Abstract
Some experiments of hardness curve of quenched steels (low carbon-for carburizing, medium carbon-for constructional and high carbon steels for tools) are described. It was found that
(1) there are two kinds of hardness curve, i.e. the flat type and the two step type and this two step type appears often in the steels containing much hardsoluble carbide, i.e. Cr-V-, Cr-Mo-, Gr-W steel and in the Si-Mn-Cr steel,
(2) Cr-V steel shows the agehardening on the room temperature,
(3) the quantity of residual austenite of Si-Mn-Cr steel is so much showing fair hardening by tempering.
