Role of Internal Stress for the Initial Yielding of Ferrite-Martensite Dual Phase Steels

Abstract

Role of internal stress for the initial yielding and for the masking of Lüders band is discussed as follows:
1) The martensite transformation causes transformation-induced yielding in the ferrite phase. The resultant distribution of the plastic strain in the ferrite surrounding the martensite islands and the distribution of the internal stress in the ferrite and martensite phases are calculated based on the continuum mechanics.
2) There are preferentially yielding zones around each martensite island and initial yielding begins in these zones under very low applied stress compared to the yield strength of the ferrite because the internal stress assists the initial yielding.
3) There are a number of preferentially yielding zones in the dual phase steels, therefore, LUders band is masked as in the case of temper-rolled rimmed steel sheets.