Effects of Tempering, Prior-austenite Grain Size and Shape of Test Specimen on the Delayed Fracture of Low-alloyed Steels

Abstract

Effects of tempering condition, prior-austenite grain-size, and shape of test specimen on the behavior of hydrogen-induced delayed fracture have been investigated for several low alloysteels for high strength bolt. The main results are as follows;(1) The tempering at temperatures above 500°C improves the resistance to delayed fracture, except for secondary hardenable steels. This resistance depends on the strength level and the strain hardening behavior.(2) Both steels with fine (ASTM 9-10) and coarse (ASTM 0-3) grains of prior-austenite have a tendency to be more susceptible to delayed fracture than these with medium grain size (ASTM 4-5).(3) The thinning of specimen width results in decreasing of the susceptibility to delayed fracture owing to the change of stress condition, from plain strain to plain stress.