Low-cost 800MPa-grade axle housing steel based on CSP production line and production method of low-cost 800MPa-grade axle housing steel

Abstract

The invention discloses low-cost 800MPa-grade axle housing steel based on a CSP production line. The low-cost 800MPa-grade axle housing steel is prepared from chemical components in percentage by weight as follows: 0.04%-0.07% of C, 0.05%-0.20% of Si, 1.20%-1.60% of Mn, smaller than or equal to 0.020% of P, smaller than or equal to 0.008% of S, 0.015%-0.060% of Als, 0.09%-0.15% of Ti, smaller than or equal to 0.005% of N and the balance of Fe and inevitable impurities. The thickness ranges from 1.5 mm to 6.0 mm, the yield strength is larger than or equal to 700 MPa, the tensile strength is larger than or equal to 800 MPa, the ductility A is larger than or equal to 16%, and the plate shape unevenness is smaller than or equal to 5 mm / m. The invention further discloses a production method of the steel plate, the rolling pressure of the first two times is controlled to be 2 * 10 < 4 >-3 * 10 < 4 > KN, the rolling pressure of the first four times can be reduced through the production method, the pressure is evenly distributed, and the plate shape quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge shell steel manufacturing, and specifically relates to a low-cost 800MPa-grade bridge shell steel based on a CSP production line and a production method thereof. Background Art

[0002] Bridge housing steel is widely used in automobile bridge housings, chassis and stamping structural parts. The common process route for thin hot-rolled steel is cold charging / hot charging and hot delivery of ingots + hot rolling production line rolling, which has high manufacturing energy consumption and long process time. CSP process can improve production efficiency, reduce energy consumption, and has unique advantages in producing thin high-strength steel.

[0003] The Chinese patent document with publication number CN115491589A and publication date December 20, 2022, and named "800MPa grade CSP short process hot-rolled high-strength structural steel and manufacturing method" discloses an 800MPa grade CSP short process hot-rolled high-strength structural steel and a preparation method thereof. The structural steel includes the following chemical components by weight percentage, C: 0.045~0.069%, Si: ≤0.20%, Mn: 1.3~1.7%, P: ≤0.012%, S: ≤0.003%, Ti: 0.12~0.20%, Cr: 0.15~0.50%, Als: 0.06~0.20%, As≤0.012%, N≤0.005%, and the balance is Fe and unavoidable impurities. The thin steel plate strip with a yield strength ≥800MPa produced by this invention has low process cost and alloy cost, tensile strength ≥850MPa, and elongation ≥18%, but contains the environmentally unfriendly Cr element, the alloy cost is high, and the strength is too high, which can only meet the use of automobile structural parts. Its cold bending and forming properties are insufficient and it is not suitable for the production of automobile bridge shell components. Summary of the invention

[0004] The purpose of the present invention is to address the shortcomings of the background technology and to provide a low-cost 800MPa grade bridge shell steel and production method based on the CSP production line. The low-cost alloy and process design are used to ensure the high strength and excellent cold bending performance of the bridge shell steel, and more importantly, it has extremely low plate unevenness.

[0005] To achieve the above purpose, the present invention designs a low-cost 800MPa-grade bridge shell steel based on a CSP production line, which is special in that the bridge shell steel is composed of the following chemical components in weight percentage: C: 0.04-0.07%, Si: 0.05-0.20%, Mn: 1.20-1.60%, P≤0.020%, S≤0.008%, Als: 0.015-0.060%, Ti: 0.09-0.15%, N≤0.005%, and the rest is Fe and unavoidable impurities;

[0006] The thickness of the bridge shell steel is 1.5-6.0 mm, the yield strength is ≥700 MPa, the tensile strength is ≥800 MPa, the elongation A is ≥16%, and the plate unevenness is ≤5 mm / m.

[0007] Furthermore, the content of Mn is 1.45-1.55%, and the content of Ti is 0.13-0.15%.

[0008] Furthermore, the thickness of the 800MPa grade bridge housing steel is 1.5 to 3.0mm.

[0009] The present invention also proposes a method for producing low-cost 800MPa-grade bridge shell steel based on a CSP production line, which is special in that it includes the following steps:

[0010] First, the molten iron is desulfurized, and then it is smelted in a converter and then sent to a ladle furnace for refining treatment, and the chemical composition and weight percentage of the molten steel are controlled to be C: 0.04-0.07%, Si: 0.05-0.20%, Mn: 1.20-1.60%, P≤0.020%, S≤0.008%, Als: 0.015-0.060%, Ti: 0.09-0.15%, N≤0.005%, and the rest is Fe and unavoidable impurities;

[0011] Afterwards, the molten steel is subjected to thin slab continuous casting and rolling production: the thickness of the cast steel slab is 40-80 mm; the cast slab is heated in a soaking furnace at a temperature of 1210-1250°C; and rolled in a 7-stand finishing mill at a finishing rolling start temperature of ≥1100°C. The first two rolling pressures are controlled at 2×10 4 ~3×10 4 KN, the reduction rate of the last three passes is ≥40%, the rolling speed is controlled at 4.0-10.0 m / s, the final rolling temperature is controlled at 860-910°C, and the rolling thickness is 1.5-6.0 mm;

[0012] Laminar cooling: Cool at a rate of 20-50°C / s, cool uniformly to 590-650°C and then coil.

[0013] Furthermore, the temperature of the cast billet out of the soaking furnace is controlled at 1220-1245°C.

[0014] Furthermore, the rolling thickness is 1.5 to 3.0 mm.

[0015] Furthermore, the laminar cooling is uniformly cooled to 605-630° C. and then coiled.

[0016] The reasons for setting the composition range and process key points in the present invention are as follows:

[0017] 1) C is the cheapest element to improve material strength, but the carbon content between 0.07 and 0.15% will cause peritectic reaction in the molten steel during casting, increasing the risk of continuous casting leakage. As the carbon content increases, the hardness and strength increase, but the plasticity, toughness and welding performance decrease. Taking all factors into consideration, the C weight percentage is 0.04 to 0.07%.

[0018] 2) Si can reduce the diffusion rate of carbon in ferrite, promote the formation of ferrite, and also deteriorate the surface quality. Taking all factors into consideration, the Si weight percentage is preferably 0.05-0.20%.

[0019] 3) Mn significantly reduces Ar1 temperature and austenite decomposition rate, improves the stability of supercooled austenite, promotes stress release of austenite, increases the residual austenite content in the final structure, and improves cold bending performance. However, if the Mn content is too high, it will increase temper brittleness and cause serious center segregation. Taking all factors into consideration, the Mn weight percentage is preferably 1.20-1.60%.

[0020] 4) Als can deoxidize steel, reduce the inclusion content, and also play a role in refining grains. Taking all factors into consideration, Als is between 0.015% and 0.060%.

[0021] 5) Ti can combine with N to form stable TiN during the solidification process of steel, which can strongly hinder the migration of austenite grain boundaries, thereby refining austenite grains. When Ti is dissolved in ferrite, its strengthening effect is higher than that of Al, Mn, Ni, Mo, etc. Taking all factors into consideration, the weight percentage of Ti is preferably 0.09-0.15%.

[0022] 6) P and S are harmful impurity elements in steel. P in steel is easy to form segregation in steel, reducing the toughness and welding performance of steel. S is easy to form plastic sulfide, causing stratification of steel plate and deteriorating the performance of steel plate. Therefore, the lower the P and S content, the better. Taking comprehensive consideration, the P and S content of steel is P≤0.020%, S≤0.008%.

[0023] 7) Nitrogen is easily combined with Ti in steel, affecting the strengthening effect of Ti and greatly affecting the plasticity of steel. Nitrogen is controlled at N≤0.005%.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1) The 800MPa-grade bridge shell steel produced by the present invention has a yield strength of ≥700MPa, a tensile strength of ≥800MPa, an elongation A of ≥16%, a thickness of 1.5-6.0mm, a cold bending performance D=a, and a qualified 180°, and has excellent cold bending forming performance;

[0026] 2) Due to the thinness of the continuous casting billet, the production method of the present invention can reduce the rolling pressure of the first two passes and control the rolling pressure of the first four passes to 2×10 4 ~3×10 4 KN controls the uniform deformation of each pass during steel plate rolling, improves the plate shape quality, reduces the internal stress of the steel plate, and makes it easier for subsequent users to perform leveling and straightening treatment so that the final plate shape unevenness is no more than 5mm / m.

[0027] 3) The present invention only uses the main component elements such as C, Mn, Ti and Als for solid solution and precipitation strengthening effects to produce 800MPa-grade bridge shell steel with low alloy composition, which does not contain environmentally friendly Cr elements, and uses thin slab continuous casting and rolling production technology to further reduce the heating energy consumption in the process, thereby realizing extremely low-cost green and environmentally friendly steel products. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to specific embodiments.

[0029] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0030] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0031] Table 3 shows various properties of various embodiments and comparative examples of the present invention measured according to national standards GB / T228 and GB / T232.

[0032] Each embodiment of the low-cost 800MPa-grade bridge shell steel production method based on the CSP production line of the present invention is produced according to the following steps:

[0033] First, the molten iron is desulfurized, and then it is smelted in a converter and then sent to a ladle furnace for refining treatment, and the chemical composition and weight percentage of the molten steel are controlled to be C: 0.04-0.07%, Si: 0.05-0.20%, Mn: 1.20-1.60%, P≤0.020%, S≤0.008%, Als: 0.015-0.060%, Ti: 0.09-0.15%, N≤0.005%, and the rest is Fe and unavoidable impurities;

[0034] Afterwards, the molten steel is subjected to thin slab continuous casting and rolling production: the thickness of the cast steel slab is 40-80 mm; the cast slab is heated in a soaking furnace at a temperature of 1210-1250°C; and rolled in a 7-stand finishing mill at a finishing rolling start temperature of ≥1100°C. The first two rolling pressures are controlled at 2×10 4 ~3×10 4KN, the reduction rate of the last three passes is ≥40%, the rolling speed is controlled at 4.0-10.0 m / s, the final rolling temperature is controlled at 860-910°C, and the rolling thickness is 1.5-6.0 mm. The rolling thickness here is the thickness of the final bridge shell steel;

[0035] Laminar cooling: Cool at a rate of 20-50°C / s, cool uniformly to 590-650°C and then coil.

[0036] The present invention only uses the main component elements such as C, Mn, Ti and Als for solid solution and precipitation strengthening effect, produces 800MPa grade bridge housing steel with low alloy composition, does not contain environmentally unfriendly Cr elements, and uses thin slab continuous casting and rolling production technology to further reduce the heating energy consumption in the process, thereby realizing extremely low-cost green and environmentally friendly steel products; in addition, the production method of the present invention can reduce the rolling pressure of the first two passes due to the thin continuous casting slab, and control the rolling pressure of the first four passes within 2×10 4 ~3×10 4 KN, compared to the existing 3×10 4 ~4×10 4 KN is greatly reduced, which controls the uniform deformation of each pass during steel plate rolling, improves the plate shape quality, reduces the internal stress of the steel plate, and makes it easy for subsequent users to perform leveling and straightening treatment so that the final plate shape unevenness is no more than 5mm / m.

[0037] Table 1 below is a list of chemical compositions of various embodiments and comparative examples of the present invention. A total of ten embodiments use CSP production lines, and two comparative examples use the production method of existing production lines. The bridge shell steel produced by the existing production lines contains Nb elements. However, the bridge shell steel produced by the CSP production line used in the embodiments of the present invention does not contain Nb elements, thereby reducing production costs.

[0038] Table 1:

[0039] C / ％ Si / % Mn / % P / ％ S / ％ Als / % Nb / % N / ％ Ti / % Example 1 0.046 0.15 1.55 0.013 0.003 0.027 0 0.0031 0.150 Example 2 0.061 0.05 1.60 0.014 0.008 0.015 0 0.0021 0.090 Example 3 0.056 0.17 1.37 0.013 0.003 0.044 0 0.0035 0.142 Example 4 0.065 0.12 1.52 0.015 0.003 0.028 0 0.0038 0.130 Example 5 0.066 0.10 1.20 0.017 0.003 0.034 0 0.0041 0.141 Example 6 0.070 0.18 1.56 0.017 0.001 0.060 0 0.0050 0.125 Example 7 0.061 0.20 1.48 0.020 0.004 0.028 0 0.0026 0.142 Example 8 0.058 0.11 1.56 0.017 0.005 0.027 0 0.0028 0.118 Example 9 0.059 0.13 1.45 0.016 0.004 0.036 0 0.0042 0.136 Example 10 0.040 0.19 1.55 0.013 0.006 0.028 0 0.0031 0.135 Comparative Example 1 0.072 0.06 1.55 0.010 0.002 0.035 0.050 0.0040 0.088 Comparative Example 2 0.145 0.45 1.63 0.012 0.003 0.025 0.033 0.0035 0.012

[0040] Table 2 below lists the main process parameters of various embodiments and comparative examples of the present invention.

[0041] Table 2:

[0042]

[0043] Table 3 below shows various properties of various embodiments and comparative examples of the present invention measured according to national standards GB / T228 and GB / T232.

[0044] Table 3:

[0045]

[0046] As can be seen from Table 3, the thickness of the 800MPa bridge housing steel of the present invention is 1.5-6.0mm, where 800MPa is the tensile strength, the yield strength is ≥700MPa, the tensile strength is ≥800MPa, the elongation A is ≥16%, and the plate unevenness is ≤5mm / m. Here, the plate unevenness is more difficult to control as the thickness becomes thinner, especially for a steel plate with a thickness of 1.5-3.0mm, it is difficult to achieve within 5mm / m, while it is easier to achieve this index for a thickness of more than 8mm in the comparative example. The elongation in comparative example 1 is equivalent to that in the embodiment, and the elongation in comparative example 2 is higher than that in the embodiment, but the yield strength, tensile strength, and cold bending performance in comparative examples 1 and 2 are lower than those in the embodiment.

[0047] As shown in Table 1, the content of Mn is 1.45-1.55%, and the content of Ti is 0.13-0.15%, and the performance of the bridge shell steel finally obtained is better.

[0048] Combined with what is shown in Table 2, the temperature of the ingot out of the soaking furnace is controlled at 1220-1245°C, and the ingot is uniformly cooled to 605-630°C for coiling by laminar cooling, and the performance of the bridge shell steel finally obtained is better.

[0049] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-cost 800MPa grade bridge shell steel based on CSP production line, characterized in that: The bridge shell steel is composed of the following chemical components in weight percentage: C: 0.04-0.07%, Si: 0.05-0.20%, Mn: 1.20-1.60%, P≤0.020%, S≤0.008%, Als: 0.015-0.060%, Ti: 0.09-0.15%, N≤0.005%, and the rest is Fe and unavoidable impurities; the thickness of the bridge shell steel is 1.5-6.0 mm, the yield strength is ≥700 MPa, the tensile strength is ≥800 MPa, the elongation A is ≥16%, and the plate unevenness is ≤5 mm / m.

2. The low-cost 800MPa grade bridge shell steel based on the CSP production line according to claim 1, characterized in that: The content of Mn is 1.45-1.55%, and the content of Ti is 0.13-0.15%.

3. The low-cost 800MPa grade bridge shell steel based on the CSP production line according to claim 1, characterized in that: The thickness of the 800MPa grade bridge shell steel is 1.5 to 3.0mm.

4. A method for producing low-cost 800MPa grade bridge shell steel based on a CSP production line, characterized in that: The following steps are involved: First, the molten iron is desulfurized, and then it is smelted in a converter and then sent to a ladle furnace for refining treatment, and the chemical composition and weight percentage of the molten steel are controlled to be C: 0.04-0.07%, Si: 0.05-0.20%, Mn: 1.20-1.60%, P≤0.020%, S≤0.008%, Als: 0.015-0.060%, Ti: 0.09-0.15%, N≤0.005%, and the rest is Fe and unavoidable impurities; Afterwards, the molten steel is subjected to thin slab continuous casting and rolling production: the thickness of the cast steel slab is 40-80 mm; the cast slab is heated in a soaking furnace at a temperature of 1210-1250°C; and rolled in a 7-stand finishing mill at a finishing rolling start temperature of ≥1100°C. The first two rolling pressures are controlled at 2×10 4 ~3×10 4 KN, the reduction rate of the last three passes is ≥40%, the rolling speed is controlled at 4.0-10.0 m / s, the final rolling temperature is controlled at 860-910°C, and the rolling thickness is 1.5-6.0 mm; Laminar cooling: Cool at a rate of 20-50°C / s, cool uniformly to 590-650°C and then coil.

5. The method for producing low-cost 800MPa grade bridge shell steel based on a CSP production line according to claim 4, characterized in that: The temperature of the cast billet out of the soaking furnace is controlled at 1220-1245°C.

6. The method for producing low-cost 800MPa grade bridge shell steel based on a CSP production line according to claim 4, characterized in that: The rolling thickness is 1.5 to 3.0 mm.

7. The method for producing low-cost 800MPa grade bridge shell steel based on a CSP production line according to claim 4, characterized in that: The laminar cooling is uniformly cooled to 605-630° C. for coiling.

Images