2015 年 101 巻 8 号 p. 426-434
The effects of partitioning of Mn and Si during intercritical annealing on transformation behavior and mechanical properties of low alloyed TRIP-assisted steel sheets were investigated by using 0.17%C-1.5%Si-1.7%Mn steel. During intercritical annealing, Mn and Si were concentrated in austenite and ferrite by partitioning, respectively. This partitioning of Mn and Si suppressed bainite transformation during austempering and decreased the volume fraction of retained austenite and its C content. This could be mainly because partitioning of Mn and Si shifted the T0’ curve to the lower C concentration region and stopped bainite transformation at a lower C concentration in residual austenite. The decrease in the volume fraction of retained austenite and its C content deteriorated the ductility of low alloyed TRIP-assisted steel sheets. Although proper intercritical annealing is necessary to increase C content in retained austenite, it should be noted that excessive intercritical annealing can deteriorate the ductility of low alloyed TRIP-assisted steel sheets because of partitioning of Mn and Si.
