Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels
Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility.
Hydrogen induced stress cracking in UNS S32750 super duplex stainless steel tube weld joint
Abstract In this work, the hydrogen embrittlement of super duplex stainless steel tubes UNS S32750 under different hydrogen charging conditions was investigated. Hydrogen charging was performed both in unloaded and in elastically stressed specimens. The tubes were charged and tested under two conditions: as-received and welded. The samples were submitted to tensile tests in order to evaluate how the mechanical properties are affected by the hydrogen inserted into the microstructure. The fracture surfaces were analyzed in order to identify the failure active micro mechanisms. Combined tensile test results and microstructural investigations indicated that elastic stress applied to samples during hydrogen charging enhanced hydrogen solubility and permeability, resulting in greater loss of ductility. As pointed by fractographies of welded H-charged tubes, the microstructural changes induced by welding increased hydrogen diffusivity. The fracture surface of the hydrogen charged as-received tubes exhibited a quasi-cleavage aspect, indicating a mixed failure mechanism composed by plastic strain in austenite and cleavage on ferrite. Otherwise, the main mechanism of failure on welded tubes was cleavage.
Globalization and the Internationalization of Legal Education in the United States: An Annotated Bibliography
Globalization and its influence on legal education is a topic of growing interest to the legal profession and to legal educators alike. The first articles on the subject appeared in the mid-1990s, and the frequency of publications has been increasing ever since. This bibliography provides annotations to English-language law journal articles published between 1995 and 2008 that focus on the impact of globalization on legal education in the United States.