Some rules for phase transformations in 000N18K9M5T steel

Conclusions

• 1. At the normally used rates of heating the α»γ transformation occurs in the aged martensitic matrix, which together with phase work hardening from the α»γ transformation causes the formation of austenite with an increased hardness. With an increase in the austenitizing temperature the strength of the austenite drops, approaching the strength of the austenite in unaged steels.

• 2. The formation of a large quantity of austenite, up to 30%, after short heating in the α»γ transformation does not reduce the strength of N18K9M5T steel. The loss of strength with long holds in the α »γ region may be explained by overaging of the α-matrix. It is also possible that there is a loss of strength in the austenite.

• 3. If in the α»γ transformation the steel does not lose strength, the presence in the structure of a large quantity of austenite does not increase the impact strength.

• 4. The form of the austenite particles and their distribution in the α-matrix is determined by the quantity of austenite and does not depend upon the temperature and holding time at which this quantity is obtained.

• 5. The increase in the strength of the austenite after heating to temperatures close to the Ac₃ (720–820°C) is inherited by the martensite, preserved after low temperature aging up to 500°C, but disappears after high temperature aging above 530°C.