JPS6263650A - Bearing steel and its production - Google Patents

Abstract

PURPOSE:To provide excellent durability and life to a titled steel by incorporating an adequate ratio each of C, Si, Mn and Cr into the steel, decreasing the contents of P, S, O and Ti as far as possible and decreasing the amt. of oxide and sulfide inclusions as far as possible. CONSTITUTION:The compsn. of the bearing steel is specified, by weight %, to 0.7-1.1 C, 0.15-1.6 Si, 0.15-1.15 Mn, <0.012 P, <0.002 S, 0.5-1.6 Cr, <0.0008 O, <0.0015 Ti and the balance Fe and impurity elements. The slag on the molten steel tapped from a melting furnace into another vessel is sucked by a vacuum slag cleaner and the steel is subjected to reduction refining with strong stirring while the bath temp. is adjusted by electrode heating in the presence of the high basicity slag having >=3 basicity in an inert atmosphere above the atm. pressure in the stage of producing the above-mentioned steel. The steel is then subjected to high reflux for 2/3 the treatment time and weak reflux for 1/3 the treatment time by a reflux type vacuum degassing device, by which the vacuum degassing refining is executed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a bearing steel that is commonly used in ball bearings, roller bearings, etc. used in automobiles and various industrial machines, and has excellent durability and cold forgeability. and its manufacturing method.

(Prior art) Bearings used in automobiles and industrial machinery are designed to improve the performance of these devices.
As steels are used at high speeds, durability has come to be considered important, and various developments have been made to develop steels that can further improve durability.

Conventionally, methods have been implemented to reduce the amount of oxide-based inclusions such as AI in order to improve the durability life.

(Problems to be Solved) However, the method of reducing A1U0] in steel does not provide a satisfactory durability life under high loads and high speeds.

In addition, the inner and outer rings that make up the bearing are formed by hot forging, heat treated, and finished by cutting, but in recent years, processing technology has rapidly advanced, and In the 1-stroke process, there is a transition from some hot to cold handling, and in addition to durable life, cold machinability is also required.

However, the conventionally used SUJ 2 does not have sufficient deformability and cannot withstand high-level cold working, resulting in the problem of cracking.

Generally, Atyu-OJ in steel is used to improve cold forgeability.
Although methods have been adopted to reduce the amount of oxide-based inclusions such as oxide inclusions, it has not been possible to obtain satisfactory cold forgeability only by reducing ni and oj.

In recent years, as the proportion of cold forging has increased, higher processing rates and higher speeds have been required, and cold forgeability has become important in bearing steels as well.

If oxides produce large inclusions that significantly reduce durability and cold forgeability, and if there are very few oxide inclusions, sulfide inclusions may also reduce durability and cold forgeability. In addition, it was discovered that Ti generates carbonitrides, and even a small amount of Ti significantly reduces durability life and cold forgeability, and impurity elements such as P also have a negative effect on durability life. It is.

Based on these findings, the present invention reduces the amount of O to 0.0008%.
By carefully selecting the raw materials and reducing the inclusion-forming elements that impede the durability life and cold forgeability by keeping Ti below 0.0015% and S below 0.002% as much as possible. Metal inclusions I (JIS (A+B
+C)) is 0.015% or less, and the average level of personality is 19. czm or less, the rated life (Blo) is 2.6 times longer than conventional steel, and the average life (Blo) is
This steel has a significantly superior durability life of 5.7 times (5.7 times), and also has a cracking incidence of 0 at an upsetting rate of 75%, making it possible to obtain a steel with excellent cold forgeability. It is.

In the present invention, raw materials are carefully selected to produce low oxygen, low sulfur, low phosphorus, and low TiO high cleanliness steel, and the molten steel is oxidized and refined in an electric furnace and tapped into a ladle. DeP treatment is performed during or after tapping the molten steel, the oxidized slag on the molten steel is sucked out by a vacuum slag cleaner, and then highly basic slag with a basicity of 3 or more (FeO + MnO≦0
．． 5% reducibility and CaO/Si]0/AIJ
4 = slag with a JliS capacity of 0.3 to 0.4) is slaged by electrical heating, and while adjusting the bath temperature,
Inert gas is blown into the molten steel using a double porous brick, and reduction refining is performed while stirring the molten steel, resulting in an S content of 0.002%.
Below, we aim to reduce O to 0.0020% or less and to lower Ti, and then perform vacuum degassing refining with high reflux for 2/3 of the processing time using a reflux type vacuum degassing device and weak reflux for the remaining 1/3. It was discovered that bearing steel with high purity can be obtained by further reducing the amount of N and performing insulation casting.

The steel of the present invention will be explained in detail below.

The first invention steel has a weight ratio of C0.70 to 1.10%,
Si 0.15-1.60%, Mr+ 0.15-1.
15%, P 0.012% or less, S 0.002% or less, Cr 0.50-1.60%, 00; The second invention steel is the first invention steel containing 0.05 to 0.50% Mo to further improve the hardenability of the first invention steel, and the third invention steel is the first invention steel. V0.05~0.30%, Nb0805~ in invention steel
It contains one or two of 0.30% to further improve the wear resistance of the first invention steel, and contains two or more of these to improve the machinability of the first invention steel. The fifth
．． When manufacturing the above-mentioned No. 1.3 invention steel, the slag on the molten steel discharged from the melting furnace into a separate container is sucked by a vacuum slag cleaner, and then in the presence of highly basic slag, the bath temperature is lowered. This method of manufacturing bearing steel is characterized by performing reduction refining with strong stirring while adjusting the amount of steel, and then performing vacuum degassing refining with high reflux and weak reflux using a reflux type vacuum degassing device.

The reasons for limiting the composition of the steel of the present invention will be explained below.

C is hardness III required for steel for rolling bearings? C6
This is an element necessary to ensure a content of 0 or more, and the content must be 0.70% or more. However, if the content exceeds 1.10%, giant carbides are likely to be formed, and the durability life is shortened.
Since cold forgeability deteriorates, the upper limit was set at 1.10%.

Si is an element that improves the deoxidizing effect and hardenability, as well as the durability life and impact fatigue, and must be contained in an amount of 0.15% or more. However, if the content exceeds 1.60%, the rolling life characteristics, cold forgeability, and machinability deteriorate, so the upper limit was set at 1.60%.

Mn is an element that improves deoxidizing effect and hardenability, and has a content of 0.1
The content must be 5% or more. However, even if it is contained in a large amount, the improvement in the effect is small, and MnS is generated, which reduces the rolling life, so the upper limit was set at 1.15%.

Like Mn, Cr is an element that improves hardenability and is also an element that promotes carbide spheroidization, and must be contained in an amount of at least 0.50% or more.

However, if the content is too large, the carbides will become coarse and the cold forgeability and machinability will deteriorate, so the upper limit was set at 1.60%. P is an element that reduces rolling life and toughness, so it is necessary to reduce its content as much as possible, and the upper limit is set to 0.0.
It was set at 12%.

S is an element that combines with Mn to form sulfide-based inclusions, which significantly reduces durability and cold forgeability. The purpose of the present invention is to reduce sulfide-based inclusions as much as possible and significantly improve durability life and cold forgeability, so it is necessary to strictly control the content, and the upper limit is set to 0.00.
It was set at 2%.

O is an element that forms oxide inclusions such as AI]03 and StOY in steel, and significantly deteriorates rolling life characteristics and cold forgeability. In the present invention, 'ζ significantly reduces the amount of nonmetallic inclusions and controls the size of inclusions, thereby greatly improving rolling life characteristics and cold forgeability, and its content is strictly controlled. Because of necessity, the above ■ was set as o,ooos%.

Ti combines with N and remains in the steel as TiN inclusions,
If the content increases, large inclusions will be formed and the rolling life characteristics and cold forgeability will be significantly deteriorated, so it is necessary to reduce the content as much as possible, and the upper limit was set at 0.0015%.

Mo is an element that improves hardenability, and when contained in a small amount, the hardenability can be increased. In the present invention, Mo is included in an amount of 0.05% or more as necessary. However, Mo is an expensive element, and even if it is contained in an amount exceeding 0.50%, the effect will not improve much, so the upper limit has been set to 0.50%.
%.

V and Nb are elements that generate carbonitrides and improve strength and toughness, and to obtain these effects, each must be 0.05
% or more is required. However, both VlNb and 0.
Even if the content exceeds 30%, the improvement in effectiveness is small.
The upper limit was set at 0.30%.

! 'b, Tes Se, Ca are elements that improve machinability, and in the present invention they are added as necessary, PB is 0.05% or more, Te is 0.01% or more5,
The required machinability can be obtained by containing Se in an amount of o.o.i.% or more and Ca in an amount of o.o.i.% or more. However, if Pb, L'e, S, and Ca are contained in excess of the necessary amount, the excellent durability life and cold forgeability of the present invention will be impaired, so the upper limit thereof will be clarified in Examples.

Table 1.2 shows the chemical composition of these test steels.

In Table 1.2 of Cumulative T food stone, A and B steels are conventional steels, and A steel is 5UJ.
2. Steel B is 5IIJ3, steel C-F is comparative steel, and steels G to V are steels of the present invention, which were produced by the above-mentioned melting method.

Table 3 shows the test steel of Table 1.2 at 850℃ x 30℃.
The amount of non-metallic inclusions, their average length, durability life,
The cold forgeability was investigated and the results are shown.

The amount of nonmetallic inclusions and their average length were investigated by cutting out the 65φ rolled material subjected to the above treatment.
It is expressed as an index with steel A, which is a conventional steel, set as 1.

The durability life was determined by using a Mori thrust type durability tester to prepare a specimen with an outer diameter of 65 φ x an inner diameter of 18 φ x a thickness of 10 mm, and expressed as an index with the steel A as 1. Regarding cold forgeability, the upsetting rate of 20 dragon φX 30tm is 75
This is an investigation of the incidence of cracking in %.

As is known from Table 3, steel C, which is a comparison steel, has improved durability and cold forgeability compared to conventional steel, but the amount of nonmetallic inclusions and average length are improved compared to steel A and B.
It is on the same level as steel.

In addition, due to the high sl of D steel, there is a large amount of nonmetallic inclusions, resulting in poor cold forgeability.As for E steel, due to the high O content, durability life and cold forgeability are poor. However, F steel has a poor durability life due to its high s and ol. .

In contrast, G to Vil, which are the steels of the present invention, reduce the amount of nonmetallic inclusions by reducing the amount of 0 to 0.0008% or less, the amount of S to 0.002% or less, and reducing Ti, Pg as much as possible. is l/6 to 1/ of conventional steel A steel.
15, the average length is 1/2, and the non-metallic inclusions are significantly superior to A steel.
Therefore, regarding the durability life, the rated life (BlO) is 2.
It is significantly superior to steel A, which is a conventional steel, with an average life (B m ) of 4 to 7 times. In addition, regarding cold forgeability, the crack occurrence rate at an upsetting rate of 75% was 0%, which is far superior to conventional steel.

In this way, the steels G to V, which are the steels of the present invention, have nonmetallic inclusions,
In terms of durability and cold workability, it has superior properties compared to All.

In addition, although the steel of the present invention has a low S content of 0.002% or less, by significantly reducing oxide inclusions, it has machinability comparable to conventional steel, and P -, 3% 0. By reducing the amount of Ti as much as possible, oxide-based,
By reducing the amount of sulfide inclusions as much as possible, the steel of the present invention has a rated life of 2.6 times and an average life of 5 times that of conventional steel.
．． It has successfully achieved an excellent durability life of 7 times, has high deformability, and has cold forgeability that can withstand advanced processing. High-quality bearing steel that can handle high loads and high speeds and its manufacturing method will make an extremely large contribution to industry.

Claims (6)

[Claims] (1) C 0.70-1.10%, Si by weight ratio
0.15-1.60%, Mn 0.15-1.15%
, P 0.012% or less, S 0.002% or less, Cr
0.50-1.60%, O 0.0008% or less, T
A bearing steel characterized in that it contains 0.0015% or less of i, with the remainder consisting of Fe and impurity elements. (2) C 0.70-1.10%, Si
0.15-1.60%, Mn 0.15-1.15%
, P 0.01% or less, S 0.002% or less, Cr
0.50-1.60%, O 0.0008% or less, Ti
Contains 0.0015% or less, and further contains Mo 0.05%
A bearing steel characterized by containing ~0.50%, with the remainder consisting of Fe and impurity elements. (3) C 0.70-1.10%, Si
0.15-1.60%, Mn 0.15-1.15%
, P 0.012% or less, S 0.002% or less, Cr
0.50-1.60%, O 0.0008% or less, T
Contains i 0.0015% or less, and further contains V 0.05
0.30%, Nb 0.05-0.30%, and one or two of Nb 0.05-0.30%, with the remainder consisting of Fe and impurity elements. (4) C 0.70-1.10%, Si
0.15-1.60%, Mn 0.15-1.15%
, P 0.012% or less, S 0.002% or less, Cr
0.50-1.60%, O 0.0008% or less, T
Contains 0.0015% or less of i, and further contains 0.0
5-0.15%, Te 0.01-0.15%, Se
0.01-0.15%, Ca 0.001-0.01%
A bearing steel characterized by containing one or more of the above, with the remainder consisting of Fe and impurity elements. (5) C 0.70-1.10%, Si
0.15-1.60%, Mn 0.15-1.15%
, P 0.012% or less, S 0.002% or less, Cr
0.50-1.60%, O 0.0008% or less, T
When producing steel containing 0.0015% or less of Fe and impurity elements, the slag on the molten steel discharged from the melting furnace into a separate container is sucked by a vacuum slag cleaner, and then the salinity is reduced. In the presence of 3 or more highly basic slag and in an inert atmosphere above normal pressure, reduction refining is performed with strong stirring while adjusting the bath temperature by electrode heating, and then a reflux type vacuum degassing device. A method for manufacturing bearing steel, characterized in that vacuum degassing refining is performed by high reflux for 2/3 of the processing time and weak reflux for 1/3 of the processing time. (6) C 0.70-1.10%, Si
0.15-1.60%, Mn 0.15-1.15%
, P 0.012% or less, S 0.002% or less, Cr
0.50-1.60%, O 0.0008% or less, T
i 0.0015% or less, and further contains V 0.0015% or less.
When producing steel containing one or two of Nb 0.05 to 0.30% and Nb 0.05 to 0.30%, with the balance consisting of Fe and impurity elements, the steel was tapped from a melting furnace into a separate container. The slag on the molten steel is sucked up by a vacuum slag cleaner, and then in the presence of highly basic slag with a basicity of 3 or more and in an inert atmosphere at normal pressure or higher, the bath temperature is adjusted by electrode heating, Reduction refining is performed with strong stirring, and then a reflux type vacuum degassing device is used for 2 hours of processing time.
1. A method for manufacturing bearing steel, characterized by performing vacuum degassing refining by high reflux of 1/3 and weak reflux of 1/3.