고온 가스질화 된 STS 430 스테인리스강의 냉간 가공성에 미치는 항온변태 열처리 시간 변화의 영향

Abstract

This study is to investigate the phase changes and cold workability after isothermal transformation at by using the high temperature gas nitrided (HTGN) STS 430 ferritic stainless steel specimens. The phase diagram of STS 430 steel obtained by calculation showed that the phase appeared at showed as with increasing nitrogen concentration. Also, the transformation of during heat treatment isothermally at , nitrogen pearlite with lamellar type was fully formed at the nitrogen permated surface layer for 10 hrs. However, this transformation was not completed for 1 hr, resulting nitrogen pearlite plus martensite. The cold rolled specimen of isothermally transformed at for 10 hrs after high temperature gas nitriding decreased the layer thickness of nitrogen pearlite inducing the deformation of hard phase. the dissolution rate of phase increased rapidly with increasing cold rolling ratio. Specimens with the microstructure of nitrogen pearlite (isothermally transformed at for 10 hrs) were possible to cold rolling without crack formation. However, the mixed structures of nitrogen pearlite + martensite (isothermally transformed at for 1 hr) were impossible to cold deformation without cracking.