Recrystallization of martensite and precipitation of austenite during in situ annealing of cold rolled 17Ni-0.2C martensite steel studied by neutron diffraction

中性子回折による冷間圧延17Ni-0.2Cマルテンサイト鋼焼き戻し中のマルテンサイト再結晶とオーステナイト析出

徐 平光   ; Harjo, S.   ; Vogel, S. C.*; 伊藤 崇芳*; 友田 陽*

Xu, P. G.; Harjo, S.; Vogel, S. C.*; Ito, Takayoshi*; Tomota, Yo*

Ultrafine grained ferrite-austenite duplex steels have better ductility than ultrafine grained ferrite-cementite steels. The static recrystallization of cold rolled martensite steel is easy to get a uniform refined microstructure. The in situ microstructure evaluations from TAKUMI time-of-flight neutron diffraction during the isothermal annealing showed that at 773 K, the austenite precipitation did not initiate before isothermal holding and the austenite transformation rate was slow. On the other hand, the peak did not become shape, the recrystallization behavior was not apparent. At 823 K, the austenite precipitation took place and the peak became stronger and stronger, revealing that the austenite precipitation was evident. The flatten peak became weaker and shaper, revealing that the cold rolled martensite was recrystallized. At 873 K, the austenite transformation was dominated and the transformation rate was much rapid. However, the austenite was meta-stable and some austenite transformed into martensite again during rapid cooling to room temperature. In addition, the in situ texture evolutions during isothermal annealing at above temperatures were investigated by using HIPPO time-of-flight neutron diffraction and the ex situ textures were measured for confirmation by using the MUSASI-L angle dispersive neutron diffraction.