The presence of a certain amount of retained austenite improves the resistance to contact fatigue failure. The lath martensite has better resistance than the plate twin martensite.

The results indicated that the steel is composed of quasi bainite, lath martensite and twin martensite under air cooling condition, and also has better combination of strength and toughness.

The paper discusses the twin theory and other theses on the habit plane of the lath martensite, the direction relationship and the relative oriented relationship between laths.