Microstructure evolution during isothermal annealing of 17Ni-0.2C martensite steel studied by neutron diffraction

その場中性子回折を用いた17Ni-0.2Cマルテンサイト鋼等温焼き戻し中の組織変化

徐 平光   ; Harjo, S.   ; 伊藤 崇芳; 鈴木 裕士  ; 秋田 貢一; Li, J.*; 友田 陽*

Xu, P. G.; Harjo, S.; Ito, Takayoshi; Suzuki, Hiroshi; Akita, Koichi; Li, J.*; Tomota, Yo*

Ultrafine grained austenite-ferrite duplex steels have much better strength-ductility than ultrafined grained ferrite-cementite steels, because the large volume of dispersive austenite can increase the work hardening ability and prevents the early necking phenomenon. However, the crystallographic observation is urgently needed to clarify the competition behavior between the precipitation of austenite and the recrystallization of ferrite considering the meta-stability of low-carbon austenite, which is very important for the development of new-generation commercial austenite-ferrite duplex steel. In this paper, TAKUMI time-of-flight (TOF) neutron diffractometer at JAEA/J-PARC was employed to carry out the in situ neutron diffraction during isothermal annealing and MUSASI-L angle dispersive neutron diffractometer at JAEA/JRR-3 was used to confirmed the changes of crystallographic textures at room temperature. The GSAS Rietveld refinement of neutron diffraction spectra showed that the annealing treatment promoted the solute carbon in martensite to diffuse into the precipitated austenite. In addition, the inverse pole figures and crystallographic textures of ferrite based on the GSAS Rietveld spectrum refinement showed a clear difference in crystallographic orientation before and after 823K isothermal annealing, which was related to the recrystallization of ferrite.