464 / 2018-12-30 22:01:06

Phase Transformation Behavior and Precipitating Phase of a New High Nitrogen Martensite/Ferrite Heat Resistant Cast Steel

Martensite/ferrite, microstructure, phase transition precipitates

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A new type of high nitrogen martensite/ferrite heat-resistant cast steel with 0.2% nitrogen content was designed and prepared. The phase transformation behavior of the new steel was investigated by quenching phase transformation instrument, and a reasonable heat treatment process was carried out. The microstructure and precipitation phases in the as-cast and heat treatment process were analyzed by OM, SEM and TEM. The results show that the austenite start temperature (Ac1) of the new type of high nitrogen martensite/ferrite heat resistant steel is about 872.3 ℃, the austenite finish temperature (Ac3) is about 1035.8℃, and the transformation temperature of austenite to δ-ferrite is 1165±10℃. It is found after tempering the microstructure is tempered martensite and ferrite, and, there are a lot of dislocation lines and dislocation networks in the tempered material,with more (V, Nb) N phases precipitate along the martensite lath boundary, and a large number of M6C (Fe3W3C), Laves phases and Cr2N precipitate on the ferrite matrix. The existence of these phases may pin dislocations, hinder the movement of dislocations, and guarantee the high temperature properties of materials.