Abstract
Tests have been performed on a cold-worked 18Mn–4Cr austenitic steel to measure rates of slow crack growth under constant load in gaseous hydrogen. The behaviour of the steel differs from that of quenched-and-tempered low-alloy steels in a number of ways: (i) slow crack growth occurs in vacuum over a wide range of stress intensity K, and hydrogen appears to accelerate this crack growth by a factor which does not depend strongly on K; (ii) the dependence of crack growth rate on K does not follow a three-stage curve, as is commonly observed in a wide range of steels; (iii) there is a strong temperature dependence of the threshold stress intensity Kth below ∼30°C; (iv) a relatively large environmental addition of oxygen is only partially effective in inhibiting the effect of the hydrogen. Increased crack growth rates and scatter in the data are thought to be associated with bands of segregation and relatively high concentrations of phosphorus on some grain boundaries.
MST/132
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