Carburizing bearing steel for heavy haul railway roller and production method of carburizing bearing steel

Abstract

The invention relates to carburized bearing steel for a heavy haul railway roller. The carburized bearing steel comprises the following chemical components in percentage by mass: 0.17-0.23% of C, 0.15-0.40% of Si, 0.60-0.90% of Mn, less than or equal to 0.020% of P, less than or equal to 0.025% of S, 0.35-0.85% of Cr, 0.020-0.060% of Al, less than or equal to 0.30% of Cu, less than or equal to 0.10-0.30% of Mo, 0.40-0.80% of Ni, less than or equal to 0.065% of As + Sn + Sb, less than or equal to 0.0010% of Ti, less than or equal to 0.0005% of Ca, less than or equal to 0.0008% of O, 0.008-0.012% of N and the balance of Fe and inevitable The invention further provides a manufacturing method of the carburizing bearing steel for the heavy haul railway roller. The manufacturing method comprises the following steps: continuously casting a CCM large continuous casting billet, slowly cooling, heating and rolling to prepare an intermediate billet, slowly cooling, carrying out surface treatment, heating and rolling a wire rod, slowly cooling and finishing. Compared with electroslag steel, the structure of the steel is more uniform, the grain size is smaller, the number of harmful elements is smaller, the DI value fluctuation is more stable, the core hardenability is better, the production cost is lower, and the quality level and the market competitiveness of the steel are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and specifically relates to carburized bearing steel for heavy-load railway rollers and a production method thereof. Background Art

[0002] In recent years, with the continuous changes in my country's railway transportation pattern, the replacement speed of railway freight cars has accelerated and the maintenance cycle has been extended. In this case, higher requirements are placed on the parts used in the vehicles. As an important component of railway freight cars, the performance of rolling bearings will directly affect the safe operation of the entire railway vehicle, which is bound to place higher requirements on the quality control of rollers, the core components of railway bearings.

[0003] Railway rollers are generally large in size, work under high load contact stress, and are frequently subjected to impact and wear. Therefore, in addition to the requirements for general bearings, the rolling elements of these large bearings also require sufficient toughness, high compressive strength and hardness in the core, so carburized bearing steel can be used for manufacturing. Among them, after carburizing quenching and low-temperature tempering, the surface of the carburized steel has high hardness, wear resistance and contact fatigue strength, while the carbon content in the core is low. It has good toughness and can withstand the impact of large loads. It is very suitable for manufacturing rolling elements of large bearings.

[0004] At present, the national standard GB / T 3203 for carburized bearing steel clearly stipulates that high-grade carburized steel must be produced using the electroslag remelting process. Since the steel produced by the electroslag remelting process has many quality advantages such as fine and evenly distributed non-metallic inclusions, high uniformity of organization and high density, its quality stability has always been good. However, the electroslag remelting production process also has obvious disadvantages such as very low production efficiency and production capacity, and very high energy consumption and production costs. Therefore, the market competitiveness of electroslag remelting steel is very low.

[0005] Patent CN 114774771 A discloses a carburized bearing steel for heavy-load rolling mill bearings and a production method thereof. The steel is adjusted by trace alloying elements such as Nb and V, and the Ni content is as high as 3.25-3.75%. The addition of trace elements increases the difficulty of smelting and the intensity of workers. At the same time, the high Ni content will greatly increase the cost. In this invention, only Al and N are used to adjust the grain size and performance, which greatly reduces the production cost while meeting the working conditions required for the use of railway rollers.

[0006] Patent CN 112030065 B discloses a carburized bearing steel and its preparation method. The smelting method described in the invention is electroslag smelting, double vacuum smelting, refining outside the furnace or vacuum induction furnace smelting. The present invention adopts a high-efficiency, high-capacity, low-cost process route of vacuum degassing, continuous casting, and rolling, and optimizes and controls the key processes, so that the steel has a higher purity, smaller grain size, more uniform structure and more stable DI value, which meets the use requirements of heavy-duty railway bearings, greatly improves production efficiency and production capacity, and greatly reduces energy consumption and production costs, thus having more competitive advantages.

[0007] The steel of the present invention is based on the technical standard requirements of advanced high-quality steel G20CrNiMo specified in the existing national standard GB / T 3203. By optimizing the design of the components, adopting a high-efficiency, high-capacity, low-cost process route of vacuum degassing, continuous casting and rolling, and optimizing the control of key processes, the steel has a higher purity, a smaller grain size, a more uniform structure and a more stable DI value, thereby improving the contact fatigue performance of carburized bearing steel to meet the use requirements of heavy-duty railway bearings, and replacing the current electroslag remelting production process, greatly improving production efficiency and production capacity, and greatly reducing energy consumption and production costs, and thus having more competitive advantages. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a carburized bearing steel for heavy-duty railway roller bearings and a manufacturing method thereof in view of the above-mentioned prior art, so that the carburized bearing steel for heavy-duty railway roller bearings can meet the quality requirements and the product has strong market competitiveness.

[0009] The technical solution adopted by the present invention to solve the above-mentioned problem is: a carburized bearing steel for heavy-duty railway rollers, the chemical composition of the steel plate and its mass percentage are C: 0.17-0.23%, Si: 0.15-0.40%, Mn: 0.60-0.90%, P: ≤0.020%, S: ≤0.025%, Cr: 0.35-0.85%, Al: 0.020-0.060%, Cu≤0.30%, Mo≤0.10-0.30%, Ni: 0.40-0.80%, As+Sn+Sb≤0.065%, Ti≤0.0010%, Ca≤0.0005%, O≤0.0008%, N: 0.008-0.012%, and the remainder is Fe and unavoidable impurity elements.

[0010] This steel is produced by continuous casting process, overcoming the obvious disadvantages of the existing electroslag remelting production process, such as low production efficiency, low capacity, high energy consumption and high production cost. By optimizing the composition, smelting, continuous casting process, and reasonable heating and rolling process, the obtained wire rod has excellent quality and can meet the inclusions: low multiple should not be greater than S1, R1, C1; non-metallic inclusions: A coarse ≤ 1.5, A fine ≤ 2.5, B coarse ≤ 0.5, B fine ≤ 1.5, D coarse ≤ 0.5, D fine ≤ 1.0, DS ≤ 1.0; DI value 2.2 ~ 2.6; decarburization ≤ 0.10mm; grain size ≤ 8 levels.

[0011] The following is a detailed description of the effects and dosage of the components in the present invention:

[0012] C: Carbon is an important element that affects the tensile strength and yield strength of steel. It also has a great influence on the toughness of steel. The role of carbon in steel is a double-edged sword. As the carbon content of steel increases, the yield point and tensile strength of steel will continue to increase, but the plasticity and impact resistance will decrease significantly. Slight fluctuations in carbon in steel can lead to significant changes in the strength and toughness of steel. The magnitude of the fluctuation of carbon on the cross section of steel determines the stability of the strength and toughness of steel. Therefore, the selection range of carbon content in the present invention is C: 0.17-0.23%.

[0013] Si: Silicon can form an alloy with the iron in steel, changing its atomic structure. This alloying effect can make the steel stronger and more durable. The interaction between silicon and iron atoms can increase the lattice strength of the steel, thereby improving the overall strength of the steel. In addition, adding ferrosilicon in the early stage of refining can also play a role in assisting deoxidation. The Si content of the present invention is controlled to be 0.15-0.40%.

[0014] Mn: Adding an appropriate amount of ferromanganese during the steelmaking process can play a good deoxidation role under strong argon stirring in the early stage of refining, and the manganese element in the steel can effectively improve the strength of the steel. However, a higher manganese content will cause the steel of the present invention to produce more obvious temper brittleness, and the control range is 0.60-0.90%.

[0015] P: Phosphorus in the present invention is a harmful element. Phosphorus can make steel brittle at room temperature, resulting in a significant decrease in the strength and toughness of the steel. Therefore, the selection range of phosphorus in the steel of the present invention is P: ≤ 0.020%.

[0016] S: The sulfur in the steel of the present invention is easy to combine with manganese to form manganese sulfide inclusions, resulting in a decrease in the tensile strength and impact properties of the steel. Therefore, the sulfur content in the steel must be strictly controlled. The selection range of sulfur in the steel is S: ≤0.025%.

[0017] Cr and Mo: Both Cr and Mo elements are elements that increase hardenability. For 5.5Ni steel plates with low C and low Ni, in order to ensure the hardenability of the steel plates, it is necessary to add additional Cr and Mo elements to make up for the lack of C content and improve the hardenability of the steel plates. At the same time, the alloy elements are diffused into austenite in the later stage to stabilize the austenite structure. However, it cannot be ignored that Cr and Mo elements have a certain negative impact on low-temperature impact toughness. Therefore, the present invention controls the content of Cr: 0.35-0.85%; Mo≤0.10-0.30%.

[0018] N: Nitrogen will form hard and brittle compounds with iron in steel, and will also combine with other elements to form corrosion-resistant compounds, thereby improving the corrosion resistance of steel. It can also easily make steel produce a martensitic structure with strong toughness and wear resistance, thereby enhancing the hardness and strength of steel. At the same time, at high temperatures, nitrogen can also prevent excessive growth of grain boundaries and excessive structural refinement of steel during quenching, thereby reducing the occurrence of quenching brittleness, thereby improving the toughness of steel and extending its service life. The nitrogen content of the steel in the present invention is set in the range of 0.008-0.012%, more preferably 0.009-0.010%.

[0019] Al: In addition to being a deoxidizer to reduce the oxygen content in steel, aluminum can also form aluminum nitride with nitrogen to refine grains, has a strong solid solution strengthening effect, and improves tempering stability. In order to control the residual austenite ratio of the final product and obtain better hardness and wear resistance, the Al content should be designed to be greater than 0.020%. However, since the product of aluminum deoxidation, Al2O3, is relatively brittle, it breaks during forging and rolling and forms chain-like strips along the deformation direction, affecting fatigue performance. At the same time, steel with high aluminum content has poor surface quality of the ingot. In order to ensure comprehensive performance, the Al content range of the steel in the present invention is set to 0.020-0.060%, and more preferably 0.035-0.045%.

[0020] Ni: It can improve the strength of steel while maintaining good plasticity and toughness. It is insoluble in carbides and completely enters austenite, forming an infinite solid solution, and its role in improving hardenability can be fully exerted. It refines ferrite grains and improves the plasticity and toughness of steel, especially low-temperature toughness, under the condition of the same strength. The range of Ni content in the present invention is determined to be 0.40-0.80%.

[0021] Another object of the present invention is to provide a method for producing carburized bearing steel for heavy-duty railway rollers, wherein the blank is smelted by continuous casting instead of electroslag remelting, and the main steps are as follows:

[0022] (1) Smelting: This steel is made entirely from hot metal. Deoxidation is carried out by a combination of precipitation and diffusion during refining. Nitrogen is used throughout the refining stirring and RH raising process. The alloy composition is not adjusted after refining and the purity of the molten steel is strictly controlled.

[0023] (2) Continuous casting: Advanced electromagnetic stirring at the beginning and end, weak cooling, and light pressure are used to match the advanced equipment processes. The pouring superheat is controlled at 10-20°C to obtain 390mm*510mm continuous casting billets with excellent segregation quality.

[0024] (3) Slow cooling of continuous casting billets: Slow cooling of continuous casting billets is to slowly cool the continuous casting billets down the pit, wherein the pit temperature is greater than 650°C, the pit slow cooling time is greater than 48 hours, and the pit exit temperature is less than 200°C.

[0025] (4) Rolling into intermediate billet: In a heating furnace with a neutral or weakly oxidizing atmosphere, the temperature is raised at a rate of 150-250°C / h to 1020-1220°C for insulation for 4.5-7.5h; the billet is rolled using a large compression ratio rolling process, with a rolling temperature of ≥1050°C, an initial rolling compression ratio of ≥2.5, a continuous rolling temperature of ≥980°C, a final rolling temperature of ≥800°C, a bottom line temperature of ≥500°C, a total compression ratio of ≥4.5, and the billet is rolled into 120-240mm. 2 Square intermediate blank.

[0026] (5) Rolling wire rod: heat the intermediate square billet at a heating rate of 600-800℃ / h; heat to 1050±30℃ and keep warm for 0.5-1h; set the start rolling temperature of the wire rod to ≥900℃, the initial rolling reduction ratio to ≥1.5, the intermediate rolling temperature to ≥900℃, the finishing rolling temperature to 930±30℃, the spinning temperature to 900±30℃, and the total compression ratio to ≥40.

[0027] (6) Controlled cooling: After spinning, the wire rods are air-cooled to a temperature of 700-800°C, and then enter the heat preservation cover for slow cooling to ≤450°C for winding and unloading.

[0028] (7) Inspection: The wire rod off the production line is inspected for DI value, grain size, inclusions, and decarburization. If all of them are qualified, the finished product of carburized bearing steel hot-rolled wire rod for heavy-duty railway rollers is obtained.

[0029] The metallographic structure of the hot-rolled wire rod obtained by the present invention is a pearlite + bainite + ferrite structure with a sheet spacing of 0.10 to 0.25 μm. The structure is easy to spheroidize during the subsequent heat treatment process. At the same time, the structure is fine needle martensite + nano austenite + fine-grained carbide after quenching + tempering. About 15% of the residual austenite in the structure is mainly in the form of ultrafine grain block. The ultrafine grain block residual austenite is relatively stable and helps to improve the fatigue life of the rolling element.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] 1) The present invention adopts a composite deoxidation method in the initial stage of refining, and no composition adjustment is performed at the end of refining. RH vacuum and soft blowing are used to fully float Al2O3 and large-particle composite inclusions, thereby improving the cleanliness of molten steel.

[0032] 2) The present invention adopts converter + refining LF + vacuum degassing RH + continuous casting process, which can significantly reduce harmful elements O, Ti and Ca compared with the electroslag remelting process, so O can be controlled at ≤0.0008%, Ti at ≤0.0010%, Ca at ≤0.0005% and As+Sn+Sb at ≤0.065%.

[0033] 3) In the continuous casting process, low superheat (10-20°C) pulling and pouring are adopted, and heavy pressure >12mm is adopted at the end, combined with high current electromagnetic stirring (>300A) at the end to reduce the core segregation and effectively improve the segregation of the billet.

[0034] 4) In the initial rolling process, high-reduction rolling is adopted. By combining large-section ingots with non-uniform temperature rolling in the production process and combining the production technology of initial rolling with high reduction, the matrix structure in the steel can be greatly refined and homogenized.

[0035] 5) Carry out slow cooling treatment on the continuous casting billet and intermediate billet to avoid surface cracking of the steel due to surface and internal thermal stress and structural stress changes, and ensure the surface quality of the wire rod.

[0036] 6) The present invention performs controlled rolling and controlled cooling treatment on the wire rod, performs high temperature initial rolling and low temperature final rolling, obtains hot-rolled pearlite + bainite + ferrite structure, and the structure after quenching + tempering can significantly improve fatigue life.

[0037] 7) The carburized bearing steel wire rod for heavy-duty railway rollers produced by the present invention has high purity, shallow decarburization, fine grains, good material homogeneity, low production cost, high production efficiency, and greatly improves the yield rate compared with the electroslag process, improves the environment, meets the low-carbon needs of customers, and can achieve ultra-long service life and increase customer adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a 100X metallographic photograph of the material structure in the embodiment of the present invention.

[0039] Figure 2 This is a 500X metallographic photograph of the material structure in the embodiment of the present invention.

[0040] Figure 3 This is a 200X metallographic photograph of the grain size in the embodiment of the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0042] Implementation Cases 1-2

[0043] The carburized bearing steel for heavy-duty railway rollers of the present invention is manufactured according to the following steps:

[0044] 1) Smelting: After smelting in a 100-ton steelmaking furnace, refining is carried out outside the furnace, and the molten steel is then vacuum degassed. The mass percentage of each chemical element is strictly controlled as required.

[0045] 2) Continuous casting: Continuously cast into 390mm×510mm square billets, and control the overheating degree of the tundish to be 10~20℃. In order to control the segregation of the material, advanced end electromagnetic stirring, current>300A, and continuous casting total light pressure of 10mm are used during continuous casting. The chemical composition percentage of the obtained continuous casting billet is shown in Table 1 below:

[0046] Table 1. (wt.%, the balance is Fe and other unavoidable impurity elements)

[0047]

[0048]

[0049] 3) The temperature of the continuous casting billet in the pit is 680℃, the slow cooling time in the pit is 52 hours, and the temperature out of the pit is 85℃.

[0050] 4) Billet heating + billet opening: The billet is cold loaded into a step-beam heating furnace for heating, and the temperature is rapidly raised to 1100-1200℃ at 200℃ / h for uniform heat preservation, and the uniform heat preservation time is ≥4.5 hours. The starting rolling temperature is ≥1050℃, the final rolling temperature is ≥800℃, and the billet is rolled into 150mm 2 intermediate billet.

[0051] The main specific process parameters in the above embodiments are shown in Table 2 below:

[0052] Table 2. (Main specific process parameters for billet heating and hot rolling)

[0053]

[0054] 5) Intermediate billet heating + rolling wire rod + controlled cooling of wire rod: After the surface of the intermediate billet is cleaned to a depth of 2.0mm, it is cooled and loaded into the furnace, and the temperature is quickly raised to 800℃ in 1h, and then raised to the temperature of the soaking section 1050±30℃ in 0.5h, and kept warm for 0.5~1h. Set the starting rolling temperature ≥900℃, the intermediate rolling temperature ≥900℃, the finishing rolling temperature 930±30℃, and the wire laying temperature 900±30℃. After laying, the wire rod is air-cooled to a temperature of 700~800℃, and slowly cooled to ≤450℃ in the insulation cover for coiling and unloading.

[0055] The main specific process parameters in the above embodiments are shown in Table 3 below:

[0056] Table 3. (Main specific process parameters for intermediate billet heating and hot rolling)

[0057]

[0058] The finished carburized bearing steel wire rods for heavy-duty railway rollers in Examples 1 and 2 were subjected to relevant tests, and the purity, grain size, carbide and core segregation were measured as shown in Table 4 below:

[0059] Table 4 (purity, grain size, DI value and segregation results of finished wire rod)

[0060]

[0061] As can be seen from Table 4, the inclusions, grain size, DI value and center segregation in the embodiment meet the design requirements, indicating that the material has very high cleanliness, fine grains, excellent homogeneity, and uses a new component optimization design, which greatly reduces the cost and obtains a low-cost, high fatigue life carburized railway roller.

[0062] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carburized bearing steel for heavy-duty railway rollers, characterized in that: The chemical composition of the steel plate and its mass percentage are C: 0.17-0.23%, Si: 0.15-0.40%, Mn: 0.60-0.90%, P: ≤0.020%, S: ≤0.025%, Cr: 0.35-0.85%, Al: 0.020-0.060%, Cu≤0.30%, Mo≤0.10-0.30%, Ni: 0.40-0.80%, As+Sn+Sb≤0.065%, Ti≤0.0010%, Ca≤0.0005%, O≤0.0008%, N: 0.008-0.012%, and the balance is Fe and unavoidable impurity elements.

2. The carburized bearing steel for heavy-duty railway roller according to claim 1, characterized in that: The low multiple of the bearing steel is not greater than S1, R1, C1; non-metallic inclusions: A coarse ≤ 1.5, A fine ≤ 2.5, B coarse ≤ 0.5, B fine ≤ 1.5, D coarse ≤ 0.5, D fine ≤ 1.0, DS ≤ 1.0; DI value 2.2-2.6; decarburization ≤ 0.10 mm; grain size ≤ 8 levels.

3. The carburized bearing steel for heavy-duty railway roller according to claim 1, characterized in that: The metallographic structure of the bearing steel is a pearlite + bainite + ferrite structure with a sheet spacing of 0.10 to 0.25 μm. The structure is easy to spheroidize during the subsequent heat treatment process. At the same time, the structure is fine needle martensite + nano-austenite + fine-grained carbide after quenching + tempering. About 15% of the residual austenite in the structure is mainly in the form of ultrafine grain blocks.

4. A method for producing carburized bearing steel for heavy-duty railway rollers according to claim 1, characterized in that: The method comprises the following steps: (1) Smelting: All hot metal smelting, refining uses precipitation and diffusion composite deoxidation, refining stirring and RH raising gas uses nitrogen throughout the process, the alloy composition is no longer adjusted after refining, and the purity of the molten steel is strictly controlled; (2) Continuous casting: electromagnetic stirring at the beginning and end, weak cooling, and light pressure reduction are matched, and the pouring superheat is controlled at 10-20°C to obtain 390mm*510mm continuous casting billets with excellent segregation quality; (3) Slow cooling of continuous casting billet: Slow cooling of continuous casting billet in pit, with the exit temperature less than 200℃; (4) Rolling into intermediate billet: The billet is rolled using a large compression ratio rolling process, with a rolling temperature of ≥1050°C, an initial rolling compression ratio of ≥2.5, a continuous rolling temperature of ≥980°C, a final rolling temperature of ≥800°C, a bottom line temperature of ≥500°C, a total compression ratio of ≥4.5, and the billet is rolled into 120-240 mm. 2 Square intermediate blank; (5) Wire rod rolling: the wire rod controlled rolling setting starting rolling temperature is ≥900℃, the initial rolling compression ratio is ≥1.5, the intermediate rolling temperature is ≥900℃, the finishing rolling temperature is 930±30℃, the wire laying temperature is 900±30℃, and the total compression ratio is ≥40; (6) Controlled cooling: After spinning, the wire rod is air-cooled to a temperature of 700-800°C, and then enters the heat preservation cover to slowly cool to ≤450°C for winding and unloading; (7) Inspection: The wire rod off the production line is inspected for DI value, grain size, inclusions, and decarburization. If all are qualified, the finished hot-rolled wire rod of carburized bearing steel for heavy-duty railway rollers is obtained.

5. The method for producing carburized bearing steel for heavy-duty railway rollers according to claim 4, characterized in that: In step (3), the temperature of the lower pit is greater than 650° C., and the slow cooling time of the lower pit is greater than 48 hours.

6. The method for producing carburized bearing steel for heavy-duty railway rollers according to claim 4, characterized in that: Before rolling in step (4), the temperature is raised to 1020-1220° C. at a rate of 150-250° C. / h in a heating furnace with a neutral or weakly oxidizing atmosphere, and the temperature is kept at this temperature for 4.5-7.5 h.

7. The method for producing carburized bearing steel for heavy-duty railway rollers according to claim 4, characterized in that: In step (5), the intermediate square billet is heated before the wire rod is rolled, with a heating rate of 600 to 800° C. / h; the temperature is raised to 1050±30° C. and kept warm for 0.5 to 1 h.

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