抄録
Effect of Si content on the various mechanical properties and microstructures in B-treated Cr-Mo-Nb steels has been investigated.
1) By increasing Si content, Charpy transition temperature of shear area (vTrsraises due to solution hardening and coarsening of austenite grain size, when coarse boro-carbides are not formed along grain boundaries during tempering treatment at high temperature.
2) Si suppresses the coarsening of intergranular boro-carbides in case of high temperature tempering. As a result, in a steel containing excess dissolved B and so having boro-carbides along grain boundaries, it is considered that Si does not change vTrs spite of solution hardening and coarsening of austenite grain size due to increase of Si content.
3) In an as quenched condition, austenite grain boundaries in a low Si content steel are clearly revealed, but those in a high Si content steel are not clearly observed after conventional etching. Consequently, it is considered that Si affects the grain boundary segregation.
