CN115418560B - Steel for high-speed motor train traction motor bearing and production method thereof - Google Patents

Steel for high-speed motor train traction motor bearing and production method thereof Download PDF

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CN115418560B
CN115418560B CN202210858717.4A CN202210858717A CN115418560B CN 115418560 B CN115418560 B CN 115418560B CN 202210858717 A CN202210858717 A CN 202210858717A CN 115418560 B CN115418560 B CN 115418560B
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CN115418560A (en
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陈敏
白云
尹青
李文彬
吴小林
刘烨
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Jiangyin Xingcheng Special Steel Works Co Ltd
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Jiangyin Xingcheng Special Steel Works Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Treatment Of Steel In Its Molten State (AREA)

Abstract

The invention relates to steel for a high-speed motor car traction motor bearing and a production method thereof, wherein the steel comprises the following elements in percentage by weight: is C:0.85 to 0.93, si:0.60 to 0.80, mn:1.40 to 1.60, cr:1.35 to 1.65, mo: less than or equal to 0.08, ni: less than or equal to 0.25, less than or equal to 0.05 of Al, less than or equal to 0.015 of P, less than or equal to 0.010 of S, less than or equal to 0.20 of Cu, and Nb:0.02 to 0.06, V:0.10 to 0.40 percent, ca is less than or equal to 0.0010, ti is less than or equal to 0.0015, O is less than or equal to 0.0008, and the balance is Fe and unavoidable impurities. The production process comprises the following steps: primary smelting, refining, vacuum degassing refining, continuous casting, cogging, intermediate billet rolling into a material and finishing. The metallographic structure is carbide and sorbite structure, the carbide net is less than or equal to 2.0 level, the carbide band is less than or equal to 2.0 level, the grain size is more than or equal to 8 level, and the strength, toughness and impact resistance of the steel are ensured.

Description

Steel for high-speed motor train traction motor bearing and production method thereof
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to bearing steel and a production method thereof.
Background
In recent years, in order to meet the requirements of railway transportation in China, the running speed of railways is continuously improved, and motor train units with the speed per hour of more than 250 km are becoming main vehicles for passenger railway transportation. According to the national 'medium-long term railway network planning', the scale of the national railway network reaches about 17.5 kilometers by 2025, wherein the high-speed railway is about 3.8 kilometers, and the construction of the high-speed railway brings great market demands for the manufacturing industries of railway vehicles and related parts. The running part, namely the bogie, of the high-speed rail motor train unit is a core component for ensuring the high-speed, safe and stable running of the train, and the bearing is one of key parts. The high-speed rail bearing mainly refers to an axle box bearing, a traction motor bearing and a gear box bearing in a high-speed railway rolling stock. The first requirement for railway transportation is safety, and particularly for passenger trains, safe operation is of even greater importance.
The traction motor of the high-speed motor car is the core of the motor car, so that higher requirements are also put forward on the traction motor: the device has the advantages of small volume, light weight and high output power, can output large starting torque when the high-speed motor train is started, and can smoothly regulate the speed within a wider speed range so as to realize the torque control of the high-speed motor train, so that very high performance requirements are provided for key component bearings in a traction motor of the high-speed motor train, and the requirements on raw material bearing steel for manufacturing the bearings are more strict naturally. At present, the steel for the high-speed motor car bearings in China is required to be imported from abroad, and has high dependence on the China where the bearing steels such as Germany, swedish, japan and the like are produced.
The bearing materials of the high-speed trains of countries with developed Japanese, american and European bearing manufacturing always adopt a high-cleanliness and high-strength design route, and for the steel for the bearing of the traction motor of the high-speed motor train, the element components mainly adopt GCr15, and the requirements of the steel for the bearing of the traction motor of the high-speed motor train are met by improving the purity and the toughness of the materials.
Domestic bearing enterprises start later in the aspect of application of the high-speed motor car traction motor bearing, and because a great gap exists between the bearing and the international bearing huge head in the aspects of subsequent heat treatment, accurate grinding and assembly of the bearing, the bearing processed by adopting the traditional GCr15 material cannot compete with the international bearing enterprises.
The basic thought of the preparation method of the carburized bearing steel for the high-speed railway disclosed by application numbers 201110156409.9 and 201110156392.7 is that Cr is reduced, ni is increased, trace V, nb is added to refine grains, and a process combining vacuum induction and vacuum consumable remelting technology is adopted to improve the purity of steel, but the process is complex, the production efficiency is low, the cost is far higher than that of the market, and the competitiveness is difficult to form; application number 200510027394.0 describes a method for producing an extremely high purity high carbon chromium bearing steel by smelting in a vacuum induction furnace of more than 1 ton. High cleanliness and tissue uniformity are important dependences for ensuring long-period and high-stability operation of the high-speed rail bearing.
Disclosure of Invention
The invention aims to provide steel for the bearing of the traction motor of a high-speed motor car and a production method thereof, so that the steel has stronger market competitiveness on the basis of meeting the quality requirement of the steel for the bearing of the traction motor of the high-speed motor car.
The invention provides a composition design of novel high-carbon bearing steel different from the steel types listed in the current national standard GB/T18254 by carrying out composition design on the bearing steel, and in addition, the control of high purity and high uniformity of the bearing steel material of the traction motor of the high-speed motor train is realized by innovative optimization on the high-efficiency modern steelmaking process of vacuum degassing, continuous casting and rolling.
The invention adopts the technical scheme that: the steel for the high-speed motor car traction motor bearing comprises the following chemical components in percentage by mass: 0.85 to 0.93 percent, si:0.60 to 0.80 percent, mn:1.40 to 1.60 percent, cr:1.35 to 1.65 percent, mo: less than or equal to 0.08 percent, ni: less than or equal to 0.25 percent, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.20 percent of Cu, and Nb:0.02 to 0.06 percent, V:0.10 to 0.40 percent, ca is less than or equal to 0.0010 percent, ti is less than or equal to 0.0015 percent, O is less than or equal to 0.0008 percent, and the balance is Fe and unavoidable impurities.
The design of the main chemical components of the steel is as follows:
1) Determination of C content
In high-carbon chromium bearing steel, the carbon content is generally about 1.0%, and is one of the most important elements for ensuring the hardenability, hardness and wear resistance of the bearing steel. However, the carbon content is high, the influence on hardness is small, on the contrary, the carbide of the bearing steel is easy to generate, and the toughness of the bearing steel is also reduced. The C content of the invention is lower than that of the traditional high-carbon chromium bearing steel (0.95-1.05), and the range is determined to be 0.85-0.93%.
2) Determination of Si content
Si is added into the steel, so that ferrite can be reinforced, and the strength, the elastic limit and the hardenability are improved, and the Si content is designed to be 0.60-0.80%.
3) Determination of Mn content
Mn is used as deoxidizing element in steel making process, and has solid solution strengthening effect and raised hardenability, and the Mn content is 1.40-1.60%.
4) Determination of Cr content
Cr is carbide forming element, can improve the hardenability, wear resistance and corrosion resistance of steel, but Cr content is too high, combine with carbon in steel, easy to form massive carbide, this indissolvable carbide makes the toughness of steel reduce, the bearing life is reduced, the range of Cr content of the invention designs to be 1.35-1.65%.
5) Determination of Nb and V contents
The CCT curve of the steel can move downwards to the right through the cooperation of Nb and V, the stability of austenite can be increased, the concentration of C in austenite is reduced due to the precipitation of NbC compounds formed by Nb in the steel at the austenite grain boundary, the diffusion rate of C in the austenite is also reduced, the nucleation and growth of pearlite transformation are delayed, the whole transformation process is prolonged, the transformation is more complete, and the pearlite lamellar is finer. The Nb content is designed to be 0.02-0.06%, and the V content is designed to be 0.10-0.40%
6) Determination of Al content
Al is added as deoxidizing element in steel, and Al and N form fine aluminum nitride inclusion to refine crystal grains. However, when the Al content is too high, large-particle Al is easy to form in the molten steel smelting process 2 O 3 Brittle inclusions are removed, the purity of molten steel is reduced, and the service life of a finished product is influenced. The Al content of the present invention was determined to be 0.05% or less.
7) Determination of Ca content
The Ca content increases the number and size of spot-shaped oxides in the steel, and at the same time, since the spot-shaped oxides have high hardness and poor plasticity, they are not deformed when the steel is deformed, and voids are easily formed at the interface, thereby deteriorating the performance of the steel. The Ca content of the present invention was determined to be 0.001% or less.
8) Determination of Ti content
Ti element and N element are combined to form titanium nitride inclusion, and the titanium nitride inclusion has high hardness and sharp angle, and is easy to cause stress concentration during bearing operation and has great effect on bearing life, so that Ti is less than or equal to 0.0015%
9) Determination of O content
The oxygen content represents the total amount of oxide inclusions, and the limitation of the oxide brittle inclusions affects the service life of the finished product, and a large number of experiments show that the reduction of the oxygen content is remarkably beneficial to improving the purity of steel, particularly reducing the content of the oxide brittle inclusions of steel types. The oxygen content of the present invention was determined to be O.ltoreq.0.0008%.
10 Determination of P, S content
The P element causes element segregation during solidification of steel, and is dissolved in ferrite to distort and coarsen grains and increase cold brittleness, so that P is less than or equal to 0.015 percent; s element is easy to cause hot brittleness of steel, the ductility and toughness of the steel are reduced, and formed sulfide also damages the continuity of the steel, so that S is less than or equal to 0.010 percent.
The production method of the steel for the traction motor bearing of the high-speed motor train mainly comprises the following steps:
step one, smelting molten steel:
(1.1) primary refining: and carrying out low phosphating and low titanation of molten steel. The oxygen blowing smelting is adopted to improve the oxidizing property of molten steel, the high alkalinity and strong oxidizing property in the molten steel are beneficial to P removal, ti removal is carried out under the condition that the molten steel contains higher oxygen content, so that titanium is oxidized into titanium oxide and enters slag, and then the titanium oxide is removed by the modes of primary smelting furnace slag retention and tapping and slag skimming after the furnace. Controlling the content of harmful elements in molten steel.
The specific process comprises the following steps: the main component added before tapping is CaCO 3 Carrying out composite treatment of P removal and Ti removal; the dynamic balance relation exists between C and O in molten steel, the terminal point C is controlled to be more than or equal to 0.20 percent, P is controlled to be less than or equal to 0.015 percent when primary smelting tapping is performed, the tapping temperature T is controlled to be more than or equal to 1620 ℃, and the addition amount of Al-Fe is added when tapping is performed according to the content of the terminal point C, so that the molten steel reaches the first of a refining furnaceThe sample Al is controlled between 0.040% and 0.055%, namely, the whole addition of Al blocks is completed during primary smelting tapping, slag is left during tapping, slag skimming is performed after tapping by adopting furnace tapping after tapping, the residual phosphorus content of molten steel is controlled, and simultaneously, the Ti and O contents of the primary smelting molten steel are controlled, thereby creating good conditions for subsequent refining and vacuum degassing.
In order to prevent the increase of Ti content in the subsequent process, low-titanium ferrochrome is adopted, low-titanium refining slag, a ladle covering agent, a tundish covering agent and continuous casting covering slag with the titanium content lower than 0.1 percent are adopted, and the final molten steel Ti is ensured to be less than or equal to 0.0015 percent through the combination of the technical measures.
(1.2) ladle refining: al iron is added to adjust Al to a target range during primary refining tapping, the content of Al is not adjusted in the refining process, the Al is basically controlled to be 0.020-0.028% at the end of refining, the refining deoxidation adopts a mode of uniformly spraying SiC into a ladle to carry out slag surface diffusion deoxidation of molten steel (preferably, an automatic spray pipe is adopted to uniformly spray SiC into the ladle, the gas in the spray pipe is inert gas argon, and molten steel is prevented from being polluted), and CaO-Al is adopted as refining slag 2 O 3 -SiO 2 Ternary slag system with CaO 45-55 wt% and SiO 2 The weight percentage of Al is 7-15 percent 2 O 3 The weight percentage of MgO is 20-35%, the weight percentage of MgO is 5-10%, the content of FeO+MnO in the slag is less than 1, the alkalinity and the fluidity of the slag are ensured, the good deoxidizing performance is ensured, the free oxygen content in the process is ensured to be lower, and the advantage of removing inclusions in the smelting of an LF furnace is exerted.
(1.3) vacuum degassing: the highest vacuum degree is less than or equal to 1.33mbar, the high vacuum time is more than or equal to 15min, inert gas is used for stirring molten steel under vacuum, and the effect of removing impurities is fully exerted while degassing is ensured. After the degassing is finished, the Al content is 0.015-0.020%, soft stirring is carried out after the vacuum degassing is finished, the soft blowing time is more than or equal to 25min, and the whole process is free from adding calcium-containing alloy (lump materials or wires) on the basis that molten steel is not exposed in the air;
step two, continuous casting: the size of the continuous casting blank is more than 300mm multiplied by 400mm, and the compression ratio from the continuous casting blank to the final steel is more than 4;
step three, hot delivering of continuous casting billets: the continuous casting blank is directly sent to a heating furnace by heat, the heat sending temperature is not lower than 750 ℃, and the continuous casting blank is prevented from being broken during heating in a plastic sensitive temperature range. Fully heating in a heating furnace to homogenize tissues and carry out element solid solution, and then rolling into an intermediate billet with the thickness of 200mm by 200mm to 300mm by 300 mm;
step four, slow cooling of the intermediate blank;
step five, heating the intermediate blank: through the thermoplastic curve test of the product, the product is heated below 750 ℃ to be in a plastic sensitive area, and the area shrinkage rate is very low, so that the heating speed is not high when the product is heated below 750 ℃, the cracking of a middle blank is prevented, the steel heated to above 750 ℃ can be rapidly heated after being completely austenitized, the temperature of a preheating section is controlled between 650 ℃ and 750 ℃, the temperature of a heating section is controlled between 1000 ℃ and 1050 ℃, the total heating time of a soaking section is controlled between 1150 ℃ and 1200 ℃ and is not less than 4 hours, and the preheating section time is not less than 2 hours.
Step six, rolling into a product: the initial rolling temperature is controlled to be higher than 950 ℃, the rolling is carried out by a plurality of rolling mills, the final rolling temperature is 850-950 ℃, the rolling is carried out to the target specification, the cooling is carried out by blast air after the finishing rolling is finished on a cooling bed, the cooling speed of the steel surface is controlled to be 3-8 ℃/s, the sorbite transformation is carried out within the sorbite phase transformation temperature range which is cooled to 550-700 ℃ faster, and meanwhile, the temperature interval in which a large amount of carbide network of the steel is separated out is jumped out, thereby improving the carbide network of the steel. And then the steel is normally cooled down in room temperature.
And step seven, carrying out finishing procedures such as straightening and flaw detection on the steel. All the products need to be subjected to nondestructive testing by 100 percent, and the products are qualified after being detected to be qualified.
Preferably, each sampling during the refining process must ensure the accuracy of the sampling, in an effort to tune the composition to an internal control target for 2 samples.
Preferably, in the second step, the continuous casting adopts crystallizer electromagnetic stirring, solidification end electromagnetic stirring, tundish induction heating and light reduction, so that the superheat degree of molten steel is reduced, and the casting blank segregation is improved. The casting process protects molten steel and casting flow from secondary oxidation of contact air, and the superheat degree DeltaT of a tundish is less than or equal to 20 ℃; the pouring ladle molten steel volume is 30-35 tons, the solidification end adopts seven rollers to implement light pressing, the accumulated pressing volume is 15.5mm, the 7 times of distribution volume is 0.55mm-1.55mm-4.55mm-7.55mm-105mm-12.55mm-15.5mm, and the pouring pull rate is 0.45-0.55min/m.
Preferably, in the third step, the temperature of a preheating section in the heating furnace is 800-900 ℃, the temperature of a heating section is 1100-1250 ℃, and the temperature of a soaking section is 1150-1250 ℃, so that the blank is ensured to be heated uniformly, thereby improving the segregation of steel carbide, eliminating carbide liquation, simultaneously preventing microscopic pores and exceeding the standard of decarburization caused by overlong heating time, and the total heating time is 10-15 hours.
Preferably, in the fourth step, the intermediate blank is put into a pit for slow cooling, the pit-in temperature is more than or equal to 600 ℃, the pit-lifting temperature is less than or equal to 200 ℃, the slow cooling time is more than or equal to 48 hours, and the intermediate blank is put into a heating furnace for heating and rolling again within 24 hours after the intermediate blank is slowly cooled out of the pit to form a product.
Compared with the prior art, the invention has the advantages and the characteristics that:
(1) From the viewpoint of manufacturing process, the bearing steel of the traction motor of the high-speed motor train is smelted by adopting a vacuum induction furnace or electroslag remelting process in the past, and the production process of vacuum degassing and continuous casting is adopted, so that the production efficiency is improved, the large-scale production is realized, and the stability of the material components and the product quality is improved. In the smelting process, the invention is to control the content of P to be lower, and a composite P removing agent is added during primary smelting of molten steel; to control Al in molten steel 2 O 3 Al iron is added in place at one time during the process of inclusion and tapping, and Al is not added for deoxidization in the subsequent refining process, so that Al generation is reduced 2 O 3 Inclusion; during refining deoxidation, siC particles are uniformly sprayed into the steel ladle by adopting an automatic spray pipe to perform molten steel slag surface diffusion deoxidation, so that the uniform deoxidation is ensured, and the purity of the steel is further improved.
(2) Compared with common high-carbon bearing steel, the invention adds a small amount of alloying elements Nb and V, and the Nb and V are added into the steel in a matching way, so that the CCT curve of the steel moves downwards to the right, the austenite stability can be increased, the precipitation of NbC compounds formed by Nb in the steel in an austenite grain boundary reduces the concentration of C in austenite, the diffusion rate of C in austenite is also reduced, the nucleation and growth of pearlite transformation are delayed, the whole transformation process is prolonged, the transformation is more sufficient, the pearlite sheet is finer, meanwhile, blast cooling is adopted in the rolling process of a finished product material, and the finally formed metallographic structure is carbide+sorbite structure, which is different from the carbide+pearlite structure formed by the traditional high-carbon bearing steel. The sorbite is pearlite with smaller lamellar spacing, and in addition, the smaller lamellar spacing is, the better the tensile strength of the steel is, so that the toughness of the steel is improved.
The bearing steel of the traction motor of the high-speed motor car meets the following requirements:
the microscopic inclusion is tested according to GB/T10561A method, the B fine system is less than or equal to 1.0 level, the B coarse system is less than or equal to 0.5 level, the D fine system is less than or equal to 1.0 level, the D coarse system is less than or equal to 0.5 level, the DS system is less than or equal to 1.0 level, and the microscopic inclusion comprises A-class and C-class plastic inclusions and B-class and D-class brittle inclusions, and the microscopic inclusion is strictly required to be included in the microscopic inclusion and the macroscopic inclusion according to the method shown in the table 1. Because the brittle inclusions are hard particles in the steel, stress concentration is generated during bearing operation, and cracks are easily separated from a matrix during the deformation process of the steel, so that the stress concentration is more serious, the cracks are easily caused, the larger the inclusion particles are, the longer the length is, and the larger the damage is; the plastic inclusion is soft particle in the steel, and is not easy to separate from the matrix in the deformation process of the steel, so that the damage is less.
TABLE 1
Macroscopic inclusions significantly reduce the wear resistance of the steel, cause severe stress concentrations and easily cause early failure in the use process of the bearing. The macroscopic defect of the bearing steel is subjected to water immersion high-frequency flaw detection by adopting SE9 1927 method, and the total ultrasonic defect index is required not to exceed 5mm/dm 3 The maximum length of a single ultrasonic defect is not allowed to exceed 2mm.
The low-power structure adopts GB/T1979 to grade the steel low-power structure, the center porosity is less than or equal to 1.0 level, the general porosity is less than or equal to 1.0 level, the ingot segregation is less than or equal to 1.0 level, the center segregation is less than or equal to 1.0 level, and shrinkage cavities, cracks and subcutaneous bubbles are avoided.
The metallographic structure of the steel is carbide+sorbite structure (the normal structure of the bearing steel comprises carbide+pearlite structure, if the carbide is biased to form carbide bands and networks), the carbide networks are less than or equal to 2.0 levels, the carbide bands are less than or equal to 2.0 levels, carbide liquid separation and microscopic pores are not present, the grain size is more than or equal to 8 levels, and the depth of a surface decarburized layer is less than or equal to 0.8 percent D (D is the diameter). The strength, toughness and impact resistance of the steel are ensured.
Detailed Description
The invention is described in further detail below in connection with the following examples, which are exemplary and intended to illustrate the invention, but are not to be construed as limiting the invention.
The manufacturing flow of the high-speed motor car traction motor bearing steel of the embodiment of the invention adopts a forming process of top-bottom combined blown converter BOF (or high-power electric arc furnace EAF), ladle refining furnace LF-vacuum circulating degassing furnace RH (or VD furnace), large-section continuous casting CCM large continuous casting blank, hot delivery, heating and rolling into an intermediate blank, slow cooling, heating and rolling into a material, and finishing to produce the steel.
Specifically, high-quality molten iron, scrap steel and raw and auxiliary materials are selected during smelting, and high-quality deoxidizer and refractory materials are selected. In the production process of the electric furnace/converter, the tapping end point C of the three embodiments is controlled to be 0.30-0.45%, the end point P is controlled to be less than or equal to 0.015%, the tapping temperature is 1620-1700 ℃, al iron is added for pre-deoxidation in the tapping process, the superheat degree of continuous casting is controlled to be less than or equal to 20 ℃, and the continuous casting drawing speed is controlled to be 0.45-0.55m/min. And (3) hot-conveying the produced continuous casting blank to a heating furnace and rolling the continuous casting blank into an intermediate blank, and then slowly cooling the intermediate blank in a pit, wherein the pit-descending temperature is higher than 600 ℃, the pit-descending slow cooling time is longer than 48 hours, and the pit-descending temperature is lower than 200 ℃. After the completion of the slow cooling, the intermediate billet is heated in a heating furnace in a neutral or weakly oxidizing atmosphere and rolled into a product. And then carrying out subsequent flaw detection finishing and the like on the bar.
The chemical composition (wt%) of the inventive examples and (by comparison) of the GCr15 currently used in the market is shown in Table 2.
TABLE 2
TABLE 2
From the aspect of composition, the main chemical components of the invention and the comparative steel are different, such as C, si, mn and the like, and the invention is added with relevant Nb and V elements, thereby meeting better performance.
TABLE 3 detection of nonmetallic inclusion in examples and comparative steels
The invention is close to the index of the comparative steel in terms of nonmetallic inclusion detection.
TABLE 4 grain size, metallographic structure, carbide banding, network and liquid separation for each example
According to the invention, a small amount of alloying elements Nb and V are added from a metallographic structure, and the Nb and V are added into the steel in a matching way, so that the CCT curve of the steel moves downwards to the right, the austenite stability can be increased, the precipitation of NbC compounds formed by Nb in the steel at an austenite grain boundary reduces the concentration of C in austenite, the diffusion rate of C in austenite is also reduced, the nucleation and growth of pearlite transformation are delayed, the whole transformation process is prolonged, the transformation is more sufficient, the pearlite lamellar is finer, meanwhile, blast cooling is adopted in the rolling process of a finished product material, and the finally formed metallographic structure is a carbide+sorbite structure which is different from the carbide+pearlite structure formed by the traditional high-carbon bearing steel. In addition, the control modes of high-temperature diffusion, special rolling control and cooling control and the like are adopted in the production process, so that the control level of the carbide net shape and the carbide strip shape is better than that of the control steel.
In addition to the above embodiments, the present invention also includes other embodiments, and all technical solutions that are formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims (9)

1. A steel for a high-speed motor car traction motor bearing is characterized in that: the steel comprises the following chemical components in percentage by mass: 0.85 to 0.93 percent, si:0.60 to 0.80 percent, mn:1.40 to 1.60 percent, cr:1.35 to 1.65 percent, mo: less than or equal to 0.08 percent, ni: less than or equal to 0.25 percent, less than or equal to 0.05 percent of Al, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.20 percent of Cu, and Nb:0.02 to 0.06 percent, V:0.10 to 0.40 percent, ca is less than or equal to 0.0010 percent, ti is less than or equal to 0.0015 percent, O is less than or equal to 0.0008 percent, and the balance is Fe and unavoidable impurities;
the production method of the steel comprises
Step one, smelting molten steel:
(1.1) primary refining: oxygen blowing smelting is adopted to improve the oxidizing oxidation Ti of molten steel, a composite P removing agent is added before tapping, and P and Ti removing composite treatment is carried out; controlling the tapping endpoint C to be more than or equal to 0.20 percent and the tapping temperature P to be less than or equal to 0.015 percent, wherein the tapping temperature T to be more than or equal to 1620 ℃, adding the addition amount of Al-Fe when tapping according to the content of the endpoint C, controlling the Al of a first sample of molten steel in a refining furnace to be between 0.040 and 0.055 percent, and carrying out slag-retaining and slag-skimming after tapping by adopting tapping after the furnace;
(1.2) ladle refining: al iron is added to adjust Al to a target range during primary refining tapping, the content of Al is not adjusted in the refining process, the Al is controlled to be 0.020-0.028% after refining, the refining deoxidization adopts a mode of uniformly spraying SiC into a ladle to carry out molten steel slag surface diffusion deoxidization, and the refining slag adopts CaO-Al 2 O 3 -SiO 2 Ternary slag system with CaO 45-55 wt% and SiO 2 The weight percentage of Al is 7-15 percent 2 O 3 The weight percentage of MgO is 20-35%, the weight percentage of MgO is 5-10%, and the content of FeO+MnO in the slag is less than 1, so that the alkalinity and the fluidity of the slag are ensured;
(1.3) vacuum degassing: the highest vacuum degree is less than or equal to 1.33mbar, the high vacuum time is more than or equal to 15min, inert gas is used for stirring molten steel under vacuum, the Al content is controlled to be 0.015-0.020% after the degassing is finished, soft stirring is carried out after the vacuum degassing is finished, the soft blowing time is more than or equal to 25min, and the whole process is free from adding calcium-containing alloy on the basis that the molten steel is not exposed in the air;
step two, continuous casting: the size of the continuous casting blank is more than 300mm multiplied by 400mm, and the compression ratio from the continuous casting blank to the final steel is more than 4;
step three, hot delivering of continuous casting billets: directly heating the continuous casting blank to a heating furnace, wherein the temperature of the heating furnace is not lower than 750 ℃, fully heating in the heating furnace to homogenize tissues and form solid solutions of elements, and then rolling into an intermediate blank with the thickness of 200 mm-300 mm;
step four, slow cooling of the intermediate blank;
step five, heating the intermediate blank: the temperature of the preheating section is controlled to be 650-750 ℃, the temperature of the heating section is controlled to be 1000-1050 ℃, the temperature of the soaking section is controlled to be 1150-1200 ℃, and the total heating time is not less than 4 hours, wherein the time of the preheating section is not less than 2 hours;
step six, rolling into a product: the initial rolling temperature is controlled to be higher than 950 ℃, the final rolling temperature is controlled to be between 850 and 950 ℃, the steel is rolled to the target specification, the cooling bed is cooled by blast air after finishing the final rolling, the cooling speed of the steel surface is controlled to be 3 to 8 ℃/s, the steel is cooled to be within the sorbite phase transition temperature range of 550 to 700 ℃ for sorbite transformation, and then the steel is cooled down normally at room temperature.
2. The steel for a high-speed motor car traction motor bearing according to claim 1, characterized in that: the microscopic brittle inclusions in the structure satisfy the following conditions: the B fine system is less than or equal to 1.0 level, the B coarse system is less than or equal to 0.5 level, the D fine system is less than or equal to 1.0 level, the D coarse system is less than or equal to 0.5 level, and the DS system is less than or equal to 1.0 level.
3. The steel for a high-speed motor car traction motor bearing according to claim 1, characterized in that: carrying out water immersion high-frequency flaw detection on macroscopic defects in tissues, wherein the total ultrasonic defect index is not more than 5mm/dm 3 The maximum length of a single ultrasonic defect does not exceed 2mm.
4. The steel for a high-speed motor car traction motor bearing according to claim 1, characterized in that: the GB/T1979 is adopted to grade the steel macrostructure, and the following conditions are satisfied: the center porosity is less than or equal to 1.0 level, the general porosity is less than or equal to 1.0 level, the ingot segregation is less than or equal to 1.0 level, the center segregation is less than or equal to 1.0 level, and shrinkage cavities, cracks and subcutaneous bubbles are avoided.
5. The steel for a high-speed motor car traction motor bearing according to claim 1, characterized in that: the metallographic structure is carbide+sorbite structure, the carbide net is less than or equal to 2.0 level, the carbide band is less than or equal to 2.0 level, the grain size is more than or equal to 8 level, the depth of the surface decarburized layer is less than or equal to 0.8% D, and D is the diameter.
6. A method of producing steel for high speed motor car traction motor bearings according to any one of claims 1 to 5, characterized by: comprising
Step one, smelting molten steel:
(1.1) primary refining: oxygen blowing smelting is adopted to improve the oxidizing oxidation Ti of molten steel, a composite P removing agent is added before tapping, and P and Ti removing composite treatment is carried out; controlling the tapping endpoint C to be more than or equal to 0.20 percent and the tapping temperature P to be less than or equal to 0.015 percent, wherein the tapping temperature T to be more than or equal to 1620 ℃, adding the addition amount of Al-Fe when tapping according to the content of the endpoint C, controlling the Al of a first sample of molten steel in a refining furnace to be between 0.040 and 0.055 percent, and carrying out slag-retaining and slag-skimming after tapping by adopting tapping after the furnace;
(1.2) ladle refining: al iron is added to adjust Al to a target range during primary refining tapping, the content of Al is not adjusted in the refining process, the Al is controlled to be 0.020-0.028% after refining, the refining deoxidization adopts a mode of uniformly spraying SiC into a ladle to carry out molten steel slag surface diffusion deoxidization, and the refining slag adopts CaO-Al 2 O 3 -SiO 2 Ternary slag system with CaO 45-55 wt% and SiO 2 The weight percentage of Al is 7-15 percent 2 O 3 The weight percentage of MgO is 20-35%, the weight percentage of MgO is 5-10%, and the content of FeO+MnO in the slag is less than 1, so that the alkalinity and the fluidity of the slag are ensured;
(1.3) vacuum degassing: the highest vacuum degree is less than or equal to 1.33mbar, the high vacuum time is more than or equal to 15min, inert gas is used for stirring molten steel under vacuum, the Al content is controlled to be 0.015-0.020% after the degassing is finished, soft stirring is carried out after the vacuum degassing is finished, the soft blowing time is more than or equal to 25min, and the whole process is free from adding calcium-containing alloy on the basis that the molten steel is not exposed in the air;
step two, continuous casting: the size of the continuous casting blank is more than 300mm multiplied by 400mm, and the compression ratio from the continuous casting blank to the final steel is more than 4;
step three, hot delivering of continuous casting billets: directly heating the continuous casting blank to a heating furnace, wherein the temperature of the heating furnace is not lower than 750 ℃, fully heating in the heating furnace to homogenize tissues and form solid solutions of elements, and then rolling into an intermediate blank with the thickness of 200 mm-300 mm;
step four, slow cooling of the intermediate blank;
step five, heating the intermediate blank: the temperature of the preheating section is controlled to be 650-750 ℃, the temperature of the heating section is controlled to be 1000-1050 ℃, the temperature of the soaking section is controlled to be 1150-1200 ℃, and the total heating time is not less than 4 hours, wherein the time of the preheating section is not less than 2 hours;
step six, rolling into a product: the initial rolling temperature is controlled to be higher than 950 ℃, the final rolling temperature is controlled to be between 850 and 950 ℃, the steel is rolled to the target specification, the cooling bed is cooled by blast air after finishing the final rolling, the cooling speed of the steel surface is controlled to be 3 to 8 ℃/s, the steel is cooled to be within the sorbite phase transition temperature range of 550 to 700 ℃ for sorbite transformation, and then the steel is cooled down normally at room temperature.
7. The method for producing steel for high-speed motor car traction motor bearings according to claim 6, characterized by: in the second step, the continuous casting adopts crystallizer electromagnetic stirring, solidification end electromagnetic stirring, tundish induction heating and light pressing, the casting process protects molten steel and casting flow from secondary oxidation caused by contact air, and the tundish superheat degree DeltaT is less than or equal to 20 ℃; the pouring ladle molten steel volume is 30-35 tons, the solidification end adopts seven rollers to implement light pressing, the accumulated pressing volume is 15.5mm, the 7 times of distribution volume is 0.55mm-1.55mm-4.55mm-7.55mm-105mm-12.55mm-15.5mm, and the pouring pull rate is 0.45-0.55min/m.
8. The method for producing steel for high-speed motor car traction motor bearings according to claim 6, characterized by: in the third step, the temperature of a preheating section in the heating furnace is 800-900 ℃, the temperature of a heating section is 1100-1250 ℃, the temperature of a soaking section is 1150-1250 ℃, and the total heating time is 10-15 hours.
9. The method for producing steel for high-speed motor car traction motor bearings according to claim 6, characterized by: and fourthly, slowly cooling the intermediate blank in a pit, wherein the pit entering temperature is more than or equal to 600 ℃, the pit lifting temperature is less than or equal to 200 ℃, the slow cooling time is more than or equal to 48 hours, and the intermediate blank is sent to a heating furnace again to be heated and rolled into a product within 24 hours after slowly cooling.
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