JPS6263651A - Bearing steel and its production - Google Patents

Abstract

PURPOSE:To provide excellent durability and life to the 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, <0.01 P, <0.008 S, 0.5-1.6 Cr, 0.0008 O, <0.0025 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 basicic slag having >=3 basicity in an inert atmosphere below the atmospheric 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 (Industrial Field of Application) The present invention is directed to ball bearings, roller bearings, etc. used in automobiles and various industrial machines, which have excellent durability, machinability, and cold forgeability. Concerns steel 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 resin 3 in order to improve the durability life.

(Problem to be solved) However, A1.0 in steel. However, the methods for reducing this have not been able to provide a satisfactory durability life under high loads and high speeds.

In addition, the inner and outer rings that make up a bearing are formed by hot forging, heat treated, and finished by cutting, but in recent years, as processing technology has rapidly advanced and high-speed cutting has increased, the durability has increased. In addition to this, machinability has also become a requirement.

However, the conventionally used SUJ 2 has problems such as insufficient machinability, rapid wear of the cutting tool during high-speed cutting, the need to replace the cutting tool early, and low productivity.

Conventionally, machinability has been improved by adding 0.080% S to improve machinability, but due to an increase in sulfide-based inclusions, durability life and cold forgeability are significantly reduced. It had the following drawback.

(Means for Solving the Problems) The present invention was made in view of the drawbacks of conventional steels, and the present inventors have developed various alloy elements with improved durability, machinability, and cold forgeability. As a result of research on the effects of
Among oxide-based inclusions, alumina-based oxides in particular form large inclusions, significantly reducing durability, machinability, and cold forgeability, and Ti forms carbonitrides.
It was discovered that the durability life and cold forgeability are reduced, and impurity elements such as P also have a negative effect on the durability life.

Based on these findings, the present invention minimizes elements that generate inclusions that impede durability life, machinability, and cold forgeability by setting the O content to 0,00% or less and Tt to 0.0025% or less. Furthermore, the amount of S has been reduced to less than o, oos% compared to conventional steel, and the impurity elements have also been reduced to P 0.01.
By reducing the amount of nonmetallic inclusions c, yls (A+B+C)) present in the steel to 0.0% or less,
30% or less, and the average size is 27μ
m or less, the rated life (B
io), and the average life (B and N> are both more than double, which is a significantly superior durability life).

In the present invention, raw materials are carefully selected to produce low oxygen, low sulfur, and low TiO high purity steel, and the molten steel is oxidized and refined in an electric furnace and tapped into a ladle. Alternatively, after tapping the steel, perform a dephosphorous treatment and suck the oxidized slag on the molten steel using a vacuum slag cleaner, and then reduce the basicity to 3.
High basicity slag (FeO+MnO≦0.5% reducing property, and CaO/Sin>/ALOa=
A slag with an excellent Bs capacity of 0.3 to 0.4) is made into slag by electrode heating, and while adjusting the bath temperature, inert gas is blown in using double porous bricks, and the molten steel is reductively refined while being strongly stirred. and s o, oos% or less, O0.
0.020% or less and low Ti, and then perform vacuum degassing refining using a reflux type vacuum degassing device under high reflux for 2/3 of the processing time and weak reflux for the remaining 1/3.
It was discovered that bearing steel with high cleanliness can be obtained by further reducing the amount of steel and performing gas closed casting.

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

The first invention steel has an M content ratio of C0.70 to 1.10%,
Si 0.15-1.60%, Mn 0.15-1.1
5%, P 0.010% or less, S 0.008% or less,
Cr 0.50-1.60%, 00.0008% or less,
The second invention steel contains 0.0025% or less of Ti and the balance consists of Fe and impurity elements, and the second invention steel is the first invention steel containing 0.05 to 0.50% Mo to further improve hardenability. Therefore, the third invention steel is v o
, os ~ 0030%, Nb 0.05-0.30%, and the wear resistance of the first invention steel is further improved, and the fourth invention steel is the steel of the first invention. P on steel
b 0.05-0.15%, Te 0.01-0.15
%, Se 0.01~0.15%, Ca 0.001~
Containing one or more of 0.07%, the first
The invention further improves the machinability of the invented steel, and the 5.6 invention is such that when manufacturing the above-mentioned 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 A bearing characterized in that reduction refining is performed in the presence of basic slag with strong stirring while adjusting the bath temperature, and then vacuum degassing refining is performed with high reflux and weak reflux using a reflux type vacuum degassing device. It is a method of manufacturing steel.

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

C is an element necessary to ensure a hardness of C60 or more required for steel for rolling bearings, and must be contained in an amount of 0.70% or more. However, if the content exceeds 1.10%, giant carbides are likely to be formed and durability life, cold forgeability, and impact fatigue are reduced, so 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 transfer life characteristics and machinability will deteriorate, so the upper limit is set at 1.6%.
It was set to 0%.

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 a large amount is present, 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%.

Cr, like Mn, 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%. However, if a large amount of carbon is contained, the carbide becomes coarse and the machinability deteriorates, 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 0.01.
It was set to 0%.

S is an element that combines with Mn to form sulfide-based inclusions and improves machinability, but on the other hand, it is an element that significantly reduces durability and cold forgeability. In the present invention, the upper limit is set to o and oos% in consideration of durability life and machinability.

0 is Al in steel 03. Si0. It is an element that generates oxide-based inclusions such as, and significantly deteriorates rolling life characteristics, machinability, and cold forgeability.

In the present invention, by significantly reducing the amount of nonmetallic inclusions and regulating the size of the inclusions, durability life, machinability, and cold forgeability are significantly improved, and the content is suppressed. and the upper limit is 0.000
It was set at 8%.

Ti combines with N and remains in the steel as TiN inclusions,
It is an element that generates large inclusions when its content increases, significantly deteriorating durability life, machinability, and cold forgeability.It is necessary to reduce its content, and the upper limit is set at 0.002.
It was set at 5%.

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 improvement in effectiveness is small, so the upper limit is set at 0.50%.
And so.

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, V.

Even if Nb is contained in an amount exceeding 0.30%, the improvement in the effect is small, so the upper limit was set at 0.30%.

Pbs Tes Ses Ca is an element that improves machinability, and it is necessary to contain 0.05% of Pb, 0.01% of Te, 0.01% of Se, and o, ooi% or more of Ca. However, Pb, Te, Se, and Ca are elements that degrade durability and cold forgeability, so the upper limit is set at Pb5T.
e-, Se is 0.15%, and Ca is 0.01%, all of which will be clarified in Examples.

Table 1.2 shows the chemical composition of these test steels.

In Table 1.2, A and B steels are conventional steels, and A steels are SUJ steels.
2. Steel B is 5IIJ3, steel C-F is comparative steel, and steel 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 material was subjected to oil cooling, air cooling at 170°C for 90 minutes, quenching and tempering, and the amount of nonmetallic inclusions, their average length, durability life, cutting layer, and cold forgeability were investigated, and the results are presented. It is something.

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 type thrust type durability tester to prepare a sample having an outer diameter of 65φ x an inner diameter of 18φ x a thickness of 10n+, and expressed as an index with 11i1 as 1. The machinability was evaluated by preparing five 40mφXIQm materials, using a 5φSKH9 straight drill as a cutting tool, and measuring the drill drilling time at a rotation speed of 114 Orpm and a thrust force of 30 pupils (weight free fall method).

Regarding cold forgeability, the upsetting rate of 2011φ x 30 Tsuru is 75
This is an investigation of the incidence of cracking in %.

As is known from Table 3 of Table 3, the comparison steel C steel has excellent cold forgeability, but the amount of nonmetallic inclusions is 0.69, the average length is 1, As for the durable life, the rated life (B+o) was 1.51 and the average life (Jo) was 1.53, which were not satisfactory in terms of nonmetallic inclusions and durable life.

Also, for D and F steels, 0. , because the S content is lower than that of A1B steel, the durability life is shorter than the rated life (
B+o) is 1.92.1.51, which is a considerable improvement, but it is still not satisfactory, and the cold forgeability is also low, with a cracking incidence of 20% or more. Further, although F steel has excellent cold forgeability, its durability is not satisfactory.

In contrast, the i-F steel, which is the steel of the present invention, has a
．． By setting the S amount to 0.008% or less and lowering the Ti amount, the amount of nonmetallic inclusions is 1/3 to 1/2 that of conventional steel A steel, and the average length thereof is 0.9 to 0.75 times, which is significantly superior to Steel A in terms of non-metallic inclusions, and in terms of durability, both the rated life and average life are 2 times higher than that of Steel A and B.
In terms of machinability, the steel of the present invention has a low S content of 0.008% or less, but by significantly reducing oxide inclusions, it is 1 times as much as the conventional steel. ．．
It has about twice the machinability, and the cracking rate at an upsetting rate of 75% is O, which is superior to conventional steels in terms of cold forgeability.

As described above, steels J to V, which are the steels of the present invention, are significantly superior to ASB steels in terms of nonmetallic inclusions, durable life, machinability, and cold workability.

In this way, the steel of the present invention has C% Sis Mn=, C
By appropriately containing r and reducing the amount of P,..., S, 0, and Ti, and reducing the amount of oxide and sulfide inclusions, the steel of the present invention has a longer rated life and average life than conventional steel. Both have succeeded in achieving an excellent durability life of more than double, and also have excellent machinability and cold forging properties, making them suitable for high loads and high speeds as industrial machinery and vehicles become more sophisticated. We are making an extremely large contribution to industry through our high-quality bearing steel, which can be used in ball bearings, roller bearings, etc., and its manufacturing method.

Claims (6)

[Claims] (1) C 0.70-1.10%, Si by weight ratio
0.15-1.60%, Mn 0.15-1.15%
, P 0.010% or less, S 0.008% or less, Cr
0.50-1.60%, O 0.0008% or less, T
A bearing steel characterized in that it contains 0.0025% 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 0.010% or less, S 0.008% or less, Cr
0.50-1.60%, O 0.0008% or less, T
Contains 0.0025% or less of i, and furthermore 0.0% of Mo.
A bearing steel characterized in that it contains 5 to 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 0.010% or less, S 0.008% or less, Cr
0.50-1.60%, O 0.0008% or less, T
Contains i 0.0025% 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 0.010% or less, S 0.008% or less, Cr
0.50-1.60%, O 0.0008% or less, T
Contains 0.0025% 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 0.010% or less, S 0.008% or less, Cr
0.50-1.60%, O 0.0008% or less, T
When producing steel containing 0.0025% 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 0.010% or less, S 0.008% or less, Cr
0.50-1.60%, O 0.0008% or less, T
i 0.0025% or less, and further contains V 0.0025% 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.