Influence of silicon on secondary hardening of 5 wt% Cr steels

Silicon is long-known in the literature for its effect in the strength and tempering reactions of carbon steels, but only recently the effects of silicon in 5% Cr tool steels were deeply studied. The effects of Si on the toughness and fracture behavior in this class of steels were clearly elucidated, but the understanding on the tempering hardening was still open, due to the difficulties in splitting the two important contributions of silicon, i.e. solid solution strengthening and the implications in the precipitation of alloy carbides. In the present paper, these effects were separated, by excluding the solid solution contributions from Si, Mn and Cr, as well as, comparing the different steels to a typical tempering behavior of a reference carbon steel. This procedure leads to a clear observation, not yet shown in the literature, for the negative effect of silicon on the precipitation hardening during tempering. The correlation with secondary carbide distributions and other data from literature reinforces the mechanical behavior observed in the tempering curves.