WO2024169713A1

WO2024169713A1 - Bearing steel for vehicle hub and manufacturing method for bearing steel

Info

Publication number: WO2024169713A1
Application number: PCT/CN2024/075902
Authority: WO
Inventors: 刘湘江; 黄瑞; 陈志平; 姚赞
Original assignee: 宝山钢铁股份有限公司
Priority date: 2023-02-17
Filing date: 2024-02-05
Publication date: 2024-08-22
Also published as: CN118516619A

Abstract

Disclosed in the present invention is bearing steel for a vehicle hub. The bearing steel comprises Fe and inevitable impurities, and further comprises the following chemical elements in percentage by mass: 0.70-0.80% of C; 0.50-0.70% of Si; 0.95-1.05% of Mn; 0.60-0.70% of Cr; 0.10-0.25% of Cu, 0.010-0.040% of Al; 0.025-0.035% of Nb; and 0.10-0.15% of V. Accordingly, also disclosed in the present invention is a manufacturing method for the bearing steel for a vehicle hub. The present invention can ameliorate the Brinell indentation phenomenon of a rolling bearing raceway of the vehicle hub, and prevent breakage caused by micro-cracks generated due to Brinell damage of a contact part of a rolling body and a raceway roller.

Description

Bearing steel for vehicle hub and manufacturing method thereof

Technical Field

The present invention relates to a steel material and a manufacturing method thereof, and in particular to a bearing steel and a manufacturing method thereof.

Background Art

The function of automobile wheel hub bearings is to support the vehicle body and guide the rotation of the wheels. They bear both axial and radial loads.

In the prior art, the bearing steel used to manufacture automobile wheel hub bearings is generally medium carbon bearing steel, such as S55C, whose chemical composition is: C: 0.52-0.58%, Si: 0.15-0.35%, Mn: 0.60-0.90%, Cr≤0.20%, P≤0.030%, S≤0.035%, Ni≤0.20%, Cu≤0.30%, Ni+Cr≤0.35%.

However, automobile wheel hub bearings made of existing bearing steel are prone to failure during use. The failure modes of wheel hub bearings mainly include fatigue failure, wear, corrosion, electrolytic corrosion, plastic deformation, and cracks. Therefore, wheel hub bearing steel needs to have fine grains, uniform hardness, corrosion resistance, high purity, and also good upsetting performance and die life.

In this regard, a Chinese patent document with publication number CN101376948B, publication date March 30, 2011, and titled "A method for manufacturing low-cost and high-purity medium-carbon bearing steel for automobile wheels" discloses a medium-carbon carbon bearing steel optimized on the basis of S55C, which reduces the range of carbon content to obtain a smaller _raceway hardness difference, and limits the Al content to refine the grain size and reduce _Al2O3 type inclusions.

In addition, a Chinese patent document with publication number CN105568134A, publication date May 11, 2016, and titled “A micro-alloyed carbon wheel hub bearing steel for passenger cars” has a chemical composition of C 0.45-0.70%, Si 0.10-0.50%, Mn 0.30-0.70%, Cr 0.20-0.60%, P ≤ 0.025%, S 0.003-0.030%, Mo ≤ 0.1%, Ni ≤ 0.2%, and Al ≤ 0.04%, and refines the grains by limiting the Al element content.

Summary of the invention

One of the purposes of the present invention is to provide a bearing steel for a vehicle hub, which aims to improve the quenched martensite structure in the raceway of the automobile hub bearing steel by adding a trace amount of vanadium and niobium to the steel for microalloying, using alloy elements such as carbon, silicon, manganese, copper and performing corresponding composition design, in particular to improve the brinelling indentation phenomenon in the raceway of the automobile hub rolling bearing, and prevent the contact part between the rolling element and the raceway wheel from breaking due to the initiation of microcracks caused by Brinell damage.

In order to achieve the above object, the present invention provides a bearing steel for a vehicle wheel hub, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

C: 0.70～0.80%; Si: 0.50～0.70%; Mn: 0.95～1.05%; Cr: 0.60～0.70%; Cu: 0.10～0.25%; Al: 0.010～0.040%; Nb: 0.025～0.035%; V :0.10～0.15%.

The present invention also provides a bearing steel for a vehicle wheel hub, wherein the mass percentage of each chemical element is:

C: 0.70～0.80%; Si: 0.50～0.70%; Mn: 0.95～1.05%; Cr: 0.60～0.70%; Cu: 0.10～0.25%; Al: 0.010～0.040%; Nb: 0.025～0.035%; V: 0.10～0.15%; the balance is Fe and inevitable impurities.

The inventors found through research that the Brinell indentation phenomenon on the raceway of automobile wheel hub rolling bearings will reduce the fracture strength of the rings. During micro-vibration, the Brinell damage caused by vibration and shaking at the contact part of the rolling element and the raceway wheel is often the origin of micro-cracks. More than 50% of the wear caused by pseudo-Brinell indentation in the wheel hub bearing unit can be improved by packaging and lubrication. In addition, it is related to the texture of the martensite structure of the hardened layer.

Based on this, the present invention improves the quenched martensite structure in the raceway of the automobile hub bearing steel through the design of the chemical element composition system supplemented by an adaptive process, thereby improving the brinelling phenomenon of the raceway of the automobile hub rolling bearing and preventing the contact part between the rolling element and the raceway wheel from breaking due to the initiation of microcracks caused by Brinell damage.

In the bearing steel for vehicle wheel hub of the present invention, the design principles of each chemical element are as follows:

C: It is generally believed that carbon will deteriorate toughness. However, in the present invention, carbon is an important element to ensure the strength, wear resistance and hardenability of bearing steel. In order to make the hardness of the high-frequency quenching raceway surface of the automobile hub bearing steel of the present invention reach 730-780HV and the depth of the hardened layer of the raceway surface reach 2.0-3.5mm, it is necessary to design a carbon content of 0.70-0.80%.

Si: Silicon can partially replace chromium and nickel elements to improve strength, and is also a good reducing agent and deoxidizer in the smelting process. In addition, in the present invention, silicon can reduce the concentration gradient of carbon, promote carbon diffusion in the austenite state, inhibit the precipitation of carbides, and improve toughness. Based on this, the silicon content of the present invention is controlled at 0.50-0.70% to meet the strength and toughness requirements in combination with other elements.

Mn: Manganese can partially replace chromium to maintain strength, and manganese is the main element that can significantly improve hardenability. However, manganese has the disadvantage of promoting austenite grain growth in steel, and the manganese content should be controlled. Based on this, the present invention adds manganese content of 0.95-1.05%, so that it cooperates with carbon element to ensure that the hardness of the high-frequency quenching raceway surface reaches 730-780HV, and the depth of the hardened layer of the raceway surface reaches 2.0-3.5mm.

Cr: Chromium can significantly improve strength, hardness and wear resistance, but at the same time reduce plasticity and toughness. Chromium and carbon in steel mainly form M23C. 0.60-0.70% chromium is added to the steel of the present invention.

Cu: Copper is generally controlled as a harmful element because the disadvantage of copper is that it is easy to become hot brittle during hot working, especially when the copper content exceeds 0.5%, the plasticity is significantly reduced. Due to different smelting methods, electric arc furnace smelting (the raw material is mainly scrap steel) often has a copper content of 0.10-0.20% without special control, while converter smelting (the raw material is mainly blast furnace iron) The copper content is generally less than 0.05% and requires additional addition of copper alloy. However, unlike the general prior art, 0.10-0.25% of Cu is added to the steel of the present invention to improve strength and toughness, and in addition, it can also improve atmospheric corrosion resistance. The inventor has shown through multiple rounds of laboratory experiments that 0.10-0.25% of copper can effectively improve the corrosion resistance of automobile wheel hub bearings, especially reduce atmospheric pitting and reduce surface peeling of bearings.

Al: It is generally believed that aluminum is a deoxidizer and a grain-refining element. However, the inventors have found through experiments that excessive Al often forms _Al2O3 _- type non-metallic inclusions. These non-metallic inclusions that are difficult to deform often become fatigue fracture sources and affect the impact resistance of the bearing. Based on this, the present invention controls the aluminum content in the finished steel to be 0.010-0.040%.

Nb and V: These two elements are microalloying elements added in the present invention. The present invention forms composite dispersed nano-scale carbide type precipitates by adding 0.025-0.035% niobium and 0.10-0.15% vanadium. The carbide type precipitates are mainly in the form of point-shaped and short rod-shaped carbides. Based on the basic components of the invention steel, the composite microalloy form of niobium and vanadium can refine the matrix structure and refine the texture of martensite in the raceway of the automobile hub bearing.

Mo: Mo can generally improve hardenability and heat resistance and prevent temper brittleness. However, since ferromolybdenum alloy is a precious alloy element, in the present invention, in order to avoid the formation of molybdenum-containing carbides that are difficult to deform, the present invention controls its upper limit to 0.01%.

Furthermore, the chemical element mass percentage of the bearing steel for vehicle hub of the present invention also satisfies: 10Nb+V≥0.40%. In some embodiments, 10Nb+V is in the range of 0.40-0.50%, preferably in the range of 0.40-0.46%.

Satisfying the above formula can further ensure the microalloying effect of the present invention.

Furthermore, among the inevitable impurities in the bearing steel for vehicle hub according to the present invention, each element satisfies at least one of the following conditions: S≤0.015%; P≤0.015%; O≤0.0006%; H≤0.0001%; Ti≤0.0015%; Pb≤0.002%, As≤0.04%, Sn≤0.05%, Sb≤0.004%, Ca≤0.0010%.

The above-mentioned elements are all impurity elements in the steel of the present invention, which will significantly reduce the plasticity and toughness of the steel. Therefore, their content should be reduced as much as possible under the technical conditions.

Furthermore, the microstructure of the local quenching area of the bearing steel for vehicle hub of the present invention is a fine and uniform martensitic structure. In some embodiments, in the martensitic structure, the length of the needle-shaped martensite is ≤10 μm.

Furthermore, the bearing steel for vehicle hub of the present invention has a microstructure of ferrite+pearlite in the region not subjected to local quenching. In some embodiments, in the microstructure of the region not subjected to local quenching, the area ratio of pearlite is ≤8%, preferably ≤5%.

Furthermore, the grain size of the local quenching area of the bearing steel for vehicle hub described in the present invention is 7-9.

Furthermore, the maximum size of a single inclusion at any position of the bearing steel for vehicle hub of the present invention is ≤27 μm. In some embodiments, the maximum size of a single inclusion at any position of the bearing steel for vehicle hub of the present invention is 9 to 27 μm.

Furthermore, the local quenching area of the bearing steel for vehicle hub according to the present invention has dispersedly distributed composite nano-scale carbide precipitates, and the size of the carbide precipitates is 15nm-35nm.

Furthermore, the microhardness of the local quenching area of the bearing steel for vehicle hub described in the present invention is 730-780 HV, and the depth of the hardened layer is 2.0-3.5 mm.

Furthermore, the microhardness deviation of the bearing steel for vehicle hub according to the present invention at the same hardened layer depth in the local quenching area is ≤40HV, such as 20-40HV or 30-40HV.

Furthermore, the tensile strength of the bearing steel for vehicle wheel hub of the present invention is ≥830MPa, preferably ≥850MPa. In some embodiments, the tensile strength of the bearing steel for vehicle wheel hub of the present invention is in the range of 850-880MPa.

Furthermore, in the bearing steel for vehicle hub according to the present invention, the center segregation index, ie, center C%/melting C%, is in the range of 0.95 to 1.05, preferably in the range of 0.98 to 1.02.

Another object of the present invention is to provide a method for manufacturing bearing steel for vehicle wheel hubs, wherein the bearing steel for vehicle wheel hubs obtained can improve the brinelling phenomenon of the raceway of automobile wheel hub rolling bearings and prevent the contact part between the rolling element and the raceway wheel from breaking due to the initiation of microcracks caused by Brinell damage.

In order to achieve the above object, the present invention provides a method for manufacturing a bearing steel for a vehicle wheel hub as described above, comprising the steps of:

(1) Smelting, refining and casting;

(2) heating the ingot using a heating furnace;

(3) using a primary rolling mill to produce a steel billet;

(4) heating the steel billet and then rolling it into a bar;

(5) Local quenching of the area used as the wheel hub raceway surface.

In the manufacturing method of high-temperature carburized bearing steel of the present invention, a three-step process flow can be adopted: the first step: initial smelting in an electric arc furnace (or converter) → vacuum refining in a ladle furnace → continuous casting; the second step: hot processing and rolling in a rolling mill; the third step: local quenching.

In step (1), an electric arc furnace (or converter) can be used for primary smelting of molten steel, followed by ladle refining, and then continuous casting to produce a steel billet of a certain size having a chemical composition in accordance with the present invention.

Wherein, during the initial refining of the molten steel, the molten steel tapped from the primary refining furnace can reach: [P]≤0.025%, [C]≥0.05%, T≥1620°C for tapping. In some embodiments, the molten steel tapped from the primary refining furnace reaches: [P]≤0.015%, [C]≥0.10%, T≥1630°C for tapping. Manganese-aluminum alloy is added to the ladle during tapping, and Mn is added to the upper limit of the product composition at a recovery rate of 100%. When the primary refining furnace is a converter, Cu alloy is added during tapping to control Cu to 0.10-0.20%. In some embodiments, the aluminum content of the added manganese-aluminum alloy can be 15-25%.

Among them, in the ladle refining furnace, the heating station of the outer refining furnace (LF), low-basicity synthetic slag is added to the ladle for slag making, Al particles are used for precipitation deoxidation, Si-C powder is used for slag surface deoxidation, and the addition amount and batch are adjusted according to the slag condition and the silicon content in the steel, so that the refining process always maintains good deoxidation. In the early stage of LF, the low-basicity slag can be adjusted once to control the basicity of the refining furnace top slag to 2-4. In some embodiments, low-basicity synthetic slag with ingredients such as those shown in Table 1 of this application is added for slag making. The addition amount of synthetic slag can be 1 to 5 kg/t.

Among them, ferroniobium and ferrovanadium can be added before vacuum degassing. Aluminum wire is fed to supplement aluminum to 0.025-0.040%. No aluminum wire is added after vacuum pumping. The temperature of the molten steel after vacuum degassing is 1530-1560℃.

During pouring, after vacuum refining, the ladle is calmed for more than 40 minutes, and Ar is soft-blown. The Ar pressure and flow rate are suitable for the liquid surface to vibrate slightly. The molten steel is poured continuously, and the superheat is controlled to be ≤35℃. The soft pressure at the end of solidification and electromagnetic stirring technology are used to improve the segregation of steel.

Furthermore, in step (2) of the manufacturing method described in the present invention, the temperature of the ingot entering the furnace is controlled to be 600-900°C and kept warm for 20-40 minutes; then the temperature is raised to 1180-1220°C after 120-200 minutes and kept warm for 80-180 minutes.

Further, in step (4) of the manufacturing method of the present invention, the heating temperature of the steel billet is controlled to be 1160-1200° C., the heating time is 80-180 min, the temperature difference on the surface of the steel billet is ≤40° C., and the final rolling temperature is 760-900° C. In some embodiments, the temperature difference on the surface of the steel billet is controlled to be in the range of 20-40° C., such as 30-40° C.

The present invention does not improve the local quenching process. In the present invention, an induction quenching device can be used for local quenching, the quenching temperature can be 880°C±10°C, and the cooling method is water cooling.

Compared with the prior art, the bearing steel for vehicle wheel hub and the manufacturing method thereof according to the present invention have the following advantages and beneficial effects:

The bearing steel for vehicle hub of the present invention is micro-alloyed by adding trace amounts of vanadium and niobium into the steel, and adopts alloy elements such as carbon, silicon, manganese, copper and the like and makes corresponding compositions, so as to form dispersed composite nano-scale carbide precipitates, thereby refining the structure of martensite in the raceway of the automobile hub bearing.

The microhardness of the bearing steel for the vehicle hub of the present invention on the working surface can reach 730-780HV, the depth of the hardened layer can reach 2.0-3.5mm, and the microhardness deviation of the same hardened layer depth is ≤40HV.

The bearing steel for the vehicle wheel hub of the present invention has a low impurity content, and the maximum size of a single inclusion is ≤27 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the microstructure of a non-local quenching region of a bearing steel for a vehicle hub according to Example 3 of the present invention.

FIG. 2 shows the microstructure of a local quenched area of a bearing steel for a vehicle hub according to Example 3 of the present invention.

FIG. 3 shows the depth of the hardened layer in the local quenching area of the vehicle hub bearing steel according to Example 3 of the present invention.

DETAILED DESCRIPTION

The bearing steel for vehicle wheel hub and the manufacturing method thereof according to the present invention will be further explained and illustrated below in conjunction with the drawings and specific embodiments of the specification. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

Examples 1-7

The bearing steels for vehicle hubs of Examples 1-7 are all prepared by the following steps:

(1) Smelting, refining and casting:

Primary refining: The steel liquid is primary refining in a 150-ton electric arc furnace. The tapping of steel from the primary refining furnace begins when the molten steel reaches: [P] ≤ 0.015%, [C] ≥ 0.10%, T ≥ 1630°C. In the later stage of tapping, an appropriate amount of synthetic slag is added. When tapping, a manganese-aluminum alloy is added to the ladle, in which the Al content can be 22%, and Mn is added to the upper limit of the product composition at a 100% recovery rate.

Ladle refining furnace: In the heating station of the refining furnace (LF), low basicity synthetic slag is added to the ladle. The composition of the synthetic slag can be shown in Table 1) 2kg/t slag making, Al particles are used for precipitation deoxidation, Si-C powder is used for slag surface deoxidation, and the addition amount and batch are adjusted according to the slag condition and the silicon content in the steel. For example, a batch can be added every 15 minutes, and the dosage can be 0.2-0.8kg/t, so that the refining process should always maintain good deoxidation. Adjust the low basicity slag once at the beginning of LF, and control the basicity of the top slag of the refining furnace to 2-4 or 3-4. Add ferroniobium and ferrovanadium before vacuum degassing, and the recovery rate is calculated as 95%. Feed aluminum wire to supplement aluminum to 0.025-0.040%. No aluminum wire is added after vacuum pumping. The temperature after vacuum is over is 1530-1560℃.

Pouring: After vacuum refining, the ladle is calmed for more than 40 minutes, and Ar is softly blown (the Ar pressure and flow rate are suitable for slight vibration of the liquid surface). The molten steel is continuously poured, and the superheat is controlled to be ≤35℃. The end light pressure and electromagnetic stirring technology are used to improve the segregation of the steel. A 320mm×425mm square billet with chemical composition in accordance with the table is produced.

(2) Use a heating furnace to heat the ingot: control the ingot temperature to 600-900°C and keep it at that temperature for 20-40 minutes; then heat it to 1180-1220°C after 120-200 minutes and keep it at that temperature for 80-180 minutes.

(3) The steel ingot is rolled into a 200 mm × 200 mm square steel billet using a primary rolling mill according to a conventional rolling process.

(4) Heating the steel billet and then rolling it into bars: The steel billet is transferred to the heating furnace of the rolling mill for heating. The heating temperature of the steel billet is controlled to be 1160-1200°C, the heating time is 80-180 min, the temperature difference on the surface of the steel billet is ≤40°C, and the final rolling temperature is controlled to be 760-900°C.

(5) Local quenching of the area used as the wheel hub raceway surface (i.e., the working surface): the induction quenching temperature is 880°C ± 10°C, and the cooling method is water cooling.

Table 1 lists a low-basicity synthetic slag used in the refining step of Examples 1-7 of the present invention, which is only illustrative and not limiting of the present invention.

Table 1. (wt%)

Table 2-1 and Table 2-2 list the mass percentages of various chemical elements in the bearing steels for vehicle hubs of Examples 1-7 of the present invention.

Table 2-1. (wt%, the balance is Fe and other inevitable impurities except S, P, O, H, Ti, Pb, As, Sn, Sb, Ca)

Table 2-2. (wt%, the balance is Fe and other inevitable impurities except S, P, O, H, Ti, Pb, As, Sn, Sb, Ca)

Table 3-1 and Table 3-2 list the specific process parameters of the vehicle wheel hub bearing steel in each step of Examples 1-7.

Table 3-1.

Table 3-2.

The inventors sampled the rolling bearing steel for vehicle hub Example 3 without local quenching and observed its microstructure under an optical microscope, as shown in FIG1 .

As shown in FIG. 1 , the microstructure of the vehicle hub bearing steel in the area not subjected to local quenching is ferrite+pearlite.

In addition, the inventors also sampled the partially quenched vehicle wheel hub bearing steel Example 3 and observed its microstructure under an optical microscope, as shown in FIG. 2 .

As shown in Figure 2, the microstructure of the local quenching area of the bearing steel for vehicle hub is a fine and uniform martensite structure, the needle-like structure is not obvious, and the length of the needle-like martensite is ≤10μm. In addition, it can be seen that the local quenching area has dispersed composite nano-scale carbide precipitates, and the size of the carbide precipitates is 15nm-35nm.

Various tests were performed on the samples of each embodiment, and the test results obtained are listed in Table 4. The relevant performance test methods are as follows:

Hardness test: Test according to the testing standard GB/T4043-1999 "Metal Vickers hardness test".

Depth of hardened layer: After induction quenching, the hardness measuring instrument is used to test the depth of the hardened layer. When the microhardness tester detects the gradient to a certain value, the displacement from the surface is measured. The specific hardness value is tested according to the test standard GB/T4043-1999 "Metal Vickers Hardness Test". Specifically: the hardness indentation should be made on one or more parallel lines perpendicular to the surface, and within the 1.5mm width area, the distance between the center of the indentation closest to the surface and the surface is 0.15mm, and the distance from the surface to the center of each successive indentation should increase by 0.1mm each time. When the hardness value is HV=550, the hardness is no longer measured, and the displacement from the surface to the point where the hardness value of HV=550 is located is calculated as the depth of the surface hardened layer.

Mechanical property test: At room temperature, GB/T228 was used to test and the tensile strength of Examples 1-7 was measured.

Central segregation index test: refer to GB/T 223.86 "Determination of total carbon content of steel and alloys - Infrared absorption method after induction furnace combustion" to analyze the carbon content of any bar cross section.

Grain size test: The grain size of the bearing steel for vehicle wheel hub prepared in Examples 1-7 was evaluated by carburizing method.

Maximum inclusion size test: refer to GB/T 10561-2005 Standard rating chart microscopic inspection method for determination of non-metallic inclusion content in steel, inspection area ≥ 300mm2, select the largest field of view for inclusion assessment.

Table 4 lists the test results of the vehicle wheel hub bearing steels of Examples 1-7.

Table 4.

Note: The depth of the hardened layer in the local quenching area in Table 4 is a range value rather than a fixed value because the depth of the hardened layer in different positions of the same product is different. Therefore, the depth of the hardened layer of the same product is reflected as a range value rather than a fixed value.

As can be seen from Table 4, after local quenching treatment, the hardness of the local quenching area of the bearing steel for vehicle hub of Examples 1-7 designed by the present invention is 730-780HV, the depth of the hardened layer is 2.0-3.5mm, the microhardness deviation of the local quenching area at the same hardened layer depth is ≤40HV, and the tensile strength is ≥852MPa. Therefore, it can effectively improve the Brinell indentation phenomenon of the raceway of the automobile hub rolling bearing and prevent the contact part of the rolling element and the raceway wheel from breaking due to the initiation of microcracks caused by Brinell damage.

It can also be seen from FIG. 3 that the depth of the hardened layer in the local quenching area of the bearing steel for a vehicle hub in Example 3 of the present invention is 2.0 to 3.5 mm.

It should be noted that the prior art in the protection scope of the present invention is not limited to the embodiments given in the present application documents. All prior art that does not contradict the scheme of the present invention, including but not limited to prior patent documents, prior public publications, prior public uses, etc., can be included in the protection scope of the present invention.

In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

It should also be noted that the above examples are only specific embodiments of the present invention, and the present invention is obviously not limited to the above examples, and there are many similar variations. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should fall within the protection scope of the present invention.

Claims

A bearing steel for a vehicle wheel hub, containing Fe and unavoidable impurities, characterized in that it also contains the following chemical elements in the following mass percentages:

C: 0.70～0.80%; Si: 0.50～0.70%; Mn: 0.95～1.05%; Cr: 0.60～0.70%; Cu: 0.10～0.25%; Al: 0.010～0.040%; Nb: 0.025～0.035%; V :0.10～0.15%; Mo≤0.01%.
The bearing steel for a vehicle hub as claimed in claim 1 is characterized in that the mass percentage of each chemical element is:

C: 0.70～0.80%; Si: 0.50～0.70%; Mn: 0.95～1.05%; Cr: 0.60～0.70%; Cu: 0.10～0.25%; Al: 0.010～0.040%; Nb: 0.025～0.035%; V: 0.10～0.15%; Mo≤0.01%; the balance is Fe and unavoidable impurities.
The bearing steel for a vehicle hub as claimed in claim 1 or 2 is characterized in that the mass percentage of chemical elements also satisfies: 10Nb+V≥0.40%.
The bearing steel for vehicle wheel hub as described in claim 1 or 2 is characterized in that each element in the inevitable impurities satisfies at least one of the following items: S≤0.015%; P≤0.015%; O≤0.0006%; H≤0.0001%; Ti≤0.0015%; Pb≤0.002%, As≤0.04%, Sn≤0.05%, Sb≤0.004%, Ca≤0.0010%.
The bearing steel for a vehicle wheel hub as claimed in claim 1 or 2 is characterized in that the microstructure of the local quenching area is a uniform martensitic structure, wherein the length of the needle-shaped martensite is ≤10 microns.
The bearing steel for a vehicle wheel hub as claimed in claim 1 or 2, characterized in that the microstructure of the area not subjected to local quenching is ferrite+pearlite; preferably, the area ratio of pearlite is ≤8%.
The bearing steel for a vehicle wheel hub as claimed in claim 1 or 2, characterized in that the grain size of the local quenching area is 7-9.
The bearing steel for a vehicle wheel hub as claimed in claim 1 or 2, characterized in that the maximum size of a single inclusion in the bearing steel is ≤27 μm.
The bearing steel for a vehicle wheel hub as claimed in claim 1 or 2 is characterized in that the local quenching area thereof has dispersedly distributed composite nano-scale carbide precipitates, and the size of the carbide precipitates is 15nm-35nm.
The bearing steel for a vehicle wheel hub as claimed in claim 1 or 2 is characterized in that the microhardness of the local quenching area is 730 to 780 HV, and the depth of the hardened layer is 2.0 to 3.5 mm.
The bearing steel for a vehicle wheel hub as claimed in claim 1 or 2 is characterized in that the microhardness deviation of the local quenching area at the same hardened layer depth is ≤40HV.
The bearing steel for a vehicle hub as claimed in claim 1 or 2 is characterized in that its tensile strength is ≥930 MPa, and/or the center segregation index, i.e., center C%/melting C%, is in the range of 0.95 to 1.05, preferably in the range of 0.98 to 1.02.
A method for manufacturing a bearing steel for a vehicle hub as claimed in any one of claims 1 to 12, characterized in that it comprises the steps of:

(1) Smelting, refining and casting;

(2) heating the ingot using a heating furnace;

(3) using a primary rolling mill to produce a steel billet;

(4) heating the steel billet and then rolling it into a bar;

(5) Local quenching of the area used as the wheel hub raceway surface.
The manufacturing method as described in claim 13 is characterized in that in step (2), the temperature of the ingot entering the furnace is controlled to be 600-900°C and kept warm for 20-40 minutes; then the temperature is raised to 1180-1220°C after 120-200 minutes and kept warm for 80-180 minutes.
The manufacturing method as described in claim 13 is characterized in that in step (4), the heating temperature of the steel billet is controlled to be 1160-1200°C, the heating time is 80-180min, the surface temperature difference of the steel billet is ≤40°C, and the final rolling temperature is 760-900°C.