CN107043895B - Component design and production method of 1500 MPa-grade low-carbon medium-manganese copper-containing steel - Google Patents
Component design and production method of 1500 MPa-grade low-carbon medium-manganese copper-containing steel Download PDFInfo
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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Abstract
The invention relates to a component design and production method of 1500 MPa-grade low-carbon medium-manganese copper-containing steel, which comprises the following chemical components in percentage by mass: c: 0.20% -0.23%, Si: 0.5-0.8%, Mn: 3.5% -4.0%, Al: 1.2-2.0%, Cr: 0.5% -1.0%, Cu: 0.6% -1.0%, Ni: 0.2% -0.5%, N: 0.003-0.012%, B: 0.00051-0.003% and the balance Fe and inevitable impurities. According to the invention, part of alloy elements are added on the basis of the traditional TRIP steel, so that the manganese content is greatly improved to reach the medium manganese range, and Al is used for replacing Si and simultaneously retaining proper Si element, so that the two elements are matched for use; adding a certain amount of Cu element capable of separating out and strengthening, and matching with a proper amount of Ni element for use, thereby eliminating the phenomenon of 'hot brittleness' caused by Cu during hot processing of the material. In addition, a small amount of Cr element is added, a proper amount of N element and Al element are added for matching use, and martensite, retained austenite and precipitated second-phase particle tissues with ultrahigh strength and good plasticity are obtained through the matching of hot rolling and a hot distribution process, wherein the tensile strength is more than 1500 MPa.
Description
Technical Field
The invention relates to a component design and production method of automobile high-strength steel, in particular to a component design and production method of 1500 MPa-level low-carbon medium-manganese copper-containing steel.
Background
At present, in order to save energy, reduce fuel consumption and reduce exhaust emission, the production of energy-saving and environment-friendly automobiles becomes one of the main targets of automobile enterprises in the world, therefore, many automobile enterprises at home and abroad adopt a series of measures, one of the most effective measures is automobile lightweight, data shows that if advanced high-strength steel (AHSS) plates are used, automobile body steel plates with the original thickness of 1.0-1.2 mm can be thinned to 0.7-0.8 mm, the automobile body weight is reduced by 15-20%, the oil is saved by 8-15%, up to now, various advanced high-strength steel plates have been developed in various countries in the world, such as first-generation advanced high-strength steel, dual-phase (DP) steel, multiphase (CP) steel, transformation induced plasticity (TRIP) steel and the like, which mainly use ferrite as a matrix, the product of tensile strength and elongation after fracture is generally below 15 GPa%, second-generation advanced high-strength steel, twin-Induced Plasticity (IP) steel, induced plasticity (L-IP) steel and SIP (SIP) steel, which mainly use ferrite as the product of tensile strength and martensite, the steel with the size of a small amount of martensite, and the martensite, the martensite of the first-austenite steel is more than 50%, and the steel, the steel with the martensite, the size of the martensite, the martensite of the martensite is more than 20%, and the martensite.
The first generation of advanced high-strength steel is multi-phase steel mainly comprising ferrite tissues, has low alloy content and low cost, but cannot meet the requirements of light weight and safety of future automobiles due to small product of strength and elongation, has excellent mechanical properties, but has greatly increased cost due to high alloy content, and simultaneously, the welding performance and the coating performance of a steel plate are poor due to excessively high alloy content. And the processing difficulty of these steel plates is also very large, so under the condition that both the first generation and the second generation AHSS have certain defects, researchers are working on the research of the third generation AHSS, the strength of the steel is 800-1500 MPa, the product of strength and elongation exceeds 30GPa ·%, the production cost is relatively low, and the steel is easy to realize in production, so the third generation AHSS becomes the research hotspot of the automobile lightweight material at present and in the future.
AHSS plays an important role in the future development of automobiles as one of main materials for supporting the concept of lightweight automobiles. The development of AHSS for automobiles is generally oriented to a steel sheet having high strength and good ductility, toughness and formability. With the continuous progress of technology, the development and application of the AHSS for vehicle with higher performance will be more developed in the near future.
Disclosure of Invention
Aiming at the challenges of light weight of automobiles, the invention provides 1500 MPa-grade low-carbon medium-manganese copper-containing steel, which aims to combine hot rolling and Q & P processes through reasonable design and optimization of components to obtain a component design and production method which has high production efficiency, is easy to produce in actual production and can greatly improve the comprehensive performance of hot stamping Q & P steel plates.
The design idea of the invention is as follows: the composition proportion of the invention is realized by changing the content of certain elements and adding some alloy elements which can strengthen and improve the mechanical property of steel materials on the basis of TRIP steel, and follows the principle of 'multi-element and small-amount' alloying, and simultaneously, the invention obtains the structure of martensite, residual austenite, precipitated second phase particles with ultrahigh strength and good plasticity by the cooperation of hot rolling and Q & P (quenching-partitioning) heat treatment process, and the tensile strength of the structure exceeds 1500MPa and has excellent plasticity and toughness.
It is characterized in that: (1) greatly improves the content of Mn to reach the content of Mn in the medium manganese steel.
(2) If Al is used together with Cr and Si, the high-temperature non-peeling property of the steel can be obviously improved, so that the surface property of the steel plate can be improved; and the added Al causes the density of the steel to be reduced.
(3) A certain amount of Cu element capable of generating precipitation strengthening is added and matched with a proper amount of Ni element for use, so that the phenomenon of 'hot brittleness' caused by Cu in hot processing of the material is eliminated; in addition, Ni also has the functions of improving the strength of the steel and keeping good plasticity and toughness.
(4) A small amount of Cr element which can improve the comprehensive performance of the steel is added.
(5) Proper amount of N element is added and matched with Al element for use, and AlN with grain refining effect and residual austenite content increasing effect can be generated to further improve the performance of the steel.
In order to achieve the purpose, the technical scheme of the invention is as follows: the low-carbon medium-manganese copper-containing steel comprises the following chemical components in percentage by weight: c: 0.20% -0.23%, Si: 0.5-0.8%, Mn: 3.5% -4.0%, Al: 1.2-2.0%, Cr: 0.5% -1.0%, Cu: 0.6% -1.0%, Ni: 0.2% -0.5%, N: 0.0035% -0.012%, B: 0.0005 to 0.003 percent, and the balance of Fe and inevitable impurities; the tensile strength of the low-carbon medium-manganese copper-containing steel is more than 1500 MPa.
In the preferable chemical components (all in weight percentage) of the low-carbon medium-manganese copper-containing steel, the content of Si is 0.55-0.8%, the content of Al is 1.2-1.5%, the content of Mn is 3.5-3.8%, the content of Cr is 0.6-0.8%, the content of Cu is 0.6-0.8%, the content of Ni is 0.25-0.4%, the content of N is 0.008-0.01%, and the content of B is 0.001-0.003%.
In the component design of the 1500 MPa-level low-carbon medium-manganese copper-containing steel, the effects and the contents of the elements in the steel are designed according to the following steps: (1) carbon: carbon can greatly improve the properties of strength, hardness and the like of the material, but at the same time, since it strongly reduces the plasticity, toughness and weldability of the material, when the carbon content exceeds 0.23%, the weldability of the steel becomes poor. Therefore, the carbon content of the low-carbon steel for welding is generally not more than 0.23%; in view of the above, the carbon content in the composition ratio is still kept within the carbon content range of the low carbon steel.
(2) Manganese: mn is a main element in TRIP steel, the content of Mn is generally between 1% and 2%, the actual production is usually kept about 1.5%, the strength of the material can be improved, the strength of the steel can reach 1500MPa, although the strength can be achieved by improving the carbon content and other alloy elements (such as Cr), the formability, the weldability and the like of the steel can be severely deteriorated due to the too high carbon content, the price of the alloy elements is too high, the reserves of part of the elements are very scarce, the cost is low, and the two approaches are very important market competition factors of the automobile steel, so the two approaches are not suitable; the Mn element can improve the strength of the steel, has low price and can improve the content and stability of the residual austenite; therefore, considering the combination of performance, price, resource reserves, etc., Mn is the most suitable choice, and although Mn deteriorates weldability of the material, it has much less adverse effect than other alloying elements. Therefore, the content thereof is increased to the lower limit of the medium manganese range in the composition ratio.
(3) Silicon and aluminum: the content of Si in TRIP is basically the same as that of Mn, the Si can obviously improve the elastic limit, yield point and tensile strength of steel, and the plasticity of the steel is not obviously reduced; most importantly, Si inhibits the precipitation of cementite, but too high Si content adversely affects the weldability of steel and reduces the surface coating properties of steel sheet. Therefore, the content of Si is reduced in the composition proportion, and when the content of Si in the steel is in the range of 0.8-1.0%, the plasticity and the toughness of the steel are remarkably reduced; therefore, the content of Si is less than 0.8 percent, and another alloy element Al can also inhibit cementite precipitation, the surface quality of the high Al steel is better, the coating performance is improved, but different from Si, Al does not have the effect of solid solution strengthening and can cause strength reduction, but the strength loss caused by reducing the content of silicon or replacing silicon with aluminum can be compensated by adopting various measures for improving the strength (such as increasing the content of Mn); in addition, Al also has the functions of refining grains and improving the impact toughness of the steel plate. Therefore, in consideration of the mechanical property and physical property of the steel plate, the easy realization of the process in the actual production and other factors, the Al-Si matching is a good compromise scheme, and therefore, the scheme of replacing part of Si elements by Al is adopted in the component proportion of the invention.
(4) Chromium: cr is an alloy element which is widely applied in actual industrial production, can obviously improve the strength, hardness and high-temperature mechanical property of steel, and has good oxidation resistance, corrosion resistance and wear resistance and simultaneously has no obvious adverse effect on the plasticity and toughness of the steel plate. The research shows that: when the Cr content is in the range of 0.5-1.65%, the steel has high strength, high wear resistance, and good hardenability and fatigue resistance. The improvement of Cr on the steel strength is only lower than that of carbon element from the calculation formula of the low-carbon alloy steel strength, but the reserve of Cr in China is less, and the Cr is used for saving or replaced by other elements as much as possible, so that 0.5-1.0% of Cr element is added into the component proportion of the invention in consideration of the factors of strength, resource reserve, cost and the like.
(5) Copper and nickel: at present, many high-strength structural steels contain copper in the range of 0.20-1.50%, Cu has an enrichment effect in the steel and can be distributed in a martensite matrix by second-phase particles with a certain size to play a role in dispersion strengthening, and a steel plate has good welding performance and corrosion resistance by adding Cu element in low-carbon steel, and the defects that when the content of Cu exceeds 0.5%, the steel is easy to generate a 'hot brittleness' phenomenon in a hot working process, and when the content of Cu in the steel exceeds 0.60%, Cu can be in a supersaturated state and is precipitated in a copper-rich phase form after heat treatment, so that the steel generates a second-phase particle precipitation strengthening effect. The research shows that: the welding performance is considered to be slightly influenced when the content of Cu is increased to at least 0.75%, and meanwhile, in order to avoid the phenomenon of hot brittleness, Ni element is required to be added (the content ratio of Ni to Cu is optimal when the content ratio of Ni to Cu is 1: 3-l: 2); in addition, the Cu and Ni containing steel has larger volume fraction of retained austenite and higher stability, and most importantly, when the steel is impacted, the TRIP effect can be maintained to a high strain region, which is one of the excellent properties of the advanced high-strength steel for vehicles; in addition, Ni does not reduce plasticity while improving steel strength, and therefore, in consideration of the above-mentioned factors, Cu: ni =1: 2-1: 3.
(6) Nitrogen: typical nitrogen content (about 0.003-0.012%) has obvious effect on strength, and N can improve the strength and low-temperature toughness of steel and improve weldability. The research result shows that: the density of AlN precipitates is increased along with the increase of the nitrogen content, the precipitates delay austenite transformation in the cooling and isothermal processes, so that a large amount of residual austenite is remained in the structure after quenching, and AlN has the function of precipitation strengthening, thereby improving the product of strength and elongation of the steel plate. In addition, the existence of AlN has the effect of refining austenite, which just improves the overheating sensitivity caused by higher manganese content, and considering the characteristics of N and the higher content of Al element in the component proportion, the component proportion of the invention is preferably added with 0.008% -0.01% of N element.
(7) Boron: the main function of B is to improve the hardenability of steel, trace boron element has obvious effect on improving the hardenability of products in low and medium carbon structural steel, the hardenability of steel can be greatly improved by adding a very small amount of boron (0.0005% -0.003%), and the boron brittleness phenomenon caused by the fact that the toughness of the steel is strongly reduced when the content of B is more than 0.004% is considered, so that 0.002% of B element is preferably added into the composition proportion of the invention.
The invention relates to a production method of low-carbon medium-manganese copper-containing steel, which comprises the following steps of (1) smelting and casting processes, wherein mixed alloy powder with the chemical components of 0.20-0.23% of C, 0.55-0.8% of Si, 3.5-3.8% of Mn, 1.2-1.5% of Al, 0.6-0.8% of Cr, 0.6-0.8% of Cu, 0.2-0.4% of Ni, 0.008-0.01% of N, 0.001-0.003% of B and the balance of Fe and inevitable impurities is smelted in an electric arc furnace, a converter and an open-hearth furnace, and then the smelted alloy powder is transferred into an L F refining furnace, and the required nitrogen pressure in the furnace is maintained during smelting so as to dissolve nitrogen elements in an alloy melt, and finally a casting blank or an ingot is cast.
(2) Heating and heat preservation: and transferring the casting blank or the cast ingot into a continuous furnace for heating and heat preservation, so that the alloy elements are uniformly dissolved in austenite, the heating temperature is kept between 1050 ℃ and 1100 ℃, and the heat preservation time is 1.5-2 hours.
(3) A hot rolling procedure: and after the heat preservation is finished, rolling the casting blank or the cast ingot, keeping the initial rolling temperature at 1000-1050 ℃, and then, when the temperature of the intermediate blank is reduced to 850-950 ℃, carrying out multi-pass final rolling on the intermediate blank to obtain a steel plate with the thickness of 1.8 mm.
(4) Q & P Heat treatment Process: after finishing rolling, preserving heat of a steel plate at 830-850 ℃ for 120s, cooling the steel plate to 170-200 ℃ at a cooling rate of more than 50 ℃/s, preserving heat for 20s, immediately transferring the steel plate into a heating furnace, heating to 350-365 ℃, carrying out element distribution, preserving heat for 45-60 s, and finally water-quenching the steel plate to room temperature to obtain a structure with martensite, residual austenite and precipitated second-phase particles; finally, the low-carbon medium-manganese copper-containing steel plate has tensile strength exceeding 1500MPa and also has excellent plasticity and toughness.
The 1500 MPa-grade low-carbon medium-manganese copper-containing steel has the advantages that the temperature is below 1100 ℃ in the austenitizing heat preservation stage, because the copper element is added into the components, the melting point of compounds formed among crystal grain boundaries is about 1100 ℃ generally, and if the heat preservation temperature is higher than the melting point of the compounds, the phenomenon of copper brittleness is easily caused; in addition, if the heating temperature of the steel is lower than 1050 ℃ or the holding time is too short, the diffusion and homogenization of the alloying elements in the austenite are not facilitated.
The 1500 MPa-grade low-carbon medium-manganese copper-containing steel has the heat preservation temperature (Q) in the heat preservation stage after rapid quenchingT) Before quenching, according to the martensite content to be obtained theoretically, the formula V is utilizedM=1-exp[a(Ms-QT)]Calculated (in the formula V)MIs the volume fraction of martensite; a is a constant, depending on the composition of the material, a = -0.011 for carbon steels with carbon content below 1.1%; ms is the martensite start temperature).
The 1500 MPa-grade low-carbon medium-manganese copper-containing steel has the advantages that the heat preservation temperature cannot be too low in the distribution heat preservation stage, and the heat preservation temperature is selected to be within the range of 20-40 ℃ above Ms due to the fact that the 1500 MPa-grade low-carbon medium-manganese copper-containing steel contains a large amount of manganese elements capable of stabilizing residual austenite. Secondly, the holding temperature cannot be too high, otherwise, carburization easily occurs, and the original carbon element is consumed to lower the stability of the retained austenite. In addition, the temperature for holding at this stage should be neither too long nor too short, so that cementite is easily formed and the strength of martensite is lowered if it is too long, and it is not preferable to stabilize the retained austenite if it is too short.
Drawings
FIG. 1 is a flow chart of a production process of 1500MPa grade low-carbon medium-manganese copper-containing steel.
FIG. 2 is a hot rolling and heat treatment process diagram of 1500MPa grade low-carbon medium-manganese copper-containing steel.
Detailed Description
The following detailed description is made with reference to the accompanying drawings and examples, as shown in fig. 1 and 2.
Example 1A method for designing and producing a 1500MPa grade low-carbon medium-manganese copper-containing steel comprises the following steps of (1) smelting and casting, wherein mixed alloy powder consisting of 0.2% of C, 3.5% of Mn, 0.8% of Si, 1.2% of Al, 0.8% of Cr, 0.8% of Cu, 0.4% of Ni, 0.008% of N, 0.002% of B and the balance of Fe is smelted in an electric arc furnace, a converter or an open hearth furnace, then transferred into an L F furnace, and maintained at a required nitrogen pressure in the furnace during smelting so as to add the N element, and finally cast into a casting blank or an ingot.
(2) Heating and preserving heat. And transferring the casting blank or the cast ingot into a continuous furnace for heating and heat preservation to enable alloy elements to be uniformly dissolved in austenite, keeping the heating temperature between 1050 ℃ and preserving the heat for 2 hours.
(3) And (5) hot rolling. And after the heat preservation is finished, rolling the casting blank or the cast ingot, keeping the initial rolling temperature at 1000 ℃, and then performing multi-pass final rolling on the intermediate blank when the temperature of the intermediate blank is reduced to 870 ℃ to obtain a steel plate with the thickness of 1.8 mm.
(4) And Q & P heat treatment process. After finishing rolling, keeping the temperature of the steel plate at 830 ℃ for 120s, then cooling the steel plate to 170 ℃ at the cooling rate of 100 ℃/s, keeping the temperature for 20s, immediately transferring the steel plate into a heating furnace, heating the steel plate to 350 ℃, keeping the temperature for 90s, and finally water-quenching the steel plate to room temperature to obtain a structure with martensite, residual austenite and precipitated second-phase particles; finally, the low-carbon medium-manganese copper-containing steel plate has the tensile strength of 1645MPa and also has excellent plasticity and toughness.
Example 2A method for designing and producing a 1500MPa grade low-carbon medium-manganese copper-containing steel comprises the following steps of (1) smelting and casting, wherein mixed alloy powder consisting of 0.21% of C, 3.6% of Mn, 0.7% of Si, 1.35% of Al, 0.7% of Cr, 0.7% of Cu, 0.3% of Ni, 0.009% of N, 0.002% of B and the balance of Fe is smelted in an electric arc furnace, a converter or an open hearth furnace, then transferred into an L F refining furnace, and the nitrogen pressure required in the furnace is maintained during smelting so as to add the N element, and finally cast into a casting blank or an ingot.
(2) Heating and preserving heat. And transferring the casting blank or the cast ingot into a continuous furnace for heating and heat preservation to enable alloy elements to be uniformly dissolved in austenite, keeping the heating temperature between 1070 ℃ and keeping the heat preservation time for 1.8 hours.
(3) And (5) hot rolling. And after the heat preservation is finished, rolling the casting blank or the cast ingot, keeping the initial rolling temperature at 1020 ℃, and then performing multi-pass final rolling on the intermediate blank when the temperature of the intermediate blank is reduced to 900 ℃ to roll the intermediate blank into a steel plate with the thickness of 1.8 mm.
(4) And Q & P heat treatment process. After finishing rolling, keeping the temperature of the steel plate at 840 ℃ for 120s, then cooling the steel plate to 185 ℃ at a cooling rate of 100 ℃/s, keeping the temperature for 20s, immediately transferring the steel plate into a heating furnace, heating the steel plate to 360 ℃, keeping the temperature for 60s, and finally water-quenching the steel plate to room temperature to obtain a structure with martensite, residual austenite and precipitated second-phase particles; finally, the low-carbon medium-manganese copper-containing steel plate has the tensile strength of 1591MPa and also has excellent plasticity and toughness.
Example 3A method for designing and producing a 1500MPa grade low-carbon, medium-manganese copper-containing steel comprises the steps of (1) smelting and casting, wherein a mixed alloy powder containing 0.23% of C, 3.8% of Mn, 0.55% of Si, 1.5% of Al, 0.6% of Cr, 0.6% of Cu, 0.25% of Ni, 0.01% of N, 0.002% of B and the balance of Fe is smelted in an electric arc furnace, a converter or an open hearth furnace, and then transferred to an L F furnace, and the nitrogen pressure required in the furnace is maintained during smelting so as to add the N element, and finally casting into a casting blank or an ingot.
(2) Heating and preserving heat. And transferring the casting blank or the cast ingot into a continuous furnace for heating and heat preservation to uniformly dissolve alloy elements into austenite, wherein the heating temperature is kept between 1100 ℃, and the heat preservation time is 1.5 hours.
(3) And (5) hot rolling. And after the heat preservation is finished, rolling the casting blank or the cast ingot, keeping the initial rolling temperature at 1050 ℃, and then performing multi-pass final rolling on the intermediate blank when the temperature of the intermediate blank is reduced to 940 ℃ to roll the intermediate blank into a steel plate with the thickness of 1.8 mm.
(4) And Q & P heat treatment process. After finishing rolling, keeping the temperature of the steel plate at 850 ℃ for 120s, then cooling the steel plate to 200 ℃ at the cooling rate of 100 ℃/s, keeping the temperature for 20s, immediately transferring the steel plate into a heating furnace, heating the steel plate to 365 ℃, keeping the temperature for 45s, and finally water-quenching the steel plate to room temperature to obtain a structure with martensite, residual austenite and precipitated second-phase particles; finally, the low-carbon medium-manganese copper-containing steel plate has the tensile strength of 1550MPa and also has excellent plasticity and toughness.
Claims (3)
1. The 1500 MPa-grade low-carbon medium-manganese copper-containing steel is characterized in that: the chemical components comprise: c: 0.20% -0.23%, Si: 0.5-0.8%, Mn: 3.5% -4.0%, Al: 1.2-2.0%, Cr: 0.5% -1.0%, Cu: 0.5% -0.8%, Ni: 0.2% -0.5%, N: 0.003-0.012%, B: 0.0005 to 0.003 percent, and the balance of Fe and inevitable impurities, wherein the contents of the elements are calculated by weight percent, and the content ratio of Ni to Cu is 1:3 to l: 2.
2. The method for producing the 1500MPa grade low-carbon medium-manganese copper-containing steel as claimed in claim 1, wherein the method comprises the following steps: the production steps comprise:
(1) smelting and casting process, namely smelting the mixed alloy powder with the chemical composition as shown in claim 1 in an electric arc furnace, a converter or an open hearth furnace, then transferring the smelted mixed alloy powder into an L F refining furnace, maintaining the required nitrogen pressure in the furnace during smelting so as to dissolve nitrogen elements in an alloy melt, and finally casting the alloy melt into a casting blank or a casting ingot;
(2) heating and heat preservation: transferring the casting blank or the cast ingot into a continuous furnace for heating and heat preservation to enable alloy elements to be uniformly dissolved in austenite, keeping the heating temperature between 1050 ℃ and 1100 ℃, and preserving the heat for 1.5-2 hours;
(3) a thermoforming step: after the heat preservation is finished, rolling a casting blank or a cast ingot, keeping the initial rolling temperature at 1000-1050 ℃, and reducing the temperature of the intermediate blank to 850-950 ℃, then carrying out multi-pass final rolling on the intermediate blank, and rolling the intermediate blank into a steel plate with the thickness of 1.8 mm;
(4) a heat treatment process: after finishing rolling, preserving heat of a steel plate at 830-850 ℃ for 120s, cooling the steel plate to 170-200 ℃ at a cooling rate of more than 50 ℃/s, preserving heat for 20s, immediately transferring the steel plate into a heating furnace, heating to 350-365 ℃, carrying out element distribution, preserving heat for 45-90 s, and finally water-quenching the steel plate to room temperature to obtain a structure with martensite, residual austenite and precipitated second-phase particles; finally, the low-carbon medium-manganese copper-containing steel has tensile strength of more than 1500MPa and excellent plasticity and toughness.
3. The 1500MPa grade low carbon medium manganese copper containing steel of claim 1, wherein: the tensile strength of the low-carbon medium-manganese copper-containing steel is more than or equal to 1500 MPa.
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| CN109433825B (en) * | 2018-11-13 | 2020-03-31 | 燕山大学 | Method for manufacturing high-strength steel plate in short process, high-strength steel plate and application of high-strength steel plate |
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