Rolling and Partitioning法で製造される1,500MPa級超高強度薄鋼板の高延性化のメカニズム

Mechanism of improved ductility of 1,500 MPa-class ultra-high strength cold-rolled steel sheet produced by rolling and partitioning method

細谷 佳弘*; 松村 雄太*; 友田 陽*; 小貫 祐介*; Harjo, S.   

Hosoya, Yoshihiro*; Matsumura, Yuta*; Tomota, Yo*; Onuki, Yusuke*; Harjo, S.

By using a steel with standardized chemical composition and conventional manufacturing processes for flat-rolled steel strip, a 1,500 MPa class stainless steel sheet, whose product of yield strength (YS) and total elongation (El) exceeds 30,000 MPa%, was developed and its mass production was established. Besides the excellent YS-El balance, the developed steel sheet has excellent performance for not only an anti-secondary work embrittlement but also high cycle fatigue endurance. The microstructure formation during the R&P process and the deformation mechanism that would bring about the excellent strength-ductility balance are discussed based on the results obtained from the in situ neutron diffraction measurement. The results have revealed that the typical Luders-like stress-strain curve of R&P steel is caused by competitive plastic flow between austenite and martensite, and an effective transformation induced plasticity phenomenon.