Abstract
Void growth caused by hydrogen attack was measured as to the specimens of 21/4Cr-1Mo and 3Cr-1Mo steels with various amounts of impurity elements exposed to hydrogen of 300kgf/cm2 at temperatures from 600 to 550°C. It was confirmed that impurity elements such as P and Sn have strong effects especially on void nucleation. Microanalysis suggested that the nucleation sites were both carbides and MnS in a Sn-bearing steel, while the nucleation at carbides was suppressed in a P-bearing steel. The data on the void growth were extrapolated to lower temperatures at various hydrogen pressures by using the equation led by CHUANG et al. for non-equilibrium void growth. Constants in the equation were determined so that the calculated results fitted the observed data. The extrapolation gave hydrogen attack limit as defined by the conditions in which total void section per unit area of grain boundary attained 5 per cent at 105 h. The limit conditions for 21/4Cr-1Mo and 3Cr-1Mo steels were affected and reversed by impurity elements.
