JPH0585629B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention is suitable for ball bearings, roller bearings, etc. used in automobiles and various industrial machines, and has a long lifespan.
This invention relates to a bearing steel with excellent machinability and cold forgeability, and a manufacturing method thereof. (Prior art) Bearings used in automobiles and industrial machinery are
In order to improve the performance of these devices, bearings are used under high loads and speeds, and durability has become important, and steel that can further improve durability has been developed. . Conventionally, methods have been implemented to reduce the amount of oxide-based inclusions such as Al ₂ O ₃ in order to improve the durability life. (Problems to be Solved) However, in the method of reducing Al ₂ O ₃ in steel, it has not been possible to obtain 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, then heat treated, and then finished by cutting, but in recent years, as processing technology has rapidly advanced and high-speed cutting has increased, In addition to durability, machinability has also come to be desired. However, the conventionally used SUJ 2 does not have sufficient cutting performance, and the cutting tool wears quickly during high-speed cutting, making it necessary to replace the cutting tool early.
There were problems such as low productivity. Conventionally, S was added at 0.080% to improve machinability.
Although machinability is improved by adding S, the increase in sulfide-based inclusions has the drawback of significantly decreasing durability and cold forgeability. (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 Ti on carbonitrides, it was found that alumina-based oxides sometimes form large inclusions among oxide-based inclusions, significantly reducing durability, machinability, and cold forgeability. It was discovered that impurity elements such as P also have a negative effect on the durability life. Based on these findings, the present invention reduces the amount of O to 0.0008%.
Below, we have reduced Ti to 0.0025% or less, an element that creates inclusions that impede durability, machinability, and cold forgeability, as much as possible, and further reduced the S content to 0.008% or less compared to conventional steel, and further reduced impurities. Also about elements
By reducing P0.010% or less, the amount of nonmetallic inclusions [JIS (A + B + C)] present in steel can be reduced.
0.030% or less, and its size is approximately 27μm or less on average, resulting in a significantly superior durability life, with both the rated life (B ₁₀ ) and average life (B ₅₀ ) more than double that of conventional steel. This is what I was able to successfully obtain. In the present invention, low oxygen, low sulfur, and low
We carefully select raw materials to produce high-clean Ti steel.
The molten steel that has been oxidized and refined in an electric furnace is tapped into a ladle, subjected to deP treatment during or after tapping, and the oxidized slag on the molten steel is sucked into a vacuum slag cleaner, and then the basicity is reduced. High basicity slag with a
CaO/SiO ₂ /Al ₂ O ₃ = 0.3 to 0.4 slag with excellent desulfurization ability) is slaged by electrode heating, and while adjusting the bath temperature, inert gas is blown in with a double porous brick to form molten steel. Reduction refining is carried out with strong stirring to achieve S of 0.008% or less, O of 0.0020% or less, and low Ti, and then high reflux is carried out for 2/3 of the processing time using a reflux type vacuum degassing device. It has been discovered that bearing steel of high purity can be obtained by subjecting the remaining 1/3 to vacuum degassing refining using weak reflux to further reduce the O and H contents, and further performing gas-insulated casting. The steel of the present invention will be explained in detail below. The first invention steel has C0.70 to 1.10% by weight,
Si0.15~1.60%, Mn0.15~1.15%, P0.010% or less,
S0.008% or less, Cr0.50~1.60%, O0.0008% or less,
Contains Ti0.0025% or less, and Pb0.05~0.15
%, Te0.01~0.15%, Se0.01~0.15% and Ca0.001
Containing one or two or more of ~0.01%,
It has improved hardenability and machinability, and is the second
In the invention, when manufacturing the above-mentioned steel, the basicity is 3 to 6.
in the presence of highly basic slag and at a pressure of 1 to 2
Reduction refining is performed under an inert atmosphere at atmospheric pressure with strong stirring while adjusting the bath temperature, followed by high reflux (2/3 of the processing time) using a reflux type vacuum degassing device.
This is a bearing steel manufacturing method characterized by performing vacuum degassing refining with weak reflux (1/3 of the processing time). The reasons for limiting the composition of the steel of the present invention will be explained below. C is the hardness H _R required for steel for rolling bearings.
An element necessary to ensure C60 or higher, 0.70%
The above content is necessary. 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 deoxidation and hardenability as well as durability and impact fatigue, and is 0.15%
The above content is necessary. However, if the content exceeds 1.60%, rolling life characteristics and machinability will deteriorate, so the upper limit was set at 1.60%. Mn is an element that improves deoxidizing action and hardenability, and must be contained at 0.15% or more. However, even if the content is increased, the improvement in effectiveness is small, and MnS is generated, reducing rolling life, so the upper limit is set at 1.15%.
And so. 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%. However, if the content is too large, the carbides become 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.
The upper limit was set at 0.010%. S combines with Mn to generate sulfide inclusions,
It is an element that improves machinability, but on the other hand, it is an element that significantly reduces durability life and cold forgeability.
In the present invention, the upper limit was set at 0.008% in consideration of durability and machinability. O is an element that forms oxide inclusions such as Al ₂ O ₃ and SiO ₂ in steel, 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. The upper limit was set at 0.0008%. Ti is an element that combines with N and remains in steel as TiN inclusions, and when its content increases, it forms large inclusions, which significantly deteriorates durability, machinability, and cold forgeability. It was necessary to lower the content, so the upper limit was set at 0.0025%. Pb, Te, Se, Ca are elements that improve machinability, Pb is 0.05%, Te is 0.01%, Se is 0.01%, Ca
must be contained at 0.001% or more. but,
Pb, Te, Se, and Ca are elements that deteriorate durability and cold forgeability, so the upper limit for Pb, Te, and Se is 0.15%.
Ca was set at 0.01%. In the method of the present invention, first, reduction refining is carried out in the presence of a highly basic slag with a basicity of 3 to 6 and under an inert atmosphere at a pressure of 1 to 2 atmospheres, due to the dissociation of components in the slag. In addition to preventing O from rising in the molten steel, by increasing the desulfurization ability, silica, alumina-based inclusions and sulfides are adsorbed to the slag, reducing the total oxygen content and S as much as possible. This is a process for rough adjustment of the components, for example, the temperature of molten steel with an average temperature of 1500°C is adjusted by electrode heating to keep the bath temperature almost constant, so that O in the atmosphere does not enter the molten steel. Inert gas such as argon is blown into the molten steel from the bottom to ensure strong stirring. Through this process, the total amount of O in the molten steel decreases, as well as the amount of S. The molten steel temperature rise in this process is about 95℃. The basicity of the slag is set to 3 to 6 because if it is less than 3, the reduction reaction and desulfurization reaction will not proceed sufficiently, making it difficult to satisfy the O and S ranges specified in the present invention. If it exceeds 6, the fluidity of the slag will worsen and the reaction between the slag and molten steel will worsen, so the upper limit was set at 6. The pressure of the inert atmosphere was set to 1 to 2 atmospheres because
This is because in order to prevent molten steel from coming into contact with the atmosphere, it is necessary to maintain the pressure inside the reduction refining equipment above atmospheric pressure to prevent air from entering the furnace. This is because a large amount of inert gas is required. Next, vacuum degassing refining is performed using a reflux type vacuum degassing equipment. By lowering the pressure inside the equipment with a vacuum pump, the molten steel is further deoxidized and high alumina inclusions are reduced. A process in which gas is used, for example, when the average temperature is
This is a process in which molten steel at 1600°C is strongly refluxed for 2/3 of the processing time and weakly refluxed for 1/3 of the processing time by controlling the lift gas flow rate until the temperature of the molten steel drops by approximately 40°C. The molten steel is strongly stirred by this strong reflux, and as a result, the N and H dissolved in the molten steel are released while bursting small lumps of the molten metal, and alumina inclusions quickly aggregate and float to the surface and are absorbed into the slag. removed. Also, due to the weak reflux, relatively small alumina-based inclusions that cannot be removed by strong stirring easily float to the surface and are absorbed and removed by the slag. It should be noted that the weak stirring referred to here means stirring with a strength that is about 1/2 that of strong stirring. Furthermore, reductive refining under a reducing atmosphere at normal pressure
This is a process that aims to remove alumina-based inclusions by levitating them to the maximum extent. Reduction refining is performed while the molten steel is stabilized by weak stirring with active gas, and the aim is to further reduce the total O content, S content, and Ti content. O in this process is 0.0008%
The S content decreased to below 0.008%, and the P
The amount decreases to below 0.010%. (Example) Next, the characteristics of the steel of the present invention will be clarified in Examples by comparing it with conventional steel and comparative steel. Tables 1 and 2 show the chemical composition of these test steels.

【table】

[Table] In Tables 1 and 2, A and B steels are conventional steels, and A steels are
SUJ2, B steel is SUJ3, C~F steel is comparison steel, R~
The V steel is a steel of the present invention, which is produced by the above-mentioned melting method. Table 3 shows the test steels in Tables 1 and 2 at 850°C.
After quenching and tempering with oil cooling for 30 minutes and air cooling at 170°C for 90 minutes, we investigated the amount of nonmetallic inclusions, their average length, durability life, machinability, and cold forgeability. This is what is shown. The amount of nonmetallic inclusions and their average length were investigated by cutting out a 65φ rolled material subjected to the above treatment, and are expressed as an index with the conventional steel A steel being 1. For the durability life, we used a Mori thrust type durability life tester, and the outer diameter 65φ x inner diameter
A specimen of 18φ x 10mm thickness was manufactured, and the index is shown with the former A steel set as 1. 40 for machinability
Prepare 5 pieces of mmφ×10mm material, use a 5φSKH9 straight drill as a cutting tool, and
The drilling time was measured and evaluated using 1140 rpm and a thrust of 30 kg (weight free fall method). Regarding cold forgeability, the upsetting rate of 20mmφ×30mm is 75
This is an investigation of the incidence of cracking in %.

[Table] As is known from Table 3, steel C, which is a comparative steel, has excellent cold forgeability, but the amount of nonmetallic inclusions is 0.69, the average length is 1,
Regarding the durable life, the rated life (B ₁₀ ) was 1.51 and the average life (B ₅₀ ) was 1.53, which were not satisfactory in terms of nonmetallic inclusions and durable life. In addition, for D and E steels, the O and S contents are A,
Compared to B steel, the durability is considerably improved by rated life (B ₁₀ ) of 1.92 and 1.51, but it is still not satisfactory, and the cracking incidence rate is 20 in terms of cold forgeability. %, which is low. Furthermore, although F steel has excellent cold forgeability, its durability is not satisfactory. In contrast, R to V steels, which are the steels of the present invention, are
By reducing the O content to 0.0008% or less, the S content to 0.008% or less, and reducing the Ti content, the amount of nonmetallic inclusions can be reduced to 1/3 to 1/3 of that of conventional steel A steel.
1/2, the average length is 0.9 to 0.75 times, and non-metallic inclusions are significantly superior to A steel, and the rated life and average life are both 2 times higher than that of A and B steels. 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 has a machinability that is about 1.3 times that of conventional steel. It has excellent machinability and cold forgeability, with a cracking rate of 0 at an upsetting rate of 75%, which is superior to conventional steel. As described above, steels R to V, which are the steels of the present invention, are significantly superior to steels A and B in terms of nonmetallic inclusions, durable life, machinability, and cold workability. In this way, the steel of the present invention contains C, Si, Mn, CrE
By appropriately containing P, S, O, and Ti, and reducing the amount of oxide-based and sulfide-based inclusions, the steel of the present invention has a rating life and an average life of 2% compared to conventional steel. It has succeeded in achieving an excellent durability life of more than twice as long, and also has excellent machinability and cold forgeability, making it compatible with the high loads and speeds associated with the increasing sophistication of industrial machinery and vehicles. The present invention will greatly contribute to the industry by providing high-quality bearing steel suitable for ball bearings, roller bearings, etc., and its manufacturing method.

Claims (1)

[Claims] 1. C0.70 to 1.10%, Si 0.15 to 1.60 by weight
%, Mn0.15~1.15%, P0.010% or less, S0.008% or less, Cr0.50~1.60%, O0.0008% or less, Ti0.0025
% or less, and further contains Pb0.05~0.15%, Te0.01
~0.15%, Se0.01~0.15%, and Ca0.001~0.01%, and the remainder consists of Fe and impurity elements, and is a nonmetallic inclusion in steel specified in JIS G 0555. 1. A bearing steel characterized in that the amount of A-based inclusions, B-based inclusions, and C-based inclusions is 0.030% or less according to the microscopic test method of 1. 2 C0.70~1.10%, Si0.15~1.60 by weight
%, Mn0.15~1.15%, P0.010% or less, S0.008% or less, Cr0.50~1.60%, O0.0008% or less, Ti0.0025
% or less, and further contains Pb0.05~0.15%, Te0.01
~0.15%, Se0.01~0.15%, and Ca0.001~0.01%, and the balance is Fe and impurity elements. In the presence of basic slag and in an inert atmosphere with a pressure of 1 to 2 atmospheres, reduction refining is performed with strong stirring while adjusting the bath temperature by electrode heating, and then transferred to a reflux type vacuum degassing device. Therefore, a method for manufacturing bearing steel is 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.