抄録
Static tensile tests and cantilever bending delayed fracture tests were performed on Cr-Mo structural steel V notched specimens which had been dipped into 5% H2SO4 solution to introduce hydrogen beforehand and tempered at the range from 250°C to 600°C.
The results obtained are as follows.
(1) The materials tempered at lower temperatures or having higher strength levels show a noticeable decrease in notch strength by hydrogen charge.
(2) There is a good correlation between the delayed fracture limit and the notch strength after hydrogen charge.
(3) The delayed fracture sensitivity varies remarkably with tempering temperature from 350°C to 500°C, corresponding to 120∼160kg/mm2 in tensile strength, 320∼480 in Vicker's hardness, and 2.6∼4.2 degree in half value breadth.
(4) Hydrogen sensitivity is affected by the residual stress near the surface caused by heat treatment and it increases with tensile residual stress.
(5) The microfracture mode changes depending upon the magnitude of delayed fracture sensitivity.
