Abstract
Changes in the mechanical properties of heat-treated steel by hydrostatic pressure have not fully been made clear. In this report, according to the “hydrostatic pressure treatment” in which contraction is first given by hydrostatic pressure and then restored to normal pressure, the hardened Cr-Mo steel, 0.41%C, 0.97%Cr, and 0.28%Mo was tempered at 150°∼450°C, and then given a hydrostatic pressure treatment of 2000∼6000 kg/cm2 to examine the change of mechanical properties of steel. The results obtained are as follows:
(1) The surface hardness of the steel is increased by the hydrostatic presssure treatment, when the hardened steel is tempered at less than approx. 350°C. When tempered at 400°∼450°C, however, its effect is not found.
(2) The tension strength of the flat material is affected by the hydrostatic pressure treatment, when tempered at less than 200°C. But, by tempering at 200°∼400°C, no effect is observed.
(3) The tension strength of the notched material is more easily affected by the hydrostatic pressure treatment than that of the flat material. When the hardened steel is tempered at less than 200°C, the tension strength increases by the hydrostatic pressure treatment. When tempered at less than 250°C, it increases and decreases. By tempering at 300°∼350°C, it decreases slightly. When tempered at 400°C, no effect is observed.
(4) The behavior of the residual strain of the notch flute bottom caused by the hydrostatic pressure treatment has been investigated.
(5) The effect of the hydrostatic pressure treatment upon the Charpy impact value agrees well with the behavior of tension strength of notched material.
(6) Within the limits of 1∼20 min, the effect of the hydrostatic pressure treatment time upon the mechanical properties is constant.
