Abstract
This report describes the influence of microstructure on the yielding behavior of continuous-annealed multi-phase sheet steels. A series of 0.05% carbon steels with various manganese contents were intercritically annealed at 800°C for 2 min and then quenched at various cooling rates ranging from 10 to 1 000°C/s. Some steels were given a pre-heat-treatment at 750°C for 3 h.
It was observed that the minimum volume fraction of martensite to achieve continuous yielding was dependent on ferrite grain size, solute carbon content in α-iron and the size of martensite. The decrease in solute carbon content was closely related to the decrease in yield ratio for steels in which yield-point elongation, due to the presence of martensite, was below 2%. The solute carbon was thus found to be one of the major structural factors that control yield ratio in the multi-phase steels.
