STUDIES ON BALL BEARING STEELS (II)

Effect of Some Metallurgical Factors on Life of Ball Bearing Steels

Abstract

The inner rings of the ball bearing, which had been known the life time in life test, was studied in order to look for the relation between some metallurgical factors and life.
As some factors the chemical composition, non-metallic inclusions, hardness, compressive load of inner rings, cementite content, grain size and forging degree were tested.
The results obtained by our investigation were summarized as follows.
(1) Generally speaking, the chemical composition had no direct relation to life of ball bearing. By our results carbon content of our home-made ball bearing steels was controlled in a higher range of the standard, but it must be controlled in a lower range to avoid the segregation and coarse carbide. Chromium content must be controlled in 1•40-1•50 per cent.
(2) Nitrogen content had no dlear relation to life of bal1 bearing steels.
But some group of the nitrogen had relation to cementite content, while the other group had no relation to cementite content.
(3) The higher hardness of after heat-treatment, the longer was life of ball bearing.
Hardness of inner ring increased mostly after life test. It is due to transformation of the retained austenite. Hardness of after 1ife test has no relation to the life.
(4) The compressive load of inner ring had no direct relation to life of ball bearing.
(5) Non-metallic inclusions had scarcely relation to life of ball bearing according to our investigation.
(6) In the forging ratio our home-made ball bearing steels were considerably lower. It must be raised by using the bigger ingot.
(7) Cementite content retained after heat-treatment had clear relation to life of ball bearing.
Maximum life was in about 6-8 percent of cementite content
(8) Grain Size had no distinct relation to life of ball bearing. But some group of it had relation to life, and the other group had no relation to life.