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

Abstract

The present invention discloses a 60 kg cold-rolled low-alloy annealed duplex steel containing Fe and inevitable impurity elements, and the following chemical elements in the following mass percent contents: C: 0.08%-0.1%, Si: 0.1%-0.2%, Mn: 1.2%-1.4%, Al: 0.01%-0.02%, and B: 0.0020-0.0030%; these chemical elements do not include Mo or Cr. The microstructure of the 60 kg cold-rolled low-alloy annealed duplex steel is martensite and ferrite. Accordingly, the present invention also discloses a method for manufacturing the 60 kg cold-rolled low-alloy annealed duplex steel. The 60 kg cold-rolled low-alloy annealed duplex steel, obtained by combining rational chemical composition design and an optimization process, combines low cost with excellent mechanical properties and has excellent prospects for use and application value.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a metallic material and a manufacturing method thereof, and more particularly to a dual-phase stainless steel and a manufacturing method thereof. [Background technology]

[0002] Background technology With the global energy crisis and the intensification of environmental problems, energy conservation and safety have become the main development directions of the automobile manufacturing industry, among which reducing vehicle weight is one of the measures to save energy and reduce emissions. In practical applications, high-strength duplex stainless steel has good mechanical properties and service performance, so it is effectively used in the production and manufacturing of vehicle structural parts.

[0003] At present, with the development of high-strength steel and changes in the market, the market and users generally expect high-strength steel to be economical and have better performance. With the continuous development of the trend of lightweighting and energy saving in the automotive industry, and the rapid improvement of steel mill levels both at home and abroad, especially in China, the future development of duplex stainless steel will inevitably be dominated by the combination of low cost and high performance.

[0004] Currently, in the field of advanced technology, researchers have made extensive research into high-strength dual-phase steel and have achieved some research results.

[0005] For example, a Chinese patent document entitled "590 MPa grade cold-rolled dual-phase steel without surface stripe defects and manufacturing method thereof" with publication number CN109112433A and publication date January 1, 2019, discloses a 590 MPa grade cold-rolled dual-phase steel without surface stripe defects, the composition of which is, in weight percent, C: 0.050% to 0.100%, Si≦0.25%, Mn: 1.20% to 2.00%, P ≦0.012%, S≦0.008%, Al: 0.05%-0.10%, Sb: 0.015-0.050%, and the balance being Fe and other unavoidable impurities. The production method used in this technical proposal includes smelting, continuous casting, hot charging, high-pressure water descaling and rough rolling, finish rolling, laminar cooling, coiling, hot-rolled strip pickling, cold continuous rolling, continuous annealing, blast cooling, and leveling coiling. The 590 MPa-grade cold-rolled duplex stainless steel produced by this technical proposal has a bright surface, is free of streaks, has excellent corrosion resistance and coating adhesion, and exhibits excellent mechanical properties. However, research has revealed that the chemical composition of this technical proposal requires the addition of Sb and a relatively high Mn content.

[0006] Another example is the Chinese patent publication No. CN109943778A, published on June 28, 2019, titled "590 MPa-class cold-rolled duplex steel with excellent hole expansion performance and its manufacturing method." This publication discloses a 590 MPa-class cold-rolled duplex steel with excellent hole expansion performance and its manufacturing method. Its chemical composition is C: 0.06-0.09%, Si+Mn: 1.4-2.1%, Nb: 0.01-0.02%, Al: 0.03-0.06%, P≦0.020%, S≦0.010%, N≦0.006%, with the balance being Fe and unavoidable impurities. The main problem with this steel is its high Mn content, which, in turn, contains Nb, a valuable alloy, resulting in high alloy costs.

[0007] As another example, a Chinese patent document with publication number CN103088258A, publication date May 8, 2013, and title "590MPa grade dual-phase steel and its manufacturing method" states that 590MPa A grade duplex stainless steel is disclosed, the mass percentages of whose components are C≦0.20%, Si≦1.80%, Mn≦2.00%, P≦0.050%, S≦0.015%, Nb≦0.10%, Ti≦0.10%; the production method adopted in this technical solution includes molten iron pretreatment-converter smelting-alloy fine-tuning station-LF-continuous casting-hot continuous rolling, in which the hot continuous rolling process has a heating temperature of 1150-1250°C, a final rolling temperature of 800-900°C, and after rolling, rapid cooling to 650-750°C, air cooling for 6-11 seconds, and then rapid cooling to the target coiling temperature of 400-500°C. This technical solution achieves precise control of the ferrite and bainite two-phase composition and mixing ratio through appropriate composition and process control, effectively reducing the strength difference between the soft and hard phases in the material and eliminating the soft-hard phase interface, resulting in products with excellent strength, good plasticity and toughness matching, and excellent elongation and flanging performance. However, the steel designed by this technical solution has a high carbon equivalent and a high Si and Mn alloy content, which is unfavorable for welding and surface quality, and does not have the characteristics of balanced performance.

[0008] As a result, although some of the existing patented technologies for designing 590MPa dual-phase stainless steels have better forming performance, these proposals use high C and Si contents or contain higher amounts of alloying elements such as Cr and Mn, which not only adversely affect the weldability, surface quality, and phosphate treatment performance of the steel, but also increase costs.

[0009] Therefore, the present invention aims to develop a new 60 kg class cold-rolled low-alloy annealed dual-phase steel that combines low cost and excellent mechanical properties to meet the current market needs. Summary of the Invention [Problem to be solved by the invention]

[0010] Contents of the invention One of the objectives of the present invention is to provide a new 60 kg cold-rolled low-alloy annealed duplex steel. This 60 kg cold-rolled low-alloy annealed duplex steel has a reasonable chemical composition design, which ensures low cost while providing excellent mechanical properties, such as yield strength ≥ 340 MPa, tensile strength ≥ 600 MPa, and A 50 The gauge length elongation at break is ≥ 25%, and it has the characteristics of high strength and excellent elongation, and has excellent usage prospects and application value. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention provides a 60 kgf / cm2 grade cold-rolled low-alloy annealed dual-phase steel containing Fe and inevitable impurity elements, and further containing the following chemical elements in the following mass percent contents: C:0.08%~0.1%, Si:0.1%~0.2%, Mn:1.2%~1.4%, Al:0.01%~0.02%, B:0.0020~0.0030%; Its chemical elements do not include Mo and Cr; The microstructure of the above 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel is martensite + ferrite.

[0012] Furthermore, in the 60 kg grade cold rolled low alloy annealed dual phase steel described in the present invention, the mass percent content of each chemical element is: C: 0.08% to 0.1%, Si: 0.1% to 0.2%, Mn: 1.2% to 1.4%, Al: 0.01% to 0.02%, B: 0.0020 to 0.0030%, and the balance is Fe and unavoidable impurities.

[0013] In the present invention, when designing the chemical composition of the dual-phase steel, a composition system mainly composed of C-Si-Mn is adopted, and at the same time, the Mn content is further reduced by adding a small amount of the high-hardenability element B. By using the above-mentioned appropriate composition design, the present invention can obtain a dual-phase steel with a strength of 60 kgf / cm2, which combines low cost with excellent mechanical properties, without adding precious alloying elements such as Mo and Cr.

[0014] In the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel described in the present invention, the design principles of each chemical element are as follows: C: In the 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel described in the present invention, the addition of C can improve the strength of the steel and the hardness of the martensite in the steel. If the C content in the steel is less than 0.08%, the strength of the steel sheet will be affected and the amount and stability of austenite will be adversely affected. On the other hand, if the C content in the steel is greater than 0.1%, the hardness of the martensite will be too high, the grain size will be too large, which will adversely affect the formability of the steel sheet, and the carbon equivalent will be too high, which will adversely affect the welding use of the steel material. Therefore, to ensure the performance of the steel material, the mass percent content of C in the 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel described in the present invention is specifically controlled to be between 0.08% and 0.1%.

[0015] Si: In the 60 kgf / cm2 cold-rolled, low-alloy, annealed duplex steel described in this invention, adding Si improves hardenability. Furthermore, the dissolved Si in the steel affects dislocation interactions, increasing the work hardening rate and moderately increasing the elongation of the duplex steel, which contributes to good formability. However, the Si content in the steel should not be too high, as too high a content can be detrimental to surface quality control. Therefore, to maximize the beneficial effects of Si, the mass percent content of Si in the 60 kgf / cm2 cold-rolled, low-alloy, annealed duplex steel described in this invention is controlled to be between 0.1% and 0.2%.

[0016] Mn: In the 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel described in the present invention, the addition of Mn not only contributes to improving 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 1.2%, the strength of the steel sheet will be insufficient; if the Mn content in the steel is more than 1.4%, the strength of the steel sheet will be too high, resulting in poor formability. Therefore, to maximize the beneficial effects of Mn, the mass percent content of Mn in the 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel described in the present invention is controlled to be between 1.2% and 1.4%.

[0017] Al: In the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel described in the present invention, the addition of Al element to the steel can exert deoxidizing and grain refinement effects. Meanwhile, the lower the Al content, the more advantageous it is for smelting malleability. Therefore, in order to exert the beneficial effects of Al element, the mass percent content of Al element in the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel described in the present invention is controlled to be between 0.01% and 0.02%.

[0018] B: In the 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel described in the present invention, the addition of B element contributes to improving the hardenability of the steel and effectively increases the strength of the steel sheet. If the B element content in the steel is less than 0.0020%, the strength of the steel sheet will be insufficient; if the B element content in the steel is more than 0.0030%, the strength of the steel sheet will be too high and the formability will be reduced. Therefore, in the 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel described in the present invention, the mass percent content of B element is controlled to be between 0.0020% and 0.0030%.

[0019] The present invention, by designing the chemical composition of the dual-phase steel described above, eliminates the need for adding valuable alloying elements such as Mo and Cr, ensuring economic efficiency. When designing the chemical composition, it is important to note that sufficient amounts of C, Mn, and B must be added to provide the dual-phase steel with sufficient hardenability and ensure a 60 kg tensile strength at a continuous annealing gas cooling rate of 40-100°C / s. However, the contents of C, Mn, and B in the dual-phase steel must not be too high, otherwise the resulting dual-phase steel will have poor welding and forming performance.

[0020] Furthermore, in the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel according to the present invention, the unavoidable impurities are P≦0.015%, S≦0.005%, and N≦0.005%.

[0021] In the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel described in the present invention, P, N, and S are all impurity elements in the steel. The lower the P, N, and S content in the steel, the better the performance of the steel. Specifically, MnS, which is formed in combination with S, has a significant impact on forming performance, and N tends to cause cracks and bubbles on the slab surface. Therefore, to obtain steel with better performance and high quality, it is necessary to reduce the content of impurity elements in the steel as much as possible within technical conditions, and specifically control the P, S, and N elements in the steel to meet the requirements of P≦0.015%, S≦0.005%, and N≦0.005%.

[0022] Furthermore, in the 60 kg grade cold rolled low alloy annealed dual phase steel according to the present invention, the volume percent content of martensite is >40% and ≦70%.

[0023] Furthermore, in the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel described in the present invention, its hardenability factor Y Q is 1.9≦Y Q ≦2.1, but Y Q =Mn+200×B, Substitute the numerical value before the mass percent symbol for each chemical element in the formula.

[0024] In the above-described embodiment of the present invention, the present invention controls the mass percent content of a single chemical element in the steel while also further controlling the elemental composition in the steel, i.e., the calculated hardenability factor Y Q is 1.6≦Y Q The Mn and B elements may be controlled so as to satisfy the condition of ≦2.0. Q = Mn + 200 × B. In some embodiments, the hardenability factor Y Q is 1.7≦Y Q ≦1.95.

[0025] In the present invention, the hardenability factor Y Q indicates the combined effect of B and Mn elements in steel, and the hardenability factor Y Q By controlling the content of Cr within the above range, it is possible to reduce the cost and further improve the mechanical properties, particularly the strength, of the dual-phase stainless steel.

[0026] In addition, in alloy design, the Mn content is the maximum equivalent that affects the overall cost. Therefore, in the present invention, by adding an appropriate amount of B, the Mn content can be further reduced, which is advantageous for cost reduction. At the same time, the combined hardenability of Mn and B can be utilized to further improve the mechanical properties of the dual-phase steel, which is also advantageous for improving the processing performance in on-site production, including the rolling stability in hot rolling and cold rolling.

[0027] Furthermore, in the 60 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel described in the present invention, the grain sizes of both martensite and ferrite are 15 μm or less.

[0028] In the above technical solution of the present invention, the grain sizes of martensite and ferrite in the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel are both 15 μm or less, which is helpful in improving the strength and processing performance of the steel.

[0029] Furthermore, in the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel described in the present invention, the martensite grain size is between 9.6-14.2 μm, and the ferrite grain size is between 10.7-14.5 μm.

[0030] Furthermore, in the 60 kg grade cold rolled low alloy annealed dual phase steel according to the present invention, the volume percent content of martensite is >40% and ≦70%, preferably the volume percent content of martensite is between 42-65%.

[0031] Furthermore, in the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel described in the present invention, its yield strength is ≥ 340 MPa, preferably ≥ 350 MPa, tensile strength is ≥ 600 MPa, preferably ≥ 620 MPa, A 50 The gauge length elongation at break is ≧25%, preferably ≧27%.

[0032] In some embodiments, the 60 kgf / cm2 cold rolled low alloy annealed dual phase steel described in the present invention has a yield strength of ≥ 360 MPa, a tensile strength of ≥ 630 MPa, and an A 50 Gauge length elongation at break ≥ 27%.

[0033] In some embodiments, the 60 kg cold rolled low alloy annealed dual phase steel described in the present invention has a yield strength between 352 and 390 MPa, a tensile strength between 603 and 683 MPa, and an A 50 The gauge length elongation at break is between 25.8 and 30.3%.

[0034] In some embodiments, the 60 kg class cold rolled low alloy annealed duplex stainless steel described in the present invention can withstand forces greater than 60 kg per square centimeter, preferably greater than 60-70 kg per square centimeter, and more preferably greater than 63-70 kg per square centimeter.

[0035] Accordingly, another object of the present invention is to provide a method for producing the above-mentioned 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel, which is convenient and easy to implement, and by employing this method, the 60 kgf / cm2 cold-rolled low-alloy annealed duplex steel described in the present invention can be effectively produced.

[0036] To achieve the above object, the present invention proposes a method for producing the above 60 kg grade cold-rolled low-alloy annealed dual-phase steel, which includes 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, 150-200 minutes), and then hot rolled to 850-890°C for final rolling. After rolling, the slab is rapidly cooled at a rate of 30-80°C / s; then, the slab is coiled, and the coiling temperature is set to 500-540°C, and the slab is air-cooled after coiling; (3) cold rolling; (4) Annealing: The annealing temperature is set to 825-855°C, and the annealing time is set to 40-200s. Then, the annealing is performed at a rate of 3-5°C / s to a quenching start temperature of 735-760°C, and then the quenching is performed at a rate of 40-100°C / s, and the quenching end temperature is controlled to 220-260°C; (5) Tempering; (6) Leveling.

[0037] In the above technical solution of the present invention, the inventors have optimized the annealing process, specifically controlling the annealing soaking temperature to 825-855°C, preferably 830-840°C. By controlling the annealing soaking temperature within the above numerical range, the grain size of the resulting dual-phase steel becomes finer, and the mechanical properties and formability are better.

[0038] Furthermore, in the manufacturing method of the present invention, the annealing soaking temperature is set to 830 to 840°C in step (4).

[0039] Furthermore, in the manufacturing method described in the present invention, in step (2), the continuously cast slab is first heated to 1160 to 1190°C, and after keeping the temperature for 150 minutes or more, it is subjected to final hot rolling at 850 to 890°C, and after rolling, it is quenched at a rate of 30 to 80°C / s; thereafter, it is coiled, the coiling temperature is set to 500 to 540°C, and after coiling, it is air-cooled.

[0040] Furthermore, in the manufacturing method described in the present invention, in step (3), the cold rolling reduction is controlled to 50 to 70%.

[0041] In the manufacturing method described in the present invention, the tempering temperature is controlled to 220 to 260° C. and the tempering time is controlled to 100 to 400 seconds in step (5).

[0042] Furthermore, in the manufacturing method described in the present invention, the leveling reduction is controlled to ≦0.5% in step (6).

[0043] The 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel and its manufacturing method described in the present invention have the following advantages and beneficial effects compared with the prior art: The present invention develops a new 60 kg class cold-rolled low-alloy annealed dual-phase steel. By adopting a rational chemical composition design and optimizing the manufacturing process, it is possible to obtain dual-phase steel that combines low cost with excellent performance (especially high strength and excellent elongation) without adding Mo or Cr.

[0044] The 60 kg cold rolled low alloy annealed dual phase steel designed in this invention has high strength and excellent elongation, its yield strength ≥ 340 MPa, tensile strength ≥ 600 MPa, A 50 The gauge length elongation at break is ≥ 25%, which can effectively meet the needs of the market and users, and has excellent usage prospects and application value. DETAILED DESCRIPTION OF THE INVENTION

[0045] Specific Embodiments The 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel and its manufacturing method according to the present invention will be further explained and illustrated below with reference to specific examples, but these explanations and interpretations should not be construed as unduly limiting the technical solutions of the present invention. [Example]

[0046] Examples 1 to 6 and Comparative Examples 1 to 14 Tables 1-1 and 1-2 show the mass percentage blends of each chemical element designed for the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 and the comparative steels of Comparative Examples 1 and 2.

[0047] [Table 1-1]

[0048] Table 1-2 shows the hardenability coefficient Y of the 60 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

[0049] [Table 1-2]

[0050] The 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1-6 and Comparative Examples 1-14 were manufactured by the following steps: (1) Smelting and casting were carried out according to the chemical composition designs shown in Tables 1-1 and 1-2, and continuous cast slabs were produced.

[0051] (2) Hot rolling: The continuously cast slab is hot rolled, where the continuously cast slab is first heated to 1160-1190°C, kept at that temperature for 150 minutes or more, and then hot rolled at a temperature of 850-890°C. After rolling, the slab is rapidly cooled at a rate of 30-80°C / s, and then coiled. The coiling temperature is controlled to 500-540°C, and the slab is air-cooled after coiling. (3) Cold rolling: The steel roll was cold rolled, and the cold rolling reduction was controlled to 50-70%.

[0052] (4) Annealing: The annealing soaking temperature was controlled to 825 to 855°C, preferably 830 to 840°C, and the annealing time was controlled to 40 to 200 s. Thereafter, the steel was cooled at a rate of 3 to 5°C / s to a quenching start temperature of 735 to 760°C, and then quenched at a rate of 40 to 100°C / s, and the quenching end temperature was controlled to 220 to 260°C.

[0053] (5) Tempering: Tempering temperature is 220~260 o C, and the tempering time was set to 100 to 400 seconds.

[0054] (6) Leveling: The leveling reduction was controlled to ≦0.5% to obtain the finished dual-phase steel.

[0055] In the technical solution designed by the present invention, the chemical composition design and related processes of the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1-6 prepared by the present invention as described above all meet the requirements of the design criteria of the present invention.

[0056] Accordingly, the comparative steel materials of Comparative Examples 1 to 14 were manufactured by adopting the component composition schemes of Tables 1-1 and 1-2 and combining the above-mentioned processes. However, in order to demonstrate the advantages of the technical solution of the present invention, the comparative steel materials of Comparative Examples 1 to 14 all have parameters in their chemical compositions and / or related manufacturing processes that do not meet the design requirements of the present invention.

[0057] Specifically, the chemical compositions of the comparative steels of Comparative Examples 1 to 6 all have parameters that do not satisfy the design requirements of the present invention; on the other hand, the chemical compositions of the steels corresponding to Comparative Examples 7 to 14 satisfy the design requirements of the present invention, but the parameters of the related processes have parameters that do not satisfy the design criteria of the present invention.

[0058] Tables 2-1 and 2-2 show the specific process parameters of the above steps (1) to (6) for the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1-6 and the comparative steels of Comparative Examples 1-14.

[0059] [Table 2-1] TIFF2025528255000004.tif133131

[0060] [Table 2-2] TIFF2025528255000006.tif133146

[0061] In Table 2-2 above, the quenching end temperature for each example and comparative example is the same as the tempering temperature, because in actual process operations, tempering is performed immediately after the quenching operation is completed.

[0062] Accordingly, after completing the above manufacturing process, the inventors sampled the finished dual-phase steels of Examples 1 to 6 and Comparative Examples 1 to 14, obtained corresponding sample steel plates, and observed and analyzed the microstructures of the sample steel plates of each Example and Comparative Example. Through the observations, it was found that the microstructures of the 60 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.

[0063] Therefore, the inventors further analyzed the microstructures of the steel sheets of Examples 1 to 6 and Comparative Examples 1 to 14 to obtain the martensite phase ratio, martensite grain size, and ferrite grain size in the microstructures of the steel sheets of each Example and Comparative Example, and the related test results are specifically shown in Table 3 below.

[0064] [Table 3]

[0065] As can be seen from Table 3 above, in the present invention, the microstructures of the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels produced in Examples 1 to 6 are all martensite + ferrite, and the volume percent content (phase ratio) of their martensite is between 42 and 65%, the martensite grain size is between 9.6 and 14.2 μm, and the ferrite grain size is between 10.7 and 14.5 μm.

[0066] In the present invention, in order to verify the performance of the steel materials of each example and comparative example, the obtained 60 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steels of Examples 1 to 6 and the comparative steel materials of Comparative Examples 1 to 14 were sampled to obtain corresponding sample steel plates. Tensile tests were performed on the obtained sample steel plates of Examples 1 to 6 and Comparative Examples 1 to 14 to obtain performance data of the steel materials of Examples 1 to 6 and Comparative Examples 1 to 14, and the test results of the related tests are listed in Table 3 below.

[0067] The methods for testing the relative mechanical performance are as follows: Tensile test: A tensile test was performed according to GB / T 228.1-2010 "Method for room temperature tensile test of metallic materials." The yield strength, tensile strength and A 50 The gauge length elongation at break was measured and the kiloforce was calculated based on the results, where A 50 The gauge breaking elongation is indicated for a tensile test specimen having a parallel length x width of 50 mm x 25 mm.

[0068] Table 3 shows the test results of the mechanical properties of the 60 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.

[0069] [Table 3]

[0070] As can be seen from Table 3, the 60 kg cold-rolled low-alloy annealed dual-phase steels of Examples 1-6 manufactured by the technical solutions designed in the present invention have fairly good mechanical properties, with their yield strengths ranging from 352 to 390 MPa, tensile strengths ranging from 603 to 683 MPa, and A 50 The gauge length elongation at break is between 25.8% and 30.3%. The duplex stainless steels of each example achieve a tensile strength of over 600 MPa without adding valuable alloying elements such as Mo or Cr. All of them are 60 kgf / cm2 cold-rolled low-alloy annealed duplex stainless steels, and have good elongation.

[0071] Compared with the 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steels of Examples 1-6, the comparative steels of Comparative Examples 1-14 have parameters in their chemical compositions and / or related manufacturing processes that do not meet the design requirements of the present invention, and therefore their overall performance is obviously inferior.

[0072] As can be seen from the above, in the present invention, by combining reasonable chemical composition design and optimization process, a phase steel with low cost and excellent performance is obtained, and its mechanical properties are excellent, and the yield strength is all ≧340 MPa, the tensile strength is all ≧600 MPa, and A 50 The gauge length elongation at break is all ≥ 25%, and the application prospects are good.

[0073] Furthermore, the combinations of the technical features in this application are not limited to the combinations described in the claims of this application or the combinations described in the specific examples, and as long as there are no contradictions, all technical features described in this application can be freely combined or combined in any form.

[0074] 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 it is clear that any similar changes or modifications that can be directly derived or easily conceived by those skilled in the art from the disclosure of the present invention are included in the protection scope of the present invention.

Claims

1. A 60 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel containing Fe and inevitable impurity elements, and further containing the following chemical elements in the following mass percent contents: C: 0.08% to 0.1%, Si: 0.1% to 0.2%, Mn: 1.2% to 1.4%, Al: 0.01% to 0.02%, B: 0.0020 to 0.0030%; Its chemical elements do not include Mo and Cr; The microstructure of the above-mentioned 60 kg class cold-rolled low-alloy annealed dual-phase steel is martensite + ferrite.

2. The mass percent content of each chemical element is: C: 0.08% to 0.1%, Si: 0.1% to 0.2%, Mn: 1.2% to 1.4%, Al: 0.01% to 0.02%, B: 0.0020 to 0.0030%, and the balance is Fe and unavoidable impurities.

2. The 60 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1.

3. 3. The 60 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the unavoidable impurities are P≦0.015%, S≦0.005%, and N≦0.005%.

4. 3. The 60 kg grade cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the volume percent content of martensite is >40% and ≦70%, preferably the volume percent content of martensite is between 42 and 65%.

5. Hardenability factor Y Ｑ is 1.9≦Y Ｑ ≦2.1, provided that Y Ｑ 3. The 60 kgf / cm2 cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the mass percent symbol is substituted for each chemical element in the formula.

6. 3. The 60 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, wherein the grain sizes of both martensite and ferrite are 15 μm or less.

7. Yield strength ≥ 340 MPa, tensile strength ≥ 600 MPa, A ５０ 3. The 60 kgf / cm2 class cold-rolled low-alloy annealed dual-phase steel according to claim 1, characterized in that the gauge length elongation at break is ≥ 25%.

8. Yield strength ≥ 360 MPa, tensile strength ≥ 630 MPa, A ５０ 8. The 60 kgf / cm2 grade cold-rolled low-alloy annealed dual-phase steel according to claim 7, characterized in that the gauge length elongation at break is ≥ 27%.

9. 3. The 60 kg class cold-rolled low-alloy annealed dual-phase steel according to claim 1 or 2, characterized in that it can withstand a force of more than 60 kg per square centimeter, preferably more than 60 to 70 kg per square centimeter.

10. A method for producing a 60 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 hot rolled to 850-890°C for final rolling. After rolling, the slab is quenched at a rate of 30-80°C / s; then, the slab is coiled, and the coiling temperature is set to 500-540°C, and the slab is air-cooled after coiling; (3) cold rolling; (4) Annealing: The annealing soaking temperature is 825-855°C, and the annealing time is 40-200s. Then, the quenching is started at a rate of 3-5°C / s to a quenching start temperature of 735-760°C, and then quenched at a rate of 40-100°C / s, and the quenching end temperature is controlled to be 220-260°C; (5) Tempering; (6) Leveling.

11. The method according to claim 10, wherein in step (4), the annealing soaking temperature is set to 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, characterized in that in step (5), the tempering temperature is controlled to 220 to 260°C, and the tempering time is controlled to 100 to 400 seconds.

14. 11. The manufacturing method according to claim 10, wherein in step (6), the leveling reduction is controlled to be ≦0.5%.

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