A method for manufacturing a high homogeneity and high purity die-cast railway carburized bearing steel

Abstract

The application provides a manufacturing method of high-homogeneity and high-purity die-casting railway carburized bearing steel, which comprises the following steps in sequence: electric furnace smelting, LF refining, RH vacuum degassing, die-casting pouring, high-temperature diffusion of the ingot, ingot rolling and breaking down, and billet rolling; in the LF refining process, the mass content of Al in the molten steel is controlled to be 0.020-0.050%, and the mass content of N in the molten steel is controlled to be 0.007-0.012%; in the high-temperature diffusion step of the ingot, the die-casting ingot is heated, the heating temperature is 1260-1290 DEG C, and the heating time is greater than or equal to 5 hours; in the billet rolling step, the billet is heated and rolled, wherein the heating temperature is 1180-1230 DEG C, the holding time is greater than or equal to 40 minutes, and the final rolling temperature is 850-950 DEG C. The preparation method effectively reduces the oxygen content, titanium content and sulfur content of the steel, reduces the inclusion content, refines the micro non-metallic inclusion size, and the macro inclusion defect is 0. The problem of insufficient purity and density of the vacuum degassing die-casting bearing steel in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of special steel metallurgy, in particular to a manufacturing method of high homogeneity and high purity die casting railway carburizing bearing steel. BACKGROUND

[0002] Bearing is a key component of railway train, railway bearing not only bears complex alternating load, but also guarantees long-term stable high-speed operation, and its performance directly affects the safety of train operation. Therefore, very strict requirements are put forward for the manufacturing of bearing and the raw material for manufacturing bearing.

[0003] In the selection of railway bearing steel material grade, foreign well-known enterprises such as NTN, Timken, Brenco mainly adopt carburizing bearing steel. The material for railway bearing ring of freight car in China is carburizing bearing steel. The bearing parts manufactured by carburizing bearing steel have high wear resistance on the surface, and the core has high impact toughness. It meets the characteristics of high speed, heavy load and impact resistance of railway bearing.

[0004] In the steel smelting production method, foreign advanced enterprises have electroslag smelting process or vacuum degassing die casting process. China has always adopted the conservative electroslag smelting process. The steel produced by electroslag smelting process has fine and uniform distribution of non-metallic inclusions, high uniformity and compactness, and the product quality fully meets the needs of railway bearing manufacturing, but there are problems such as small production batch, low production efficiency, complex batch management, high cost, serious environmental pollution and the like. Therefore, foreign advanced enterprises have begun to use low-cost and high-efficiency vacuum degassing process to produce railway bearing steel. In recent years, domestic steel plants have also begun to try to use vacuum degassing die casting or continuous casting process to produce railway bearing steel. Compared with electroslag remelting process, vacuum degassing die casting or continuous casting process can greatly improve production efficiency, shorten production cycle and greatly reduce production cost. But at the current physical level, the control of product uniformity and compactness is not stable and ideal.

[0005] The defects existing in the existing production technology of railway bearing steel are: using electroslag smelting process to produce, low production efficiency, high production cost and serious environmental pollution. Using vacuum degassing die casting process to produce, poor material organization uniformity and compactness, unstable hardenability, serious part heat treatment deformation, insufficient material purity, and it is difficult to achieve zero defect of tower type macro-inclusion detection.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] The present application aims to provide a high homogeneity and high purity die casting railway carburizing bearing steel and a manufacturing method thereof.

[0008] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0009] The present application provides a manufacturing method of high homogeneity and high purity die casting railway carburizing bearing steel, characterized in that it comprises the following steps in sequence: electric furnace smelting, LF refining, RH vacuum degassing, die casting pouring, steel ingot high temperature diffusion, steel ingot rolling and breaking down, and steel billet rolling.

[0010] In the LF refining process, the mass content of Al in the molten steel is controlled to be 0.020-0.050%, and the mass content of N in the molten steel is controlled to be 0.007-0.012%.

[0011] In the steel ingot high temperature diffusion step, the die casting steel ingot is heated, and the heating temperature is 1260-1290°C, and the heating time is ≥5 hours.

[0012] In the steel billet rolling step, the steel billet is heated and rolled, wherein the heating temperature is 1180-1230°C, the holding time is ≥40 minutes, and the final rolling temperature is 850-950°C.

[0013] Further, in the electric furnace smelting step, an eccentric bottom high-power electric arc furnace is used; preferably, the power of the eccentric bottom high-power electric arc furnace is 28000w.

[0014] Further, in the electric furnace smelting step, oxygen blowing decarburization is used, and the mass content of carbon at the smelting endpoint is controlled to be ≤0.10%; preferably, the tapping temperature is ≥1640°C; preferably, Al is added to the molten steel during tapping, and the mass of the added Al is ≥2.0kg / t; preferably, the slag in the clean ladle needs to be removed after tapping; preferably, 2.0-3.0kg / t of refining slag is added to the molten steel after smelting; preferably, the main components of the refining slag are Al2O3 and CaO, wherein the mass content of CaO is 45%-60%.

[0015] Further, in the LF refining step, a special refining slag is added into the molten steel; preferably, the adding amount of the special refining slag is 4.0-6.0 kg / t; preferably, the component contents of the special refining slag and the refining slag added after the completion of the electric furnace smelting are the same; preferably, in the LF refining process, the electrode heating is used for temperature rising, and a low-Ti alloy is added, wherein the Ti content in the alloy is ≤0.01%; preferably, the low-Ti alloy comprises at least one of Ni plate, Mo iron, and Cr iron alloy; preferably, the total refining time is ≥60 min; and preferably, the tapping temperature is 1550-1650℃.

[0016] Further, in the RH vacuum degassing step, argon is used for stirring throughout the whole process, the argon pressure is 0.1 MPa-66.7 Pa, and the holding time is >20 min.

[0017] And / or, the N content in the RH furnace is controlled to be 70-120 ppm.

[0018] And / or, in the mold casting pouring step, argon is used as the protective gas throughout the whole process, and the oxygen content in the protective gas is ≤1000 ppm; and / or, the mold casting ingot obtained through the mold casting pouring is a 3-ton ingot.

[0019] And / or, the finish rolling temperature of the ingot rolling breakdown is 900-1000℃.

[0020] Further, in the ingot high-temperature diffusion step, the heating time is 5-10 h.

[0021] And / or, in the billet rolling step, the single-pass deformation reduction is 20-40%; and preferably, the rolling compression ratio is 18-43%.

[0022] In addition, the application further provides a high-homogeneity high-purity mold casting railway carburized bearing steel, which comprises the following chemical components in mass percentage:

[0023] C: 0.20-0.22%, Si: 0.28-0.32%, Mn: 0.55-0.62%, P: 0.009-0.015%, S: ≤0.005%, Cr: 0.48-0.55%, Ni: 1.70-1.80%, Mo: 0.23-0.26%, Al: 0.020-0.050%, N: 0.0070-0.0120%, O: ≤0.00055%, Ti: ≤0.0011%, As: ≤0.005%, Pb: ≤0.0006%, Sb: ≤0.003%, Sn: ≤0.003%, Ca: ≤0.0004%, and the rest is Fe and inevitable impurities.

[0024] Further, the chemical composition includes the following mass percentages: C: 0.20-0.22%, Si: 0.28-0.32%, Mn: 0.55-0.62%, P: 0.009-0.015%, S: 0.003-0.005%, Cr: 0.48-0.55%, Ni: 1.70-1.80%, Mo: 0.23-0.26%, Al: 0.020-0.050%, N: 0.0070-0.0120%, O: 0.00045-0.00055%, Ti: 0.0007-0.0010%, As: 0.004-0.005%, Pb: 0.0005-0.0006%, Sb: 0.002-0.003%, Sn: 0.002-0.003%, Ca: 0.0003-0.0004%, and the rest is Fe and inevitable impurities.

[0025] Further, the carburizing bearing steel is detected according to the Q / CR592 standard, the macro-inclusion is 0, the micro-non-metallic inclusion is: A fine ≤1.0 level, A coarse ≤0.5 level, B fine ≤1.0 level, B coarse ≤0.5 level, D fine ≤1.0 level, D coarse ≤0.5 level, and Ds ≤0.5 level; and the low-multiple organization defect level is all ≤0.5 level.

[0026] Further, the carburizing bearing steel has a grain size level ≥8 level; and / or, the carburizing bearing steel has a hardenability band width of 3HRC-5HRC.

[0027] Compared with the prior art, the technical scheme of the present application has at least the following technical effects:

[0028] (1) In the preferred scheme of the present application, the combination of technologies such as eccentric bottom high-power electric arc furnace, slag removal after the furnace, alloy selection, special refining slag, mold casting full-process protection pouring, and low-titanium control technology, effectively reduces the oxygen content, titanium content, and sulfur content of the steel, reduces the inclusion content, refines the micro-non-metallic inclusion size, and the macro-inclusion defect is 0. The quality of the carburizing bearing steel prepared by the method of the present application is comparable to that of the carburizing bearing steel produced by the electroslag smelting process, fully meets the demand of railway bearing production, and compared with the electroslag smelting process, the preparation method of the present application eliminates the high-cost and long-cycle electroslag remelting process, not only saves the production cost, but also is more efficient and environmentally friendly.

[0029] (2) the present application adopts trace elements Al, N and other reasonable control technology (controlling trace elements to realize the control of grain size, ensuring the uniformity and compactness of the structure of the steel), quenching software simulation control technology (comprehensive calculation of various alloy element content matching control by computer software, thereby realizing the control of quenching bandwidth range), die casting automatic pouring, steel ingot high temperature diffusion, rolling large reduction and other combined technologies, which effectively improve the uniformity and compactness of the structure of the obtained steel, the macrostructure defect level of the carburizing bearing steel prepared by the present application is ≤0.5 level, the quenching bandwidth is as narrow as 3HRC, and the grain size is finer than or equal to 8 level. The quality of the carburizing bearing steel prepared by the method of the present application is equivalent to that of electroslag steel, and fully meets the demand of railway bearing production.

[0030] The present application provides a production method of high-homogeneity high-purity vacuum degassing die-casting carburizing bearing steel for railway, which adopts a series of special technologies such as vacuum degassing, electric furnace high-efficiency low-energy consumption, initial molten steel oxygen control, low-titanium carburizing steel control, RH furnace nitrogen control, protective pouring, die-casting protective slag hanging, single-pass large reduction control and the like, and a complete production technology system of high-homogeneity high-purity vacuum degassing die-casting carburizing bearing steel for railway is established through series technology integration innovation, so that the problems of insufficient purity and compactness of die-casting bearing steel are solved, the high-purity high-homogeneity high-performance die-casting carburizing bearing steel product developed by the present application reaches the level of electroslag steel, and fully meets the use requirements of railway bearing, and has strong market competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which form a part of this application, are used to provide further understanding of the application, and the illustrative embodiments of the application and their description serve the purpose of explaining the application. Of course, the application is not limited to the embodiments described and illustrated herein. Among other things, the following will be explained with reference to the drawings, in which:

[0032] Figure 1 The macrostructure detection results of the carburizing bearing steel prepared in Example 1 (the general porosity, center porosity and segregation are all 0.5 level) are shown in Table 1.

[0033] Figure 2 The macrostructure detection results of the electroslag steel (the general porosity, center porosity and segregation are all 0.5 level) are shown in Table 1. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitation to the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The process parameters not specified in the following embodiments are usually according to conventional conditions.

[0035] The endpoints of the ranges and any values described herein are not limited to the precise values recited as should be understood at the very least, the certain ranges or values should be construed as not limited to the precise range or value, but rather should be understood as having a range around the stated value or range. For example, a range from 1 to 6 should be understood as having a range from about 1 to about 6, that is, having a range from 1 to 6 inclusive of the endpoints 1 and 6, and also including ranges from 1-6, 2-5, 2-4, 2-3, 3-4, and 3-5 inclusive as well as sub-ranges and / or multiple ranges therefrom.

[0036] According to a first aspect of the present application, there is provided a method for manufacturing high homogeneity and high purity die casting railway carburized bearing steel, comprising the following steps in sequence: electric furnace smelting, LF refining, RH vacuum degassing, die casting pouring, high temperature diffusion of the ingot, roughing rolling of the ingot and rolling of the billet.

[0037] In the LF refining process, the mass content of Al in the molten steel is controlled to be 0.020-0.050% (including 0.020%, 0.030%, 0.040%, 0.050% and any numerical range between any two of them), and the mass content of N in the molten steel is controlled to be 0.007-0.012% (including 0.007%, 0.008%, 0.009%, 0.010%, 0.012% and any numerical range between any two of them).

[0038] In the high temperature diffusion step of the ingot, the die casting ingot is heated, the heating temperature is 1260-1290°C (including 1260°C, 1270°C, 1280°C, 1290°C and any numerical range between any two of them), and the heating time is ≥5 hours; here the heating time needs to be controlled to be greater than or equal to 5 hours, which can ensure that the ingot is burned through, and at the same time is beneficial to homogenization, and if the temperature is too high, the ingot is overburned, and if the temperature is too low, the plasticity is not good and easy to crack. The ingot after high temperature diffusion is roughed, and the finish rolling temperature is 900-1000°C.

[0039] In the rolling step of the billet, the billet is heated and rolled, wherein the heating temperature is 1180-1230°C (including 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C and any numerical range between any two of them), the holding time is ≥40 minutes, and the finish rolling temperature is 850-950°C (including 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C and any numerical range between any two of them). If the finish rolling temperature is too low, the plasticity is not good and easy to crack during rolling, and if the finish rolling temperature is too high, the scale is thick and the surface quality of the billet is poor.

[0040] As a preferred embodiment of the present application, in the electric furnace smelting step, an eccentric bottom high-power electric arc furnace is used; preferably, the power of the eccentric bottom high-power electric arc furnace is 28000w.

[0041] In a preferred embodiment of the present application, the carburizing bearing steel is produced by using the process route of eccentric bottom high-power electric arc furnace smelting, LF refining, RH vacuum degassing, protective atmosphere die casting, high-temperature diffusion and rolling. Through production process design, key process technology research and control, the produced carburizing bearing steel has ultra-high purity and homogeneity. According to the detection method of the Q / CR592 standard method of the carburizing bearing steel of the railway freight car in China, the mass content of oxygen is ≤0.00055%; the mass content of titanium is ≤0.0011%; the mass content of sulfur is ≤0.005%; the macroscopic inclusions are 0, the microscopic non-metallic inclusions A fine is ≤1.0 level, A coarse is ≤0.5 level, B fine is ≤1.0, B coarse is ≤0.5 level, D fine is ≤1.0 level, D coarse is ≤0.5 level, Ds is ≤0.5 level; the low-magnification organizational defect level (including general porosity, center porosity and segregation) is all ≤0.5 level; the grain size is finer than or equal to 8 level; and the quenching hardening band width is the narrowest to reach 3HRC.

[0042] As a preferred embodiment of the present application, in the electric furnace smelting step, the electric furnace oxygen blowing decarburization is used to control the mass content of the carbon at the smelting end point ≤0.10%; preferably, the tapping temperature is ≥1640℃; preferably, Al is added to the molten steel during the tapping process, and the mass of the added Al is ≥2.0kg / t; the slag in the clean ladle needs to be removed after the tapping; preferably, 2.0-3.0kg / t of refining slag is added to the molten steel after the smelting is completed; the refining slag of the present application is a special refining slag, which is different from the ordinary conventional refining slag used for electroslag steel, and the main components of the refining slag of the present application are Al2O3 and CaO, wherein the mass content of CaO is 45%-60%. The refining slag is added to the molten steel after the smelting is completed in order to better cover the molten steel to prevent oxidation and play a heat preservation role.

[0043] In the LF refining step, the special refining slag is added to the molten steel; preferably, the addition amount of the special refining slag is 4.0-6.0kg / t; preferably, the component contents of the special refining slag and the refining slag added after the electric furnace smelting are the same; the special refining slag is added in the LF refining process in order to deoxidize and remove inclusions.

[0044] Preferably, in the LF refining process, the electrode heating is warmed up, and a low-Ti alloy is added, wherein the Ti content in the alloy is ≤0.01%; the low-Ti alloy includes at least one of Ni plate, Mo iron, Cr iron and the like; the purpose of selecting the low-Ti alloy is to reduce harmful inclusions in the form of sharpness. Preferably, the total refining time is ≥60 min; the total refining time needs to be controlled to be more than 60 min, and if the time is too short, the purity of the molten steel is not ideal. Preferably, the tapping temperature is 1550-1650℃.

[0045] As a preferred embodiment of the present application, in the RH vacuum degassing step, argon is used for stirring throughout the whole process, the argon pressure is 0.1MPa-66.7Pa, and the holding time is >20min; the N content in the RH furnace is controlled to be 70-120ppm; the N content controlled in this range is beneficial to refining the grains of the steel and improving the performance.

[0046] In the mold casting pouring step, argon is used as the protective gas throughout the whole process to prevent secondary oxidation of the molten steel, and the oxygen content in the protective gas is monitored in real time throughout the whole process to control the oxygen content to be ≤1000PPM to ensure the purity of the protective gas. In addition, the pouring speed in the present application is generally gentle, which can ensure the stable quality of the steel. In the embodiment, the mold casting ingot obtained by the mold casting pouring is a 3-ton ingot, and the specification of the ingot is generally determined according to the finished product specification.

[0047] As a preferred embodiment of the present application, in the high-temperature diffusion step of the ingot, the heating time is 5-10h;

[0048] In the billet rolling step, the single-pass deformation reduction rate is 20-40%; preferably, the rolling compression ratio is 18-43% (including 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42% and 43% and any value range between any two points).

[0049] According to a second aspect of the present application, a high-homogeneity high-purity mold casting railway carburizing bearing steel is provided, which is prepared by the above manufacturing method and includes the following chemical components in mass percentage:

[0050] C: 0.20-0.22%, Si: 0.28-0.32%, Mn: 0.55-0.62%, P: 0.009-0.015%, S: ≤0.005%, Cr: 0.48-0.55%, Ni: 1.70-1.80%, Mo: 0.23-0.26%, Al: 0.020-0.050%, N: 0.0070-0.0120%, O: ≤0.00055%, Ti: ≤0.0011%, As: ≤0.005%, Pb: ≤0.0006%, Sb: ≤0.003%, Sn: ≤0.003%, Ca: ≤0.0004%, and the rest is Fe and inevitable impurities.

[0051] The carburizing bearing steel contains low content of metal inclusions (Ti, As, Pb, Sb, Sn, Ca) and non-metallic inclusions (P, S, N, O), and is a high-purity, high-homogeneity and high-performance carburizing bearing steel, which has the same quality as the steel smelted by the electroslag process and meets the demand of high-end railway bearing manufacturing.

[0052] As a preferred embodiment of the present application, the carburizing bearing steel comprises the following chemical components in percentage by mass:

[0053] C: 0.20-0.22%, Si: 0.28-0.32%, Mn: 0.55-0.62%, P: 0.009-0.015%, S: 0.003-0.005%, Cr: 0.48-0.55%, Ni: 1.70-1.80%, Mo: 0.23-0.26%, Al: 0.020-0.050%, N: 0.0070-0.0120%, O: 0.00045-0.00055%, Ti: 0.0007-0.0010%, As: 0.004-0.005%, Pb: 0.0005-0.0006%, Sb: 0.002-0.003%, Sn: 0.002-0.003%, Ca: 0.0003-0.0004%, and the rest is Fe and inevitable impurities.

[0054] As a preferred embodiment of the present application, the carburizing bearing steel is detected according to the Q / CR592 standard, and the macroscopic inclusions are 0, the microscopic non-metallic inclusions are as follows: A fine ≤1.0 level, A coarse ≤0.5 level, B fine ≤1.0 level, B coarse ≤0.5 level, D fine ≤1.0 level, D coarse ≤0.5 level, and Ds ≤0.5 level; and the low-multiple organizational defect level is ≤0.5 level.

[0055] As a preferred embodiment of the present application, the carburizing bearing steel has a grain size level ≥8 level; and / or, the carburizing bearing steel has a hardenability band width of 3HRC-5HRC.

[0056] The application will be described in further detail below in connection with specific examples and comparative examples.

[0057] It should be noted that the grain size detection method in the following examples and comparative examples is in accordance with GB / T6394, and the detection standard is ≥6 grade; the hardenability detection method is in accordance with GB / T225, and the detection standard is J9 = 35-38 HRC.

[0058] The electroslag steel used for comparison is self-made The bar and its preparation method are as follows:

[0059] (1) Electric furnace smelting: the oxygen blowing decarburization of an eccentric bottom high-power electric arc furnace with a power of 28000w is adopted, the mass content of the carbon at the smelting end point is controlled to be 0.11%, the tapping temperature is 1666℃, 2.0kg / t of Al is added into the molten steel during the tapping process, and 150kg of refining slag (the main components of the refining slag are Al2O3, MgO and CaO, wherein the mass content of CaO is 40%) is added into the molten steel after the smelting is completed.

[0060] (2) LF refining: 800kg of refining slag is added into the molten steel, the component content of the refining slag is the same as that of the refining slag added in the above-mentioned converter smelting step, the electrode is heated to be warmed, alloys including Ni plate, Mo iron, Cr iron and the like are added, the mass content of Al in the molten steel is controlled to be 0.040-0.060%, and the total refining time is 46min, and the tapping temperature is 1645℃.

[0061] (3) RH vacuum degassing: argon gas stirring is adopted throughout the process, the argon gas pressure is 0.1MPa, and the holding time is 25min.

[0062] (4) Continuous casting: 390mm round billets are continuously cast, the whole process from the ladle to the tundish, the tundish to the tundish and the tundish to the crystallizer is protected by argon gas, and the liquid level fluctuation of the crystallizer is controlled; the superheat degree of the molten steel is 22-35℃, and the drawing speed is 0.45m / min;

[0063] (5) Electroslag remelting: the iron oxide scale on the surface of the consumable electrode rod is removed before the electroslag remelting, and CaO and Al2O3 slag system is adopted for the electroslag remelting smelting; argon gas protection is adopted throughout the electroslag remelting process, the melting speed is 7kg / min, and 3 tons of ingots are poured.

[0064] (6) Ingot heating: the die-cast ingot is heated, the heating temperature is 1281℃, and the heating time is 2.5 hours. After the heated ingot is rolled and bloomed, the final rolling temperature is 980℃, and 240mm square billets are obtained.

[0065] (7) Steel billet rolling: the steel billet is heated and rolled to obtain the electroslag carburizing bearing steel, wherein the heating temperature is 1185-1197℃, the holding time is 35 minutes, the finish rolling temperature is 870℃, and the rolling compression ratio is 26.2. The finished product specification is

[0066] Example 1

[0067] (1) Electric furnace smelting: an eccentric bottom high-power electric arc furnace with a power of 28000w is used to perform oxygen blowing decarburization, the mass content of the carbon at the smelting endpoint is controlled to be 0.08%, the tapping temperature is 1645℃, 2.2kg / t of Al is added to the molten steel during the tapping process, the slag in the clean ladle needs to be removed after tapping, and 200kg of refining slag (the main components of the refining slag are Al2O3 and CaO, wherein the mass content of CaO is 45%) is added to the molten steel after smelting is completed.

[0068] (2) LF refining: 600kg of special refining slag is added to the molten steel, the component content of the special refining slag is the same as that of the refining slag added in the above electric furnace smelting step, the electrode is heated to increase the temperature, and alloys including Ni plate, Mo iron, and Cr iron are added, the mass content of Al in the molten steel is controlled to be 0.020-0.050%, the mass content of N in the molten steel is controlled to be 0.007-0.012%, and the total refining time is 65min, and the tapping temperature is 1580℃.

[0069] (3) RH vacuum degassing: argon gas is used for stirring throughout the process, the argon gas pressure is 0.1MPa, and the holding time is 30min.

[0070] (4) Mold casting pouring: argon gas protection is used throughout the process to prevent secondary oxidation of the molten steel, the oxygen content in the protective gas is monitored in real time throughout the process to ensure that the purity of the protective gas is lower than 950PPM, the pouring speed is strictly controlled, and the pouring process is ensured to be smooth, and 3 tons of ingots are poured.

[0071] (5) Steel ingot high-temperature spreading: the mold cast steel ingot is heated, the heating temperature is 1281℃, and the heating time is 5.5 hours.

[0072] (6) After the high-temperature diffusion of the steel ingot, the steel ingot is rolled and broken down, the finish rolling temperature is 965℃, and the 240mm square billet is obtained.

[0073] (7) Steel billet rolling: the steel billet is heated and rolled to obtain the electroslag carburizing bearing steel, wherein the heating temperature is 1185-1195℃, the holding time is 45 minutes, the finish rolling temperature is 880℃, and the rolling compression ratio is 42.1%. The finished product specification is

[0074] Two samples of the carburizing bearing steel prepared in the example were taken as example steel 1-1 and example steel 1-2, and were subjected to ultrasonic and surface flaw detection, and the performance detection results are shown in Tables 1 and 2, wherein the macro-inclusion tower type and high-frequency flaw detection are both 0, and the low-magnification organizational defect level is 0.5 level.

[0075] Example 2

[0076] (1) Electric furnace smelting: an eccentric bottom high-power electric arc furnace with a power of 28000w is used for electric furnace oxygen blowing decarburization, the mass content of carbon at the smelting endpoint is controlled to be 0.07%, the tapping temperature is 1646℃, 2.2kg / t of Al is added to the molten steel during tapping, the slag in the clean ladle needs to be removed after tapping, and 200kg of refining slag (the main components of the refining slag are Al2O3 and CaO, wherein the mass content of CaO is 60%) is added to the molten steel after smelting is completed.

[0077] (2) LF refining: 600kg of special refining slag is added to the molten steel, the component content of the special refining slag is the same as that of the refining slag added in the above electric furnace smelting step, the electrode is heated to increase the temperature, and alloys including Ni plate, Mo iron, Cr iron are added, the mass content of Al in the molten steel is controlled to be 0.020-0.050%, and the mass content of N in the molten steel is controlled to be 0.007-0.012%, the total refining time is 70min, and the tapping temperature is 1576℃.

[0078] (3) RH vacuum degassing: argon gas is used for stirring throughout the process, the argon gas pressure is 0.1MPa, and the holding time is 35min.

[0079] (4) Mold casting: argon gas protection is used throughout the process to prevent secondary oxidation of the molten steel, the oxygen content in the protective gas is monitored in real time throughout the process to ensure that the purity of the protective gas is less than 970PPM, the pouring speed is strictly controlled, and the pouring process is ensured to be smooth, and 3 tons of ingots are poured;

[0080] (5) High-temperature spreading of the ingot: the mold cast ingot is heated, the heating temperature is 1283℃, and the heating time is 5.3 hours.

[0081] (6) After high-temperature diffusion, the ingot is rolled and bloomed, and the final rolling temperature is 970℃, and 240mm square billets are obtained.

[0082] (7) Billet rolling: the billet is heated and rolled to obtain the carburizing bearing steel of the application, wherein the heating temperature is 1190-1200℃, the holding time is 46min, the final rolling temperature is 890℃, and the rolling compression ratio is 33.3%. The finished product specification is

[0083] Two portions of the carburizing bearing steel prepared in the example were extracted, denoted as example steel 2-1 and example steel 2-2, and subjected to ultrasonic and surface flaw detection, and the performance detection results are shown in Tables 1 and 2, wherein the macro-inclusion tower type and high-frequency flaw detection are both 0, and the low-magnification structure defect level is 0.5 grade.

[0084] Example 3

[0085] (1) Electric furnace smelting: an eccentric bottom high-power electric arc furnace with a power of 28000w is used for oxygen blowing and decarburization, the mass content of carbon at the smelting endpoint is controlled to be 0.08%, the tapping temperature is 1646℃, 2.2kg / t of Al is added to the molten steel during tapping, the slag in the clean ladle needs to be removed after tapping, and 200kg of refining slag (the main components of the refining slag are Al2O3 and CaO, wherein the mass content of CaO is 50%) is added to the molten steel after smelting is completed.

[0086] (2) LF refining: 600kg of special refining slag is added to the molten steel, the component content of the special refining slag is the same as that of the refining slag added in the above electric furnace smelting step, the electrode is heated to increase the temperature, and alloys including Ni plate, Mo iron, Cr iron are added, the mass content of Al in the molten steel is controlled to be 0.020-0.050%, and the mass content of N in the molten steel is controlled to be 0.007-0.012%, the total refining time is 68min, and the tapping temperature is 1586℃.

[0087] (3) RH vacuum degassing: argon gas is used for stirring throughout the process, the argon gas pressure is 0.1MPa, and the holding time is 35min.

[0088] (4) Mold casting: argon gas protection is used throughout the process to prevent secondary oxidation of the molten steel, the oxygen content in the protective gas is monitored in real time throughout the process to ensure that the purity of the protective gas is lower than 950PPM, the pouring speed is strictly controlled, and the pouring process is ensured to be smooth, and 3 tons of ingots are poured;

[0089] (5) High-temperature spreading of the ingot: the mold cast ingot is heated, the heating temperature is 1282℃, and the heating time is 5.4 hours.

[0090] (6) Billet rolling: the billet is heated and rolled to obtain the carburizing bearing steel of the application, wherein the heating temperature is 1195-1205℃, the holding time is 48min, the finish rolling temperature is 895℃, and the rolling compression ratio is 18.7%. The finished product specification is

[0091] Two portions of the carburizing bearing steel prepared in the example were extracted, denoted as example steel 3-1 and example steel 3-2, and subjected to ultrasonic and surface flaw detection, and the performance detection results are shown in Tables 1 and 2, wherein the macro-inclusion tower type and high-frequency flaw detection are both 0, and the low-magnification structure defect level is 0.5 grade.

[0092] Comparative Example 1

[0093] This comparative example is substantially the same as Example 1, except that in the LF refining, the total refining time is < 60 minutes.

[0094] The chemical composition of the carburized bearing steel prepared in this comparative example is: C: 0.21%, Si: 0.30%, Mn: 0.59%, P: 0.009%, S: 0.003%, Cr: 0.53%, Ni: 1.78%, Mo: 0.24%; the grain size is 7 grade; comparable to the example steel; the hardenability band width is 3HRC, comparable to the example steel; the non-metallic inclusions (A fine 2.5 grade, B fine 2.5 grade, C class 0 grade, D fine 1.0 grade), the grade is higher than the test steel, not meeting the standard requirements; the macrostructure defect level (general porosity, center porosity, segregation are all 0.5 grade), comparable to the example steel, meeting the standard requirements.

[0095] Comparative Example 2

[0096] This comparative example is substantially the same as Example 1, except that in the rolling step, the single pass deformation reduction rate is less than 18%.

[0097] The chemical composition of the carburized bearing steel prepared in this comparative example is: C: 0.22%, Si: 0.29%, Mn: 0.58%, P: 0.010%, S: 0.003%, Cr: 0.52%, Ni: 1.75%, Mo: 0.24%;

[0098] the grain size is 7 grade; comparable to the example steel; the hardenability band width is 3HRC, comparable to the example steel; the non-metallic inclusions (A fine 1.0 grade, B fine 0.5 grade, C class 0 grade, D fine 1.0 grade), comparable to the example steel, meeting the standard requirements; the macrostructure defect level (general porosity, center porosity, all are 1.5-2.0 grade, segregation is all 0.5 grade), not as dense as the macrostructure of the example steel, not meeting the standard requirements.

[0099] Comparative Example 3

[0100] This comparative example is substantially the same as Example 1, except that in the LF refining process, the mass content of Al in the molten steel is controlled to be 0.010%, and the mass content of N in the molten steel is controlled to be 0.005%;

[0101] The chemical composition of the carburized bearing steel prepared in the present comparative example is: C: 0.21%, Si: 0.29%, Mn: 0.59%, P: 0.009%, S: 0.003%, Cr: 0.52%, Ni: 1.75%, Mo: 0.24%; the grain size is 3-4 grade, which is not as fine and uniform as the steel in the examples and does not meet the standard requirement; the hardenability band width is 5HRC, which is not as stable as the steel in the examples; the non-metallic inclusions (A fine 0.5 grade, B fine 0.5 grade, C class 0 grade, D fine 1.0 grade) are comparable to the steel in the examples and meet the standard requirement; the macrostructure defect level (general porosity, center porosity, segregation are all 0.5 grade) is comparable to the steel in the examples and meets the standard requirement.

[0102] Table 1 Chemical composition of carburized bearing steel

[0103]

[0104] Table 2 Inclusion and macroscopic detection results of carburized bearing steel

[0105]

[0106] The above only describes the preferred embodiments of the present application and is not used to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for manufacturing high-homogeneity, high-purity die-casting carburized bearing steel for railways, characterized in that, In order, they include: Electric furnace smelting, LF refining, RH vacuum degassing, ingot casting, high-temperature diffusion of steel ingots, steel ingot rolling and billet rolling steps; In the LF refining process, the mass content of Al in the molten steel is controlled at 0.020-0.050%, and the mass content of N in the molten steel is controlled at 0.007-0.012%. In the high-temperature diffusion step of steel ingots, the ingots are heated to a temperature of 1270-1290℃ for a duration of ≥5 hours. In the billet rolling process, the billet is heated and rolled, wherein the heating temperature is 1180-1230℃, the holding time is ≥40 minutes, and the final rolling temperature is 850-950℃. In the electric arc furnace smelting process, Al is added to the molten steel during tapping, with an added Al mass of ≥2.0 kg / t; after tapping, the slag in the clean ladle needs to be removed; after smelting, 2.0-3.0 kg / t of refining slag is added to the molten steel; the main components of the refining slag are Al2O3 and CaO, wherein the mass content of CaO is 45%-60%; oxygen blowing decarburization is carried out in the electric arc furnace, and the mass content of carbon at the smelting endpoint is controlled to be ≤0.10%; In the LF refining step, a special refining slag is added to the molten steel; the amount of the special refining slag added is 4.0-6.0 kg / t; the composition content of the special refining slag and the refining slag added after the electric furnace smelting is the same; during the LF refining process, the electrode is heated to increase the temperature, and a low-Ti alloy is added, wherein the Ti content in the alloy is ≤0.01%; the total refining time is ≥60 min; During the RH vacuum degassing process, the nitrogen content inside the RH furnace is controlled at 70-120 ppm; In the billet rolling process, the single-pass deformation reduction rate is 20%–40%. The high-homogeneity, high-purity die-cast railway carburized bearing steel comprises the following chemical composition by mass percentage: C: 0.20~0.22%, Si: 0.28~0.32%, Mn: 0.55~0.62%, P: 0.009~0.015%, S: ≤0.005%, Cr: 0.48~0.55%, Ni: 1.70~1.80%, Mo: 0.23~0.26%, Al: 0.020-0.050%, N: 0.0070-0.0120%, O: ≤0.00055%, Ti: ≤0.0011%, As: ≤0.005%, Pb: ≤0.0006%, Sb: ≤0.003%, Sn: ≤0.003%, Ca: ≤0.0004%, with the remainder being Fe and unavoidable impurities.

2. The manufacturing method according to claim 1, characterized in that, In the electric arc furnace smelting process, an eccentric bottom high-power electric arc furnace is used.

3. The manufacturing method according to claim 2, characterized in that, The power of the eccentric bottom high-power electric arc furnace is 28000W.

4. The manufacturing method according to claim 1, characterized in that, In the electric furnace smelting process, the tapping temperature is ≥1640℃.

5. The manufacturing method according to claim 1, characterized in that, In the LF refining step, the low-Ti alloy includes at least one of Ni plate, Mo iron, and Cr iron alloy.

6. The manufacturing method according to claim 1, characterized in that, In the LF refining process, the tapping temperature is 1550-1650℃.

7. The manufacturing method according to claim 1, characterized in that, In the RH vacuum degassing step, argon gas is used for stirring throughout the process, with an argon gas pressure of 0.1MPa~66.7Pa and a holding time of >20min; And / or, during the ingot casting process, argon is used as the protective gas throughout, and the oxygen content in the protective gas is ≤1000ppm; And / or, the ingot obtained by ingot casting is a 3-ton ingot; And / or, the final rolling temperature of the steel ingot rolling process is 900-1000℃.

8. The manufacturing method according to claim 1, characterized in that, In the high-temperature diffusion process of steel ingots, the heating time is 5-10 hours.

9. The manufacturing method according to claim 1, characterized in that, In the high-temperature diffusion process of steel ingots, the rolling compression ratio is 18-43%.

10. The manufacturing method according to claim 1, characterized in that, The high-homogeneity, high-purity die-cast railway carburized bearing steel comprises the following chemical composition by mass percentage: C: 0.20~0.22%, Si: 0.28~0.32%, Mn: 0.55~0.62%, P: 0.009~0.015%, S: 0.003~0.005%, Cr: 0.48~0.55%, Ni: 1.70~1.80%, Mo: 0.23~0.26%, Al:

0. 020-0.050%, N: 0.0070-0.0120%, O: 0.00045~0.00055%, Ti: 0.0007~0. 0010%, As: 0.004~0.005%, Pb: 0.0005~0.0006%, Sb: 0.002~0.003%, Sn: 0.002~0.003%, Ca: 0.0003~0.0004%, the remainder being Fe and unavoidable impurities.

11. The manufacturing method according to claim 1, characterized in that, The carburized bearing steel was tested according to the Q / CR592 standard. The macroscopic inclusions were 0, and the microscopic non-metallic inclusions were: A fine ≤ 1.0 grade, A coarse ≤ 0.5 grade, B fine ≤ 1.0 grade, B coarse ≤ 0.5 grade, D fine ≤ 1.0 grade, D coarse ≤ 0.5 grade, and Ds ≤ 0.5 grade; the low-magnification structural defect level was ≤ 0.5 grade.

12. The manufacturing method according to claim 1, characterized in that, The grain size of the carburized bearing steel is ≥8; and / or the hardenability bandwidth of the carburized bearing steel is 3HRC~5HRC.

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