Influence of Martensite Morphology on Initial Yielding and Strain Hardening in a 0.11C-1.36Mn Dual-phase Steel

Abstract

The influence of the martensite morphology (the network structure, the isolated island and the finegrained island) on the mechanical properties, particularly initial yielding and strain hardening, of a dualphase steel was examined and discussed on the basis of the micromechanics.
(1) The network structure of martensite increased 0.2% proof stress, ultimate tensile strength and strainhardening rate compared with the isolated martensite island. One of the reasons for this is that the internal stress arising from the difference between the strengths of the ferrite and the martensite was not so much relaxed in the former structure as in the latter one.
(2) A dual-phase steel with fine-grained isolated martensite islands exhibited rather higher 0.2% proof stress and ultimate tensile strength due to mainly fine-grained strengthening, and also the highest uniform and total elongation and reduction of area since the void formation around the martensite islands was suppressed.