Abstract
Some Hadfield steels with 1%Si, 2%Al, 0.8% Mo, 4% Cr, or 0.5%V were studied mainlyby micrography on isothermal carbide precipitation after solution treatment. Isothermal precipitation diagrams for all steels were determined as C-urve, fundamentally similar to that of standard Hadfield steel. By addition of 1% Si, the carbide precipitation in steel was little affected, but the temperature range in which pearlitic constituent (PC) appeared was slightly extended. By addition of 2%Al, the grain boundary carbide precipitation in high temperature range was accelerated, but the transformation into PC wasretarded and its temper ature range was limited in a slightly narrower range. Moreover, matrix precipitation of carbide in high temperature range was disturbed remarkably by addition of Al. By addition of carbide forming elements such as Mo, Cr, and V, the precipitation of carbide was accelerated especially in high temperature range, and the precipitation temperature range was extended to higher temperature. However, transformation into PC was retarded by addition of these elements, and addition of Cr +V was markedlyeffective. By addition of 4% Cr and 4% Cr+0.5% V, matrix carbide precipitation in steel was remarkably accelerated, and its precipitation area formed a C-urve, which had a nose at 825× in the former steel, and at 800× in the later steel. Addition of V was markedly effective for precipitation hardening of steel. It is considered that the retarding behavior of transformation into PC by addition of carbide forming elements was similar to that by lowering carbon content in steel. In microstructures of V-added steel, peculiar platelet PC which was different from nodular PC in other steels was observed. The formation ofthe platelet PC is considered to be due to a large quantity of platelet carbide precipitation in steel by addition of V.
