Martensitic transformation, mechanical properties, and structure of austenitic-martensitic stainless steels

Conclusions

• 1. Austenitic-martensitic steels of the Kh15N9Yu type quenched from 800°C have a maximum M_s point (80°C) and a maximum amount of martensite, 30% after cooling to 20°C and 70% after sub-zero treatment.

• 2. After quenching from 950°C or higher, the M_s point is shifted to sub-zero temperatures, the steel is austenitic, perhaps with a low percentage of ε-martensite.

• 3. Rapid cooling in the martensite range suppresses the martensitic transformation upon cooling but intensifies such a transformation under isothermal conditions or during heating.

• 4. The steels with 35–40% of aged martensite and 60–65% austenite have maximum mechanical properties. This mixture is obtained by quenching to obtain pure austenite, sub-zero treatment and aging. Quenching from lower temperatures (∼800°C) results in an identical martensite:austenite ratio but the precipitated grain boundary carbides reduce the ductility and toughness.