INTRODUCTIONThis chapter focuses on two kinds of environmental fracture, stress corrosion cracking (SeC) and hydrogen embrittlement, and discusses the role in such failures of a number of metallurgical variables. These include chemical composition; microstructural components such as precipitate type and structure, and grain size and shape; crystallographic texture; heat treatment and its effect on the foregoing variables; and processing, particularly the thermo mechanical treatments (TMT), which are attracting increased attention for property optimization. These variables are expected to be of great importance in the development of new engineering materials to meet demanding service conditions.In recent years, understanding of the role of metallurgical variables in hydrogen embrittlement has improved significantly. One purpose of the present review is to summarize this progress. Since hydrogen is believed to be broadly involved in many environmental cracking phenomena, it is a second purpose of the review to extend that improved understanding to at least some cases of Sec. It might be expected that similar role(s) of metallurgical variables would be observed for both hydrogen embrittlement and hydrogenassisted see, particularly when hydrogen plays a dominant role.The usual definition of see is that both a corrosive environment and a tensile stress (residual or applied) act together to cause cracking, which has a macroscopically brittle appearance. It is implicit in this definition that see is a phenomenon, not a mechanism, and it is so treated in this chapter. Hydrogen embrittlement is also a phenomenon, which mayor may not occur during sec. Hydrogen as a gas or as a species evolved from chemical or electrochemical reactions could be regarded as an see corrodent. But since classical hydrogen embrittlement studies have been conducted with hydrogen dissolved within the metal, which corrodents usually are not, such studies have been cited in the past as evidence against a link between see and hydrogen embrittlement. This review concludes, as have others, that such a conclusion cannot be general. There are now known to be a number of cases in which hydrogen participates in see fracture, and the accepted balance between hydrogen cracking and, say, anodic dissolution as components of see appears to need reappraisal or revision. It is a purpose of this chapter to identify such areas.It should be strongly emphasized that we do not accept the proposition that there must be a single causative process for Sec. There are indeed instances of purely dissolution processes, or purely hydrogen embrittlement processes, giving rise to what is generally described as Sec. But in many cases there appear to be contributions from both types of processes. This chapter emphasizes the hydrogen-related behavior in order to make maximum use of the new understanding of hydrogen embrittlement, but that emphasis should not be construed as being a mechanistic emphasis.The combined literature record on see and hydrogen embrittlement is very exten...
