The role of hydrogen in the ductile fracture of plain carbon steels

Abstract

In this report we consider the problem of hydrogen induced ductility losses in a plain carbon spheroidized steel. Specifically, the effect of internal hydrogen on the formation of voids from second phase (cementite) particles and their subsequent growth and coalescence was studied by careful microscopic inspection of uniaxially strained bars, both initially cylindrical and circumferentially notched, with and without hydrogen. Void initiation occurred with lower strains and stresses with hydrogen, although an equally important contribution to the ductility loss was from hydrogen accelerated void growth and coalescence. This latter process takes place by the propagation of voids along the grain, and possibly subgrain, boundaries which interlink the cementite spheroids. The results indicate that hydrogen facilitates interface separation, possibly by accumulating at the boundaries during hydrogenation of the specimen and lowering the cohesive strength, thereby making void initiation and growth along them easier.