Effect of Natural Aging on the Structure and Properties of Steel 30KhGSA Hardened by Quenching and Partitioning

Steel 30KhGSA is studied after a quenching and partitioning (Q&P) heat treatment and after traditional quenching. Structural and x-ray analyses are performed and mechanical properties are determined. The Q&P treatment produces a martensite-austenite structure with 10 vol.% retained austenite. The use of Q&P instead of the traditional quenching elevates the impact toughness by a factor of 3 and the resistance to fatigue crack growth by a factor of 2. A long hold at room temperature (for more than a month) reduces the content of retained austenite in the Q&P-steel to 7.5 vol.% and lowers its impact toughness and crack resistance by a factor of 1.5 as compared to the state right after the hardening.