Weathering resistant steel with yield strength of 450MPa for economical rail wagon and production method of weathering resistant steel

Abstract

The invention relates to economic weathering steel with yield strength of 450MPa for a railway wagon, which comprises the following components in percentage by weight: 0.02-0.12% of C, 0.10-0.60% of Si, 0.3-1.0% of Mn, 0.02-0.15% of P, less than or equal to 0.005% of S, 0.10-0.55% of Cu and 0.05-0.15% of Ti, and the following two formulas are met at the same time: Cu + 2P + 1.5 Ti is more than or equal to 0.65%, Cu / (2Ti + P) is less than or equal to 5; the production method comprises the following steps: conventionally smelting and continuously casting into a blank; heating the casting blank; rough rolling; finish rolling; quickly cooling; and coiling. Under the conditions that the yield strength is larger than or equal to 450 MPa, the tensile strength is larger than or equal to 550 MPa, the ductility is larger than or equal to 22%, Kv2 at the temperature of-20 DEG C is larger than or equal to 100 J, the corrosion rate is 90% or below of Q450NQR1, precious alloys such as Cr and Ni do not need to be added, and therefore the production cost of the steel is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to a steel for railway vehicles and a production method, in particular to a weathering steel with a yield strength of 450MPa for economical railway freight cars and a production method. Background Art

[0002] my country's railway vehicle industry currently generally uses weathering steels such as Q450NQR1 in the TB / T 1979 standard for domestic and export freight cars. On the one hand, the above materials must be added with precious alloy elements such as Cr and Ni, resulting in high production costs, which greatly limits the profitability and market competitiveness of railway vehicle manufacturers; on the other hand, due to the long-term outdoor operation of railway freight cars, they are affected by the atmosphere, coal and other transportation media, antifreeze, water, mechanical collisions, etc., and the harsh service environment, resulting in a fast corrosion rate of Q450NQR1 car body materials and a short vehicle life. Therefore, it is urgent to develop a low-cost, highly corrosion-resistant weathering steel for railway freight cars.

[0003] CN202110317342.6 and CN202010153281.X respectively disclose an economical low yield ratio hot-rolled weathering steel plate and its manufacturing method, and a titanium micro-alloyed economical high-strength weathering steel and its production method, but both require the addition of a certain amount of precious alloy elements such as Cr and Ni; CN200510045624.6 discloses an economical weathering steel, but its yield strength is only 345MPa, which cannot meet the heavy load requirements of railway freight cars. Summary of the invention

[0004] The present invention aims to overcome the shortcomings of the prior art that there are many alloy elements and expensive elements are added, resulting in high production costs. The present invention provides a 450MPa yield strength economical weathering steel for railway freight cars and a production method, which can significantly reduce production costs while ensuring yield strength ≥450MPa, tensile strength ≥550MPa, elongation ≥22%, and making its -20℃ Kv2 ≥100J and corrosion rate below 90% of Q450NQR1.

[0005] Measures to achieve the above objectives:

[0006] A weathering steel with a yield strength of 450 MPa for economical railway freight cars, the components and weight percentage contents of which are: C: 0.02-0.12%, Si: 0.10-0.60%, Mn: 0.3-1.0%, P: 0.02-0.15%, S: ≤0.005%, Cu: 0.10-0.55%, Ti: 0.05-0.15%, and the following two formulas must be satisfied at the same time: Cu+2P+1.5Ti≥0.65%, Cu / (2Ti+P)≤5, and the rest is Fe and impurities.

[0007] Preferably, the weight percentage of Cu is 0.16-0.48%.

[0008] Preferably, the weight percentage of P is 0.026-0.125%.

[0009] Preferably, the weight percentage content of Ti is 0.06-0.072%.

[0010] A method for producing a 450MPa yield strength economical weathering steel for railway freight cars, comprising the following steps:

[0011] 1) Conventional smelting and continuous casting into billets;

[0012] 2) Heating the ingot: Control the heating temperature of the ingot at 1180-1260°C;

[0013] 3) Perform rough rolling, the starting rolling temperature of the rough rolling is not less than 1100°C;

[0014] 4) Finish rolling with the final rolling temperature at 820-890°C;

[0015] 5) Rapid cooling, cooling to the coiling temperature at a cooling rate of 40 to 120°C / S;

[0016] 6) Coil the steel sheet: control the coiling temperature at 580-650°C.

[0017] Functions and mechanisms of the components and main processes in the present invention

[0018] C is the most economical and effective alloying element for improving steel strength, but too high C content will significantly deteriorate the welding performance of steel and promote pearlite transformation, thereby reducing the corrosion resistance of steel. The present invention adopts ultra-low C design to improve the welding performance of steel, inhibit the formation of pearlite structure, and improve the corrosion resistance and low-temperature impact toughness of steel. The C content in the steel of the present invention is 0.02-0.12%.

[0019] Si accelerates carbon segregation to austenite in steel, purifies ferrite, and avoids the formation of coarse carbides during cooling. At the same time, the solid-solution silicon can be evenly extended and can also improve the corrosion resistance of steel. In addition, Si can inhibit the formation of "copper brittleness" defects on the surface of Ni-free copper-containing steel. However, excessive silicon will form Fe2SiO4 during high-temperature rolling, increase the adhesion of iron oxide scale, and deteriorate the surface quality of steel plates. Therefore, the Si content is controlled within the range of 0.10% to 0.60%.

[0020] Adding Mn to steel can not only improve the strength of the steel through solid solution strengthening of Mn, but also reduce the phase transition temperature of the steel, refine the grains, and improve the low-temperature toughness of the steel. The Mn content of the steel of the present invention is designed to be 0.3-1.0%.

[0021] S is a harmful element in steel. The generated sulfide inclusions seriously affect the low-temperature impact toughness of steel. Therefore, the S content in steel should be reduced as much as possible to below 0.005%.

[0022] Cu is the most important alloying element for improving the corrosion resistance of steel. The cathode contact between steel and the secondary Cu precipitated on the surface can promote the anode passivation of steel and form a protective rust layer, which significantly improves the corrosion resistance of steel. However, too high a Cu content will reduce the toughness of the heat-affected zone of the steel plate welding, and will produce "copper brittleness" during the continuous casting and hot rolling of the steel plate. Therefore, the Cu content is controlled at 0.10-0.55%.

[0023] P can promote the formation of a dense rust layer on the steel surface, significantly improving the weather resistance of the steel. At the same time, P can inhibit the penetration of the copper-rich phase into the austenite grain boundary, thereby inhibiting copper brittle defects. However, excessive P is prone to segregation, deteriorating cold forming performance and low-temperature impact toughness. The P content in the steel of the present invention is controlled at 0.02-0.15%.

[0024] Ti: Ti forms TiC second phase particles in steel, which hinders the growth of austenite grains, significantly refines austenite grains, increases the austenite grain boundary area, and reduces the penetration depth of the liquid Cu-rich phase on the surface of the steel matrix at the austenite grain boundary, thereby effectively suppressing the "copper brittleness" defect that is prone to occur in Ni-free Cu-containing steel. On the other hand, the addition of Ti plays a certain strengthening role. The design value of C can be reduced while maintaining the original strength level, and the C element is fixed to TiC, which further suppresses the transformation of C-rich austenite to pearlite, forms a single-phase ferrite structure, and avoids the galvanic corrosion formed between different structures in conventional ferrite-pearlite steel, thereby further improving the corrosion resistance of the steel. In addition, Ti can improve the density of the rust layer and further improve the corrosion resistance of the steel. The Ti content of the present invention is designed to be 0.05-0.15%. In addition, in order to ensure corrosion resistance, Cu+2P+1.5Ti≥0.65 is controlled, and in order to ensure the surface quality of the steel plate and suppress copper brittle defects, Cu / (2Ti+P)≤2.5 is controlled.

[0025] The reason why the heating temperature of the ingot is controlled at 1180-1260°C is to achieve sufficient austenitization and solid solution of Ti element. When the heating temperature is too low, austenitization and solid solution of Ti are insufficient; when the heating temperature is too high, the copper brittleness defect of Ni-free Cu-containing steel will be aggravated.

[0026] The reason why the rough rolling start temperature is controlled to be ≥1100° C. in the present invention is that within this temperature range, a uniform and fine structure can be obtained. When the rough rolling start temperature is too low, mixed crystals will be generated.

[0027] The reason why the final rolling temperature is controlled at 820-890°C in the present invention is to obtain a uniform and fine transformation structure, thereby improving strength and toughness. When the final rolling temperature is too low, rolling in the two-phase region will lead to mixed crystals; when the final rolling temperature is too high, the grains will be coarse and the toughness will be reduced.

[0028] The present invention controls the cooling rate to 40-120°C / S in order to match the strength and elongation. When the cooling rate is too low, the structure will not be fine enough and the strength of the steel will be insufficient; when the cooling rate is too high, the strength will be too high and the elongation will be low.

[0029] The reason why the coiling temperature is controlled at 580-650°C in the present invention is to obtain sufficient fine TiC precipitates. When the coiling temperature is too low, the dissolved Ti element cannot be fully precipitated; when the coiling temperature is too high, the precipitate size is coarsened, which will reduce the impact toughness of the steel.

[0030] Compared with the prior art, the present invention ensures that the yield strength is ≥450MPa, the tensile strength is ≥550MPa, the elongation is ≥22%, and the -20°C Kv2 is ≥100J, the corrosion rate is less than 90% of that of Q450NQR1, and there is no need to add precious alloys such as Cr and Ni, thereby significantly reducing the production cost of steel. DETAILED DESCRIPTION

[0031] The present invention is described in detail below:

[0032] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0033] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0034] Table 3 is a table of performance test results of various embodiments and comparative examples of the present invention.

[0035] Each embodiment of the present invention is produced according to the following steps

[0036] 1) Conventional smelting and continuous casting into billets;

[0037] 2) Heating the ingot: Control the heating temperature of the ingot at 1180-1260°C;

[0038] 3) Perform rough rolling, the starting rolling temperature of the rough rolling is not less than 1100°C;

[0039] 4) Finish rolling with the final rolling temperature at 820-890°C;

[0040] 5) Rapid cooling, cooling to the coiling temperature at a cooling rate of 40 to 120°C / S;

[0041] 6) Coil the steel sheet: control the coiling temperature at 580-650°C.

[0042] Table 1 Chemical composition list of various embodiments and comparative examples of the present invention (wt%)

[0043]

[0044]

[0045] Table 2 List of main process parameters of various embodiments of the present invention and comparative examples

[0046]

[0047] Table 3 List of mechanical properties test results of various embodiments of the present invention and comparative examples

[0048]

[0049]

[0050] Description: Corrosion test conditions: Refer to "TB / T 2375-93 Periodic Immersion Corrosion Test Method for Weathering Steel for Railways" for cyclic immersion corrosion test. The solution used is 0.01 mol / L NaHSO3, the temperature is 45±2℃, the relative humidity is 70±5%, and the test time is 72h.

[0051] The test results are shown in Table 3. The corrosion test results show that the corrosion rate of the steel of the present invention is less than 90% of that of the ordinary weathering steel Q450NQR1 for railway freight cars, indicating that its corrosion resistance is significantly higher than Q450NQR1, and it has excellent corrosion resistance. The yield strength of the steel is greater than 450MPa, the tensile strength is greater than 550MPa, the elongation is greater than 22%, the bending test of B=20mm, d=2a 180° is qualified, and the Kv2 at -20℃ is greater than 100J.

[0052] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A weathering steel with a yield strength of 450 MPa for economical railway freight cars, the components and weight percentages of which are: C: 0.02-0.12%, Si: 0.10-0.60%, Mn: 0.3-1.0%, P: 0.02-0.15%, S: ≤0.005%, Cu: 0.10-0.55%, Ti: 0.05-0.15%, and the following two formulas must be satisfied at the same time: Cu+2P+1.5Ti≥0.65%, Cu / (2Ti+P)≤5, the rest is Fe and impurities.

2. The weathering steel for economical railway freight cars with a yield strength of 450 MPa as claimed in claim 1, Features: The weight percentage of Cu is 0.16-0.48%.

3. The weathering steel for economical railway freight cars with a yield strength of 450 MPa as claimed in claim 1, Features: The weight percentage of P is 0.026-0.125%.

4. The weathering steel for economical railway freight cars with a yield strength of 450 MPa as claimed in claim 1, Features: The weight percentage content of Ti is 0.06-0.072%.

5. A method for producing a weathering steel for economical railway freight cars with a yield strength of 450 MPa as claimed in claim 1, comprising the following steps: 1) Conventional smelting and continuous casting into billets; 2) Heating the ingot: Control the heating temperature of the ingot at 1180-1260°C; 3) Perform rough rolling, the starting rolling temperature of the rough rolling is not less than 1100°C; 4) Finish rolling with the final rolling temperature at 820-890°C; 5) Rapid cooling, cooling to the coiling temperature at a cooling rate of 40 to 120°C / S; 6) Coil the steel sheet: control the coiling temperature at 580-650°C.

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