Railway wagon steel suitable for-60 DEG C environment and production method

Abstract

The invention relates to railway wagon steel suitable for an environment of-60 DEG C. The railway wagon steel comprises the following components in percentage by weight: 0.02-0.12% of C, 0.2-0.6% of Si, 0.6-1.5% of Mn, less than or equal to 0.01% of 5 of P, less than or equal to 0.005% of S, 0.20-1.0% of Cu, 0.7-1.50% of Cr, 0.35-1.0% of Ni and 0.010-0.045% of Ti, and the following two formulas are met at the same time: Cu + Cr is more than or equal to 1.0% and less than or equal to 2.2%, and Cu / (Ni + Ti) is less than or equal to 1.5; 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 condition 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-60 DEG C is larger than or equal to 100 J, the corrosion rate is 75% or below of Q450NQR1, and corrosion resistance is excellent.

Description

Technical Field

[0001] The invention relates to steel for railway vehicles and a production method, and in particular to steel for railway freight cars suitable for a -60°C environment and a production method. Background Art

[0002] With the deepening of international cooperation, the export volume of railway vehicles in my country has grown rapidly. The railway vehicle steel standard TB / T 1979 formulated by my country based on its own climatic characteristics requires an impact energy of more than 60J at -40℃, and the exported vehicles also generally continue to use the domestic TB / T 1979 weathering steel grade Q450NQR1. However, due to the geographical environment and climatic characteristics of different cooperating countries, the demand for steel is very different from the technical indicators required by my country, especially in some countries with lower temperatures, where the outdoor temperature can reach -60℃. To ensure safety, the materials for railway freight cars in this area require their impact test temperature to reach -60℃. In addition, due to the low temperature and longer freezing period in the above-mentioned areas than in China, the transportation of bulk cargo such as coal requires the use of antifreeze in larger doses and for longer periods of time. The chloride and other components in the antifreeze can significantly accelerate the corrosion rate of steel plates and shorten the service life of vehicles. Ordinary weathering steels such as Q450NQR1 cannot fully adapt to the above harsh corrosion environment. Therefore, it is necessary to develop weathering steel with impact toughness reaching the requirement of -60℃ and better corrosion resistance to meet the needs of my country's railway freight car companies for exports to extremely cold regions.

[0003] Patents such as CN201010291603.3, CN201510801812.0, and CN201610938070.0 provide the composition design and production methods of weathering steel, but they are all designed for environments of -40°C and above, and the impact toughness does not meet the use requirements of -60°C temperature, and the corrosion resistance is low. CN202210624001.8 provides a weathering steel and production method for use in -70°C environment, but the yield strength of the invented steel is 345MPa, which cannot meet the requirements of heavy load and lightweight body of railway freight cars. Summary of the invention

[0004] The present invention aims to overcome the shortcomings of the prior art that many alloy elements and expensive elements are added, resulting in high production costs, and to provide a railway freight car steel and a production method that ensures yield strength ≥450MPa, tensile strength ≥550MPa, elongation ≥22%, and makes its -60℃ Kv2 ≥100J, and the corrosion rate is less than 75% of Q450NQR1, and is suitable for a -60℃ environment.

[0005] Measures to achieve the above objectives:

[0006] A steel for railway freight cars suitable for use in a -60°C environment, the components and weight percentage contents of which are: C: 0.02-0.12%, Si: 0.2-0.6%, Mn: 0.6-1.5%, P: ≤0.015%, S: ≤0.005%, Cu: 0.20-1.0%, Cr: 0.7-1.50%, Ni: 0.35-1.0%, Ti: 0.010-0.045%, and the following two formulas must be satisfied at the same time: 1.0%≤Cu+Cr≤2.2%, Cu / (Ni+Ti)≤1.5, and the remainder is Fe and impurities.

[0007] Preferably, the weight percentage of Cu is 0.20-0.78%.

[0008] Preferably, the weight percentage of Cr is 0.76-1.25%.

[0009] Preferably, the weight percentage of Ni is 0.38-0.85%.

[0010] Preferably, the weight percentage content of Ti is 0.06-0.072%.

[0011] A method for producing steel for railway freight cars suitable for -60°C environment, comprising the following steps:

[0012] 1) Conventional smelting and continuous casting into billets;

[0013] 2) Heating the ingot: Control the heating temperature of the ingot at 1180-1270°C;

[0014] 3) Perform rough rolling, the starting rolling temperature of the rough rolling is ≥1100°C;

[0015] 4) Finish rolling with a final rolling temperature of 800-870°C;

[0016] 5) Rapid cooling at a cooling rate of 40 to 100°C / S;

[0017] 6) Coil the steel sheet: control the coiling temperature at 580-640°C;

[0018] Functions and mechanisms of each component and main process in the present invention

[0019] 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%.

[0020] 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 improve the corrosion resistance of 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 0.20% to 0.60%.

[0021] 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 0.6-1.5%.

[0022] P is one of the impurity elements in low alloy steel. A high P content makes the steel have a more obvious cold brittle tendency. On the other hand, P is prone to P segregation, which significantly deteriorates the cold forming performance and low temperature impact toughness. The P content in the steel of the present invention is controlled at a relatively low level, and the P content is ≤0.015%.

[0023] 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%.

[0024] Cu: It is the main weathering element in weathering steel, which can effectively improve the weathering performance of steel. Cu added to steel as an alloy element also has solid solution and precipitation strengthening effects. Therefore, the Cu content is controlled at 0.20-1.0%.

[0025] Cr: When used in combination with Cu and other elements in steel, it can significantly improve the steel's atmospheric corrosion resistance, promote the formation of a dense oxide film on the steel surface, and improve the steel's passivation ability. In addition, the Cr element can effectively improve the hardenability of steel, so the Cr content is controlled at 0.70-1.50%. 1.0≤Cu+Cr≤2.2

[0026] Ni: Ni is an element that significantly improves the low-temperature toughness of steel and can also improve its atmospheric corrosion resistance. In addition, the addition of Ni can also effectively prevent the hot brittleness of Cu. Therefore, from the perspective of improving the corrosion resistance of weathering steel and -60°C low-temperature impact toughness, the Ni content is controlled at 0.35-1.2%.

[0027] Ti: Ti forms TiC second phase particles in steel, which hinders the growth of austenite grains, refines grains, and improves the toughness of steel and welding heat affected zone. On the other hand, the addition of Ti fixes the C element as TiC, further inhibits the transformation of C-rich austenite to pearlite, forms a single-phase ferrite structure, improves the toughness of the steel, 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 has a certain inhibitory effect on copper brittle defects. The Ti content of the present invention is designed to be 0.010-0.045%, and Cu / (Ni+Ti) is controlled to be ≤2.0.

[0028] The reason why the heating temperature of the ingot is controlled at 1180-1270°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.

[0029] The reason why the rough rolling start temperature is controlled to be ≥1100°C in the present invention is that a uniform and fine structure can be obtained within this temperature range. When the rough rolling start temperature is too low, mixed crystals will be generated, reducing the impact toughness of the steel.

[0030] The reason why the final rolling temperature is controlled at 800-870°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 is likely to cause mixed crystals and reduce impact toughness; when the final rolling temperature is too high, it will cause coarse grains, and both impact toughness and strength will be reduced.

[0031] The reason why the present invention controls the cooling rate to 40-100°C / S is to match the strength and elongation. When the cooling rate is too low, the driving force of phase change is insufficient, the structure is not fine enough, and the impact toughness and strength are insufficient; when the cooling rate is too high, the strength is too high and the elongation is low.

[0032] The reason why the coiling temperature is controlled at 580-640°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, resulting in insufficient strength of the steel; when the coiling temperature is too high, the precipitate size is coarsened, which will reduce the impact toughness of the steel.

[0033] 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 -60°C Kv2 is ≥100J, and the corrosion rate is less than 75% of that of Q450NQR1, and the corrosion resistance is excellent. DETAILED DESCRIPTION

[0034] The present invention is described in detail below:

[0035] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0036] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0037] Table 3 is a table of performance test results of various embodiments and comparative examples of the present invention.

[0038] Each embodiment of the present invention is produced according to the following steps

[0039] 1) Conventional smelting and continuous casting into billets;

[0040] 2) Heating the ingot: Control the heating temperature of the ingot at 1180-1270°C;

[0041] 3) Perform rough rolling, the starting rolling temperature of the rough rolling is ≥1100°C;

[0042] 4) Finish rolling with a final rolling temperature of 800-870°C;

[0043] 5) Rapid cooling at a cooling rate of 40 to 100°C / S;

[0044] 6) Coil the steel sheet: control the coiling temperature at 580-640°C;

[0045] Table 1 Chemical composition list of various embodiments and comparative examples of the present invention (wt%)

[0046]

[0047]

[0048] Table 2 List of main process parameters of various embodiments of the present invention and comparative examples

[0049]

[0050] Table 3 List of mechanical properties test results of various embodiments of the present invention and comparative examples

[0051]

[0052] illustrate:

[0053] 1. Tensile, bending and impact tests are all conducted in the horizontal direction.

[0054] 2. 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.

[0055] 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 75% 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 of the present invention is greater than 450MPa, the tensile strength is greater than 550MPa, the elongation is greater than 22%, B=20mm, d=2a 180° bending test is qualified, -60℃ Kv2 is greater than 100J, and the low-temperature impact energy is much higher than Q450NQR1.

[0056] 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 steel for railway freight cars suitable for use in a -60°C environment, wherein the components and weight percentage contents are: C: 0.02-0.12%, Si: 0.2-0.6%, Mn: 0.6-1.5%, P: ≤0.015%, S: ≤0.005%, Cu: 0.20-1.0%, Cr: 0.7-1.50%, Ni: 0.35-1.0%, Ti: 0.010-0.045%, and the following two formulas must be satisfied at the same time: 1.0% ≤ Cu+Cr ≤ 2.2%, Cu / (Ni+Ti) ≤ 1.5, and the remainder is Fe and impurities.

2. The steel for railway freight cars suitable for -60°C environment as claimed in claim 1, characterized in that: The weight percentage of Cu is 0.20-0.78%.

3. The steel for railway freight cars suitable for -60°C environment as claimed in claim 1, characterized in that: The weight percentage content of Cr is 0.76-1.25%.

4. The steel for railway freight cars suitable for -60°C environment as claimed in claim 1, characterized in that: The weight percentage content of Ni is 0.38-0.85%.

5. The steel for railway freight cars suitable for -60°C environment as claimed in claim 1, characterized in that: The weight percentage content of Ti is 0.06-0.072%.

6. A method for producing a railway freight car steel suitable for -60°C environment 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 1180-1270°C; 3) Perform rough rolling, the starting rolling temperature of the rough rolling is not less than 1100°C; 4) Finish rolling with a final rolling temperature of 800-870°C; 5) Rapid cooling, cooling to the coiling temperature at a cooling rate of 40 to 100 ° C / S; 6) Coil the steel sheet and control the coiling temperature between 580 and 640 °C.

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