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G. Stechauner, E. Kozeschnik:
"Investigation of a possible mechanism for the formation of reverted austenite in 13-8 PH steel";
Talk: EUROMAT 2015, Warszawa; 2015-09-20 - 2015-09-24.

High alloyed, precipitation hardening steel of 13-8 PH grade is widely used wherever high strength, as well as ductility and resistance against environmental damage is needed. Mechanical properties are governed by the precipitation of NiAl-B2 phase, which can be controlled efficiently by proper heat treatments between 500 and 600°C. At the lower boundary of this temperature region, only B2-phase is stable, however, upon increasing temperature, austenite can form from martensite up to phase fractions of 25%. The amount of reverted austenite can be increased with a re-austenitising step after quenching from solid-solution annealing. In this work we show that the governing mechanism is the formation of austenite cells during heating to austenite temperature, leading to considerable segregation of Ni. Diffusion calculations show that extensive annealing in the austenite region is required to remove this segregation. If tempered for short times, these segregated cells act as nucleation sites for reverted austenite during annealing at aging temperature.