Phase transitions in rapidly solidified stainless steels cathodically hydrogen charged

The effects of cathodic hydrogen charging and subsequent aging on phase transitions and microstructures of rapidly solidified (RS) austenitic stainless steels (types 310 RS, 316 RS, and 316TiM RS) were investigated. The behavior of the martensitic phases, α′(bcc) and ε(hcp), as well as the austenite phase, γ (fcc), of the RS steels during aging after charging was compared to the behavior of these phases of equivalent conventionally processed commercial solution-treated (ST) austenitic stainless steels (types 310 ST, 316L ST, and 316TiM ST) following identical cathodic-charging conditions by means of X-ray and electron diffraction techniques. The behavior of the α′ phase of both RS and ST steels (that form α′ phase) during aging was found to be very similar, while the behavior of both γ and ε phases during aging of all of the RS steels studied, as compared to the equivalent ST steels, was different. The development of lower internal stresses and minor lattice expansion of the RS steels, as compared to the ST steels, is probably due to a different distribution of hydrogen within the near-surface layer of the RS steels than that of the ST steels, which appears to be related to the markedly different microstructural characterizations of the RS steels from the ST steels. Scanning and transmission electron microscopy (SEM and TEM) observations indicated that the tendency toward cracking along the columnar-like structure is typical of all of the charged RS steels studied.