A high-surface-hardness high-strength high-plasticity steel with a yield strength of 600 MPa and a manufacturing method thereof

Abstract

The application discloses a yield 600MPa high surface hardness high strength high plasticity steel, which is characterized by the following chemical components: C: 0.13-0.19%, Si: ≤0.10%, Mn: 1.5-2.0%, P: ≤0.020%, S: ≤0.004%, Ti: 0.075-0.130%, Nb: 0.03-0.06%, and the balance is iron and inevitable impurities; the manufacturing method comprises the following steps: the billet is put into the furnace at a temperature of greater than or equal to 900 DEG C, the heating temperature is controlled to be 1200-1240 DEG C, and the heating time is greater than or equal to 70 min; the rough rolling end temperature is controlled to be 1080-1120 DEG C; the finish rolling final rolling temperature is controlled to be 800-880 DEG C; the first section adopts high-pressure water cooling, the steel plate cooling speed is 80-210 DEG C / s, and the cooling is stopped at 600-640 DEG C; the second section adopts air cooling, and the cooling time is 3-6 s; the third section adopts laminar flow water cooling, and the cooling speed is 60-80 DEG C / s; and the coiling temperature is controlled to be 500-580 DEG C; the product yield strength is greater than or equal to 600 MPa, the tensile strength is 700-820 MPa, the elongation A is greater than or equal to 23%, and the steel surface hardness HV0.1 is greater than or equal to 220.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a high-strength, high-plasticity steel with a yield strength of 600MPa and high surface hardness, and its manufacturing method. Background Technology

[0002] High-strength steel is the development trend of steel markets such as automobiles, construction machinery, and building. However, with the increase in steel strength and the reduction in thickness and weight, a series of processing and service problems have also been brought about. The increased difficulty in forming high-strength steel and the reduced service life after thinning have all restricted the application of high-strength steel.

[0003] Chinese patent application number CN200810026086.X discloses a 600MPa grade high-strength weathering steel and its preparation method. This 600MPa grade high-strength weathering steel is prepared using an electric furnace-slab continuous casting and rolling process. The main chemical composition of the refined molten steel used to prepare this high-strength weathering steel is: C: 0.045~0.07wt%, Si: 0.10~0.29wt%, Mn: 0.8~1.5wt%, P: 0.005~0.030wt%, S: 0.002~0.008wt%, Cu: 0.20~0.5wt%, Cr: 0.3~0.7wt%, Ni: 0.15~0.35wt%, Ti: 0.06~0.079wt%, Nb: 0.035~0.050wt%, Alt: 0.025~0.050wt%. The 600MPa grade high-strength weathering steel has advantages such as low cost, strong competitiveness, and excellent cold forming and welding performance, making it suitable for manufacturing railway vehicles, containers, bridges, heavy-duty trucks, towers, etc. This patent does not address surface hardness indicators and has a relatively low elongation.

[0004] Chinese patent application number CN202110579277.4 discloses a high-fatigue-performance 600MPa grade hot-rolled automotive beam steel strip and its preparation method. The chemical composition by mass percentage is: C 0.02 0.06%, Si≤0.08%, Mn 1.0-2.0%, P≤0.015%, S≤0.01%, Nb 0.0 01 0.015%, Ti 0.02 The composition is 0.05%, N ≤ 0.005%, with the remainder being Fe and unavoidable impurities. The preparation method sequentially includes smelting, continuous casting, heating, rough rolling, UFC intermediate billet cooling, finish rolling, laminar flow cooling, and coiling steps. The produced 600MPa grade hot-rolled automotive beam steel strip has excellent surface quality, fatigue performance, formability, and toughness. This patent does not cover surface hardness indicators and does not possess high plasticity characteristics.

[0005] Chinese patent application CN201310203012.X discloses a 600MPa grade high-strength hot-rolled structural steel and its manufacturing method. The chemical composition of the structural steel by weight percentage is: C: 0.14-0.24%, Si: ≤0.50%, Mn: 0.5-1.5%, P: ≤0.020%, S≤0.010%, Ti: 0.04-0.15%, B: 0.0005-0.003%, Al≤0.05%, with the remainder being Fe and unavoidable impurities. Based on the above composition, the structural steel of this invention is obtained through deep desulfurization of molten iron, ladle refining, continuous casting into slabs, slab reheating, controlled rolling, controlled cooling, and coiling. It exhibits a yield strength ≥600MPa, tensile strength ≥650MPa, elongation ≥16%, impact energy at -20℃ ≥100J, and excellent cold bending forming performance. The patent does not involve surface hardness indicators and does not have high plasticity characteristics.

[0006] Chinese patent application CN202011049304.9 discloses a niobium-titanium microalloyed steel plate with a yield strength of 600 MPa and resistant to acid corrosion, as well as its production method. The steel plate comprises the following chemical composition by weight percentage: C: 0.06–0.10%; Si: 0.20%–0.40%; Mn: 1.30–1.70%; P: ≤0.015%; S: ≤0.005%; Cr: 0.70–1.00%; Ni: 0.10–0.20%; Cu: 0.25–0.30%; Nb: 0.045–0.060%; Ti: 0.025–0.045%; Sb: 0.08–0.10%; Als: 0.020–0.040%; the balance being Fe and unavoidable inclusions. Furthermore, the weather resistance index I of the steel plate is greater than 6. 0.0; It is produced using a process flow of hot metal pretreatment with deep desulfurization → converter smelting → LF furnace refining → continuous casting → slab heating → rough rolling → finish rolling → laminar flow cooling → coiling; its yield strength reaches 600MPa level, and it has good resistance to acid media and atmospheric corrosion, while also possessing excellent strength-toughness matching and cold bending forming performance. This patent does not cover surface hardness indicators and does not exhibit high plasticity characteristics.

[0007] Chinese patent application CN202110398829.1 discloses a hot-rolled high-strength weather-resistant steel plate with a yield strength of 600 MPa and its production method. This belongs to the field of high-strength weather-resistant steel. The main chemical composition of the steel plate, by mass percentage, is as follows: C: 0.06%–0.09%, Si: 0.25%–0.50%, Mn: 0.40%–0.70%, P: 0.015%–0.030%, S: ≤0.005%, Cr: 0.40%–0.70%, C… The composition of this high-strength weather-resistant steel is as follows: u: 0.22%–0.40%, Als: 0.020%–0.045%, Ti: 0.055%–0.080%, N ≤ 0.0040%, O ≤ 0.0035%, with the remainder being Fe and unavoidable impurities. The chemical composition must also satisfy the condition [Ti]-3.42[N]-3[S] ≥ 0.040%. The microstructure of the steel plate is quasi-polygonal ferrite + pearlite, with a pearlite content of 3%–5%. This significantly reduces the production cost of the high-strength weather-resistant steel and provides excellent atmospheric corrosion resistance, weldability, and comprehensive mechanical properties. However, this patent does not address surface hardness and does not exhibit high plasticity.

[0008] How to ensure that the yield strength of steel reaches more than 600MPa while maintaining the surface hardness and high plasticity of the steel so that the steel has good processing performance and service life has become an urgent technical problem to be solved. Summary of the Invention

[0009] The purpose of this invention is to provide a high-strength automotive steel with a yield strength of 600MPa and high plasticity, and its manufacturing method. The steel has a yield strength ≥600MPa, a tensile strength of 700~820MPa, an elongation A ≥23%, and a surface hardness HV0.1 ≥220.

[0010] To achieve the above objectives, the following technical solution is adopted:

[0011] A high-strength, high-plasticity steel with a yield strength of 600 MPa and high surface hardness has the following chemical composition by mass percentage: C: 0.13~0.19%, Si: ≤0.10%, Mn: 1.5~2.0%, P: ≤0.020%, S: ≤0.004%, Ti: 0.075~0.130%, Nb: 0.03~0.06%, with the balance being balance iron and unavoidable impurities.

[0012] According to the above scheme, the mass percentage of Ti is 0.079 to 0.119%.

[0013] According to the above scheme, the mass percentage of Nb is 0.035% to 0.052%.

[0014] The manufacturing method of the above-mentioned high-strength, high-plasticity steel with a yield strength of 600 MPa and high surface hardness includes the following steps:

[0015] 1) Heating the billet: The billet temperature upon entering the furnace is ≥900℃, the heating temperature is controlled at 1200~1240℃, and the heating time is ≥70min;

[0016] 2) Rough rolling of the heated billet: control the finishing temperature of rough rolling at 1080~1120℃;

[0017] 3) Perform finish rolling on the slab after rough rolling: control the final rolling temperature at 800~880℃;

[0018] 4) Different media are used to cool the rolled steel plates: the first stage uses high-pressure water cooling, with a cooling rate of 80~210℃ / s, and stops when the temperature reaches 600~640℃; the second stage uses air cooling, with a cooling time of 3~6s; the third stage uses laminar flow water cooling, with a cooling rate of 60~80℃ / s.

[0019] 5) Coil the cooled steel plate: Control the coiling temperature at 500~580℃.

[0020] According to the above scheme, the heating temperature in step 1 is controlled at 1200~1230℃.

[0021] According to the above scheme, in step 4, the first stage of cooling is at a cooling rate of 90~160℃ / S to cool to 610~635℃; the second stage of air cooling takes 3.5~5.5s; and the third stage of cooling is at a cooling rate of 25~40℃ / S.

[0022] According to the above scheme, the resulting product has a yield strength ≥600MPa, a tensile strength of 700~820MPa, an elongation A ≥23%, and a surface hardness HV0.1 ≥220.

[0023] The role and rationale for controlling the main components and processes in this invention:

[0024] Carbon: Carbon is an inexpensive solid solution strengthening element. If its content is less than 0.13%, the material strength requirements cannot be met; if its content is greater than 0.19%, the material's good formability cannot be met. Therefore, its content is limited to the range of 0.13% to 0.19%.

[0025] Manganese: Manganese is the most effective element for improving strength and toughness. If its content is less than 1.50%, the material strength requirements cannot be met; however, adding too much manganese will increase the hardenability of the steel, increase the susceptibility to cracking due to the formation of a weld hardened layer, and increase the alloying cost of the steel. Therefore, its upper limit is set at 2.00%, and its content is limited to the range of 1.50% to 2.00%.

[0026] Titanium: Titanium is one of the most economical elements for improving the strength of steel. With appropriate processing to maximize TiC precipitation, steel can achieve the designed strength level. If the titanium content is below 0.075%, insufficient precipitation will result in the strength failing to reach the lower limit of the design; if the titanium content is above 0.130%, the tensile strength will exceed the upper limit, which is detrimental to part forming. Therefore, its content is limited to the range of 0.075% to 0.130%.

[0027] Niobium: Niobium primarily enhances steel strength through grain refinement and precipitation strengthening. It is a strong carbon and nitrogen compound forming element, mainly existing in steel as Nb (C, N), inhibiting austenite grain growth and ultimately reducing ferrite grain size, thus refining the microstructure. When its content is below 0.03%, the high strength requirements of the material cannot be met; while an addition of niobium above 0.06% already meets the requirements for strength and formability. Further addition would significantly increase the alloy cost. Therefore, based on the performance targets of the steel grade, its content is limited to the range of 0.03%–0.06%.

[0028] The use of different cooling media after rolling steel coils is to control the steel's microstructure and achieve a reasonable balance of high strength, high plasticity, and high surface hardness. Precipitation strengthening is utilized to enhance material strength and improve formability. The first stage of high cooling rate aims to retain fine grain size and deformation substructure in the rolled steel, improving strength and surface hardness. The second stage of air cooling aims to allow for appropriate microstructure transformation, improving plasticity. The third stage of relatively high cooling rate aims to further enhance and maintain strength and surface hardness, avoiding the decrease in strength and hardness caused by prolonged air cooling at excessively high temperatures.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] Compared with the prior art, the high-strength steel produced by this invention not only meets the high strength requirement of yield strength of 600MPa, but also has good plasticity and surface hardness, thus giving the steel good processing performance and service life.

[0031] The steel obtained by this invention has a yield strength ≥600MPa, a tensile strength of 700~820MPa, an elongation A ≥23%, and a surface hardness HV0.1 ≥220, exhibiting good surface wear resistance. Detailed Implementation

[0032] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0033] The specific embodiment provides a high-strength, high-plasticity steel with a yield strength of 600MPa and high surface hardness. Its chemical composition by mass percentage is: C: 0.13~0.19%, Si: ≤0.10%, Mn: 1.5~2.0%, P: ≤0.020%, S: ≤0.004%, Ti: 0.075~0.130%, Nb: 0.03~0.06%, with the balance being balance iron and unavoidable impurities.

[0034] In a preferred embodiment, the mass percentage of Ti is 0.079 to 0.119%.

[0035] In a preferred embodiment, the mass percentage of Nb is 0.035–0.052%.

[0036] The specific implementation also provides a method for manufacturing the above-mentioned high-strength, high-plasticity steel with a yield strength of 600 MPa and high surface hardness, including the following steps:

[0037] 1) Heating the billet: The billet temperature upon entering the furnace is ≥900℃, the heating temperature is controlled at 1200~1240℃, and the heating time is ≥70min;

[0038] 2) Rough rolling of the heated billet: control the finishing temperature of rough rolling at 1080~1120℃;

[0039] 3) Perform finish rolling on the slab after rough rolling: control the final rolling temperature at 800~880℃;

[0040] 4) Different media are used to cool the rolled steel plates: the first stage uses high-pressure water cooling, with a cooling rate of 80~210℃ / s, and stops when the temperature reaches 600~640℃; the second stage uses air cooling, with a cooling time of 3~6s; the third stage uses laminar flow water cooling, with a cooling rate of 60~80℃ / s.

[0041] 5) Coil the cooled steel plate: Control the coiling temperature at 500~580℃.

[0042] In the preferred embodiment, the heating temperature in step 1 is controlled at 1200~1230℃.

[0043] In the preferred embodiment, in step 4, the first stage of cooling is performed at a cooling rate of 90~160℃ / S to cool to 610~635℃; the second stage of air cooling takes 3.5~5.5s; and the third stage of cooling is performed at a cooling rate of 25~40℃ / S.

[0044] The chemical composition design of the specific embodiments and comparative examples is shown in Table 1.

[0045] The specific process parameters for the embodiments and comparative examples are shown in Table 2.

[0046] The specific implementation examples and comparative examples' performance characterization parameters are shown in Table 3.

[0047] Table 1

[0048]

[0049] Table 2

[0050]

[0051] Table 3

[0052]

[0053] As can be seen from the results in Table 2, the steel of this invention has a yield strength ≥600MPa, a tensile strength of 700~820MPa, an elongation A ≥23%, and a surface hardness HV0.1 ≥220, exhibiting good surface wear resistance.

Claims

1. A high-strength, high-plasticity steel with a yield strength of 600 MPa and high surface hardness, characterized in that... The chemical composition by mass percentage is as follows: C: 0.17~0.19%, Si: ≤0.10%, Mn: 1.85~2.0%, P: ≤0.020%, S: ≤0.004%, Ti: 0.075~0.130%, Nb: 0.03~0.06%, with the balance being balance iron and unavoidable impurities; the elongation of the steel is A≥23%, and the surface hardness is HV0.1≥220; The manufacturing method of the high-strength, high-plasticity steel with a yield strength of 600 MPa includes the following steps: 1) Heating the billet: The billet temperature upon entering the furnace is ≥900℃, the heating temperature is controlled at 1200~1240℃, and the heating time is ≥70min; 2) Rough rolling of the heated billet: control the finishing temperature of rough rolling at 1080~1120℃; 3) Perform finish rolling on the slab after rough rolling: control the final rolling temperature at 800~880℃; 4) Different media are used to cool the rolled steel plates: the first stage uses high-pressure water cooling, with a cooling rate of 80~210℃ / s, and stops when the temperature reaches 600~640℃; the second stage uses air cooling, with a cooling time of 3~6s; the third stage uses laminar flow water cooling, with a cooling rate of 60~80℃ / s. 5) Coil the cooled steel plate: Control the coiling temperature at 500~580℃.

2. The high-strength, high-plasticity steel with a yield strength of 600 MPa as described in claim 1, characterized in that... The mass percentage of Ti is 0.079–0.119%.

3. The high-strength, high-plasticity steel with a yield strength of 600 MPa as described in claim 1, characterized in that... The mass percentage of Nb is 0.035 to 0.052%.

4. The method for manufacturing the high-strength, high-plasticity steel with a yield strength of 600 MPa as described in claim 1, characterized in that... Includes the following steps: 1) Heating the billet: The billet temperature upon entering the furnace is ≥900℃, the heating temperature is controlled at 1200~1240℃, and the heating time is ≥70min; 2) Rough rolling of the heated billet: control the finishing temperature of rough rolling at 1080~1120℃; 3) Perform finish rolling on the slab after rough rolling: control the final rolling temperature at 800~880℃; 4) Different media are used to cool the rolled steel plates: the first stage uses high-pressure water cooling, with a cooling rate of 80~210℃ / s, and stops when the temperature reaches 600~640℃; the second stage uses air cooling, with a cooling time of 3~6s; the third stage uses laminar flow water cooling, with a cooling rate of 60~80℃ / s. 5) Coil the cooled steel plate: Control the coiling temperature at 500~580℃.

5. The manufacturing method of the high-strength, high-plasticity steel with a yield strength of 600 MPa as described in claim 4, characterized in that... In step 1, the heating temperature is controlled at 1200~1230℃.

6. The method for manufacturing high-strength, high-plasticity steel with a yield strength of 600 MPa as described in claim 4, characterized in that... In step 4, the first stage of cooling is carried out at a cooling rate of 90~160℃ / s to cool to 610~635℃; the second stage of air cooling takes 3.5~5.5s; and the third stage of cooling is carried out at a cooling rate of 62~78℃ / s.

7. The method for manufacturing high-strength, high-plasticity steel with a yield strength of 600 MPa as described in claim 4, characterized in that... The resulting product has a yield strength ≥600MPa and a tensile strength of 700~820MPa.

Images