Hydrogen assisted fracture of spheroidized plain carbon steels

Abstract

The role of hydrogen in the ductile fracture of spheroidized low carbon steels was studied. In addition, the relevant literature has been reviewed to develop a certain perspective on the problem. Both initially smooth and circumferentially notched tensile specimens were electrochemically charged with hydrogen at various cathodic current densities and then uniaxially strained various amounts. Comparisons with uncharged specimens showed that hydrogen promotes void initiation at cementite particles. Void growth and coalescence were also accelerated by hydrogen. Since a large proportion of void coalescence as well as the latter stages of void growth take place along grain, and possibly subgrain boundaries, hydrogen induced losses in interfacial cohesion may account for void initiation, growth and coalescence at lower stresses and strains. A partial transition in fracture mode was observed in steels with a low particle-matrix and grain boundary interfacial area per unit specimen volume. This quasicleavage mode was generally found to be associated with nonmetallic inclusions, suggesting that they act as hydrogen sinks during the charging process and then, during deformation, release a sufficiently large amount of hydrogen to cause quasicleavage fracture to occur.