Abstract
The 12 wt-%Cr secondary hardening steel considered in this work is being evaluated for use in the first wall of fusion reactors. As the service temperature can approach 500°C, the microstructure of greatest interest has been a quenched and tempered structure obtained by tempering at 750°C after air cooling from the austenitizing temperature of 1050°C. This structure is susceptible to grain boundary failure whether internal hydrogen has been introduced by cathodic charging or not. In the uncharged condition failure is ductile, but follows prior austenite grain boundaries. Hydrogen charging results in a severe loss of ductility, and tensile fractures which are 30% brittle intergranular. This susceptibility to grain boundary fracture has been attributed both to phosphorus segregation to these grain boundaries and to a nearly continuous array of grain boundary carbides. This tendency for grain boundary fracture can be eliminated and the embrittlement associated with the introduction of internal hydrogen greatly reduced by swaging and subsequently retempering the quenched, and tempered microstructure. The improved properties of the swaged and retempered conditions are attributed to the effects of swaging on the prior austenite grain boundary structure and the orientation of the grain boundaries with respect to the tensile axis.
MST/376
Get full access to this article
View all access options for this article.