Characterization of Reverted Austenite during Prolonged Ageing of Maraging Steel CORRAX

Microstructure and mechanical properties were studied in CORRAX maraging steel during prolonged ageing up to 300 h at 798 K. Strengthening of maraging steel was caused by the formation of an intermetallic phase enriched in Ni and Al which exhibits an ordered B2 (CsCl) superlattice structure. Precipitation hardening was accompanied by an increase in micro-hardness with peak hardness after about 12 h of ageing. After 300 h of ageing, the micro-hardness value is still high, corresponding to 94% of the peak hardness. The reverse transformation of martensite to austenite does not take place during prolonged ageing as shown by X-ray and electron backscatter diffraction analyses. The experimentally determined amount of austenite (1-2 vol.%) is in good agreement with the calculated value (about 2.5 vol.%).