100 kg class cold rolled low alloy annealed dual phase steel and its manufacturing method

Abstract

The present invention discloses a 100-kilogram-class cold-rolled low-alloy annealed duplex steel, which contains Fe and inevitable impurity elements, and further contains the following chemical elements in mass percentage content: 0.1% < C ≤ 0.13%, Si: 0.5% - 0.8%, Mn: 1.6% - 1.8%, Al: 0.01% - 0.03%, Nb: 0.01 - 0.03%, Ti: 0.01 - 0.03%, B: 0.0020 - 0.0030%; the chemical elements do not contain Mo and Cr; the microstructure of the 100-kilogram-class cold-rolled low-alloy annealed duplex steel is martensite + ferrite. Correspondingly, the present invention discloses a manufacturing method of the above 100-kilogram-class cold-rolled low-alloy annealed duplex steel. The 100-kilogram-class cold-rolled low-alloy annealed duplex steel obtained by this manufacturing method not only has good economic efficiency, but also has high strength, excellent elongation and bending properties.

Description

[Technical Field]

[0001] The present invention relates to a metallic material and a method for manufacturing the same, and more particularly to a 100 kg class cold-rolled low-alloy annealed dual-phase steel and a method for manufacturing the same. [Background technology]

[0002] In recent years, with the global energy crisis and worsening environmental problems, energy conservation and safety have become the main development trends in the automobile manufacturing industry, and vehicle weight reduction is one of the measures to save energy and reduce exhaust gas emissions. In practice, high-strength duplex stainless steels have good mechanical properties and usability, so they can be effectively applied in the production and manufacturing of vehicle structural components.

[0003] With the development of ultra-high strength steels and the current changes in the market, the market and users are looking to ultra-high strength steels for their economical efficiency and superior performance. Currently, 980MPa-class low alloy steels are still the mainstream steel, accounting for 20% of all low alloy steels, and are widely used in various structural and safety applications. Furthermore, with the trend toward lightweighting and energy saving in the automotive industry and the rapid progress of steel mills both at home and abroad, especially in China, the future development of duplex stainless steels will inevitably be centered on low cost and high performance.

[0004] In the prior art, many studies have been carried out on 980 MPa-class dual-phase stainless steels, and some research results have been obtained.

[0005] For example, a Chinese patent document titled "980 MPa-grade low-carbon cold-rolled duplex steel and its manufacturing method," published on January 29, 2019, with publication number CN109280854A, discloses a 980 MPa-grade low-carbon cold-rolled duplex steel. This technical solution aims to solve the high manufacturing costs and manufacturing difficulties of conventional 980 MPa-grade cold-rolled duplex steel. Its chemical composition, in mass percent, is 0.05-0.10% C, 0.30-0.70% Si, 2.00-2.50% Mn, 0.40-0.80% Cr, and 0.01-0.06% Al. The V content of the molten iron in a converter is controlled, and the 980 MPa-grade low-carbon cold-rolled duplex steel is obtained through processes such as hot rolling, acid rolling, and annealing. The dual-phase stainless steel produced by this technology has excellent mechanical properties and excellent formability, and its cost advantages are obvious. However, this technology uses a valuable alloying element, Cr, in the steel design, and the addition of a high content of Mn not only increases the alloy cost, but also causes serious banding and can lead to uneven mechanical properties.

[0006] For example, a Chinese patent document, Publication Number CN111455285A, published on July 28, 2020, titled "Low-cost, easy-to-manufacture cold-rolled dual-phase steel with a tensile strength of 980 MPa and its manufacturing method," discloses a cold-rolled dual-phase steel with a tensile strength of 980 MPa and a manufacturing method thereof. The chemical composition of the steel is 0.080-0.095% C, 0.4-0.6% Si, 2.1-2.3% Mn, 0.06-0.08% Al, 0.2-0.4% Cr, 0.03-0.05% Nb, 0.01-0.02% Ti, 0.0015-0.0040% Ca, P≦0.012%, S≦0.005%, N≦0.005%, with the remainder being Fe and unavoidable impurities.

[0007] For example, a Chinese patent document, Publication No. CN107043888A, published on August 15, 2017, titled "980 MPa-grade cold-rolled dual-phase steel sheet with excellent cold bending performance and manufacturing method thereof," discloses a 980 MPa-grade cold-rolled dual-phase steel sheet with the following chemical composition, in mass percent: C 0.10-0.12%, Si 0.45-0.65%, Mn 2.4-2.6%, Cr 0.35-0.45%, Nb 0.05-0.075%, Ti 0.06-0.10%, Al 0.055-0.075%, P≦0.008%, S≦0.002%, N≦0.003%, with the remainder being Fe and unavoidable impurities. The dual-phase steel plate produced by this technology has excellent mechanical properties, but the contents of Cr, Nb, and Ti added to the steel are relatively high.

[0008] Although the conventional 1000MPa dual-phase stainless steel patent technology has good formability, it uses high C or Si contents or high contents of alloys such as Cr, Nb, and Ti, which are unfavorable for the weldability, surface quality, and phosphate treatment performance of the steel, and is also expensive.In addition, some high-Si steels have a very high hole expansion ratio and good bending properties, but a high yield ratio and reduced press workability.

[0009] Therefore, in order to meet the current market needs, the present invention aims to develop a 100 kg class cold-rolled low-alloy annealed dual-phase steel that is both economical and has excellent mechanical properties. Summary of the Invention [Problem to be solved by the invention]

[0010] One object of the present invention is to provide a 100 kgf / cm2 cold-rolled, low-alloy, annealed, duplex steel. This 100 kgf / cm2 cold-rolled, low-alloy, annealed, duplex steel is economical and has excellent mechanical properties. It has high strength, excellent elongation, and bending properties without adding Mo or Cr. Its yield strength is 550 MPa or more, tensile strength is 1000 MPa or more, and A 50The elongation at gauge fracture ≥ 12%, and the 90-degree bending characteristic R / t ≤ 1.0, having extremely excellent general-purpose prospects and application values. In the present invention, "100-kilogram class" means the tensile strength of steel ≥ 980 MPa, and "1000-MPa class" means the tensile strength of steel ≥ 1000 MPa.

Means for Solving the Problems

[0011] In order to achieve the above object, the present invention contains Fe and inevitable impurity elements, and further, each of the following chemical elements in mass percentage content: 0.1% < C ≤ 0.13%, Si: 0.5% - 0.8%, Mn: 1.6% - 1.8%, Al: 0.01% - 0.03%, Nb: 0.01 - 0.03%, Ti: 0.01 - 0.03%, B: 0.0020 - 0.0030%, included; The chemical elements do not contain Mo and Cr; The microstructure of the above 100-kilogram class cold-rolled low-alloy annealed duplex steel is martensite + ferrite, providing a 100-kilogram class cold-rolled low-alloy annealed duplex steel.

[0012] Furthermore, in the 100-kilogram class cold-rolled low-alloy annealed duplex steel according to the present invention, the mass percentage content of each chemical element is as follows: 0.1% < C ≤ 0.13%, Si: 0.5% - 0.8%, Mn: 1.6% - 1.8%, Al: 0.01% - 0.03%, Nb: 0.01 - 0.03%, Ti: 0.01 - 0.03%, B: 0.0020 - 0.0030%, and the rest is Fe and other inevitable impurities.

[0013] In the present invention, by using a composition system mainly composed of C-Si-Mn, the obtained cold-rolled low-alloy annealed dual-phase steel can achieve a strength of 1000 MPa grade. In the chemical composition design of this dual-phase steel, precious alloy elements such as Mo and Cr are not added, and the economic efficiency is effectively maintained. Further, the present invention achieves the effect of further reducing the Mn content by adding a trace amount of high hardenability element B in the chemical composition design. In addition, by adding trace amounts of Nb and Ti to the steel, the effect of suppressing the growth of austenite crystal grains is achieved, thereby effectively refining the crystal grains.

[0014] In the 100-kilogram-class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the design principle of each chemical element is as follows: C: In the 100-kilogram-class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the addition of C can increase the strength of the steel and the hardness of martensite. If the mass percentage content of C in the steel is less than 0.1%, not only the strength of the steel sheet is affected, but it is also disadvantageous for the formation amount and stability of austenite; and if the mass percentage content of C in the steel exceeds 0.13%, the hardness of martensite is too high, the crystal grain size becomes coarser, which is disadvantageous for the forming performance of the steel sheet, and at the same time, the carbon equivalent is too high, which is also disadvantageous for welding use. Therefore, in order to maintain the performance of the steel material, in the 100-kilogram-class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the mass percentage content of C is set to 0.1% < C ≤ 0.13%. For example, the mass percentage content of C is 0.101%, 0.105%, 0.11%, 0.115%, 0.12%, 0.125%, 0.13%, or it may also be within the range between any two of the above numerical values.

[0015] Si: In the 100 kgf / cm2 cold-rolled, low-alloy, annealed duplex steel of the present invention, the addition of Si improves the hardenability of the steel. The dissolved Si in the steel affects dislocation interactions, increasing the work-hardening rate, and appropriately improving the elongation of the duplex steel, which is beneficial for achieving better formability. However, it should be noted that the Si content in the steel should not be too high; too high a mass percent of Si in the steel is detrimental to controlling the surface quality of the steel sheet. Therefore, to maximize the beneficial effects of Si, the mass percent of Si in the 100 kgf / cm2 cold-rolled, low-alloy, annealed duplex steel of the present invention is set to 0.5% to 0.8%. For example, the mass percent of Si may be 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, or 0.8%, or may be within a range between any two of the above values.

[0016] Mn: In the 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel according to the present invention, the addition of Mn not only improves the hardenability of the steel but also effectively increases the strength of the steel sheet. If the Mn content in the steel is less than 1.6%, the strength of the steel sheet is insufficient. However, if the Mn content in the steel is more than 1.8%, the strength of the steel sheet is too high, resulting in poor formability. Therefore, taking into account the beneficial effects of Mn, the Mn content in the 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel according to the present invention is set to 1.6% to 1.8% by mass. For example, the Mn content in the steel may be 1.6%, 1.63%, 1.65%, 1.68%, 1.7%, 1.73%, 1.75%, 1.78%, or 1.8%, or may be within a range between any two of the above values.

[0017] Al: In the 100 kg class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the addition of Al has deoxidizing and grain refining effects. Meanwhile, the lower the Al content in the steel, the more advantageous it is for castability during smelting. Therefore, to maximize the beneficial effects of Al, the present invention specifies an Al content of 0.01 to 0.03% by mass. For example, the Al content may be 0.01%, 0.015%, 0.02%, 0.025%, or 0.03%, or may be within a range between any two of the above values.

[0018] Nb: In the present invention, 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel, Nb is an important element for grain refinement. Adding a small amount of Nb, a strong carbide-forming element, to microalloy steel induces strain during controlled rolling, resulting in the precipitation of phases. Through the effects of mass point pinning and subgrain boundary pinning, this significantly lowers the recrystallization temperature of deformed austenite, providing nucleation mass points, and significantly improving grain refinement. Furthermore, during continuous annealing and austenitization, the mass points of undissolved carbon and nitrides prevent the coarsening of soaked austenite grains through the grain boundary pinning mechanism, thereby effectively refining the grains. Therefore, to maximize the beneficial effects of Nb, the mass percent Nb content in the present invention is set to 0.01-0.03%. For example, the mass percent content of Nb can be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, or a range between any two of the above values.

[0019] Of course, in some preferred embodiments, the mass percentage of Nb may be more preferably 0.015 to 0.025% to obtain better effects.

[0020] Ti: In the 100 kgf / cm2 cold-rolled, low-alloy, annealed dual-phase steel according to the present invention, the addition of Ti, a strong carbide-forming element, exhibits a strong austenite grain growth suppression effect even at high temperatures. At the same time, the addition of Ti is also advantageous for grain refinement. Therefore, to maximize the beneficial effects of Ti, the Ti content in the present invention is set to 0.01 to 0.03% by mass. For example, the Ti content in the present invention may be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, or any range between any two of the above values.

[0021] Of course, in some preferred embodiments, the mass percentage of Ti may be more preferably 0.015 to 0.025% to obtain better effects.

[0022] B: In the 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel according to the present invention, the addition of B not only improves the hardenability of the steel but also effectively increases the strength of the steel sheet. If the B content in the steel is less than 0.0020%, the strength of the steel sheet is similarly insufficient. However, if the B content in the steel is greater than 0.0030%, the strength of the steel sheet is similarly too high, resulting in poor formability. Therefore, in the 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel according to the present invention, the B content in the range of 0.0020 to 0.0030% by mass is specified. For example, the B content in the range of 0.0020%, 0.0023%, 0.0025%, 0.0028%, 0.0030%, or any range between any two of the above values.

[0023] In the above-mentioned composition design, the dual-phase steel of the present invention does not contain valuable alloying elements such as Mo or Cr, making it extremely economical. At the same time, in order to ensure a tensile strength of 1000 MPa or higher at a normal continuous annealing gas cooling rate of 40 to 100°C / s, the chemical composition design must ensure the addition of alloying elements C, Mn, and B in amounts that provide sufficient hardenability. However, to ensure excellent weldability and formability and to ensure that the strength does not exceed the upper limit, there are also upper limits to the contents of the alloying elements C, Mn, and B in the dual-phase steel.

[0024] Furthermore, in the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel according to the present invention, the unavoidable impurities are P≦0.012%, S≦0.0025%, and N≦0.005%.

[0025] In the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel according to the present invention, the elements P, S, and N are all impurities in the steel, and the lower the contents of the elements P, N, and S in the steel, the better the implementation effect. Specifically, MnS formed by the element S has a significant impact on the formability of the steel, while the element N is likely to cause cracks and bubbles on the surface of the slab. Therefore, if circumstances permit, in order to obtain steel with better performance and quality, the contents of the elements P, S, and N in the steel should be reduced as much as possible, and the elements P≦0.012%, S≦0.0025%, and N≦0.005% should be controlled. In some embodiments, in the 100 kg class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the mass percent content of the element P is 0.001 to 0.012%, and / or the mass percent content of the element S is 0.001 to 0.0025%, and / or the mass percent content of the element N is 0.001 to 0.005%.

[0026] Furthermore, in the 100 kg class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the mass percent content of each chemical element satisfies at least one of the following conditions: Nb: 0.015 to 0.025%, Ti: 0.015~0.025%.

[0027] Furthermore, in the 100 kg cold-rolled low-alloy annealed dual-phase steel according to the present invention, the volume percent content of martensite is ≥ 60%, for example, the volume percent content of martensite can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any range between any two of the above values.

[0028] Furthermore, in the 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the hardenability coefficient YQ is 2.0≦YQ≦2.4, where YQ = Mn + 200 × B, where each chemical element in the formula is substituted with the numerical value before the mass percent symbol. In some embodiments, the hardenability coefficient Y Q is 2.0, 2.1, 2.2, 2.3, 2.4, or within a range between any two of the above values.

[0029] In the 100 kg class cold-rolled low-alloy annealed dual-phase steel according to the present invention, the strength of the steel is improved by the synergistic effect of the elements B and Mn. In order to ensure that the final strength of the steel meets the requirements, the present invention controls the mass percent content of each chemical element and also ensures that 2.0≦Y Q ≦2.4, provided that Y Q =Mn+200×B.

[0030] However, it should be noted that the Mn content has the greatest impact on the overall cost of the alloy. Therefore, the present invention utilizes the overall hardenability of Mn-B and adds an appropriate amount of B to further reduce the Mn content in the alloy. This is advantageous for cost reduction and further helps improve the manufacturability of on-site production.

[0031] Furthermore, in the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel according to the present invention, the grain sizes of both martensite and ferrite are 5 μm or less. For example, the grain size of martensite may be 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, or within a range between any two of the above values, and the grain size of ferrite may be 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, or within a range between any two of the above values.

[0032] Furthermore, in the 100 kg class cold rolled low alloy annealed dual phase steel according to the present invention, the microhardness difference between martensite and ferrite, ΔHV, is ≦150. In some embodiments, the microhardness difference between martensite and ferrite, ΔHV, is 90, 100, 110, 120, 130, 140, 150, or within a range between any two of the foregoing values.

[0033] Furthermore, the 100 kg class cold-rolled low-alloy annealed duplex steel according to the present invention has a yield strength of ≥ 550 MPa, a tensile strength of ≥ 1000 MPa, an A50 gauge elongation at break of ≥ 12%, and a 90 degree bend property R / t ≤ 1.0. In some embodiments, the 100 kg class cold-rolled low-alloy annealed duplex steel according to the present invention has a yield strength of 550 MPa, 600 MPa, 650 MPa, 700 MPa, or a range between any two of the foregoing values. In some embodiments, the 100 kg class cold-rolled low-alloy annealed duplex steel according to the present invention has a tensile strength of 1000 MPa, 1020 MPa, 1040 MPa, 1060 MPa, 1080 MPa, 1100 MPa, or a range between any two of the foregoing values. In some embodiments, the 100 kg class cold-rolled low-alloy annealed duplex steel according to the present invention has an A 50 The gauge elongation at break is 12%, 13%, 14%, 15%, 16%, 17%, or any range between any two of the foregoing values. In some embodiments, the 100 kg class cold rolled low alloy annealed duplex stainless steel according to the present invention has a 90 degree bend property R / t of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any range between any two of the foregoing values.

[0034] Another object of the present invention is to provide a method for producing the above 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel. This method is convenient and simple to implement, and the 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel obtained by this method has high strength and excellent elongation and bending properties, including a yield strength of ≥ 550 MPa, a tensile strength of ≥ 1000 MPa, and an A 50 The gauge breaking elongation is ≧12%, and the 90-degree bending property R / t is ≦1.0.

[0035] To achieve the above object, the present invention provides a method for producing the above-mentioned 100 kg class cold-rolled low-alloy annealed dual-phase steel, which comprises the following steps: (1) Smelting and foundry; (2) Hot rolling: The continuously cast slab is first heated to 1160-1190°C, kept at this temperature for 150 minutes or more (for example, 150-250 minutes), and then subjected to finish hot rolling at 850-890°C. After rolling, the slab is rapidly cooled at a rate of 30-80°C / s, and then coiled at a coiling temperature of 500-540°C, followed by air cooling; (3) cold rolling; (4) Annealing: The annealing temperature is 825-855°C, the annealing time is 40-200 seconds, and then the quenching is started at a rate of 3-5°C / s, and then the quenching is stopped at a rate of 40-100°C / s; however, the quenching start temperature is 735-760°C, and the quenching completion temperature is 265-290°C; (5) Tempering; (6) Leveling.

[0036] Furthermore, in the manufacturing method according to the present invention, the annealing soaking temperature is set to 830 to 840°C in step (4).

[0037] In some preferred embodiments of the technical solution according to the present invention, in order to obtain better effects, such as smaller grain size of the obtained crystal grains, suitable mechanical properties of the obtained steel material, and better formability, the more preferred annealing temperature can be between 830 and 840°C.

[0038] Furthermore, in the manufacturing method according to the present invention, in step (3), the cold rolling reduction is set to 50 to 70%.

[0039] Furthermore, in the manufacturing method according to the present invention, in step (5), the tempering temperature is set to 265 to 290°C and the tempering time is set to 100 to 400 seconds.

[0040] Furthermore, in the manufacturing method according to the present invention, in step (6), the leveling reduction is set to ≦0.3%, for example, 0.1 to 0.3%.

[0041] Compared with the prior art, the 100 kg class cold-rolled low-alloy annealed dual-phase steel and its manufacturing method according to the present invention have the following advantages and beneficial effects: This invention has developed a new 100 kgf / cm2 cold-rolled, low-alloy, annealed dual-phase steel. Through rational chemical composition design and an optimized manufacturing process, we have been able to obtain a steel sheet with a martensite-ferrite dual-phase structure that achieves a strength of 1000 MPa without adding silicon alloying elements such as Mo or Cr. This fine and uniform martensite-ferrite dual-phase structure further ensures that the steel has excellent elongation and bending properties, as well as good formability.

[0042] The 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel of the present invention is not only economical but also has high strength, excellent elongation and bending properties. Its yield strength is ≥ 550 MPa, tensile strength is ≥ 1000 MPa, and A 50 With a gauge elongation at break of ≥ 12% and a 90-degree bend property R / t ≤ 1.0, this 100 kgf / cm2 cold-rolled low-alloy annealed duplex stainless steel is easy to manufacture and has excellent general-purpose prospects and application value, effectively meeting the needs of the market and users. DETAILED DESCRIPTION OF THE INVENTION

[0043] The 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel and its manufacturing method according to the present invention will be described in more detail below with reference to specific examples, but the description does not limit the technical solution of the present invention. [Example]

[0044] Examples 1 to 6 and Comparative Examples 1 to 14 Table 1-1 shows the mass percent ratio of each chemical element in the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 and the comparative steels of Comparative Examples 1 to 14.

[0045] [Table 1-1]

[0046] Table 1-2 shows the hardenability coefficient Y of the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 and the comparative steels of Comparative Examples 1 to 14. Q Indicates the value of

[0047] [Table 1-2]

[0048] The 100 kgf / cm2 cold-rolled, low-alloy, annealed dual-phase steels of Examples 1 to 6 according to the present invention and the comparative steels of Comparative Examples 1 to 14 were all produced by the following steps: (1) Continuously cast slabs were obtained by smelting and casting with the chemical compositions shown in Tables 1-1 and 1-2.

[0049] (2) Hot rolling: The continuously cast slab was first heated to 1160-1190°C, kept at that temperature for 150 minutes or more, and then subjected to finish hot rolling at 850-890°C. After rolling, the slab was rapidly cooled at a rate of 30-80°C / s, and then coiled at a coiling temperature of 500-540°C, followed by air cooling.

[0050] (3) Cold rolling: The steel coil was cold rolled at a cold rolling reduction of 50 to 70%.

[0051] (4) Annealing: The annealing temperature was 825 to 855°C, preferably 830 to 840°C, and the annealing time was 40 to 200 seconds. The steel was cooled at a rate of 3 to 5°C / s to the quenching start temperature, and then rapidly cooled at a rate of 40 to 100°C / s. The quenching start temperature was 735 to 760°C, and the quenching completion temperature was 265 to 290°C.

[0052] (5) Tempering: The tempering temperature was 265 to 290°C, and the tempering time was 100 to 400 s.

[0053] (6) Leveling: The leveling reduction rate was ≦0.3% to obtain the finished dual-phase steel. In the technical solution designed by the present invention, the chemical composition and related processes of the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 prepared by the present invention as described above all meet the design criteria requirements of the present invention.

[0054] In contrast, the comparative steel materials of Comparative Examples 1 to 14 were still produced by the above process according to the compositions in Tables 1-1 and 1-2, but in order to demonstrate the superiority of the technical solution of the present invention, the comparative steel materials of Comparative Examples 1 to 14 have parameters in their chemical compositions and / or related processes that do not meet the design requirements of the present invention.

[0055] Specifically, the comparative steel materials of Comparative Examples 1 to 6 all have parameters in their chemical compositions that do not satisfy the design requirements of the present invention. And, while the chemical compositions of the steel materials of Comparative Examples 7 to 14 satisfy the design requirements of the present invention, the related processes all have parameters that do not satisfy the design criteria of the present invention.

[0056] Tables 2-1 and 2-2 show specific parameters in the above process steps (1) to (6) for the 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 and the comparative steels of Comparative Examples 1 to 14.

[0057] [Table 2-1]

[0058] [Table 2-2]

[0059] It should be noted that in Table 2-2 above, the quenching completion temperature for each example and comparative example is equal to the tempering temperature, because in the actual process, tempering is performed immediately after quenching is completed.

[0060] Furthermore, after completing the above manufacturing process, the inventors sampled the produced dual-phase steel products of Examples 1 to 6 and Comparative Examples 1 to 14 to obtain corresponding sample steel plates. When the microstructures of the sample steel plates of the Examples and Comparative Examples were observed and analyzed using an optical microscope, it was found that the microstructures of the 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 and the comparative steels of Comparative Examples 1 to 14 were all martensite + ferrite.

[0061] In this regard, the inventors further analyzed the microstructures of the steel sheets of each Example and Comparative Example, and obtained test results for the martensite phase fraction, martensite grain size, ferrite grain size, and microhardness difference ΔHV between martensite and ferrite in the microstructures of the steel sheets of Examples 1 to 6 and Comparative Examples 1 to 14. Specifically, the relevant test results are shown in Table 3 below. In this specification, the phase fraction refers to the proportion of each phase in the microstructure measured by the area method, and the grain size refers to the grain size of each microstructure, based on the average values ​​in the horizontal and vertical directions. The phase fraction and grain size were observed using an optical microscope and measured using analysis software attached to the optical microscope. The microhardness was measured using a Webster microhardness tester.

[0062] [Table 3]

[0063] From Table 3 above, it can be seen that in the present invention, the microstructures of the 100 kg class cold-rolled low-alloy annealed dual-phase steels produced in Examples 1 to 6 are all martensite + ferrite, the volume percent content (phase proportion) of martensite is 62 to 82%, the grain size of martensite is 3.9 to 4.7 μm, the grain size of ferrite is 4.0 to 4.6 μm, and the microhardness difference △HV between martensite and ferrite is 95 to 115.

[0064] After completing the above observations and analyses, the 100 kgf / cm2 cold-rolled, low-alloy, annealed dual-phase steels of Examples 1 to 6 and the comparative steels of Comparative Examples 1 to 14 were sampled to obtain corresponding sample steel plates in order to confirm the performance of the steels of each Example and Comparative Example. The mechanical properties of the obtained sample steel plates of Examples 1 to 6 and Comparative Examples 1 to 14 were tested to obtain data on the mechanical properties of the steels of Examples 1 to 6 and Comparative Examples 1 to 14. The relevant test results are shown in Table 4 below.

[0065] The relevant mechanical performance test methods are as follows: Tensile test: Using the room temperature tensile test method for metallic materials in GB / T228-2010, the yield strength, tensile strength, and A50 gauge breaking elongation of the steel materials obtained in Examples 1 to 6 and Comparative Examples 1 to 14 were determined. Note that the A50 gauge breaking elongation represents the breaking elongation when the parallel length*width of the tensile test sample is 50 mm*25 mm.

[0066] Bending property test: The 90-degree bending property R / t of the steel materials obtained in Examples 1 to 6 and Comparative Examples 1 to 14 was determined using the GB / T232-2010 metallic material bending test method.

[0067] Table 4 shows the results of measuring the mechanical properties of the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 and the comparative steels of Comparative Examples 1 to 14.

[0068] [Table 4]

[0069] From Table 4, it can be seen that the 100 kg class cold rolled low alloy annealed dual phase steels of Examples 1 to 6 manufactured by the technical solution designed by the present invention have excellent mechanical properties, with a yield strength of 585 to 655 MPa, a tensile strength of 1002 to 1054 MPa, and an A 50 It can be seen that the gage fracture elongation is 12.7 to 15.5%, and the 90-degree bending property R / t is 0.6 to 1.0. The dual-phase steels of each example achieved tensile strengths exceeding 1000 MPa without adding valuable alloying elements such as Mo or Cr. All of them were 100 kgf / cm2-class cold-rolled low-alloy annealed dual-phase steels, and at the same time, they had good elongation and bending properties.

[0070] Compared with the 100 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6, the comparative steels of Comparative Examples 1 to 14 had parameters in their chemical composition design and / or related manufacturing processes that did not meet the requirements of the present invention, and therefore their overall performance was clearly inferior.

[0071] As described above, the present invention provides a dual-phase steel that combines a rational chemical composition with an optimal process, has a tensile strength of over 1000 MPa, and at the same time has good elongation and bending properties, achieving both low cost and excellent mechanical performance.

[0072] It should be noted that the combination of the technical features in this application is not limited to the combinations described in the claims or the specific embodiments, and all the technical features described in this application may be freely combined or combined in any manner as long as they are not inconsistent with each other.

[0073] Furthermore, it should be noted that the above-mentioned embodiments are merely specific embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments, and similar changes and modifications thereof are directly obtained or easily conceived by those skilled in the art from the disclosure of the present invention, and therefore, all of them should fall within the protection scope of the present invention.

Claims

1. It contains Fe and unavoidable impurity elements, and further contains the following chemical elements in mass percent: 0.1%<C≦0.13%, Si: 0.5% to 0.8%, Mn: 1.6% to 1.8%, Al: 0.01% to 0.03%, Nb: 0.01 to 0.03%, Ti: 0.01 to 0.03%, B: 0.0020 to 0.0030%; Its chemical elements do not contain Mo and Cr; The microstructure of the 100 kgf / cm2 cold-rolled low-alloy annealed duplex steel is martensite + ferrite.

2. 100 kg class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the mass percent contents of each chemical element thereof are as follows: 0.1%<C≦0.13%, Si: 0.5% to 0.8%, Mn: 1.6% to 1.8%, Al: 0.01% to 0.03%, Nb: 0.01 to 0.03%, Ti: 0.01 to 0.03%, B: 0.0020 to 0.0030%, and the remainder is Fe and other unavoidable impurities.

3. 3. The 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the unavoidable impurities are P≦0.012%, S≦0.0025%, and N≦0.005%.

4. 3. The 100 kg class cold-rolled low-alloy annealed dual-phase steel according to claim 1 or 2, wherein the mass percent content of each chemical element satisfies at least one of the following conditions: Nb: 0.015-0.025%, Ti: 0.015-0.025%.

5. 3. The 100 kg class cold rolled low alloy annealed dual phase steel according to claim 1 or 2, wherein the volume percent content of martensite is ≥ 60%.

6. 3. The 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the hardenability coefficient YQ is 2.0≦YQ≦2.4, where YQ=Mn+200×B, and the numerical value before the mass percent symbol is substituted for each chemical element in the formula.

7. 3. The 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the grain sizes of martensite and ferrite are both 5 μm or less.

8. 3. The 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the microhardness difference ΔHV between martensite and ferrite is 150 or less.

9. 3. The 100 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the steel has a yield strength of ≥ 550 MPa, a tensile strength of ≥ 1000 MPa, an A50 gauge elongation at break of ≥ 12%, and a 90-degree bending property R / t of ≤ 1.

0.

10. A method for producing a 100 kg class cold-rolled low-alloy annealed dual-phase steel according to any one of claims 1 to 9, comprising the following steps: (1) Smelting and foundry; (2) Hot rolling: The continuously cast slab is first heated to 1160-1190°C, kept at this temperature for 150 minutes or more, and then subjected to finish hot rolling at 850-890°C. After rolling, the slab is rapidly cooled at a rate of 30-80°C / s, and then coiled at a coiling temperature of 500-540°C, followed by air cooling; (3) cold rolling; (4) Annealing: the annealing soaking temperature is 825 to 855°C, the annealing time is 40 to 200 seconds, and then the quenching is started at a rate of 3 to 5°C / s, and then rapidly cooled at a rate of 40 to 100°C / s; however, the quenching start temperature is 735 to 760°C, and the quenching completion temperature is 265 to 290°C; (5) Tempering; (6) Leveling.

11. The manufacturing method according to claim 10, wherein in step (4), the annealing soaking temperature is 830 to 840°C.

12. The method according to claim 10, wherein in step (3), the cold rolling reduction is 50 to 70%.

13. The manufacturing method according to claim 10, wherein in step (5), the tempering temperature is 265 to 290 ° C. and the tempering time is 100 to 400 s.

14. The method of manufacturing according to claim 10, wherein in step (6), the leveling reduction is ≦0.3%.

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