High corrosion-resistant wear-resistant steel for railway freight cars and method for manufacturing same

Abstract

This invention discloses a high corrosion-resistant wear-resistant steel for railway freight cars and its manufacturing method. The chemical composition (wt%) of the steel is as follows: C 0.061-0.079, Si 0.40-0.57, Mn 0.46-0.69, P 0.088-0.097, S ≤0.006, Cr 0.68-0.79, Cu 0.11-0.26, Mo 0.042-0.062, Al 0.046-0.066, RE 0.0144-0.0163, Ti 0.017-0.032, W 0.052-0.072, Sn 0.026-0.043, 8.0 < (P+Sn) / RE < 8.5, 8.0 < Si / Al < 9.4. The method includes a billet exit temperature of 1180–1213℃, a roughing mill exit temperature of 1132–1152℃, a finishing mill initial rolling temperature of 1048–1072℃, a final rolling temperature of 902–920℃, laminar flow cooling at 7–14℃ / s to 724–744℃, air cooling for 12–16s followed by cooling at 28–32℃ / s to 572–592℃ before coiling. The steel of this invention possesses superior resistance to atmospheric and acid corrosion, as well as wear resistance, meeting the requirements of railway freight cars.

Description

Technical Field

[0001] This invention belongs to the field of corrosion-resistant steel for railway vehicles, and relates to a high corrosion-resistant wear-resistant steel for railway freight cars and its manufacturing method. Background Technology

[0002] Railway freight cars are an important means of railway freight transport, mainly used for transporting coal, sand, gravel, bulk cargo, and other goods. Due to the superior corrosion resistance and economic efficiency of weathering steel, railway vehicles made of weathering steel can effectively extend the service life of the car body and reduce maintenance costs. To further extend the service life of the entire vehicle and enable high-speed, heavy-load transport, the steel used in railway vehicles is required to have excellent atmospheric corrosion resistance, especially for coal freight cars, where the molten coal inside the car body contains SO4. 2- Cl - Acidic ions easily cause acid corrosion to the interior of the car body. Furthermore, during coal loading and unloading, coal continuously causes wear and damage to the car body. Therefore, weathering steel for railway freight cars must not only possess excellent atmospheric corrosion resistance but also superior resistance to acidic media corrosion (the corrosion rate of the steel plate should be ≤0.8 g / m² under uniform corrosion conditions in a 10% H₂SO₄ + 3.5% NaCl solution for 24 hours). 2 While weathering steels for railway freight cars possess excellent resistance to atmospheric corrosion, acid corrosion, and wear, current steel grades cannot simultaneously achieve superior resistance to atmospheric corrosion, acid corrosion, and wear. Therefore, there is an urgent need to develop a highly corrosion-resistant (acid corrosion resistant, atmospheric corrosion resistant) and wear-resistant steel for railway freight cars to meet current technological requirements.

[0003] Prior to this invention,

[0004] (1) The composition of the paper "Coal-water resistant steel plate for railway coal transport vehicles and its manufacturing method" published by CN 107653423 B is as follows: C: 0.01%~0.15%, Si: 0.10%~0.50%, Mn: 0.20%~1.0%, P≤0.020%, S≤0.010%, Cu: 0.20%~0.60%, Ni: 0.50%~1.5%, Cr: 0.20%~2.0%, Sb: 0.030%~0.10%, Mo: 0%~0.25%, Nb: 0%~0.05%, V: 0%~0.05%, Ti: 0%~0.10%, B: 0~0.005%, with the remainder being Fe and impurities. By controlling the C, Cr, and Ni contents to ensure that 1.6% ≤ 12C + Cr / Ni ≤ 2.8%, the wear corrosion rate relative to Q450NQR1 is 20%–30%. However, the high Ni content in this invention results in high production costs, hindering its widespread adoption and application.

[0005] (2) The invention patent with publication number CN 114574782A, “A 450MPa grade wear-resistant corrosion-resistant steel and its manufacturing method”, has the following composition: C: 0.061%~0.082%, Si: 0.51%~0.79%, Mn: 0.45%~0.89%, P≤0.018%, S≤0.006%, Cr: 0.81%~1.31%, Cu: 0.14%~0.24%, Sb: 0.041%~0.075%, W: 0.15%~0.35%, Ti: 0.051%~0.072%, Als: 0.015%~0.045%, N≤0.004%, with the balance being Fe and unavoidable impurities. This invention achieves a wear resistance rate of approximately 25%–35% for SPA-H through the synergistic effect of Si, Mn, Cr, and W elements, as well as the formation of certain amounts of FeMnCrC, TiC, and WC. The high W content in this invention results in higher production costs. Furthermore, this invention focuses on the wear and corrosion resistance of shipping containers, which differs from the corrosion resistance indicators of railway freight cars.

[0006] (3) The invention patent with publication number CN 117265382A, “A weathering steel for railway vehicles and its manufacturing method”, has the following composition: C: 0.04%~0.09%, Si: 0.12%~0.24%, Mn: 0.6%~0.9%, P≤0.015%, S≤0.006%, Al: 0.02%~0.04%, Cu: 0.15%~0.35%, Cr: 0.60%~0.95%, Ni: 0.05%~0.12%, Mo: 0.03%~0.12%, Ti: 0.01%~0.02%, Nb: 0.01%~0.02%, N≤0.006%, 5≤Cr / Mo≤25, with the balance being Fe and impurity elements. The patented steel has a high content of precious metals Cu, Ni, and Mo, resulting in higher costs. Its weather resistance is comparable to that of traditional weathering steel, with a relative corrosion rate of ≤55%. Furthermore, the invention does not take into account the impact of coal loading and unloading on the steel plate.

[0007] (4) The patent CN 101423916A, entitled "A Low-Alloy Wear-Resistant and Corrosion-Resistant Steel and Its Manufacturing Method," has the following composition: C: 0.10%–0.16%, Si: 1.0%–1.6%, Mn: 0.80%–1.6%, Cr: 1.0%–1.6%, Mo: 0.3%–0.4%, Ni: 0.30%–0.40%, Al: 0.6%–1.0%, rare earth + Nb: ≤0.1%, with the balance being Fe and impurities. This patent obtains a low-alloy wear-resistant and corrosion-resistant steel suitable for marine silt abrasion and corrosion environments by forming a carbide-free bainitic steel based on the Mn–Si–Cr–Mo–Al system. It mainly adopts a high Si and high Al composition design to suppress carbide formation and adds elements such as Cr, Ni, and Mo to improve corrosion resistance. However, it focuses more on wear resistance and atmospheric corrosion resistance, which is different from the service environment of coal and water abrasion and corrosion. Summary of the Invention

[0008] The purpose of this invention is to provide a high corrosion-resistant wear-resistant steel for railway freight cars and its manufacturing method. By precisely controlling the composition and microstructure ratio, the steel for railway freight cars is ensured to have superior resistance to atmospheric corrosion, acid corrosion and wear.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] One of the technical solutions of this invention is to provide a high corrosion-resistant wear-resistant steel for railway freight cars, with the following chemical composition by weight percentage: C: 0.061%~0.079%, Si: 0.40%~0.57%, Mn: 0.46%~0.69%, P: 0.088%~0.097%, S: ≤0.006%, Cr: 0.68%~0.79%, Cu: 0.11%~0.26%, Mo: 0. 0.042%–0.062%, Al: 0.046%–0.066%, RE: 0.0144%–0.0163%, Ti: 0.017%–0.032%, W: 0.052%–0.072%, Sn: 0.026%–0.043%, where 8.0 < (P+Sn) / RE < 8.5, 8.0 < Si / Al < 9.4, and the balance is Fe and unavoidable impurities.

[0011] The reason for selecting the above alloying elements and their contents in this invention is as follows:

[0012] C: One of the effective elements for increasing the strength of steel. When dissolved in steel, it ensures the strength of the material through solid solution strengthening. It can combine with other alloying elements in steel as carbides, further improving the strength of the material through precipitation strengthening and grain refinement during rolling and cooling. However, a high C content not only deteriorates the plasticity of the material but also reduces its corrosion resistance due to the formation of more pearlite. In this invention, the C content is limited to 0.061%–0.079%.

[0013] Si: A key element in steelmaking for deoxidation, improving strength, hardness, and corrosion resistance. The specific functions of Si in this invention are: (1) deoxidation, reducing the O content in molten steel, thereby increasing the solid solution rate of rare earth elements in the steel; (2) acting as a solid solution element to improve the strength of the material; (3) interacting with C in the steel to form SiC hard particles, which can increase the wear resistance of the material. When added in combination with Cr, it can promote the formation of stable hydroxyl oxide α-FeOOH in the inner rust layer and the enrichment of P and Cu corrosion-resistant elements, thereby improving the corrosion resistance of the material. The Si content in this invention is 0.40%–0.57%. To avoid the formation of difficult-to-remove "red iron scale" Fe2SiO4 on the surface of the steel plate, it is added in combination with Al in this invention. This not only enhances the antioxidant capacity of the material but also makes the Fe2SiO4 thickness thinner, making descaling easier and significantly improving the surface quality of the steel plate. In this invention, the ratio is limited to 8.0 < Si / Al < 9.4.

[0014] Mn is one of the main strengthening elements in steel, and it can improve the strength of steel plates through solid solution strengthening. Meanwhile, in this invention, Mn, as an important austenitizing stabilizing element, can expand the austenite phase region, improve the stability of residual austenite in steel, and thus enhance the plasticity of the material. Therefore, to ensure the strength and formability of the material, the Mn content in this invention is set at 0.46%–0.69%.

[0015] Phosphorus (P): Primarily used as an effective element to improve material strength and corrosion resistance. P often accumulates at the interface between the matrix and the rust layer, reducing the conductivity of the inner rust layer by promoting the formation of dense, amorphous substances, thus significantly improving the material's corrosion resistance. When added synergistically with Sn, it can form Sn-P complex salts, becoming the nuclei for α-FeOOH crystallization, resulting in finer, denser grains in the inner rust layer and hindering SO42- formation. 2- Cl -The introduction of acidic anions can effectively improve the material's resistance to atmospheric and acid corrosion. However, both P and Sn are prone to segregation. When the content of P and Sn is too high, segregation at grain boundaries is likely to occur, which will not only reduce the material's plasticity and toughness but also worsen its corrosion resistance. Therefore, in this invention, P is added in combination with rare earth element RE, which can not only inhibit the segregation behavior of P and Sn but also significantly improve the material's corrosion resistance. In this invention, to achieve a significant corrosion resistance effect, the P content is set to 0.088%–0.097%. To reduce the segregation of P and Sn elements in the cast billet, the ratio is limited to 8.0 < (P + Sn) / RE < 8.5.

[0016] Sulfur (S) is a harmful impurity element that easily forms defects such as segregation and inclusions. Excessive S content can also lead to cracking of the steel during hot working. Therefore, the S content in this invention should be controlled below 0.006%.

[0017] Cr: In steel, Cr can form a continuous solid solution with Fe, playing a role in solid solution strengthening. Cr acts as an active cathode in steel, promoting anode passivation and facilitating the formation of a dense, strongly adhering oxide rust layer on the steel surface. When combined with Si and P, Cr can refine the stable phase α-FeOOH in the rust layer, effectively improving the selective permeability of the rust layer to cations in the corrosive medium, thereby significantly enhancing the material's corrosion resistance. Furthermore, the addition of Cr readily combines with Fe in steel to form CrFe3C and CrFe7C3 compounds. When these compounds are distributed at grain boundaries, they can strengthen the grain boundaries, thereby significantly reducing the low-temperature ductile-brittle transition temperature and improving the low-temperature impact toughness of the material. Therefore, the Cr content in this invention should be controlled between 0.68% and 0.79%.

[0018] Cu (Cu) is an effective element for improving the strength and corrosion resistance of materials. In steel, Cu can play a role in solid solution strengthening, and when added together with the rare earth element Ce, Cu4Ce precipitates can be generated through controlled rolling temperature, resulting in secondary precipitation strengthening. The addition of Cu can promote the formation and enrichment of protective CuO in the inner rust layer, improving the corrosion resistance of the material. Especially when added in combination with P, a small amount of insoluble Cu3(PO4)2 can be formed, which can improve the wear resistance of the matrix. However, excessive Cu content not only increases the cost of the alloy but also increases the occurrence of "copper embrittlement" defects. Therefore, the Cu content in this invention should be controlled between 0.11% and 0.26%.

[0019] Mo: The addition of Mo can form a hard Mo2O3 oxide film on the matrix surface, increasing the wear resistance of the matrix surface. Simultaneously, it can form stable and insoluble alloy cementite (Fe,MO)3C and carbide MoC with C in steel, significantly improving the wear resistance of the material. Mo can partially replace Fe to form ferromolybdenum hydroxide, which ultimately forms a dense and stable protective phase α-(Fe,Mo)OOH enriched in the inner rust layer in the atmosphere, thereby improving the material's atmospheric corrosion resistance. Furthermore, when Mo is added in combination with Ti, through control of the rolling process, nano-sized (Ti,Mo)C is easily precipitated between the phases. The size of this carbide is smaller than that of TiC formed by adding Ti alone, resulting in a more significant precipitation strengthening effect. However, high Mo content increases production costs; therefore, the Mo content in this invention should be controlled between 0.042% and 0.062%.

[0020] Al (Al): An important deoxidizing element, its addition helps reduce the formation of rare earth oxides in steel and improves the "red iron scale" surface quality problem caused by Si (Si). As an important nucleating agent, Al increases the number of crystal nuclei in steel, refining the grain size and improving the material's strength and toughness. Al shifts the corrosion potential of steel to the positive direction and mainly exists as Al2FeO4 in spinel-type oxides, promoting the transformation of spinel into a finer, denser structure, refining the grain size of the inner rust layer, increasing its density, and accelerating the formation of the protective phase α-FeOOH in the inner rust layer. However, excessive Al is not only detrimental to the casting process during continuous casting but also increases the number of inclusions in the steel. Therefore, this invention limits its content to 0.046%–0.066%.

[0021] RE: The main functions of rare earth ions in the steel of this invention are: (1) reducing the number of modified inclusions and decreasing the tendency for pitting corrosion. 3+ Ce 3+ (1) As a cathodic corrosion inhibitor, it is often deposited in the cathode region, which can inhibit the electrochemical reaction of the cathode and effectively slow down the further corrosion; (2) Since the present invention contains P and Sn, which are easy to segregate, the addition of rare earth elements can effectively improve the segregation problem caused by P and Sn, and thus significantly improve the plasticity and toughness of the material; (3) When added together with Cu, it can not only make Cu in steel dispersed and inhibit the generation of "copper embrittlement", but also interact with Cu. By controlling the rolling temperature, nano-sized Cu4Ce precipitates can be generated. Through precipitation strengthening, the strength of the material can be further improved; (4) The addition of Ce element helps to inhibit the decomposition of residual austenite and the precipitation of carbides, which can significantly improve the plasticity and forming performance of steel plate. The present invention limits its range to 0.0144% to 0.0163%.

[0022] Ti: One of the alloying elements that plays a strengthening role. In steel, Ti mainly exists in the forms of TiC and Ti(C,N). The Ti(C,N) formed during the heating of the cast billet can effectively inhibit the growth of austenite grains, playing a role in grain refinement and strengthening. When added in combination with Mo, it plays a precipitation strengthening role by precipitating nano-sized (Ti,Mo)C between phases during rolling and cooling. However, excessively high Ti content will deteriorate the plasticity and toughness of the material. This invention limits its content to 0.017%–0.032%.

[0023] W: Due to its strong bonding with carbon in steel, W dissolved in steel can form a (Fe, W)7C3 hard phase through substitution, which can improve the wear resistance of the steel plate. Especially when added together with Mo, the dissolved W can form a stable and insoluble nanoscale hard phase (Fe, W, Mo)7C3 with Mo in the steel. This hard phase produces a more significant wear resistance effect on the steel plate. However, excessive W content will not only increase costs but also deteriorate the impact performance of the steel plate. Therefore, this invention limits its content to 0.052% to 0.072%.

[0024] The addition of Sn facilitates the formation of a dense, well-adhesive amorphous oxide (hydrocarbon oxide) protective layer on the steel surface, which can prevent SO4 from spreading in acidic media. 2- Cl - The penetration of Sn significantly enhances its acid corrosion resistance. When added synergistically with phosphorus (P), it can form Sn-P composite salts, which become the core for α-FeOOH crystallization, resulting in finer and denser grains in the inner rust layer, further improving the material's resistance to atmospheric erosion. However, both P and Sn are prone to segregation. When the P and Sn contents are too high, segregation at grain boundaries is likely to occur, which not only reduces the material's plasticity and toughness but also deteriorates its corrosion resistance. Therefore, the Sn content in this invention should be controlled between 0.026% and 0.043%.

[0025] The microstructure of the steel of this invention consists of ferrite, bainite, and pearlite, wherein the ferrite phase accounts for 35.4%–38.2%, and the bainite phase accounts for 44.3%–47.4%. Fine reinforcing phases (Ti, Mo)C and hard phases (Fe, W, Mo)7C3 precipitate in the microstructure. The (Ti, Mo)C phase with a size range of 10–40 nm occupies 60.1%–62.3% of the area, and the (Fe, W, Mo)7C3 phase with a size range of 30–60 nm occupies 50.3%–52.8% of the area.

[0026] The second technical solution of this invention provides a method for manufacturing high corrosion-resistant wear-resistant steel for railway freight cars, including hot metal pre-desulfurization, converter steelmaking, ladle refining, slab continuous casting, slab heating, hot continuous rolling, laminar flow cooling, and coiling, wherein:

[0027] Billet heating: The billet exit temperature is 1180-1213℃, the furnace atmosphere is a reducing atmosphere, the air-fuel ratio is 1.1-1.3, the heating rate is controlled at 6.3-8.3℃ / min when the heating temperature is below 1145℃, and at 18.3-19.7℃ / min when the temperature is above 1145℃. The billet time in the furnace is 148-168min.

[0028] Hot continuous rolling: The rolling process is carried out in two stages with controlled temperature, roughing and finishing. The exit temperature of the roughing stage is 1132-1152℃, the cumulative reduction rate of the roughing stage is 73.5%-76.5%, the starting temperature of the finishing stage is 1048-1072℃, and the finishing temperature is 902-920℃.

[0029] Laminar flow cooling and winding: Laminar flow cooling adopts two-stage cooling. The first stage cools to 724-744℃ at a cooling rate of 7-14℃ / s and air-cools for 12-16s. Then, the second stage of cooling is carried out at a cooling rate of 28-32℃ / s, cooling to 572-592℃ for winding.

[0030] Furthermore, the amount of desulfurizing agent added during the pre-desulfurization of molten iron is ≥4.1kg / t, ensuring that S ≤0.014% after desulfurization; the converter steelmaking adopts the furnace top and bottom combined blowing process, the converter tapping temperature is ≥1650℃, and aluminum-iron alloy is added to deoxidize the molten steel during tapping.

[0031] Furthermore, ladle refining includes LF furnace and RH furnace refining. Before leaving the LF refining station, the S content in the molten steel is controlled to be ≤0.004%. During the RH refining process, the vacuum degree in the vacuum tank is kept less than 3 kPa. Rare earth alloys are added to the molten steel in the RH refining furnace, and then the molten steel is subjected to RH pure circulation for 2.8 to 4.8 minutes. After breaking the vacuum, the molten steel is subjected to weak blowing for 32 to 35 minutes.

[0032] Furthermore, the rare earth alloy is a La-Ce alloy, and the weak blowing is argon gas with a flow rate of 74-86 NL / min and a pressure of 0.25-0.36 MPa.

[0033] Furthermore, protective slag is used to protect the molten steel throughout the continuous casting process. The thickness of the continuously cast billet is 210-230mm. During casting, the casting speed is controlled at 1.51-1.67m / min, the superheat is controlled at 21-28℃, and electromagnetic stirring technology is adopted. The electromagnetic stirring current is 347-352A and the frequency is 4.2-6.2Hz.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The 5.0–11.0 mm thick railway freight car steel produced using the above-mentioned chemical composition and process exhibits high corrosion resistance and wear resistance. Through precise control of the composition and microstructure ratio, the steel achieves a yield strength ReL > 450 MPa, tensile strength Rm > 580 MPa, elongation after fracture A > 31%, and satisfactory cold bending performance; KV2 ≥ 52 J (minimum impact standard specimen) at -40℃, demonstrating excellent comprehensive mechanical properties. Through the selection and rational combination of wear-resistant and corrosion-resistant elements, the corrosion rate of the steel plate in a simulated acidic medium corrosion environment for coal freight cars is < 0.57 g / m². 2 Under industrial atmospheric conditions, the corrosion rate of this steel is <38.8% compared to Q345B, and the wear corrosion rate compared to the currently mainstream steel Q450NQR1 can reach 53.8%–57.3%. This invented steel possesses superior resistance to atmospheric and acid corrosion, as well as wear resistance, meeting the requirements of railway coal freight cars for corrosion resistance and wear resistance. It can significantly extend the service life of railway freight cars and has a clear competitive advantage in the application of railway freight car steel. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some embodiments of this invention, not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. The invention will be described in more detail below through embodiments.

[0037] This invention provides a high corrosion-resistant wear-resistant steel for railway freight cars, with the following chemical composition by weight percentage: C: 0.061%–0.079%, Si: 0.40%–0.57%, Mn: 0.46%–0.69%, P: 0.088%–0.097%, S: ≤0.006%, Cr: 0.68%–0.79%, Cu: 0.11%–0.26%, Mo: 0.042%. ~0.062%, Al: 0.046%~0.066%, RE: 0.0144%~0.0163%, Ti: 0.017%~0.032%, W: 0.052%~0.072%, Sn: 0.026%~0.043%, wherein 8.0 < (P+Sn) / RE < 8.5, 8.0 < Si / Al < 9.4, and the balance is Fe and unavoidable impurities. The composition of the steel in the embodiments of the present invention is shown in Table 1.

[0038] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0039]

[0040] This invention provides a method for manufacturing high corrosion-resistant wear-resistant steel for railway freight cars, including hot metal pre-desulfurization, converter steelmaking, ladle refining (LF furnace + RH furnace refining), slab continuous casting, billet heating, hot continuous rolling, laminar flow cooling and coiling, the specific contents of which are as follows.

[0041] Hot metal pre-desulfurization and converter steelmaking: The amount of desulfurizing agent added is ≥4.1kg / t, ensuring that the S content after desulfurization is ≤0.014%; the converter adopts a combined top and bottom blowing process, the converter tapping temperature is ≥1650℃, and aluminum-iron alloy is added to deoxidize the molten steel during tapping.

[0042] Ladle refining: LF refining focuses on deoxidation and desulfurization. During this stage, heating and composition fine-tuning are carried out. Before leaving the LF refining station, all components are controlled within the target range as much as possible, and the S content in the molten steel is controlled to be ≤0.004%. During RH refining, the vacuum degree in the vacuum tank is kept less than 3 kPa. Rare earth alloy (La and Ce alloy used in this case) is added to the molten steel in the RH refining furnace. After adding the rare earth alloy, the molten steel is subjected to RH pure circulation for 2.8 to 4.8 minutes. After the vacuum in the RH refining furnace is broken, the molten steel is subjected to weak blowing for 32 to 35 minutes (argon flow rate 74 to 86 NL / min, pressure 0.25 to 0.36 MPa) to ensure that inclusions float to the surface.

[0043] Slab continuous casting: During slab continuous casting, protective slag is used throughout the process to protect the molten steel and prevent it from being exposed to air. The thickness of the continuously cast slab is 210–230 mm. Because the rare earth elements (La, Ce) in the steel have a strong affinity and easily form a large number of rare earth inclusions with the O and S elements in the steel, affecting the fluidity of the molten steel, the casting speed is controlled at 1.51–1.67 m / min. To reduce the "segregation" problem of the slab caused by P and Sn in the steel, the superheat is controlled at 21–28℃. Electromagnetic stirring technology is used, with an electromagnetic stirring current of 347–352 A and a frequency of 4.2–6.2 Hz. The main process parameters for smelting and continuous casting of the steel in this embodiment are shown in Table 2.

[0044] Table 2 Main process parameters for steel smelting and continuous casting in the embodiments of the present invention.

[0045]

[0046] Billet Heating: To ensure sufficient solid solution of alloying elements such as Si, P, Sn, and W, and considering the high Si content added to the steel, to avoid the formation of difficult-to-remove Fe2SiO4 / FeO "red iron scale" during the heating process, the billet exit temperature is controlled at 1180–1213℃ in this invention. The furnace atmosphere is a reducing atmosphere, and the air-fuel ratio is controlled at 1.1–1.3, which helps to reduce Fe2SiO4 liquefaction, thinning the iron oxide scale and facilitating descaling. Below 1145℃, heating should be slow, with a heating rate controlled at 6.3–8.3℃ / min to ensure uniform temperature inside and outside the billet and sufficient alloy solidification. Above 1145℃, rapid heating is required, with a heating rate controlled at 18.3–19.7℃ / min, and the billet time in the furnace is 148–168 minutes to reduce the adhesion of liquid Fe2SiO4 to the steel plate, achieving easy descaling. The heating process parameters for the steel in this embodiment are shown in Table 3.

[0047] Table 3 Heating process of steel in embodiments of the present invention

[0048] Example Heating temperature / ℃ air-fuel ratio Slow heating rate / ℃ / min Rapid heating rate / °C / min Total heating time / min 1 1180 1.1 6.3 18.3 148 2 1184 1.1 6.7 18.5 151 3 1189 1.1 7.1 18.7 153 4 1194 1.2 7.4 18.9 155 5 1198 1.2 7.6 19.3 159 6 1203 1.2 7.8 19.4 163 7 1207 1.3 8.1 19.6 165 8 1213 1.3 8.3 19.7 168

[0049] Rolling: A two-stage temperature-controlled rolling process is adopted, consisting of roughing and finishing rolling. Roughing employs a high-temperature, high-reduction method, with an exit temperature of 1132–1152℃ and a cumulative reduction rate of 73.5%–76.5%. This stage achieves grain refinement and breaks up the iron oxide scale on the steel plate surface by increasing the reduction amount. The finishing rolling temperature is 1048–1072℃. To reduce the formation of sticky Fe2SiO4 scale while ensuring sufficient precipitation of Cu4Ce and (Ti, Mo)C strengthening phases without excessive growth of the precipitates, the finishing rolling temperature is controlled at 902–920℃.

[0050] To ensure the mechanical properties and excellent wear and corrosion resistance of the steel plate, the microstructure of the steel in this invention consists of bainite, ferrite, and pearlite. After finishing rolling, a two-stage laminar flow cooling method is used. The first stage involves cooling at a rate of 7–14°C / s to 724–744°C (this temperature range belongs to the ferrite transformation region), followed by air cooling for 12–16 seconds (to ensure sufficient formation of ferrite and hard phases). During this stage, soft ferrite microstructure is generated, and the precipitation of hard phases (Fe,W)7C3, (Fe,W,Mo)7C3, and Cu3(PO4)2 is ensured, thereby obtaining the required plasticity and wear resistance of the steel plate. Subsequently, a second stage of cooling is performed at a rate of 28–32°C / s, cooling to 572–592°C before coiling. In this stage, rapid cooling generates sufficient hard bainite and reduces the formation of pearlite in the matrix to ensure the strength of the steel plate and improve its corrosion resistance. Furthermore, this coiling temperature effectively controls grain refinement and suppresses the coarsening of precipitated phases (Ti, Mo)C. The rolling and coiling process parameters for the steel in this embodiment are shown in Table 4.

[0051] Table 4 Main process parameters for steel rolling and cooling in the embodiments of the present invention

[0052]

[0053]

[0054] The various properties of the steel in the embodiments of the present invention are shown in Table 5, the microstructure of the steel in the embodiments of the present invention is shown in Table 6, and the results of the peripheral immersion corrosion test of the steel in the embodiments of the present invention are shown in Table 7.

[0055] Table 5 shows the test results of various performance indicators in the embodiments.

[0056]

[0057] As can be seen from Table 5, the yield strength of the steel in the embodiments of the present invention is between 474 and 519 MPa, all of which reach the design strength of 450 MPa or more. The tensile strength is between 587 and 621 MPa, the elongation is greater than 31%, the cold bending performance is qualified, and the average impact energy at -40℃ is 52 to 64 J (tested with the minimum impact standard sample). This shows that the strength of the steel in each embodiment not only meets the design requirements, but also has high plasticity and low temperature impact toughness.

[0058] The wear resistance tests in Table 5 were conducted on a wet rubber wheel abrasive wear testing machine. Samples with dimensions of 57.0 mm × 25.0 mm × 6.0 mm were used for the abrasive wear test, which was performed according to the "JB / T7705-1995 Test Method for Wear of Loose Abrasives - Rubber Wheel Method". The wear resistance test results showed that the wear rate of the steel in the example was 53.8%–57.3% compared to Q450NQR1 steel, indicating that the steel in the example has higher wear resistance.

[0059] Table 6. Microstructure of steel in the embodiments of the present invention

[0060]

[0061] Table 6 shows that the microstructure of the invented steel consists of ferrite, bainite, and pearlite, with ferrite accounting for 35.4%–38.2% and bainite accounting for 44.3%–47.4%. Fine strengthening phases (Ti, Mo)C and hard phases (Fe, W, Mo)7C3 precipitated in the microstructure. The (Ti, Mo)C phase with a size range of 10–40 nm occupies 60.1%–62.3% of the area, while the (Fe, W, Mo)7C3 phase with a size range of 30–60 nm occupies 50.3%–52.8% of the area. These precipitates are beneficial for improving the strength and wear resistance of the invented steel.

[0062] To simulate corrosion under industrial atmospheric conditions, a 72-hour cyclic immersion rapid corrosion evaluation test was conducted on the invented steel according to the test method specified in TB / T 2375-1993. Simultaneously, to simulate corrosion under acidic conditions, a full immersion corrosion test was conducted according to the method in JB / T 7901 (temperature 23±2℃, immersed in a 10% H2SO4 + 3.5% NaCl solution for 24 hours). Table 7 shows the comparison results of the corrosion resistance of the steel in the embodiments of the present invention and the comparative steel. As can be seen from Table 7, the steel in the embodiments of the present invention exhibits excellent atmospheric corrosion resistance and acid corrosion resistance, and its corrosion resistance indicators all meet the technical target requirements.

[0063] Table 7 Comparison of peripheral corrosion test results between the steel of the present invention embodiment and the comparative steel.

[0064]

[0065] It is hereby noted that the above embodiments are only for illustrating the technical concept and features of the present invention, and are not intended to limit the present invention. Any equivalent substitutions or modifications made without departing from the essence of the present invention fall within the protection scope of the present invention.

Claims

1. A wear-resistant steel for high corrosion resistance railway freight cars, characterized in that, The chemical composition of the steel by weight percentage is as follows: C: 0.061%–0.079%, Si: 0.40%–0.57%, Mn: 0.46%–0.69%, P: 0.088%–0.097%, S: ≤0.006%, Cr: 0.68%–0.79%, Cu: 0.11%–0.26%, Mo: 0.042%–0.062%, Al: 0.046%–0.066%, RE: 0.01 44%–0.0163%, Ti: 0.017%–0.032%, W: 0.052%–0.072%, Sn: 0.026%–0.043%, where 8.0 < (P+Sn) / RE < 8.5, 8.0 < Si / Al < 9.4, and the balance is Fe and unavoidable impurities; the manufacturing method includes hot metal pre-desulfurization, converter steelmaking, ladle refining, slab continuous casting, slab heating, hot continuous rolling, laminar flow cooling, and coiling, wherein: Billet heating: The billet exit temperature is 1180-1213℃, the furnace atmosphere is a reducing atmosphere, the air-fuel ratio is 1.1-1.3, the heating rate is controlled at 6.3-8.3℃ / min when the heating temperature is below 1145℃, and at 18.3-19.7℃ / min when the temperature is above 1145℃. The billet time in the furnace is 148-168min. Hot continuous rolling: The rolling process is carried out in two stages with controlled temperature, roughing and finishing. The exit temperature of the roughing stage is 1132-1152℃, the cumulative reduction rate of the roughing stage is 73.5%-76.5%, the starting temperature of the finishing stage is 1048-1072℃, and the finishing temperature is 902-920℃. Laminar flow cooling and winding: Laminar flow cooling adopts two-stage cooling. The first stage cools to 724-744℃ at a cooling rate of 7-14℃ / s and air-cools for 12-16s. Then, the second stage of cooling is carried out at a cooling rate of 28-32℃ / s, cooling to 572-592℃ for winding.

2. The wear-resistant steel for high corrosion resistance railway freight cars according to claim 1, characterized in that, The steel has a yield strength ReL > 450 MPa, a tensile strength Rm > 580 MPa, an elongation after fracture A > 31%, and qualified cold bending performance; the average KV2 at -40℃ is ≥ 52 J.

3. The wear-resistant steel for high corrosion resistance railway freight cars according to claim 1, characterized in that, The corrosion rate of steel plates in simulated acidic media corrosion environment of coal freight cars is <0.57 g / m. 2 In industrial atmospheric environments, the corrosion rate of Q345B is <38.8%, while the wear rate of the currently mainstream steel Q450NQR1 is 53.8% to 57.3%.

4. The wear-resistant steel for high corrosion resistance railway freight cars according to claim 1, characterized in that, The microstructure of the steel consists of ferrite, bainite, and pearlite. Fine strengthening phases (Ti, Mo)C and hard phases (Fe, W, Mo)7C3 are precipitated in the microstructure. Among them, the area ratio of (Ti, Mo)C with a size range of 10-40 nm is 60.1%-62.3%, and the area ratio of (Fe, W, Mo)7C3 with a size range of 30-60 nm is 50.3%-52.8%.

5. The wear-resistant steel for high corrosion resistance railway freight cars according to claim 4, characterized in that, The proportion of ferrite phase is 35.4%–38.2%, and the proportion of bainite phase is 44.3%–47.4%.

6. A method for manufacturing a high corrosion-resistant wear-resistant steel for railway freight cars according to any one of claims 1 to 5, characterized in that, This includes hot metal pre-desulfurization, converter steelmaking, ladle refining, slab continuous casting, slab heating, hot continuous rolling, laminar cooling, and coiling, among which: Billet heating: The billet exit temperature is 1180-1213℃, the furnace atmosphere is a reducing atmosphere, the air-fuel ratio is 1.1-1.3, the heating rate is controlled at 6.3-8.3℃ / min when the heating temperature is below 1145℃, and at 18.3-19.7℃ / min when the temperature is above 1145℃. The billet time in the furnace is 148-168min. Hot continuous rolling: The rolling process is carried out in two stages with controlled temperature, roughing and finishing. The exit temperature of the roughing stage is 1132-1152℃, the cumulative reduction rate of the roughing stage is 73.5%-76.5%, the starting temperature of the finishing stage is 1048-1072℃, and the finishing temperature is 902-920℃. Laminar flow cooling and winding: Laminar flow cooling adopts two-stage cooling. The first stage cools to 724-744℃ at a cooling rate of 7-14℃ / s and air-cools for 12-16s. Then, the second stage of cooling is carried out at a cooling rate of 28-32℃ / s, cooling to 572-592℃ for winding.

7. The method for manufacturing a high corrosion-resistant wear-resistant steel for railway freight cars according to claim 6, characterized in that, During the pre-desulfurization of molten iron, the amount of desulfurizing agent added is ≥4.1kg / t to ensure that S ≤0.014% after desulfurization; the converter steelmaking adopts the furnace top and bottom combined blowing process, the converter tapping temperature is ≥1650℃, and aluminum-iron alloy is added to deoxidize the molten steel during tapping.

8. A method for manufacturing a high corrosion-resistant wear-resistant steel for railway freight cars according to claim 7, characterized in that, Ladle refining includes LF furnace and RH furnace refining. Before leaving the LF refining station, the S content in the molten steel is controlled to be ≤0.004%. During the RH refining process, the vacuum degree in the vacuum tank is kept less than 3 kPa. Rare earth alloys are added to the molten steel in the RH refining furnace. Then, the molten steel is subjected to RH pure circulation for 2.8 to 4.8 minutes. After breaking the vacuum, the molten steel is subjected to weak blowing for 32 to 35 minutes.

9. A method for manufacturing a high corrosion-resistant wear-resistant steel for railway freight cars according to claim 8, characterized in that, The rare earth alloy is a La-Ce alloy, and the weak blowing is argon gas with a flow rate of 74-86 NL / min and a pressure of 0.25-0.36 MPa.

10. A method for manufacturing a high corrosion-resistant wear-resistant steel for railway freight cars according to claim 6, characterized in that, During the continuous casting of slabs, protective slag is used to protect the molten steel throughout the process. The thickness of the continuously cast slab is 210-230mm. During casting, the casting speed is controlled at 1.51-1.67m / min, the superheat is controlled at 21-28℃, and electromagnetic stirring technology is adopted. The electromagnetic stirring current is 347-352A and the frequency is 4.2-6.2Hz.

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