CN114058968A - High-plasticity hot forming steel with oxidation resistance for automobile and hot forming process - Google Patents

High-plasticity hot forming steel with oxidation resistance for automobile and hot forming process Download PDF

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Publication number
CN114058968A
CN114058968A CN202111401590.5A CN202111401590A CN114058968A CN 114058968 A CN114058968 A CN 114058968A CN 202111401590 A CN202111401590 A CN 202111401590A CN 114058968 A CN114058968 A CN 114058968A
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steel
oxidation resistance
hot
hot forming
thermo
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董毅
时晓光
刘仁东
孙成钱
韩楚菲
王俊雄
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Angang Steel Co Ltd
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Angang Steel Co Ltd
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Priority to CN202111401590.5A priority Critical patent/CN114058968A/en
Priority to PCT/CN2021/132955 priority patent/WO2023087352A1/en
Priority to KR1020237002199A priority patent/KR20230074702A/en
Priority to JP2023519094A priority patent/JP2024505319A/en
Priority to EP21955263.5A priority patent/EP4215636A1/en
Publication of CN114058968A publication Critical patent/CN114058968A/en
Pending legal-status Critical Current

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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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
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    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
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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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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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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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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    • C21D2211/00—Microstructure comprising significant phases
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

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Abstract

The invention provides high-plasticity hot forming steel with oxidation resistance for an automobile and a hot forming process, wherein the hot forming steel comprises the following chemical components in percentage by mass: c: 0.18% -0.28%, Si: less than or equal to 0.20 percent, Mn: 1.20% -2.0%, P: 0.030-0.080%, S is less than or equal to 0.004%, Als: 0.02% -0.06%, Nb: 0.02% -0.06%, Ti: 0.025% -0.045%, V: 0.05% -0.15%, Cr: 0.5% -2.50%, Mo: 0.10% -0.30%, B: 0.0015 to 0.0035 percent, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities. The hot forming steel provided by the invention has high oxidation resistance and high plasticity. And the steel does not need atmosphere protection when hot forming, and shot blasting treatment is not needed after hot forming.

Description

High-plasticity hot forming steel with oxidation resistance for automobile and hot forming process
Technical Field
The invention relates to the technical field of automobile steel, in particular to high-plasticity hot forming steel with oxidation resistance for an automobile and a hot forming process.
Background
In recent years, new materials for vehicle bodies have been developed and applied to vehicle bodies, but ultra-high strength steel sheets for cold stamping of 1000MPa or higher are often used for manufacturing members having simple shapes, due to the restriction of problems such as easy cracking and large springback. The hot forming steel is formed in an austenite area by adopting a hot forming process, the resilience is small, the requirement of assembly precision can be met, the ultra-high strength component with the grade of 1500MPa and above can be obtained by pressure maintaining quenching, the vehicle body structure and the part design are effectively simplified, and the vehicle weight is greatly reduced.
Currently, hot forming steel on the market can be divided into coated hot forming steel and uncoated hot forming steel according to the surface state, wherein the uncoated steel is easy to form iron scale on the surface of the steel when being heated in a heating furnace, and the decarburization condition occurs, so that the performance of the steel is influenced, so that a protective atmosphere is required to be adopted during heating, and shot blasting treatment is required after hot forming, so that the cost and the working procedure are increased; the coated steel is provided with a layer of aluminum-silicon coating or zinc-based coating on the surface of the steel plate, so that the surface decarburization and oxidation in the steel heating process can be effectively prevented, the shot blasting procedure can be omitted after the steel is hot-formed, and the cost of the coated hot-formed steel is higher compared with that of uncoated steel. At present, the strength grade of hot forming steel produced and used in large scale in the prior art is 1500MPa, but the elongation after hot forming is only about 6-9%, the requirement of development in the field of automobiles is not met, no better technology is available, the problem of surface oxidation and decarburization can be solved while the cost of the steel is kept low after hot forming, a shot blasting process is avoided, and the steel after hot forming has higher plasticity.
Patent publication No. CN107354385B proposes a method for producing an ultrahigh-strength hot-formed steel for automobiles, which comprises the following components: 0.5-0.6%, Mn: 0.5% -2.0%, Si: 1.5% -2.5%, Cr: 1.0% -3.0%, Al: 1.0% -2.0%, Nb: 0.01% -0.03%, B: 0.001-0.005%, the strength of the steel plate after hot forming reaches 1500-2000MPa, and the elongation is 10-20%. The steel plate provided by the patent has good strong plasticity matching, but Cr and Al elements in the components are high, so that the cost and the smelting difficulty are increased. Meanwhile, the production process is complex, the existing tooling equipment can not meet the production requirements, and atmosphere protection and shot blasting treatment are required during production.
In patent publication No. CN103255340B, a high-toughness hot-formed steel sheet for automobiles and a method for producing the same are proposed, wherein the chemical components of the steel sheet are as follows: 0.1-0.5%, Si: 0.5-1.5%, Mn: 1.2% -2.4%, Ti: 0.01% -0.05%, B: 0.001% -0.005%, S: less than or equal to 0.01 percent, P: less than or equal to 0.01 percent, the tensile strength of the hot formed steel plate reaches 1600MPa, the elongation reaches 16 percent, the comprehensive performance is good, and the alloy cost is lower. However, the steel plate needs to be deformed in the heating process and then quenched twice to obtain the final structure and mechanical properties, the hot forming process is complex and cannot be realized on the existing equipment, meanwhile, the steel plate also needs to be protected by gas during heating, and shot blasting treatment is needed after hot forming.
In conclusion, the development of the high-plasticity hot forming and hot forming process for the automobile with good oxidation resistance has good application prospect.
Disclosure of Invention
In view of the above problems, the present invention provides a high-plastic hot-formed steel having oxidation resistance for automobiles and a hot-forming process thereof.
The technical means adopted by the invention are as follows:
the high-plasticity hot forming steel with oxidation resistance for the automobile comprises the following chemical components in percentage by mass:
c: 0.18% -0.28%, Si: less than or equal to 0.20 percent, Mn: 1.20% -2.0%, P: 0.030-0.080%, S is less than or equal to 0.004%, Als: 0.02% -0.06%, Nb: 0.02% -0.06%, Ti: 0.025% -0.045%, V: 0.05% -0.15%, Cr: 0.5% -2.50%, Mo: 0.10% -0.30%, B: 0.0015 to 0.0035 percent, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities.
The structure of the hot formed steel consists of ferrite, martensite and retained austenite. The volume fraction of the ferrite is 5-12%, the volume fraction of the martensite is 78-89%, and the volume fraction of the retained austenite is 6-10%.
The tensile strength of the hot forming steel is 1400MPa-1700MPa, and the oxidation resistance rate is less than 0.1 g/(m)2H), the yield strength is 900MPa-1450MPa, the elongation is more than or equal to 18.0%, the surface of the steel is not completely decarburized, the thickness of a decarburized layer is less than or equal to 15 mu m, and the thickness of the hot-formed steel plate is 0.8mm-12.0 mm.
The steel of the invention mainly comprises the following components:
c: and C is the guarantee of the steel strength, and is beneficial to increasing the hardenability of the steel. The carbon content is too low, and the strength of the steel after hot stamping cannot reach the expected target; the carbon content is too high, the strength of the hot formed steel is too high, and the plasticity is reduced. In addition, the increase of the content of C can reduce the phase transition temperature of the steel, so that the austenitizing temperature is reduced, a shot-blasting-free surface is favorably obtained, and meanwhile, the increase of the content of C is favorable for producing enough content of super-cooled austenite in the hot forming and pressure maintaining process of the steel, so that the plasticity is improved. Therefore, the optimal range of C in the present invention is 0.18% -0.28%.
Si: si is a carbide precipitation-free element in steel, has a good inhibition effect on carbide precipitation in the hot forming cooling and pressure maintaining processes, and further ensures the content and stability of retained austenite. However, too high Si content causes a large amount of defects such as scale, color difference, etc. on the surface of the hot-formed substrate, which affects the surface quality of the hot-formed part, and at the same time, too high Si element expands the two-phase region, increases the austenitizing temperature, keeps the steel at a higher temperature, and easily deteriorates the surface of the steel. Therefore, the content of Si in the steel provided by the invention is less than or equal to 0.20 percent.
Mn: mn mainly plays a role in improving the hardenability of the steel and reducing the phase transition temperature, so that the austenitizing of the steel at a lower temperature is realized; too high Mn content deteriorates the structural uniformity of the steel and tends to cause serious band-like structural defects in the structure. Therefore, the Mn content selected by the invention is 1.20-2.0%.
P: the effect of P in the invention is similar to that of Si, thereby inhibiting cementite generation and increasing the stability of retained austenite; meanwhile, P can enable the martensite laths to be refined and uniformly distributed, and the toughness is improved. The content of P in the invention is 0.030-0.080%.
S: in the invention, S is a harmful element, and S can form MnS inclusions to deteriorate the microstructure and the mechanical property of the steel, so that the S is limited to be less than or equal to 0.004 percent.
And Als: als (acid-soluble aluminum) plays a role in deoxidation and nitrogen fixation in the smelting process, but too much Als can cause a large amount of aluminum-series inclusions. Therefore, the range of Als in the invention is 0.020-0.060%.
Cr: cr is an element for improving the hardenability of steel, and in the invention, the Cr mainly plays a role in improving the high-temperature oxidation resistance of the steel, simultaneously improving the tempering stability of the steel plate and ensuring that the steel plate does not have tempered martensite within the pressure-holding temperature range. The optimal Cr content is between 0.5 and 2.50 percent.
Mo: mo is a medium-strength carbide forming element and can improve the strength and toughness of the steel. According to the invention, Mo can reduce the martensite transformation temperature, the stability of the retained austenite is obviously improved, and meanwhile, the addition of Mo element increases the oxidation resistance of the steel. The content of Mo in the invention is 0.10-0.30%.
Nb, V: nb and V mainly play roles in fine grain strengthening, precipitation strengthening and the like in steel. In the invention, the nano-scale fine carbide is dispersed and precipitated, so that the original austenite grain boundary can be effectively pinned, the structure of each phase in the hot-formed steel is further refined, and the comprehensive performance is improved. Meanwhile, the dispersed and precipitated carbide can be used as a hydrogen trap to pin diffusible hydrogen in the steel, and the delayed fracture resistance is improved. Meanwhile, the dispersed and precipitated carbide can be used as a hydrogen trap to pin diffusible hydrogen in the steel, and the delayed fracture resistance is improved. Further, precipitation of VN formed by V and N suppresses precipitation of BN, and a decrease in strength due to precipitation of B is avoided. In the invention, the Nb content is 0.020-0.060 percent, and the V content is 0.050-0.15 percent.
Ti: ti is mainly used for fixing nitrogen in boron steel so as to ensure that the through quenching effect of boron is exerted. In addition, Ti can be separated out from C element fine carbide, the hardness and the strength of martensite in a hot formed structure are reduced, and the plasticity and the toughness of steel are improved. The Ti content of the invention is between 0.025 percent and 0.045 percent.
B: boron is added into the steel, so that the hardenability of the steel can be obviously improved, and the strength stability of the steel can be ensured after quenching. If the content of B is too low, the effect is not obvious, and if the content of B is too high, B compounds are easy to form with N in the steel, so that the performance of the steel is reduced. The content of B in the invention is 0.0015% -0.0035%.
N: the lower the N content, the better, but too low will cause production difficulties and increase costs, so the N content in the present invention is less than or equal to 0.005%.
According to the invention, by adding alloy elements such as C, Mn, Cr and Mo, the austenitizing temperature is reduced, the hardenability of the steel plate is improved, the oxidation of the steel is favorably inhibited, meanwhile, the critical cooling rate of the steel after hot forming is reduced, and the production of thick hot forming steel can be carried out; in addition, through the matching of chemical components and a hot forming process, a certain content of ferrite is obtained in an air cooling stage, a certain content of retained austenite with good stability is obtained in a pressure maintaining stage after cooling, and the plasticity of the steel is improved; the addition of Si and P elements in the components inhibits carbide precipitation, ensures the content of residual austenite in the steel plate and improves the mechanical property of the steel plate; in addition, Cr and Mo in the steel plate have an antioxidation effect, so that the steel plate can be heated and kept warm under the condition of no protective atmosphere, and can be directly produced in the subsequent process without shot blasting after hot forming.
The invention also discloses a hot forming process of the high-plasticity hot forming steel with oxidation resistance for the automobile, which comprises the following steps:
(1) placing a thermoformed substrate containing the above components at a temperature AC3-AC3Heating and preserving heat in a heating furnace at the temperature of +15 ℃, wherein the preserving heat time is 180-300 s;
(2) taking out the heated hot-formed substrate from the heating furnace, air-cooling, and air-cooling to Ar3Staying at the temperature for 5-8 s, and heatingAnd (3) deforming and cooling in the forming die at a cooling speed of more than or equal to 18 ℃/s, maintaining the pressure after cooling to 180-250 ℃, keeping the pressure for 40-80 s, taking out the formed part after maintaining the pressure, and air-cooling to room temperature to obtain the hot forming steel.
The steel does not need atmosphere protection when being subjected to hot forming, shot blasting treatment is not needed after the hot forming, the subsequent procedures can be directly carried out, and the cost of the whole process is lower than that of the existing hot forming product.
The hot formed substrate is obtained by smelting, hot rolling and cold rolling. The smelted components and the mass percentage thereof are the components and the mass percentage thereof of the high-plasticity hot-forming steel with oxidation resistance for the automobile.
Compared with the prior art, the invention has the following advantages:
(1) through the matching of chemical components and a hot forming process, a certain content of ferrite and residual austenite structures are introduced into the traditional full-martensite structure, so that the plasticity of the steel is improved, and the elongation rate reaches and exceeds 18% under the condition of ensuring that the tensile strength is more than 1400 MPa;
(2) the oxidation resistance of the steel is improved by adding elements such as Cr and the like, and the oxidation resistance rate of the steel plate is less than 0.1 g/(m)2H), the oxidation resistance level reaches 1 level, the steel does not need atmosphere protection during hot forming, shot blasting treatment is not needed after hot forming, and the subsequent procedures can be directly carried out;
(3) the hot forming steel and the hot forming process can be realized on the existing equipment, equipment transformation is not needed, and the cost is low.
For the above reasons, the present invention can be widely applied to the fields of automobile steels and the like.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The described embodiments are only some embodiments of the invention, not all embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides high-plasticity hot forming steel with oxidation resistance for an automobile, which comprises the following chemical components in percentage by mass:
c: 0.18% -0.28%, Si: less than or equal to 0.20 percent, Mn: 1.20% -2.0%, P: 0.030-0.080%, S is less than or equal to 0.004%, Als: 0.02% -0.06%, Nb: 0.02% -0.06%, Ti: 0.025% -0.045%, V: 0.05% -0.15%, Cr: 0.5% -2.50%, Mo: 0.10% -0.30%, B: 0.0015 to 0.0035 percent, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities.
The structure of the hot formed steel consists of ferrite, martensite and retained austenite. The volume fraction of the ferrite is 5-12%, the volume fraction of the martensite is 78-89%, and the volume fraction of the retained austenite is 6-10%.
The tensile strength of the hot forming steel is 1400MPa-1700MPa, and the oxidation resistance rate is less than 0.1 g/(m)2H), the yield strength is 900MPa-1450MPa, the elongation is more than or equal to 18.0%, the surface of the steel is not completely decarburized, the thickness of a decarburized layer is less than or equal to 15 mu m, and the thickness of the hot formed steel is 0.8mm-12.0 mm.
The high-strength hot forming steel with excellent oxidation resistance provided in the embodiment is subjected to smelting, hot rolling and cold rolling to obtain a hot forming substrate, and the thickness of the hot forming substrate is 0.8-12.0 mm. Then carrying out hot forming process treatment, wherein the hot forming process specifically comprises the following steps:
(1) placing the thermoformed substrate at a temperature AC3-AC3Heating and preserving heat in a heating furnace at the temperature of +15 ℃, wherein the preserving heat time is 180-300 s;
(2) taking out the heated hot-formed substrate from the heating furnace, air-cooling, and air-cooling to Ar3And after the temperature is kept for 5-8 s, the steel is placed into a hot forming die for deformation and cooling, the cooling speed is more than or equal to 18 ℃/s, the steel is cooled to 180-250 ℃ and then subjected to pressure maintaining, the pressure maintaining time is 40-80 s, and after the pressure maintaining, the formed part is taken out and air-cooled to room temperature, so that the hot forming steel is obtained.
Specific components, hot forming process parameters and structures and properties of hot formed steel plates of the embodiments of the invention are shown in tables 1-3.
TABLE 1 chemical composition of inventive examples (wt%)
Figure BDA0003365351180000061
Table 2 thermoforming process of examples of the invention
Figure BDA0003365351180000071
TABLE 3 organization and Performance parameters for embodiments of the invention
Figure BDA0003365351180000072
In the embodiment, through the matching of chemical components and a hot forming process, a certain content of ferrite and residual austenite structures are introduced into the traditional full martensite structure, so that the plasticity of the steel is improved, and the elongation of the steel reaches more than 18% under the condition of ensuring that the tensile strength is more than 1400 MPa. The oxidation resistance of the steel is improved by adding elements such as Cr, Mo and the like, and the oxidation resistance rate of the steel is less than 0.1 g/(m)2H), the oxidation resistance level reaches 1 level, the steel does not need atmosphere protection during hot forming, shot blasting treatment is not needed after hot forming, and the subsequent procedures can be directly carried out; the total flow cost of the hot forming steel and the hot forming process is lower than the production cost of the existing hot forming part, and the hot forming process can be realized on the existing equipment without equipment transformation.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The high-plasticity hot forming steel with oxidation resistance for the automobile is characterized by comprising the following chemical components in percentage by mass:
c: 0.18% -0.28%, Si: less than or equal to 0.20 percent, Mn: 1.20% -2.0%, P: 0.030-0.080%, S is less than or equal to 0.004%, Als: 0.02% -0.06%, Nb: 0.02% -0.06%, Ti: 0.025% -0.045%, V: 0.05% -0.15%, Cr: 0.5% -2.50%, Mo: 0.10% -0.30%, B: 0.0015 to 0.0035 percent, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities.
2. The high thermo-plastic formed steel with oxidation resistance for automobile according to claim 1, wherein the structure of the thermo-formed steel is composed of ferrite, martensite and retained austenite.
3. The high-plastic hot-forming steel with oxidation resistance for automobiles as claimed in claim 2, wherein the volume fraction of ferrite is 5 to 12%, the volume fraction of martensite is 78 to 89%, and the volume fraction of retained austenite is 6 to 10%.
4. The high thermo-plastic forming steel with oxidation resistance for automobile according to claim 1, characterized in that the tensile strength of the thermo-forming steel is 1400MPa-1700 MPa.
5. The high thermo-plastic steel for automobile with oxidation resistance according to claim 1, wherein the thermo-plastic steel has an oxidation resistance rate < 0.1 g/(m)2·h)。
6. The high thermo-plastic forming steel with oxidation resistance for automobile according to claim 1, characterized in that the yield strength of the thermo-forming steel is 900MPa-1450 MPa.
7. The high-plastic hot-forming steel with oxidation resistance for automobiles as claimed in claim 1, wherein the elongation of the hot-forming steel is 18.0% or more.
8. The high-plasticity hot-forming steel with oxidation resistance for the automobile as claimed in claim 1, wherein the surface of the hot-forming steel is not completely decarburized, and the decarburized layer has a thickness of 15 μm or less.
9. The high thermo-plastic steel for automobile having oxidation resistance according to claim 1, wherein the thickness of the thermo-plastic steel is 0.8mm to 12.0 mm.
10. A hot forming process of high-plasticity hot forming steel with oxidation resistance for automobiles is characterized by comprising the following steps:
(1) placing a thermoformed substrate comprising the composition of any of claims 1 to 9 at a temperature AC3-AC3Heating and preserving heat in a heating furnace at the temperature of +15 ℃, wherein the preserving heat time is 180-300 s;
(2) taking out the heated hot-formed substrate from the heating furnace, air-cooling, and air-cooling to Ar3And after the temperature is kept for 5-8 s, the steel is placed into a hot forming die for deformation and cooling, the cooling speed is more than or equal to 18 ℃/s, the steel is cooled to 180-250 ℃ and then subjected to pressure maintaining, the pressure maintaining time is 40-80 s, and after the pressure maintaining, the formed part is taken out and air-cooled to room temperature, so that the hot forming steel is obtained.
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