A low-cost and high-strength steel for truck bodies and its production method

Abstract

The present invention discloses a low-cost and high-strength steel for truck bodies and its production method, belonging to the field of metallurgical technology. The chemical composition and mass percentage content of the steel for truck bodies are as follows: C ≥ 0.18%, Si ≤ 0.20%, Mn: 0.80 - 1.10%, P ≤ 0.022%, S ≤ 0.012%, and the balance is Fe and inevitable impurities. The production method includes a steelmaking process, a hot rolling process, a cold rolling process, and an annealing process. Through reasonable process control from steelmaking to the annealing process, the present invention realizes the production of cold-rolled and annealed steel for truck bodies with a tensile strength ≥ 650 MPa at a low cost.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology, and particularly relates to a steel for low-cost and high-strength freight car bodies and a production method thereof. Background Art

[0002] A van, also called a van transporter, has the advantages of a clean appearance, high safety, wide applicability, etc. It is the model with the highest demand ratio among special vehicles. And with the continuous development of the logistics industry, the increasing demand for road logistics in economic development, and the gradual improvement of national environmental protection requirements for transportation, the demand for vans will continue to increase.

[0003] At present, freight car bodies are mainly made of steel and aluminum alloy. However, due to the complex working conditions of freight car bodies and the easy occurrence of damage, considering their maintenance and turnover costs, steel bodies are more advantageous. Combining with the development direction of energy conservation and emission reduction in the automotive industry, the steel used for body manufacturing is developing towards thin specifications and high strength. At present, this type of steel mainly uses an alloy composition system adding Nb, Ti, and V, with a relatively high manufacturing cost, or realizes a martensite structure through a cold rolling and annealing process control, resulting in high production difficulty and high requirements for equipment capabilities.

[0004] The patent document with the publication number CN106636907A discloses "a thin-specification body steel strip with a yield strength of 600 MPa and a manufacturing method thereof". The chemical composition by weight percentage includes: C: 0.06 - 0.08%, Si: ≤0.20%, Mn: 1.5 - 1.7%, P ≤0.020%, S ≤0.010%, Alt: 0.10 - 0.04%, Nb: 0.025 - 0.035%, Ti: 0.08 - 0.10%, and the balance is Fe and unavoidable impurities. This patent proposes that the contents of Mn, Nb, and Ti in the alloy composition of the product are relatively high, resulting in a high production cost.

[0005] The patent document with the publication number CN201910726779.8 discloses "a low-cost lightweight 600 MPa-class automotive body steel and a production method thereof". The chemical composition by weight percentage includes: C: 0.050 - 0.090%, Si ≤0.12%, Mn: 1.00 - 1.30%, P ≤0.016%, S ≤0.005%, Als: 0.015 - 0.045%, Ti: 0.070 - 0.100%, and the balance is Fe and unavoidable impurities. This patent reduces the Mn content compared with CN106636907A and does not add Nb, but it still has the problem of high production cost because it adds 0.070 - 0.100% of Ti.

[0006] At the same time, the production methods of the box body steel given in Patent CN106636907A and CN201910726779.8 are both hot-rolled products, and the minimum product thickness specification is 2.0 mm, which is difficult to meet the current lightweight development requirements. Summary of the Invention

[0007] The present invention discloses a low-cost and high-strength steel for truck box bodies and its production method. The steel for truck box bodies obtained by this production method has the characteristics of high strength and low cost.

[0008] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A low-cost and high-strength steel for truck box bodies, the chemical composition and mass percentage content of the steel for truck box bodies are: C≥0.18%, Si≤0.20%, Mn: 0.80 - 1.10%, P≤0.022%, S≤0.012%, and the balance is Fe and unavoidable impurities.

[0009] The Si content of the steel for truck box bodies in the present invention is 0.10 - 0.20%.

[0010] The mechanical properties of the steel for truck box bodies in the present invention: Tensile strength ≥650 MPa, A 80mm Elongation ≥10%;

[0011] The thickness specification of the steel for truck box bodies in the present invention is 0.8 - 1.2 mm.

[0012] Another object of the present invention is to provide a production method of the above-mentioned low-cost and high-strength steel for truck box bodies. The production method includes a steelmaking process, a hot-rolling process, a cold-rolling process, and an annealing process; the chemical composition and mass percentage content of the continuous casting billet obtained by the steelmaking process are: C: 0.18 - 0.22%, Si: 0.10 - 0.20%, Mn: 0.80 - 1.10%, P≤0.022%, S≤0.012%, and the balance is Fe and unavoidable impurities.

[0013] The steelmaking process in the present invention adopts a converter-direct process, and the thickness of the continuous casting billet is 200 - 230 mm.

[0014] The hot-rolling process in the present invention: The laminar cooling process is three-stage controlled cooling. After the strip is finally rolled, it is first cooled to 650 - 680 °C by water cooling, then air cooling starts, the air cooling time is 2.5 - 3.5 s, and after air cooling, it is cooled to the coiling temperature of 480 - 530 °C by water cooling again. The hot-rolled base material with a ferrite + bainite structure is obtained through controlled cooling.

[0015] The hot-rolling rolling process in the present invention: The final rolling temperature is 830 - 850 °C.

[0016] The cold-rolling process in the present invention: Pickling five-stand tandem rolling is adopted, and the total reduction ratio ≥70%.

[0017] The annealing process of the present invention: the annealing temperature is 610 - 640 °C, the slow cooling section temperature is 550 - 570 °C, and the termination temperature of the rapid cooling section is 360 - 380 °C.

[0018] The beneficial effects of adopting the above technical solutions are as follows: 1. The present invention only adopts a conventional C, Si, Mn composition system, without adding high-cost alloy elements such as Nb, Ti, V, etc. The alloy cost is low, and the converter direct process is adopted for steelmaking, reducing the production process cost. 2. Through the combination of controlled cooling process in the hot rolling process, large reduction in cold rolling, and low-temperature annealing process, the present invention realizes tissue strengthening, achieves the performance control effect of high strength of the final product, and realizes the production of cold-rolled annealed steel for freight car bodies with a tensile strength ≥ 650 MPa and an 80mm elongation at break ≥ 10% at low cost. Description of the Drawings

[0019] Figure 1 It is the microstructural diagram of the low-cost high-strength steel for freight car bodies in Example 1. Detailed Description of the Invention

[0020] The present invention will be further described in detail below in conjunction with specific embodiments.

[0021] Example 1

[0022] A low-cost high-strength steel for freight car bodies, the mass percentage content of its chemical components is: C: 0.21%, Si: 0.10%, Mn: 1.09%, P: 0.016%, S: 0.010%, and the balance is Fe and unavoidable impurities.

[0023] A production method of a low-cost high-strength steel for freight car bodies includes a steelmaking process, a hot rolling process, a cold rolling process, and an annealing process. The specific process steps are as follows:

[0024] (1) Steelmaking process: Ferrosilicon, high-carbon ferromanganese, and carbon powder are added behind the converter to achieve the target composition of the molten steel. During the feeding process, argon blowing and stirring are used to ensure the uniformity of the molten steel composition;

[0025] (2) Hot rolling process: A 230 mm thick continuous casting billet is rolled to 3.5 mm through 5 passes of rough rolling and 7 passes of finish rolling, and the final rolling temperature is 835 °C; The laminar cooling process is three-stage controlled cooling. After the strip is finally rolled, it is first cooled to 680 °C by water cooling and then stopped for cooling, then air cooling starts for 3.0 s, and after air cooling, it is cooled to 510 °C by water cooling and coiled to obtain a hot-rolled base material with a ferrite + bainite structure through controlled cooling;

[0026] (3) Cold rolling process: The hot-rolled base material is thinned by an acid continuous rolling mill, with a reduction rate of 74.3% and a thickness after rolling of 0.9 mm;

[0027] (4) Annealing process: The cold-rolled steel strip is subjected to continuous annealing production. The annealing temperature is 634 °C, the slow cooling temperature is 563 °C, and the termination temperature of the rapid cooling section is 372 °C. After annealing, the tensile strength of the steel strip is 725 MPa, the yield strength is 636 MPa, and the A 80mm elongation is 10.0%. Figure 1 It is the microstructural diagram of the low-cost high-strength steel for truck bodies in Example 1 (the attached drawings of the other examples are similar and are omitted). It can be seen from the attached drawings that the finished microstructure consists of partially recovered and recrystallized deformed ferrite and the second phase, and the fibrous trend of the cold-rolled hardening is retained.

[0028] Example 2

[0029] A low-cost high-strength steel for truck bodies, the mass percentage content of its chemical composition is: C: 0.18%, Si: 0.13%, Mn: 1.02%, P: 0.018%, S: 0.009%, and the balance is Fe and unavoidable impurities.

[0030] A production method of a low-cost high-strength steel for truck bodies includes a steelmaking process, a hot rolling process, a cold rolling process, and an annealing process. The specific process steps are as follows:

[0031] (1) Steelmaking process: Ferrosilicon, high-carbon ferromanganese, and carbon powder are added after the converter to achieve the target composition of the molten steel. During the feeding process, argon blowing and stirring are used to ensure the uniformity of the molten steel composition;

[0032] (2) Hot rolling process: The 220 mm thick continuous casting billet is rolled to 3.0 mm through 5 passes of rough rolling and 7 passes of finish rolling. The final rolling temperature is 840 °C. The laminar cooling process is three-stage controlled cooling. After the steel strip is finally rolled, it is first water-cooled to 675 °C and then stopped for cooling. Then, it starts air-cooling for 2.5 s. After air-cooling, it is water-cooled to 530 °C and coiled again to obtain a hot-rolled base material with a ferrite + bainite structure through controlled cooling;

[0033] (3) Cold rolling process: The hot-rolled base material is thinned by a tandem cold rolling mill, and the reduction rate is 71.7%. The thickness after rolling is 0.8 mm;

[0034] (4) Annealing process: The cold-rolled steel strip is subjected to continuous annealing production. The annealing temperature is 625 °C, the slow cooling temperature is 570 °C, and the termination temperature of the rapid cooling section is 380 °C. After annealing, the tensile strength of the steel strip is 705 MPa, the yield strength is 646 MPa, and the A 80mm elongation is 13.0%.

[0035] Example 3

[0036] A kind of steel for low-cost and high-strength freight car bodies, the mass percentage content of its chemical components is: C: 0.22%, Si: 0.20%, Mn: 0.95%, P: 0.021%, S: 0.012%, and the balance is Fe and inevitable impurities.

[0037] A production method of a kind of steel for low-cost and high-strength freight car bodies includes a steelmaking process, a hot rolling process, a cold rolling process and an annealing process. The specific process steps are as follows:

[0038] (1) Steelmaking process: Add ferrosilicon, high-carbon ferromanganese and carbon powder behind the converter to achieve the target composition of the molten steel. During the feeding process, argon blowing and stirring are used to ensure the uniformity of the molten steel composition;

[0039] (2) Hot rolling process: The 210mm-thick continuous casting billet is rolled to 5.0mm through 5 passes of rough rolling and 7 passes of finish rolling, and the final rolling temperature is 830°C; The laminar cooling process is three-stage controlled cooling. After the strip is finally rolled, it is first cooled to 650°C by water cooling and then stopped cooling, then air cooling starts, air cooling for 3.5s, and after air cooling, it is cooled to 480°C by water cooling and coiled to obtain a hot-rolled base material with a ferrite + bainite structure through controlled cooling;

[0040] (3) Cold rolling process: The hot-rolled base material is thinned by an acid continuous rolling mill, and the reduction rate is 76.0%, and the thickness after rolling is 1.2mm;

[0041] (4) Annealing process: The cold-rolled strip is continuously annealed. The annealing temperature is 640°C, the slow cooling temperature is 558°C, the termination temperature of the fast cooling section is 360°C. After annealing, the tensile strength of the strip is 678MPa, the yield strength is 628MPa, and the 80mm elongation is 14.5%.

[0042] Example 4

[0043] A kind of steel for low-cost and high-strength freight car bodies, the mass percentage content of its chemical components is: C: 0.20%, Si: 0.17%, Mn: 0.80, P: 0.019%, S: 0.011%, and the balance is Fe and inevitable impurities.

[0044] A production method of a kind of steel for low-cost and high-strength freight car bodies includes a steelmaking process, a hot rolling process, a cold rolling process and an annealing process. The specific process steps are as follows:

[0045] (1) Steelmaking process: Add ferrosilicon, high-carbon ferromanganese and carbon powder behind the converter to achieve the target composition of the molten steel. During the feeding process, argon blowing and stirring are used to ensure the uniformity of the molten steel composition;

[0046] (2) Hot rolling process: The continuous casting billet with a thickness of 230 mm is rolled to 4.0 mm through 5 passes of rough rolling and 7 passes of finish rolling, and the final rolling temperature is 850 °C; the laminar cooling process is three-stage controlled cooling. After the strip is finally rolled, it is first water-cooled to 655 °C and then stopped for cooling, and then air-cooled for 3.0 s. After air-cooling, it is water-cooled to 500 °C for coiling, and a hot-rolled base material with a ferrite + bainite structure is obtained through controlled cooling.

[0047] (3) Cold rolling process: The hot-rolled base material is thinned by a continuous pickling and rolling mill, with a reduction rate of 75.0% and a thickness after rolling of 1.0 mm.

[0048] (4) Annealing process: The cold-rolled strip is continuously annealed. The annealing temperature is 610 °C, the slow cooling temperature is 550 °C, and the termination temperature of the rapid cooling section is 360 °C. After annealing, the tensile strength of the strip is 692 MPa, the yield strength is 626 MPa, and the 80mm elongation is 13.5%.

[0049] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified or equivalently replaced, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A steel for low-cost and high-strength freight car bodies, characterized in that: The production method of a low-cost and high-strength steel for truck bodies includes a steelmaking process, a hot rolling process, a cold rolling process, and an annealing process; the chemical composition and mass percentage content of the continuous casting billet obtained in the steelmaking process are: C: 0.21 - 0.22%, Si: 0.10 - 0.20%, Mn: 0.80 - 1.10%, P ≤ 0.022%, S ≤ 0.012%, and the balance is Fe and unavoidable impurities; The hot rolling process: The laminar cooling process is three-stage controlled cooling. After the strip is finally rolled, it is first water-cooled to 650 - 680 °C, then air-cooling starts, the air-cooling time is 2.5 - 3.5 s, and after air-cooling, it is water-cooled again to the coiling temperature of 480 - 530 °C. A hot-rolled base material with a ferrite + bainite structure is obtained through controlled cooling; The annealing process: The annealing temperature is 610 - 640 °C, the slow cooling section temperature is 550 - 570 °C, and the termination temperature of the rapid cooling section is 360 - 380 °C.

2. The low-cost and high-strength steel for truck bodies according to claim 1, characterized in that: The mechanical properties of the steel used for the freight car body: the tensile strength ≥ 650 MPa, A 80mm elongation ≥ 10%.

3. The low-cost and high-strength steel for truck bodies according to claim 1, characterized in that: The thickness specification of the steel for truck bodies is 0.8 - 1.2 mm.

4. A production method of a low-cost and high-strength steel for truck bodies according to any one of claims 1-3, characterized in that: The production method includes a steelmaking process, a hot rolling process, a cold rolling process, and an annealing process; the chemical composition and mass percentage content of the continuous casting billet obtained in the steelmaking process are: C: 0.21 - 0.22%, Si: 0.10 - 0.20%, Mn: 0.80 - 1.10%, P ≤ 0.022%, S ≤ 0.012%, and the balance is Fe and unavoidable impurities; The hot rolling process: The laminar cooling process is three-stage controlled cooling. After the strip is finally rolled, it is first water-cooled to 650 - 680 °C, then air-cooling starts, the air-cooling time is 2.5 - 3.5 s, and after air-cooling, it is water-cooled again to the coiling temperature of 480 - 530 °C. A hot-rolled base material with a ferrite + bainite structure is obtained through controlled cooling; The annealing process: The annealing temperature is 610 - 640 °C, the slow cooling section temperature is 550 - 570 °C, and the termination temperature of the rapid cooling section is 360 - 380 °C.

5. The production method of a low-cost and high-strength steel for truck bodies according to claim 4, characterized in that: The steelmaking process adopts the converter direct process, and the thickness of the continuous casting billet is 200 - 230 mm.

6. The production method of a low-cost and high-strength steel for truck bodies according to claim 4 or 5, characterized in that: The hot rolling process: The final rolling temperature is 830 - 850 °C.

7. The production method of a low-cost and high-strength steel for truck bodies according to claim 4 or 5, characterized in that: The cold rolling process: Pickling five-stand tandem rolling is adopted, and the total reduction ratio is ≥ 70%.

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