JPH048497B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an induction hardening steel that is used for rolling bearings, shafts, gears, and other power transmission machine parts and has excellent durability, impact fatigue, and fretting fatigue properties. In recent years, as automobiles have become lighter and cheaper, heat treatment is also changing from conventional heating using heavy oil to high-frequency heating, which can heat up to a predetermined temperature in a few seconds. There were problems such as a lack of heat and quench cracking and distortion. In addition, bearing members changed from roller bearings to ball bearings, and unit type bearings that omitted the outer and inner rings were used.
Conventional SUJ2 has had the problem of insufficient strength and low impact fatigue under high surface pressure. Against this background, requirements for power transmission machine parts such as rolling bearings and gears have become increasingly strict, and induction hardening is required to provide not only durability but also excellent hardenability, impact fatigue, and fretting fatigue resistance. There was a demand for the development of steel. In response to such requests, conventional SAE1050,
1566, 0.5C−1.5Mn−0.3Cr steel, 0.6C−0.8Mn−
0.8Cr steel and other materials have been proposed and some are in practical use. All of these steels can be induction hardened by lowering the C content and containing 0.8 to 1.50% Mn compared to SUJ2, and the tempering hardness H _R
Although it satisfies C60 or higher, the quench hardening depth is shallow, the durability life is short, and fretting.
They were also unsatisfied with the durability. The present invention was made in view of the drawbacks of conventional steels, and as a result of various studies conducted by the present inventors, it was found that induction hardening and 160℃ tempering are required to obtain a durable life longer than SUJ2, which is a high carbon chromium steel. In H _R
We discovered that it is necessary to ensure a hardness of C60 or higher and a hardening depth of 2 to 4 mm.To this end, we found that the optimum amount of C in the matrix is about 0.6%, and that Si is effective in reducing impact stress. It is an element that improves impact fatigue of 30×10 ³ Kgfcm or more.
It is necessary to contain 0.50% or more of Si and lower the upper limit of C content as much as possible, and furthermore, to improve fretting and fatigue properties (indentation forming properties), it is necessary to contain 0.50% or more of Si. I discovered that. Based on these findings, the present invention has developed a rolling material that can achieve a predetermined hardness and hardening depth through induction hardening, and has excellent durability, long life, impact fatigue, and fretting/fatigue properties that can reduce weight and cost. The company succeeded in developing power transmission mechanical parts such as bearings, shafts, and gears. The present invention will be explained in detail below. The first invention steel has C0.40 to 0.70% by weight,
Si0.50~1.50%, Mn0.70~1.10%, Cr0.70~1.60
%, O0.0013% or less, and the second invention steel is the first invention steel containing one of V0.30% or less and Nb0.30% or less to further improve impact fatigue. It has excellent properties as a power transmission machine component such as rolling bearings, shafts, and gears. The reasons for limiting the composition of the steel of the present invention will be explained below. C is the hardness required for power transmission machine parts
It is an element necessary to ensure H _R C60 or higher, so the lower limit was set at 0.40%. However, if the content exceeds 0.70%, durability life and impact fatigue will decrease, and quench cracking distortion will likely occur, so the upper limit was set at 0.70%. Si is a main element in the present invention, which aims to improve durability, impact fatigue, and fretting fatigue properties as well as deoxidizing properties. However, if the content exceeds 1.50%, rolling life characteristics deteriorate, so the upper limit was set at 1.50%. Mn is an element necessary to improve hardenability and ensure a hardening depth of 2 mm or more, and to obtain this effect, the content must be 0.70% or more. However, even if a large amount is added, the improvement in effectiveness is small, so the upper limit should be set.
It was set at 1.10%. Like Mn, Cr is an element that improves hardenability, and in order to obtain a hardening depth of 2 mm or more, it must be contained at 0.70% or more, and the lower limit was set at 0.70%. However, if the content is too large, the carbide becomes hard and machinability deteriorates, so the upper limit was set at 1.60%. O is an element that combines with Al, Si, etc. in steel to form hard oxide inclusions and significantly deteriorates rolling life characteristics.It is necessary to reduce its content as much as possible, and the upper limit is set at 0.0013%. And so. S and P are elements that deteriorate rolling life characteristics, and it is preferable to reduce their content as much as possible. Especially when considering rolling fatigue characteristics,
It is desirable to keep it below 0.010%. V and Nb are elements that generate carbonitrides and improve strength and toughness. However, both V and Nb are 0.30
Even if the content exceeds 0.3%, the effect will not improve much, so the upper limit was set at 0.30%. Next, the characteristics of the steel of the present invention will be clarified in Examples by comparing it with conventional steel and comparative steel. Table 1 shows the chemical composition of these test steels.

【table】

[Table] In Table 1, steels A and B are conventional steels, and steel A is
SUJ2 and B steels are SAE1566, C to E steels are comparison steels, and F to M steels are the invention steels. Table 3 shows the test steels A to M in Table 1, which were heated using a high-frequency heating device at 920°C for 5 seconds, cooled in oil, and then tempered at 160°C for 1 hour. This shows the results of an investigation into depth, durability, impact fatigue, and fretting/fatigue properties. The hardening depth indicates the distance from the surface where a hardness of H _R C60 or higher has been obtained through the quenching and tempering treatment described above, and the durability life is measured using a Mori thrust type durability life tester. We made 10 specimens each with an outer diameter of 60φ x inner diameter of 18φ x thickness of 10mm,
Test load 400Kg, rotation speed 900rpm, 60 as lubricant
# Measured using spindle oil and shows the ratio to the calculated life. Regarding impact fatigue, a test piece with a length of 160 mm x diameter of 15 mm and a notch of 2.5 R was prepared using a Matsumura-type cyclic impact fatigue tester, and a test was conducted at an impact energy of 20 kgf cm. Regarding fretting and fatigue properties, tapered roller bearing L45449/10 (inner side)
and LM11749/10 (outer side) were combined to simulate the actual machine conditions using the actual machine assembly. Test conditions are shown in Table 2.

[Table] There is a correlation between the acoustic value and the total indentation depth, and although there is some variation, they are almost proportional.

【table】

[Table] Regarding the hardening depth, conventional steels A and B have
1.5mm and 1.8mm are both shallow at 2.0mm or less, whereas steels F to M, which are the steels of the present invention, can all secure a hardening depth of 2.0mm or more, making them suitable for induction hardening. It has the hardness and hardening depth necessary for steel. In addition, regarding the durability life, conventional steel A,
As mentioned above, steel B has a shallow hardening depth of 2.0 mm or less, so the values are 1.8 and 2.0, and the comparative steels C and
For D steel, 0.3 due to the difference in Si content.
0.4, which is low, but in contrast, steels F to M, which are the steels of the present invention, are all 2.0 or higher, SUJ2,
It has superior durability compared to SAE1566. Furthermore, the impact fatigue properties of conventional steels A and B and comparative steels C and E are low at 4.0 to 7.0×10 ³ Kgf・cm due to their low Si content. On the other hand, F~ which is the steel of the present invention
All M steels have a value of 30×10 ³ Kgf.cm or more due to the Si content of 0.50% or more, and have excellent impact fatigue properties. Regarding fretting/fatigue properties and acoustic values, conventional steel and comparative steel have low Si content as well as impact fatigue properties, resulting in 16.8 to 20.3 μm and 300 to 400 volts.
In contrast, the steels F to M, which are the steels of the present invention, all have a Si content of 0.50% or more.
Small, less than 10.5μm and less than 225Volt, SUJ2,
It has superior fretting and fatigue properties and acoustic values compared to SAE1566. In this way, the steel of the present invention has found the optimum content of C, Si, Mn, and Cr, and has also reduced the amount of O as much as possible, thereby ensuring a hardening depth of 2 mm or more with H _R C60 or higher, and superiority of SUJ2, SAE 1566 or higher. It is an industrial steel for induction hardening and is suitable for power transmission machine parts such as rolling bearings, shafts, and gears, which can reduce weight and cost. This is an extremely large contribution.

Claims (1)

[Claims] 1. C0.40~0.66%, Si0.50~1.50 in weight ratio
%, Mn0.70~1.10%, Cr0.70~1.60%, O0.0013
% or less, with the remainder consisting of Fe and impurity elements. 2 Weight ratio: C0.40~0.66%, Si0.50~1.50
%, Mn0.70~1.10%, Cr0.70~1.60%, O0.0013
% or less, further V0.30% or less, Nb0.30
A steel for induction hardening, characterized in that it contains one of the following: % or less, with the remainder consisting of Fe and impurity elements.