings
FIG. 1 shows a structure obtained by an embodiment of the present invention.
Detailed Description
The principles and features of this invention are described below in conjunction with examples which are set forth to illustrate, but are not to be construed to limit the scope of the invention.
2000 MPa-grade delayed cracking resistant hot forming steel comprises the following components in percentage by weight:
c: 0.20-0.40%, Si: 0.20-0.80%, Mn: 0.5-1.5%, P is less than or equal to O.O06%, S is less than or equal to 0.004%, Als: 0.050% -0.085%, Cr: 1.0% -1.5%, Ni: 0.50-0.80%, Ti: 0.020-0.050%, Nb 0.020-0.050%, Cu: 0.20 to 0.40 percent; b: 0.002% -0.005% and the balance of Fe and inevitable impurities.
The production method of the 2000 MPa-grade delayed cracking resistant hot-formed steel comprises the following steps:
desulfurizing molten iron and smelting in a converter, wherein the tapping temperature is 1700-1780 ℃;
smelting in a converter and casting into a slab with the thickness of 200-250 mm;
slowly cooling the casting blank, exhausting gas in steel, heating the casting blank to 1200-1250 ℃ in the hot rolling process, controlling the heating rate to 350-400 ℃/h for rough rolling, and controlling the outlet temperature of rough rolling to 1080-1120 ℃; then, fine rolling is carried out, and the finish rolling temperature of the fine rolling is controlled to be 850-900 ℃; then carrying out laminar cooling at the cooling speed of 20-30 ℃/second, carrying out hot rolling and coiling, and controlling the coiling temperature at 600-650 ℃;
in the cold rolling process, conventional pickling and cold rolling are firstly carried out, and the total cold rolling reduction is controlled to be 55-65%; then annealing is carried out, the annealing temperature is controlled to be 780-840 ℃, and the temperature drop speed is controlled to be 8-10 ℃/s;
leveling, wherein the leveling elongation is controlled to be 1.1% -1.5%;
carrying out dehydrogenation treatment, heating to 200-250 ℃ in a dehydrogenation heating furnace, keeping the temperature for 100-150 minutes under the protection of nitrogen in the whole process, and slowly cooling;
performing conventional finishing and shearing, and blanking the sheared material on a cold stamping die;
heating the sample wafer in the protective atmosphere of nitrogen at the temperature of 830-880 ℃, and keeping the temperature for 5-7 minutes;
stamping and quenching are carried out at the temperature of 800-820 ℃, and the cooling speed is controlled at 50-80 ℃/s.
Yield strength R of the resulting formed steelpO.21200MPa to 1400MPa, tensile strength RmNot less than 2000MPa, elongation A50mmNot less than 6 percent and hydrogen embrittlement sensitivity Iε≤50％。
The chemical composition of the steel sheets was as follows in table 1:
table 1 shows the chemical composition value lists (wt%) of each example and comparative example of the present invention
Figure BDA0003092194560000091
Figure BDA0003092194560000101
Table 2 shows the main processes of the examples of the present invention and the comparative examples
Figure BDA0003092194560000102
Comparing the conventional mechanical properties of the example steel with those of the comparative example steel, and the results are shown in Table 3; meanwhile, the delayed cracking performance of the test steel and the comparative steel are compared, an SSRT slow tensile test is carried out in 0.1mol/L HCl, and the tensile strain rate is 1.0 multiplied by 10-5The loss of elongation (hydrogen embrittlement index I) I is calculatedε＝(εA-εE)/εATo evaluate the delayed cracking resistance, IεSmaller values indicate better delayed cracking resistance, and the comparison of the delayed cracking resistance of the comparative steel with that of the hydrogen embrittlement resistant hot-formed steel produced by the method is shown in Table 3:
table 3 shows the results of the performance tests of the examples of the present invention and the comparative examples
Figure BDA0003092194560000103
Figure BDA0003092194560000111
From the test results in table 3, it can be seen that the implementation cases 1 to 8 all have better performance, the yield strength is 1200MPa to 1400MPa, the tensile strength is greater than 2000MPa, the elongation is greater than 6%, the tensile strength and the yield strength of the 2 comparison cases are equivalent to the performance of the product produced by the method, the elongation performance of the implementation cases is obviously superior to that of the comparison cases, and fig. 1 is an organization chart of the formed steel obtained in the embodiment.
Hydrogen embrittlement sensitivity IHEThe experimental conditions of (1): both in 0.1mol/L HCl for SSRT slow tensile test with tensile strain rate of 1.0 × 10-5(s) evaluation of the resistance to hydrogen induced delayed cracking by calculation of the loss of elongation (hydrogen embrittlement index I)εSmaller values represent better hydrogen induced hysteresis crack resistance.
From the hydrogen embrittlement sensitivity indexes of table 3, the hydrogen embrittlement sensitivity performance of 8 embodiments is better, and is between 41% and 49%, wherein, the implementation cases 5 and 8 have the lowest hydrogen embrittlement sensitivity, the hydrogen embrittlement sensitivity indexes of 2 comparison cases are respectively 88% and 91%, and the performance of the implementation case is obviously better than that of the comparison case.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (3)

1. The 2000 MPa-grade delayed cracking resistant hot forming steel is characterized by comprising the following components in percentage by weight:
c: 0.20-0.40%, Si: 0.20-0.80%, Mn: 0.5-1.5%, P is less than or equal to O.O06%, S is less than or equal to 0.004%, Als: 0.050% -0.085%, Cr: 1.0% -1.5%, Ni: 0.50-0.80%, Ti: 0.020-0.050%, Nb 0.020-0.050%, Cu: 0.20 to 0.40 percent; b: 0.002% -0.005% and the balance of Fe and inevitable impurities.
2. The 2000MPa grade delayed cracking resistant thermoformed steel of claim 1, wherein 2000MYield strength R of Pa grade delayed cracking resistant hot forming steelpO.21200MPa to 1400MPa, tensile strength RmNot less than 2000MPa, elongation A50mmNot less than 6 percent and hydrogen embrittlement sensitivity Iε≤50％。
3. A method for producing 2000MPa grade delayed cracking resistant hot formed steel according to claim 1 or 2, characterized by the steps of:
desulfurizing molten iron and smelting in a converter, wherein the tapping temperature is 1700-1780 ℃;
smelting in a converter and casting into a slab with the thickness of 200-250 mm;
slowly cooling the casting blank, exhausting gas in steel, heating the casting blank to 1200-1250 ℃ in the hot rolling process, controlling the heating rate to 350-400 ℃/h for rough rolling, and controlling the outlet temperature of rough rolling to 1080-1120 ℃; then, fine rolling is carried out, and the finish rolling temperature of the fine rolling is controlled to be 850-900 ℃; then carrying out laminar cooling at the cooling speed of 20-30 ℃/second, carrying out hot rolling and coiling, and controlling the coiling temperature at 600-650 ℃;
in the cold rolling process, conventional pickling and cold rolling are firstly carried out, and the total cold rolling reduction is controlled to be 55-65%; then annealing is carried out, the annealing temperature is controlled to be 780-840 ℃, and the temperature drop speed is controlled to be 8-10 ℃/s;
leveling, wherein the leveling elongation is controlled to be 1.1% -1.5%;
carrying out dehydrogenation treatment, heating to 200-250 ℃ in a dehydrogenation heating furnace, keeping the temperature for 100-150 minutes under the protection of nitrogen in the whole process, and slowly cooling;
performing conventional finishing and shearing, and blanking the sheared material on a cold stamping die;
heating the sample wafer in the protective atmosphere of nitrogen at the temperature of 830-880 ℃, and keeping the temperature for 5-7 minutes;
stamping and quenching are carried out at the temperature of 800-820 ℃, and the cooling speed is controlled at 50-80 ℃/s.
CN202110598881.1A 2021-05-31 2021-05-31 2000 MPa-grade delay-cracking-resistant hot forming steel and production method thereof Pending CN113430456A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113957358A (en) * 2021-10-12 2022-01-21 北京科技大学 High-strength hot-forming steel substrate with tensile strength of more than 2200MPa and preparation method thereof
CN114672732A (en) * 2022-03-30 2022-06-28 江苏永钢集团有限公司 Cr-Ni steel bar and production process thereof
CN114921619A (en) * 2022-05-23 2022-08-19 武汉钢铁有限公司 Steelmaking method capable of improving delayed cracking resistance of hot formed steel in CSP production line

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CN111748736A (en) * 2020-06-24 2020-10-09 武汉钢铁有限公司 1800 MPa-grade low-hydrogen delayed cracking sensitive hot forming steel and production method thereof
CN112126860A (en) * 2020-09-25 2020-12-25 重庆科技学院 Cold-formed ultrahigh-strength low-alloy martensitic steel

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111748736A (en) * 2020-06-24 2020-10-09 武汉钢铁有限公司 1800 MPa-grade low-hydrogen delayed cracking sensitive hot forming steel and production method thereof
CN112126860A (en) * 2020-09-25 2020-12-25 重庆科技学院 Cold-formed ultrahigh-strength low-alloy martensitic steel

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113957358A (en) * 2021-10-12 2022-01-21 北京科技大学 High-strength hot-forming steel substrate with tensile strength of more than 2200MPa and preparation method thereof
CN114672732A (en) * 2022-03-30 2022-06-28 江苏永钢集团有限公司 Cr-Ni steel bar and production process thereof
CN114921619A (en) * 2022-05-23 2022-08-19 武汉钢铁有限公司 Steelmaking method capable of improving delayed cracking resistance of hot formed steel in CSP production line
CN114921619B (en) * 2022-05-23 2023-11-03 武汉钢铁有限公司 Steelmaking method capable of improving delayed cracking resistance of hot forming steel in CSP production line

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Application publication date: 20210924