JP2020521053A - Bearing steel for automobile hub and manufacturing method thereof - Google Patents

Abstract

Chemical composition in percentage by weight: carbon: 0.58 to 0.61%; silicon ≤ 0.15%; manganese: 0.87 to 0.95%; copper: 0.10 to 0.25%; molybdenum: 0 12 to 0.18%; Chromium: 0.10 to 0.20%; Sulfur ≤ 0.015%; Phosphorus ≤ 0.015%; Aluminum: 0.008 to 0.015%; Oxygen ≤ 0.0006% Nitrogen: 0.006 to 0.015%; Hydrogen ≤ 0.0001%; Titanium ≤ 0.0015%; The balance is iron and inevitable impurities, and C% + Mn%/3 = 0.87 to 0.95. , Al/N=0.85 to 1.15 at the same time, and an automobile hub bearing steel and a manufacturing method thereof. The bearing steel according to the present invention has features such as corrosion resistance, fine crystal grains, high purity, and excellent toughness; bearing steel has a tensile strength of 800 to 900 MPa and is induction hardened. It can be guaranteed that the hardness of the race surface reaches 730 to 780 HV and the quench hardened layer depth of the race surface reaches 2.0 to 3.5 mm.

Description

The present invention relates to a bearing steel, and more particularly to a bearing steel for an automobile hub and a manufacturing method thereof.

The automobile hub bearing has a function of supporting the body and a function of guiding the wheel rotation, and receives an axial load and a radial load. Automotive hub bearing units are currently developing up to the third generation, with the range of usage and usage increasing, the first generation consisting of double-row angular bearings; the second generation is outer. The race has a flange for fixing the bearing, and the bearing can be externally attached to the wheel spindle and easily fixed with nuts; the third generation hub bearing unit has an anti-lock braking system (ABS) by the bearing unit. It works together. The hub unit is designed to have an inner flange and an outer flange, the inner flange is fixed to the drive shaft with bolts, and the outer flange is entirely equipped with bearings. With the advent of the third generation hub bearings, the installation and maintenance of hub bearings will become more convenient, but the demands on the performance of the hub bearing steel will also increase.

The bearing steel for manufacturing automobile hub bearings is usually medium carbon bearing steel, for example S55C is adopted, the chemical composition of which is: C: 0.52-0.58%, Si: 0.15-0. 35%, Mn: 0.60 to 0.90%, Cr≦0.20%, P≦0.030%, S≦0.035%, Ni≦0.20%, Cu≦0.30%, Ni+Cr ≦0.35%.

In accordance with the development of forging technology, automobile hub blanks are heated from a normal heating furnace (heating medium: natural gas or gas) + free forging production process, and hot forged bearing sleeve blanks by a multi-station high-speed upset forging press. Has evolved into a production process.

The new high-speed upsetting forging process employs a heating by a medium-frequency induction heating furnace and a tower forging process. The tower forging process is a process of rolling into a single piece, upsetting thickly, and then tower forging. Then, the outer ring and the inner ring are separated, the outer ring is rolled, and the inner ring is perforated. Adopting the new high-speed upset forging process, the production efficiency is high, the dimensional accuracy is high, the material yield is high, the metal grain flow distribution is good, the crystal grains are fine, and the internal structure of metal is improved. However, the requirements for steel materials for bearings of automobile hubs become more stringent. Furthermore, when a defective hub product returned from the market in an automobile joint venture was analyzed and classified, five types of fracture patterns frequently occurring in hub bearings were fatigue fracture, wear, corrosion, electrolytic corrosion, plastic deformation, and cracks. Including. Therefore, the hub bearing steel must have fine crystal grains, uniform hardness, corrosion resistance, and high purity (including non-metallic inclusions, residual elements and gases), as well as good upsetting forging performance and die. It should have a long life, and especially in the subsequent step of induction hardening, not only a hardness of 730 to 780 HV is obtained on the race surface, but also a certain hardening layer depth is required.

Chinese Patent Application No. 200710045281.2 and Chinese Patent Application No. 201610001624.4 are invention patents of bearing steel for automobile hubs. Chinese Patent Application No. 200710045281.2 is a medium carbon bearing steel optimized based on S55C, in which the carbon content range is narrowed so as to reduce the difference in hardness of the race surface, the grain size is refined, and the Al2O3 series is used. The Al content was limited to reduce inclusions, and the harmful element Ti was controlled. Patent application No. 2016100001624.4 is a microalloy sedan carbon hub bearing steel, and the grain size is refined mainly by adding Al element in addition to the limitation to the application.

However, simply adding Al to refine the crystal grains often fails to achieve the corresponding grain refinement effect; conventional automobile hub bearing steels have a relatively low carbon content, so The hardness of the bearing race surface cannot be effectively improved, and the hub bearing steel bar material has a corresponding variation in the hardness of the hub bearing race surface due to too large variations in the carbon in the center and peripheral areas. 50 HV; the purity of the conventional hub bearing steel is not well controlled, and due to the high oxygen content and titanium content in particular, spherical oxide and titanium nitride-based inclusions exceed 27 μm in a single grain, and hub bearing This will lead to early peeling and destruction of the race surface.

The present invention is a bearing steel having features such as corrosion resistance, fine crystal grains, high purity, and excellent toughness, a tensile strength of 800 to 900 MPa, and induction hardening. An object of the present invention is to provide an automobile hub bearing steel capable of ensuring that the hardness of the race surface reaches 730 to 780 HV and the quench hardened layer depth of the race surface reaches 2.0 to 3.5 mm, and a manufacturing method thereof. And

To achieve the above object, the technical solution of the present invention is:
Automotive hub bearings are required to have a hardness of 730 to 780 HV after induction-quenching of the race surface, the quench hardened layer depth of the race surface reaches 2.0 to 3.5 mm (excluding the ground portion), The hardness variation is ≦50 HV. In order to achieve the above technical index stably, it is necessary to control the depth of the quench hardened layer and the uniformity of the structure. In the component design, the main alloying elements C and Mn are rationally matched (taking into consideration the quench hardening layer depth and wear resistance performance), the hardenable element Mo is increased, and AlN is scattered in the grain boundaries. The Al and N elements are controlled so as to control the precipitation and prevent the appearance of Al ₂ O ₃ and TiN-based inclusions while suppressing the growth of crystal grains. The alloy design in which Mn and Cu elements are added is also for the corrosion resistance performance of the hub bearing, and prevents peeling of the work surface due to localized pitting corrosion. The design for refining the crystal grain size further includes selecting and adding an Nb element, and in addition to refining the secondary crystal grains in the forging process of the hub, the crystal grains are finally refined. You can acquire an organization.

Specifically, the present invention is based on the weight percentage of chemical components: carbon: 0.58 to 0.61%; silicon ≤ 0.15%; manganese: 0.87 to 0.95%; copper: 0.10. ~0.25%; molybdenum: 0.12 to 0.18%; chromium: 0.10 to 0.20%; sulfur ≤ 0.015%; phosphorus ≤ 0.015%; aluminum: 0.008 to 0. 015%; oxygen ≤ 0.0006%; nitrogen: 0.006 to 0.015%; hydrogen ≤ 0.0001%; titanium ≤ 0.0015%; balance is iron and inevitable impurities, and C% + Mn%/ It is an automobile hub bearing steel that simultaneously satisfies 3=0.87 to 0.95 and Al/N=0.85 to 1.15.

Further, it contains niobium: 0.020 to 0.040%.
Further, the impurities include Pb≦0.002%, As≦0.04%, Sn≦0.005%, Sb≦0.004% or Ca≦0.0010%.

In the composition design of the steel according to the present invention:
Carbon: Carbon element deteriorates the toughness, but is an important element to maintain the strength and wear resistance of the bearing steel. In the automobile hub bearing steel, the hardness of the induction-hardened race surface reaches 730-780HV, The carbon content should be controlled to 0.58-0.61% to ensure that the quench hardened layer depth of the surface reaches 2.0-3.5 mm.

Silicon: Silicon dissolves in ferrite and austenite to improve the hardness and strength of the steel, but in this steel type, a high content of silicon can promote coarsening of ferrite crystal grains. In the steel according to the invention, silicon is controlled to ≤0.15%.

Manganese: Manganese is a main element that can partially replace chromium to maintain strength and significantly improve hardenability. However, manganese has the drawback of promoting the growth of austenitized grains in steel, so the manganese content should be controlled. In the steel according to the present invention, the content of manganese added to the steel is 0.87 to 0.95%, and the hardness of the induction-hardened race surface reaches 730 to 780 HV together with the carbon element. , Acts as a main element to ensure that the quench hardened layer depth of the race surface reaches 2.0 to 3.5 mm.

Mn forms a solid solution with Fe and improves the strength of ferrite and austenite; Mn is a weak carbide forming element that makes the structure uniform, and enters cementite to replace some Fe atoms. In addition, Mn also has the function of improving wear resistance. Therefore, according to the calculation of the structure of the phase and the research of the experiment, the Mn content is controlled to be 0.87 to 0.95% and combined with other elements, the corresponding action in the invention can be exerted.

Chromium: Chromium can significantly improve strength, hardness and wear resistance, but reduces plasticity and toughness. Chromium can also improve the oxidation resistance and corrosion resistance of steel, and 0.10 to 0.20% of chromium is added to the steel according to the present invention.

Aluminum: Aluminum is a deoxidizing agent and is an element for refining crystal grains. According to the test, too much Al often forms Al ₂ O ₃ -based nonmetallic inclusions, and these are difficult to deform. Non-metallic inclusions are often the source of fatigue cracks and affect the impact resistance of bearings. In this steel type, controlling the product to be 0.010 to 0.015% is a remarkable technical feature.

Niobium: A typical grain refining element, and by selecting and adding 0.020 to 0.040% niobium, it is possible to improve the grain size of the steel material and obtain good toughness. .. However, too much niobium often leads to the accumulation of corresponding carbides, often leading to a decrease in toughness.

Nitrogen: Nitrogen is an important alloying element for the steel according to the present invention, and AlN formed by aluminum and nitrogen, and NbCN formed by niobium and nitrogen, etc., are refined at the crystal grain boundaries. Grain sizes of levels 7-9 are obtained and the nitrogen content is controlled to 0.0060-0.015%.

Copper: The drawback of copper is that it is prone to thermal embrittlement during hot working. Especially, when the copper content exceeds 0.5%, the plasticity remarkably decreases, so the copper element is usually a harmful element. Controlled as. In the arc furnace smelting (raw material is mainly waste steel), the copper content is often 0.10 to 0.20% due to the difference in the smelting means, and it is not necessary to control the copper content. In smelting (the raw material is mainly blast furnace molten iron), the copper content is often less than 0.05%, and it is necessary to add a copper alloy additionally. When it is added to the steel according to the present invention in an amount of 0.10 to 0.25%, strength and toughness can be improved, and particularly atmospheric corrosion performance can be improved. As can be seen in multiple experiments in the laboratory, 0.10-0.25% copper effectively improves the corrosion resistance performance of automobile hub bearings, especially reduces atmospheric pitting corrosion and results in bearing delamination. Can be reduced.

Molybdenum: Elemental molybdenum can refine the crystal grains of steel, improve hardenability, and improve mechanical performance. Further, brittleness of alloy steel due to fire can be suppressed. In order to control the quench hardened layer depth of the race surface to be 2.0 to 3.5 mm, in the present invention, by controlling molybdenum to be 0.12 to 0.18%, a corresponding action can be exhibited.

Phosphorus, sulfur, titanium: Impurity elements in steel, which significantly reduce the plasticity and toughness of steel. In particular, the damage caused by phosphorus and titanium is the largest, with sulfur ≤ 0.015%, phosphorus ≤ 0.010% ≤, and titanium ≤ 0.0015%. At the same time, lead, antimony, bismuth, and oxygen are impurity elements in the steel, and if technically allowed, their contents should be reduced as much as possible.

The method for manufacturing an automobile hub bearing steel according to the present invention is characterized by including the following steps:
1) Smelting/casting Smelting using an arc furnace or converter, smelting ladle, continuous casting, casting ingot according to the above components;
2) The rolling ingot is heated, the heating furnace temperature is set to 600 to 900° C., the ingot is put in the furnace and kept warm for 20 to 40 minutes; after 120 minutes to 200 minutes, the temperature is raised to 1180 to 1220° C., and 80 Keep warm for ~180 minutes;
Roll in a slab and slab the ingot into a billet;
Roll the billet into bars with normal rolling;
The billet heating temperature is set to 1160 to 1200° C. and the heating time is set to 80 minutes to 120 minutes; normal rolling and finish rolling temperature are set to 760 to 900° C.

Preferably, in the ladle refining, low basicity synthetic slag is put in a ladle of a secondary refining furnace in an amount of 1.5 to 3 kg/t of molten steel, smelted, precipitated and deoxidized with Al particles, and Si- Degreasing the slag surface with C powder, adding 1 batch every 15 minutes, adding 2 to 3 batches, and adding each batch to 0.2 to 0.8 kg/t molten steel; secondary refining furnace The basicity of top slag is controlled to 2 to 4.

Preferably, a low basicity synthetic slag is adopted in the secondary refining, and the components of the synthetic slag are in weight percentage: CaO 51 to 53%, MgO 15 to 19%, Al ₂ O ₃ 5 to 11%, SiO ₂ 22 _2. ˜24%, P ₂ O ₅ ≦0.10%, S ≦0.05%, H ₂ O ≦0.6%, CaO/SiO ₂ 2.08 to 2.44; the particle size of the synthetic slag is 5 Is about 20 mm.

Preferably, before entering the vacuum degassing, the molten steel temperature is set to 1580 to 1610° C.; before the vacuum degassing, the chromium nitride wire is fed, the nitrogen content is adjusted to 60 to 150 ppm, and the aluminum wire is fed to feed the aluminum. Replenish to 0.015-0.025%.

Preferably, after the vacuum refining is completed, the ladle is allowed to stand for 40 minutes or more, Ar is soft blown, molten steel is continuously cast, the superheat degree is controlled to ≦35° C., the final solidification light pressure reduction and the electromagnetic stirring technique are used. Improve the segregation of steel materials.

Hub bearings are subjected to heavy loads during operation and are very sensitive to non-deformable inclusions in the hub bearing steel, and in the smelting process, residual elements such as O, Ti, S, P and H are contained in a predetermined content. Besides being controlled to be reduced below, it is also necessary to control single-grain, non-deformable spherical inclusions, in particular the maximum size should not exceed 27 μm. According to the present invention, a customized refining process and refining slag system are designed to control the size and number of non-deformable inclusions.

The advantageous effects of the present invention are
1. In the present invention, alloying elements such as silicon, manganese, molybdenum, copper and nitrogen are added to steel, and corresponding components are designed. By refining automobile hub bearing steel with low basicity synthetic slag, the size of single-grain oxide and nitride inclusions is effectively controlled; segregation by processes such as light pressure reduction and electromagnetic stirring Improved effectively.

2. The latest high-speed upset forging is suitable for automobile hub bearing steel, the hardness of the induction-hardened race surface reaches 730-780HV, and the quench-hardened layer depth of the race surface is 2.0-3. It can be guaranteed that it reaches 5 mm and the tensile strength is 800-900 MPa.

3. The grain size of automobile hub bearing steel is level 7-9.
4. Automotive hub bearing steel is high in purity, the maximum size of single-grained inclusions is ≦27 μm, the oxygen content is ≦6 ppm, and the titanium content is ≦0.0015%.

Specific Embodiment Hereinafter, the present invention will be further described based on Examples.

The components of the examples of the steel according to the present invention are shown in Tables 1 and 2, and the performance parameters of the steels of the examples are shown in Table 3.

The manufacturing method according to the present invention adopts a two-step process: the first step is arc furnace (or converter) primary smelting → ladle furnace vacuum refining → ingot casting; the second step is heat treatment in a rolling mill. The steel material is rolled by hot working.

First stage: Primary smelting of molten steel was carried out in a 150 ton arc furnace; Ladle refining was carried out at a corresponding tonnage; Continuous casting; 320 mm x 425 mm ingot with chemical composition meeting the standard was produced.

(1) Primary smelting furnace: The primary smelting furnace was an arc furnace. The molten steel tapped from the primary smelting furnace reaches [P]≦0.015% and [C]≧0.10%, and starts tapping when T≧1630° C. Added synthetic slag. At the time of tapping, a manganese-aluminum alloy (Al content: 22%) was put in a ladle, and Mn was added at a recovery rate of 100% up to the upper limit of product components.

(2) Ladle refining furnace: The processed portion is heated in a secondary refining furnace (LF), 2 kg/t of low basicity synthetic slag is put into the ladle, and it is slagged. The slag surface is deoxidized with C powder, and the addition amount and the number of addition batches are adjusted according to the slag condition and the silicon content condition in the steel. Usually, one batch is added every 15 minutes to deoxidize the slag during the refining process. The amount used was 0.2 to 0.8 kg/t so that

The basicity of the smelting furnace top slag was controlled to 3 to 4 by adjusting the low basicity slag in the initial stage of LF.

Before vacuum degassing, chromium nitride wire was fed (to adjust the nitrogen content to 60-150 ppm) and aluminum wire was fed to replenish the aluminum to 0.015-0.025%; before entering vacuum degassing. In addition, the molten steel temperature was set to 1580 to 1610° C., the low degree of vacuum (≦0.3 kPa) was controlled in vacuum deaeration, and the holding time was set to 15 min; the temperature after completion of the vacuum was set to 1530 to 1560° C.

(3) Casting: After the vacuum refining was completed, the ladle was allowed to stand still for 40 minutes or more to softly blow Ar (Ar pressure flow rate is preferably such that the liquid surface slightly fluctuates). Molten steel was continuously cast, the degree of superheat was controlled to ≤35°C, and the segregation of the steel material was improved by light reduction at the end of solidification and electromagnetic stirring technology.

Second stage: The ingot was hot-transported to the heating furnace, the furnace entrance temperature was 860° C., and the temperature was kept for 35 minutes; after 160 minutes, the temperature was raised to 1260 to 1280° C.; the temperature was kept for 160 minutes; The ingot that passed was slab-rolled into a billet of 200 mm x 200 mm by a slab mill by a conventional rolling process; the billet was transferred to a rolling mill, the heating temperature of the heating furnace was set to 1140°C, and the heating time was changed. For 130 minutes; the finishing rolling temperature was 835°C.

An automobile hub bearing steel rod produced by carrying out the present invention was surrounded by an automobile hub bearing, mounted on a famous model by an automobile joint venture, and tested, and each performance satisfies practical requirements, The service life is superior to conventional medium carbon bearing steel such as S55C.

Claims (10)

Chemical composition by weight percentage:
Carbon: 0.58 to 0.61%;
Silicon: ≤0.15%;
Manganese: 0.87-0.95%;
Copper: 0.10-0.25%;
Molybdenum: 0.12-0.18%;
Chromium: 0.10 to 0.20%;
Sulfur: ≤0.015%;
Phosphorus: ≤0.015%;
Aluminum: 0.008 to 0.015%;
Oxygen: ≤0.0006%;
Nitrogen: 0.006-0.015%;
Hydrogen: ≤ 0.0001%;
Titanium: ≤0.0015%;
The balance is iron and unavoidable impurities, and simultaneously satisfies C%+Mn%/3=0.87-0.95, Al/N=0.85-1.15,
Automotive hub bearing steel. The automobile hub bearing steel according to claim 1, further comprising niobium: 0.020 to 0.040%. 2. The impurity according to claim 1, wherein Pb≦0.002%, As≦0.04%, Sn≦0.005%, Sb≦0.004% or Ca≦0.0010%. 2. Automotive hub bearing steel according to 2. The automobile hub bearing steel has a tensile strength of 800 to 900 MPa, the hardness of the induction hardened race surface reaches 730 to 780 HV, and the quench hardened layer depth of the race surface is 2.0 to 3.5 mm. Automotive hub bearing steel according to any of claims 1 to 3, characterized in that it can be guaranteed to reach. The method for producing an automobile hub bearing steel according to claim 1 or 2, comprising the following steps.
(1) Smelting/casting According to the composition of claim 1 or 2, smelting using an arc furnace or a converter, smelting ladle, continuous casting, casting ingot;
(2) The rolling ingot is heated, the heating furnace temperature is set to 600 to 900° C., the ingot is placed in the furnace and kept warm for 20 to 40 minutes; after 120 minutes to 200 minutes, the temperature is raised to 1180 to 1220° C., Incubate for 80-180 minutes;
Roll in a slab and slab the ingot into a billet;
Roll the billet into bars with normal rolling;
The billet heating temperature is set to 1160 to 1200° C. and the heating time is set to 80 to 120 minutes; rolling is performed normally, and the finish rolling temperature is set to 760 to 900° C. In the ladle refining, a low basicity synthetic slag was put in a ladle of a secondary refining furnace in an amount of 1.5 to 3 kg/t molten steel, smelted, precipitated and deoxidized with Al particles, and Si-C powder was used. Perform slag surface deoxidation, add 1 batch every 15 minutes, add 2 to 3 batches, add 0.2 to 0.8 kg/t molten steel per batch; top slag in secondary refining furnace The method for producing an automobile hub bearing steel according to claim 5, wherein the basicity is controlled to 2 to 4. Low basicity synthetic slag is adopted in the secondary refining, and the components of the synthetic slag are in weight percentage: CaO 51-53%, MgO 15-19%, Al ₂ O ₃ 5-11%, SiO ₂ 22-24%. , P ₂ O ₅ ≦0.10%, S≦0.05%, H ₂ O≦0.6%, CaO/SiO ₂ 2.08 to 2.44; the particle size of the synthetic slag is 5 to 20 mm. The method for manufacturing automobile hub bearing steel according to claim 5, wherein Before entering the vacuum degassing, bring the molten steel temperature to 1580 to 1610°C; feed the chromium nitride wire before vacuum degassing, adjust the nitrogen content to 60 to 150ppm, and feed the aluminum wire to 0.015 aluminum. The method for manufacturing an automobile hub bearing steel according to claim 5, wherein the supplementation is 0.025%. After the vacuum refining is completed, the ladle is allowed to stand for 40 minutes or longer, Ar is soft blown, molten steel is continuously cast, the superheat degree is controlled to ≤35°C, segregation of steel materials by light pressure at the end of solidification and electromagnetic stirring technology. The method for manufacturing an automobile hub bearing steel according to claim 5, characterized in that The automobile hub bearing steel has a tensile strength of 800 to 900 MPa, the hardness of the induction hardened race surface reaches 730 to 780 HV, and the quench hardened layer depth of the race surface is 2.0 to 3.5 mm. The method for manufacturing an automobile hub bearing steel according to claim 5, characterized in that it can be guaranteed to reach.