MARCINIAK Szymon Warsaw University of Technology

Spoluautoři ŚWIĄTNICKI Wiesław

The subject of this study is the temperature stability of a microstructure in X37CrMoV5-1 hot-work tool steel. Conventionally treated by quenching and high-tempering this steel is used for tools working at temperature up to 550 oC. In this study a non-conventional treatment consisting of austempering at 300oC, which is slightly higher than Ms = 293 oC, was used. As a result a microstructure of carbide-free bainite with residual austenite was created. This microstructure ensures a very good compromise between high strength and plasticity at room temperature. The aim of this study was to determine temperature stability of the obtained microstructure in a range of temperatures higher than the temperature of the heat treatment (350 – 600 oC) by means of dilatometric tests and hardness measurements. steel samples containing carbide-free bainite with residual austenite were subjected to dilatometric tests during continuous heating and isothermal annealing at various temperatures. Phase transformations were also recorded during cooling of the samples after continuous and isothermal heating. These investigations allowed us to determine the highest temperature up to which any phase transformation was not observed to occur during dilatometric tests. The effect of the annealing time on the phase transformations in the produced microstructure was also studied. The changes occurring in the carbide-free bainite with residual austenite after exceeding the critical temperature were characterised. The impact of the observed changes occurring in the microstructure above the critical temperature on the degradation of mechanical properties of the steel was discussed.