CN117660831A - Dual-phase steel and manufacturing method thereof - Google Patents

Dual-phase steel and manufacturing method thereof Download PDF

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Publication number
CN117660831A
CN117660831A CN202211014289.3A CN202211014289A CN117660831A CN 117660831 A CN117660831 A CN 117660831A CN 202211014289 A CN202211014289 A CN 202211014289A CN 117660831 A CN117660831 A CN 117660831A
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percent
phase steel
dual
steel
equal
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李伟
朱晓东
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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Priority to CN202211014289.3A priority Critical patent/CN117660831A/en
Priority to PCT/CN2023/114295 priority patent/WO2024041539A1/en
Publication of CN117660831A publication Critical patent/CN117660831A/en
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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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0242—Flattening; Dressing; Flexing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

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

Abstract

The invention discloses a dual-phase steel which comprises more than 90% of Fe and unavoidable impurities, and also comprises the following components in percentage by mass: c:0.09% -0.11%, si:0.1 to 0.3 percent of Mn:1.4 to 1.6 percent of Al:0.01% -0.03%, nb:0.01 to 0.03 percent of Ti:0.01% -0.03%, B:0.0020 to 0.0030 percent. The invention obtains the dual-phase steel with low cost and high mechanical property through reasonable control of the chemical components of the steel. The invention also discloses a manufacturing method of the dual-phase steel.

Description

Dual-phase steel and manufacturing method thereof
Technical Field
The invention relates to the field of metallurgy, in particular to dual-phase steel and a manufacturing method thereof.
Background
With the exacerbation of global energy crisis and environmental problems, energy conservation and safety have become the main development directions of the automobile industry. Among them, the reduction of the vehicle weight is one of energy saving and emission reduction measures. The high-strength dual-phase steel has good mechanical property and service performance, and has wide application in the production and manufacture of vehicle structural members.
With the development of ultra-high strength steel and the change of the current market, the ultra-high strength steel is expected to have both low cost and high performance. At present, 780DP (dual-phase) steel is still mainly used steel, accounting for about 60 percent of the total amount of the dual-phase steel, and is widely applied to various structural members and safety members.
Canadian patent document CA2526488 (publication date: 12/2/2004) discloses a cold-rolled steel sheet comprising the chemical components: c:0.05 to 0.09 percent; si:0.4 to 1.3 percent; mn:2.5 to 3.2 percent; mo may optionally be added: 0.05 to 0.5 percent or Ni:0.05 to 2 percent; p:0.001 to 0.05 percent; s is less than or equal to 0.08 x ti-3.43 x n+0.004; n is less than or equal to 0.006%; al: 0.005-0.10%; ti: 0.001-0.045%, nb less than or equal to 0.04% or B:0.0002 to 0.0015 percent, ca can be added for treatment; the others are Fe and unavoidable impurities. The bainite content in the steel plate is more than 7%, pcm is less than or equal to 0.3, hot rolling is carried out at a temperature above Ar3, coiling is carried out at a temperature below 700 ℃, cold rolling is carried out, annealing is carried out at a temperature between 700 and 900 ℃, rapid cooling is started at a temperature between 550 and 700 ℃, and finally the high-strength steel with a strength above 780MPa is obtained. The steel has the characteristics of strong local deformability and low hardness of a welding area. However, the steel has a high Mn content in the design, which causes serious banding structure, thereby causing non-uniformity of mechanical properties of the steel. In addition, in the case of adding high Mn, relatively more Si is added, which is detrimental to the surface quality and weldability of the steel.
US patent document US20050167007 (publication date: 8/4/2005) discloses a method for producing a high-strength steel sheet, which comprises the following steps: c:0.05 to 0.13 percent, si:0.5 to 2.5 percent, mn:0.5 to 3.5 percent, cr:0.05 to 1 percent, mo:0.05 to 0.6 percent, al is less than or equal to 0.1 percent, S is less than or equal to 0.005 percent, N is less than or equal to 0.01 percent, P is less than or equal to 0.03 percent, and Ti can be selectively added: 0.005-0.05%, nb: 0.005-0.05%, or V: 0.005-0.2%. Hot rolling is carried out at the temperature of Ar3 or above, coiling is carried out at 450-700 ℃, cooling quenching is carried out at the cooling speed of 100 ℃/s from 700-600 ℃ after annealing, tempering is carried out at the temperature of 180-450 ℃, and finally the high-strength steel with the expansion ratio of 780MPa of tensile strength of more than 50% is obtained. The main problem of the steel is that the total alloy amount is too high, the Si content is high, and the weldability and the phosphating performance of the steel are not good.
Chinese patent document CN101363099a (publication date 2009, 2, 11) discloses an ultra-high strength dual phase steel comprising C:0.14 to 0.21 percent, si:0.4 to 0.9 percent, mn:1.5 to 2.1 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, and Nb:0.001 to 0.05 percent, V: 0.001-0.02%, and the balance of Fe and unavoidable impurities. The high-strength dual-phase steel is obtained by heat preservation at 760-820 ℃ after hot rolling and cold rolling, cooling speed of 40-50 ℃/s and aging time of 180-300 s at 240-320 ℃. However, the carbon equivalent design in this steel is high and does not have the characteristics of a balance of properties.
Chinese patent document CN103060703a discloses a 780MPa grade cold-rolled dual-phase strip steel, whose microstructure is a fine equiaxed ferrite matrix and martensite islands uniformly distributed on the ferrite matrix, and whose chemical element mass percentage content is: c:0.06 to 0.1 percent; si is less than or equal to 0.28 percent; mn:1.8 to 2.3 percent; cr:0.1 to 0.4 percent; when Cr is more than or equal to 0.3%, mo is not added; mo=0.3-Cr when Cr < 0.3%; al:0.015 to 0.05 percent; at least one of Nb and Ti, wherein Nb+Ti is in the range of 0.02-0.05%; the balance being Fe and other unavoidable impurities. The 780 MPa-grade cold-rolled dual-phase strip steel has higher strength, good ductility, better phosphating property and smaller mechanical property anisotropy. However, the alloy design in the invention contains more Cr, mo and other alloy contents, which is not beneficial to reducing the cost.
Therefore, in the prior art, although some dual-phase steel has better forming performance, the dual-phase steel contains high content of C or Si or contains more alloy content of Cr, ni, mo and the like, which is not beneficial to the weldability, the surface quality and the phosphating performance of the steel, and has higher cost; while some steels with high Si content have high hole expansibility and good bending properties, but have high yield ratios and reduced stamping properties. To date, 780MPa dual-phase steel with high mechanical properties and low cost is not obtained.
Disclosure of Invention
In order to solve the problems, the invention provides the dual-phase steel with low cost and excellent mechanical properties through reasonable element composition design.
In a first aspect of the present invention, there is provided a dual phase steel comprising, in addition to more than 90% Fe and unavoidable impurities, the following components in mass percent: c:0.09% -0.11%, si:0.1 to 0.3 percent of Mn:1.4 to 1.6 percent of Al:0.01% -0.03%, nb:0.01 to 0.03 percent of Ti:0.01% -0.03%, B:0.0020 to 0.0030 percent.
In a second aspect of the invention, a dual phase steel is provided, comprising the following component C in mass percent: 0.09% -0.11%, si:0.1 to 0.3 percent of Mn:1.4 to 1.6 percent of Al:0.01% -0.03%, nb:0.01 to 0.03 percent of Ti:0.01% -0.03%, B:0.0020 to 0.0030 percent, and the balance being Fe and unavoidable impurities.
Preferably, the dual phase steel of the present invention is free of Mo and Cr.
The component design of the dual-phase steel is mainly C-Si-Mn, and simultaneously, a trace amount of high-hardenability element B is added to further reduce the Mn content, and in addition, the trace addition of Nb and Ti can inhibit the growth of austenite grains and effectively refine the grains. The invention allows obtaining the dual-phase steel with 80 kg strength, which has low cost and excellent mechanical property, under the condition of not adding noble alloy elements such as Mo, cr and the like through the proper composition design.
In the invention, the design principle of each chemical element is as follows:
c: the addition of the element C can improve the strength of the steel and the hardness of martensite in the steel. If the content of C in the steel is less than 0.09%, the strength of the steel sheet is affected and the formation amount and stability of austenite are adversely affected; when the content of C in the steel is higher than 0.11%, the martensite hardness is too high, the grain size is coarse, the formability of the steel plate is not facilitated, and meanwhile, the carbon equivalent is too high, so that the welding use of the steel is not facilitated. Therefore, the content of C is controlled to be between 0.09% and 0.11% in the present invention.
Si: the addition of Si element to steel can improve hardenability. And Si dissolved in the steel can influence the interaction of dislocation, so that the work hardening rate is increased, the elongation of the dual-phase steel can be properly improved, and better formability is beneficial to obtaining. However, it should be noted that if the Si content in the steel is too high, the control of the surface quality is not favored. Therefore, in the present invention, the Si content is controlled to be between 0.1% and 0.3%.
Mn: the addition of Mn element is favorable for improving the hardenability of steel and can effectively improve the strength of the steel plate. When the Mn content in the steel is less than 1.4%, the strength of the steel sheet is insufficient; when the Mn content in the steel is more than 1.6%, the strength of the steel sheet is excessively high, so that the formability thereof is deteriorated. Therefore, in the present invention, the Mn content is controlled to be 1.4% to 1.6%.
B: the addition of the B element is beneficial to improving the hardenability of the steel, and can effectively improve the strength of the steel plate. When the content of B in the steel is less than 0.0020%, the strength of the steel sheet is insufficient; when the content of B in the steel is more than 0.0030%, the strength of the steel sheet is excessively high, so that the formability thereof is deteriorated. Therefore, in the present invention, the content of B is controlled to be 0.0020% to 0.0030%.
Al: the addition of Al element in steel can play the roles of deoxidizing and refining grains. On the other hand, the lower the Al content, the more advantageous the castability of the smelting, in the present invention, the Al content is controlled to be between 0.01% and 0.03%.
Nb: nb is a strong carbide forming element for refining grains, after a small amount of Nb is added into the microalloyed steel, the Nb can obviously reduce the recrystallization temperature of deformed austenite by strain-induced precipitated phases through the actions of particle pinning and subgrain boundaries in the controlled rolling process, and provide nucleation particles, so that the effect on refining the grains is obvious; in the continuous annealing austenitizing process, the points of the soaking undissolved carbon and nitriding substances can prevent coarsening of soaking austenite grains through a particle pinning grain boundary mechanism, so that the grains are effectively refined. But the Nb content cannot be too high, otherwise the production cost increases. Thus, in the present invention, the content of Nb is controlled to be between 0.01 and 0.03%, preferably between 0.015 and 0.025%.
Ti: similar to the effect of Nb, the strong carbide forming element Ti added to steel also shows a strong effect of suppressing austenite grain growth at high temperature, contributing to grain refinement. Meanwhile, if Ti is added in a large amount, the production cost is also increased. Therefore, in the present invention, the Ti content is controlled to be between 0.01 and 0.03%, preferably between 0.015 and 0.025%.
According to the invention, through the composition design of the dual-phase steel, noble alloy elements such as Mo, cr and the like do not need to be added, so that the economical efficiency can be ensured. The dual-phase steel provided by the invention needs to ensure enough alloy addition of C, mn and B to provide enough hardenability for the dual-phase steel, and ensure that the dual-phase steel obtains 80 kg-level high strength at a continuous annealing gas cooling speed of 40-100 ℃/s. However, the content of the C, mn, B alloying elements in the dual-phase steel should not be too high, otherwise it is difficult to ensure that the finally obtained dual-phase steel has excellent welding performance and formability.
Preferably, in the dual phase steel of the present invention, the content of Nb is 0.015% to 0.025% and/or the content of Ti is 0.015% to 0.025%. Wherein when the content of Nb and Ti is small, the corresponding grain refining effect is insignificant, and when the content of Nb and Ti is too high, the cost is increased.
Preferably, the hardenability factor Y of the dual-phase steel of the invention Q The method meets the following conditions: y is more than or equal to 1.9 Q Less than or equal to 2.1, calculated according to the following formula: y is Y Q =mn+200×b, wherein Mn and B represent values before the percentage by mass of the corresponding element. Hardenability factor Y Q Embodying the composite action of B and Mn in steel by using the hardenability factor Y Q The control of the two-phase steel within the numerical range can further improve the mechanical properties, especially the strength, of the two-phase steel while reducing the cost. If Y Q The steel strength obtained cannot reach the level of 80 kg if the value is lower than 1.9; if Y Q If the value is higher than 2.1, the elongation of the corresponding steel is not satisfactory. It should be noted that in the alloy design, the Mn content is the maximum equivalent affecting the overall cost, so the invention can further reduce Mn by adding proper amount of BThe content is favorable for reducing the cost, and the comprehensive hardenability of Mn and B is utilized to further improve the mechanical properties of the dual-phase steel, and the improvement of the processing properties of field production, including the rolling stability of hot rolling and cold rolling, is also favorable.
Preferably, in the dual phase steel of the present invention, the content of the impurity element in mass percent satisfies: p is less than or equal to 0.015 percent, S is less than or equal to 0.003 percent, and N is less than or equal to 0.005 percent.
P, N and S are both unavoidable impurity elements in steel, and the lower the content of P, N and S elements in steel, the better the performance of the steel. Specifically, mnS formed by S seriously affects formability, and N easily causes cracks or bubbles on the surface of a slab. Therefore, in the dual-phase steel disclosed by the invention, P is controlled to be less than or equal to 0.015%, S is controlled to be less than or equal to 0.003%, and N is controlled to be less than or equal to 0.005%.
In the present invention, the microstructure of the dual phase steel includes martensite and ferrite, and preferably, the microstructure of the dual phase steel of the present invention is composed of martensite and ferrite, wherein the volume percentage of martensite is 55% or more and 85% or less. The content of martensite in the steel structure is directly related to the strength of the dual-phase steel, and meanwhile, a part of ferrite needs to exist in the steel so that the hardness and the softness can be matched and coordinated when the steel is deformed, and the overall performance of the steel is improved.
Preferably, the average grain size of the martensite and ferrite in the dual phase steel of the present invention is 5 microns or less, more preferably, the grain size of the martensite and ferrite in the dual phase steel is 5 microns or less, which contributes to the improvement of the strength and workability of the steel.
Preferably, the dual-phase steel is 80 kg-grade dual-phase steel, the yield strength is more than or equal to 420MPa, the tensile strength is more than or equal to 800MPa, and A 50 The elongation at break of the gauge length is more than or equal to 18 percent.
Another aspect of the present invention provides a method of manufacturing the above dual phase steel, comprising the steps of: smelting and continuously casting molten steel to obtain a continuous casting blank; hot rolling the continuous casting billet; cold rolling; annealing; tempering; leveling.
Preferably, in the annealing step, the annealing soaking temperature is controlled to be 825-855 ℃, the annealing time is controlled to be 40-200 s, then the annealing soaking temperature is cooled to the rapid cooling starting temperature of 735-760 ℃ at the speed of 3-5 ℃/s, and then the rapid cooling is performed at the speed of 40-100 ℃/s, and the rapid cooling ending temperature is 220-260 ℃.
Preferably, the annealing soaking temperature is 830-840 ℃. The annealing soaking temperature is in the numerical range, so that the grain size of the obtained dual-phase steel is finer, and the mechanical property and the forming property are better.
Preferably, in the hot rolling step, the continuous casting blank is firstly heated to 1160-1190 ℃, kept at the temperature for more than 150min, then hot rolled and finally rolled at 850-890 ℃, and rapidly cooled at the speed of 30-80 ℃/s after rolling; the coiling temperature is controlled to be 500-540 ℃, and air cooling is performed after coiling. The 80 kg-level dual-phase steel can meet the production requirement without slow cooling or other treatment on the hot rolled coil.
Preferably, in the cold rolling step, the cold rolling reduction is 50 to 70%.
Preferably, in the tempering step, the tempering temperature is 220-260 ℃ and the tempering time is 100-400 s. The long tempering time is beneficial to the reduction of the difference of hardness between ferrite and martensite two phases of the dual-phase steel. But the tempering time cannot be too long, otherwise a steel with a strength of less than 80 kg is obtained.
Preferably, in the flattening step, the flattening reduction is 0.3% or less.
The invention adopts reasonable chemical composition design and matches with optimized manufacturing process, allows to obtain the dual-phase steel with low cost and excellent performance (especially high strength and excellent elongation) on the premise of not adding Mo and Cr, the dual-phase steel is 80 kg-grade dual-phase steel, the microstructure comprises martensite and ferrite, the yield strength is more than or equal to 420MPa, the tensile strength is more than or equal to 800MPa, A 50 The elongation at break of the gauge length is more than or equal to 18 percent.
Drawings
FIG. 1 is a photograph showing the microstructure of a dual phase steel according to example 1 of the present invention.
Detailed Description
The dual phase steel and the method of manufacturing the same according to the present invention will be further explained and illustrated with reference to specific examples. However, the following description is illustrative description for explaining the present invention, and is not intended to limit the technical scope of the present invention to only the description scope.
Examples 1 to 5 and comparative examples 1 to 14
The dual phase steels of examples 1-5 of the present invention were prepared by the following steps:
(1) Smelting and continuously casting molten steel according to the formula shown in the following table 1 to obtain a continuous casting blank;
(2) Carrying out hot rolling on a continuous casting blank, wherein the continuous casting blank is firstly heated to 1160-1190 ℃, kept for more than 150 minutes, then subjected to hot rolling and finish rolling at 850-890 ℃, rapidly cooled at a speed of 30-80 ℃/s after rolling, then coiled, wherein the coiling temperature is 500-540 ℃, and air-cooled after coiling;
(3) Cold rolling: the cold rolling reduction rate is 50-70%;
(4) Annealing: the annealing soaking temperature is 825-855 ℃, the annealing time is 40-200 seconds, then the annealing is cooled to the rapid cooling starting temperature of 735-760 ℃ at the speed of 3-5 ℃/s, then the rapid cooling is performed at the speed of 40-100 ℃/s, and the rapid cooling ending temperature is 220-260 ℃;
(5) Tempering: the tempering temperature is 220-260 ℃, and the tempering time is 100-400 seconds.
(6) Leveling: the flattening rolling reduction is less than or equal to 0.3 percent.
Steels of comparative examples 1 to 14 were also produced according to the formulations shown in Table 1 below in substantially the same manner as in the above-described examples of the present invention, except that one or more of the chemical element contents or the manufacturing process parameters of comparative examples 1 to 14 did not satisfy the requirements of the present invention.
The 80 kg-level dual-phase steel of the present invention means that the microstructure of the steel of the present invention includes two phases, and the steel of the present invention can bear 80 kg per square centimeter.
Table 1 shows the chemical compositions of the dual phase steels of examples 1 to 5 and the steels of comparative examples 1 to 14, and the corresponding hardenability factors Y Q Is a value of (2).
Table 1 (wt.%), the balance Fe and unavoidable impurities other than P, S, N
The specific process parameters for the dual phase steels of examples 1-5 and the steels of comparative examples 1-14 are set forth in tables 2-1 and 2-2.
TABLE 2-1
TABLE 2-2
In table 2-2, the rapid cooling end temperature of each example and comparative example was the same as the tempering temperature, because the tempering operation was performed after the rapid cooling operation was completed during the actual process operation.
The obtained dual phase steels of examples 1 to 5 and steels of comparative examples 1 to 14 were sampled, respectively, to obtain corresponding samples. The properties of the obtained steel templates were subjected to a tensile test and a Charpy impact test to obtain the property data of the steels of examples and comparative examples. The test results of the test for the steels of each example and comparative example are shown in Table 3.
Table 3 shows the results of the performance tests of the dual phase steels of examples 1-5 and the steels of comparative examples 1-14.
TABLE 3 Table 3
Note that: kilogram force, i.e., kilo-gram force, is a common unit of force, and the international unit of force is newton. 1 kg force refers to the weight force (i.e., 9.8N) to which 1 kg of the object is subjected. So 1 kilo-gram force = 9.8 newtons.
As is clear from Table 3, examples 1 to 5 of the present invention are excellent in combination properties, and have a yield strength of 420MPa or more, a tensile strength of 800MPa or more, A 50 The elongation at break of the gauge length is more than or equal to 18 percent. The dual-phase steel of each embodiment obtains more than 80 on the premise of not adding noble alloy elements such as Mo, cr and the likeTensile strength of 0MPa and better elongation. The dual phase steels of examples 1-5 of the present invention were significantly better in combination than comparative examples 1-14.
The performance test method is carried out by adopting a GB/T228-2010 metal material room temperature tensile test method, and the A50 gauge length fracture elongation represents that the parallel length multiplied by the width of a tensile sample is 50mm multiplied by 25mm.
As can be seen from tables 1 to 3, the steels of examples 1 to 5 of the present invention fall within the claimed range in comparison with the steels of comparative examples 1 to 14, while matching optimized process parameters, thereby obtaining dual phase steels having both low cost and high performance.
The microstructure of the dual phase steel after corrosion with 4% (volume fraction) nitric alcohol of examples 1 to 5 and comparative examples 1 to 14 was observed with an optical microscope, and the volume fraction and size of martensite and ferrite in the steel were determined by image analysis software. The microstructure of example 1 is shown in FIG. 1. As can be seen from fig. 1, the microstructure of the dual phase steel of example 1 of the present invention includes martensite and ferrite, the percentage of martensite in the drawing is 63%, the dual phase steel of the present invention has a uniform structure, the percentage of martensite shown in any section of the steel can be regarded as the volume percentage of martensite in the steel, that is, the volume fraction of the dual phase steel of example 1 is 63%, and the average grain size of martensite and the average grain size of ferrite are both 5 μm or less.
Table 4 shows the microstructure of the steels of examples 1-5 and comparative examples 1-14, the volume fraction of martensite in the steel, and the average grain sizes of martensite and ferrite in the steel.
Table 4.
Sequence number Microstructure of microstructure Volume fraction/%of martensite Mean particle size of martensite/um Ferrite average particle diameter/um
Example 1 Martensitic+ferritic 63 4.3 3.8
Example 2 Martensitic+ferritic 69 4.2 4.1
Example 3 Martensitic+ferritic 78 4.5 3.7
Example 4 Martensitic+ferritic 58 3.8 4.0
Example 5 Martensitic+ferritic 66 3.9 4.2
Comparative example 1 Martensitic+ferritic 52 5.5 5.8
Comparative example 2 Martensitic+ferritic 92 3.5 3.8
Comparative example 3 Martensitic+ferritic 49 5.6 5.7
Comparative example 4 Martensitic+ferritic 90 4.2 4.4
Comparative example 5 Martensitic+ferritic 53 5.8 5.2
Comparative example 6 Martensitic+ferritic 90 4,1 4.3
Comparative example 7 Martensitic+ferritic 48 6.2 6.0
Comparative example 8 Martensitic+ferritic 94 4.4 3.9
Comparative example 9 Martensitic+ferritic 95 3.4 3.7
Comparative example 10 Martensitic+ferritic 50 5.8 6.0
Comparative example 11 Martensitic+ferritic 47 6.3 6.5
Comparative example 12 Martensitic+ferritic 95 3.8 4.0
Comparative example 13 Martensitic+ferritic 92 3.5 4.4
Comparative example 14 Martensitic+ferritic 51 6.2 5.8
As is clear from Table 4, the dual phase steels of examples 1 to 5 had a martensitic and ferritic structure, and the volume fractions of martensite in the steels were all between 55% and 85% defined in the present invention, and the average grain sizes of martensite and ferrite were all 5 μm or less. The steels of comparative examples 1 to 14 also had the martensite and ferrite structures, but since the chemical composition or the manufacturing process thereof did not satisfy the conditions defined in the present invention, the microstructure intended in the present invention could not be obtained, and the volume fraction of the martensite was not within the range defined in the present invention.
In conclusion, the dual-phase steel with low cost and excellent performance is obtained through reasonable chemical composition design and combination of the optimization process.
It should be noted that all technical features described in this application may be freely combined or combined in any way, unless contradiction is caused between each other. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a further embodiment. Accordingly, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims (14)

1. The dual-phase steel is characterized by comprising more than 90% of Fe and unavoidable impurities, and further comprising the following components in percentage by mass: c:0.09% -0.11%, si:0.1 to 0.3 percent of Mn:1.4 to 1.6 percent of Al:0.01% -0.03%, nb:0.01 to 0.03 percent of Ti:0.01% -0.03%, B:0.0020 to 0.0030 percent.
2. The dual phase steel according to claim 1, comprising the following components in mass percent: c:0.09% -0.11%, si:0.1 to 0.3 percent of Mn:1.4 to 1.6 percent of Al:0.01% -0.03%, nb:0.01 to 0.03 percent of Ti:0.01% -0.03%, B:0.0020 to 0.0030 percent, and the balance being Fe and unavoidable impurities.
3. The dual phase steel according to claim 1 or 2, characterized in that it is free of Mo and Cr.
4. The dual phase steel according to claim 1 or 2, characterized in that the hardenability factor Y of the dual phase steel Q The method meets the following conditions: y is more than or equal to 1.9 Q Not more than 2.1, wherein Y Q =mn+200×b, wherein Mn and B represent values before the percentage by mass of the corresponding element.
5. The dual phase steel according to claim 1 or 2, wherein the content of impurity elements in mass percent satisfies: p is less than or equal to 0.015 percent, S is less than or equal to 0.003 percent, and N is less than or equal to 0.005 percent.
6. The dual phase steel according to claim 1 or 2, characterized in that the microstructure of the dual phase steel comprises martensite and ferrite, preferably consists of martensite and ferrite, more preferably the martensite is present in a volume percentage of 55% or more and 85% or less.
7. The dual phase steel of claim 6, wherein the grain size of both the martensite and the ferrite is below 5 microns.
8. The dual phase steel according to claim 1 or 2, characterized in that it is 80 kg grade dual phase steel and has the following properties: the yield strength is more than or equal to 420MPa; the tensile strength is more than or equal to 800MPa; a50 gauge length fracture elongation is more than or equal to 18 percent.
9. A method of manufacturing a dual phase steel according to any one of claims 1 to 8, characterized in that the method comprises the steps of:
1) Smelting and continuously casting molten steel to obtain a continuous casting blank;
2) Hot rolling the continuous casting billet;
3) Cold rolling;
4) Annealing;
5) Tempering; and
6) Flattening to obtain the dual-phase steel.
10. The manufacturing method according to claim 9, wherein in the annealing step, the annealing soaking temperature is 825 to 855 ℃, the annealing time is 40 to 200 seconds, then the annealing is performed at a speed of 3 to 5 ℃/s to a rapid cooling start temperature of 735 to 760 ℃, and then the rapid cooling is performed at a speed of 40 to 100 ℃/s, and the rapid cooling end temperature is 220 to 260 ℃; preferably, the annealing soaking temperature is 830-840 ℃.
11. The production method according to claim 9 or 10, wherein in the hot rolling step, the continuous casting slab is first heated to 1160 to 1190 ℃, kept for 150 minutes or more, then hot-rolled and finish-rolled at 850 to 890 ℃, and rapidly cooled at a speed of 30 to 80 ℃/s after rolling; and then coiling, wherein the coiling temperature is 500-540 ℃, and air cooling is performed after coiling.
12. The manufacturing method according to claim 9 or 10, characterized in that in the cold rolling step, a cold rolling reduction is 50 to 70%.
13. The manufacturing method according to claim 9 or 10, wherein in the tempering step, the tempering temperature is 220 to 260 ℃ and the tempering time is 100 to 400s.
14. The manufacturing method according to claim 9 or 10, wherein in the flattening step, a flattening reduction is 0.3% or less.
CN202211014289.3A 2022-08-23 2022-08-23 Dual-phase steel and manufacturing method thereof Pending CN117660831A (en)

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