Notched tensile testing of T-200 maraging steel and its laser welds in hydrogen

Abstract

Notched tensile tests were carried out to investigate the influence of gaseous hydrogen on the susceptibility to hydrogen embrittlement (HE) of aged T-200 maraging steel. The results indicated that the under-aged steel plates and their laser welds suffered great notched tensile strength (NTS) losses in hydrogen, whereas the over-aged specimens were resistant to HE with essentially no NTS losses. In general, the laser welds exhibited the lower hardness and NTS than the steel plates of the same aging treatment. At the same strength level, the over-aged specimens were far superior to the under-aged ones in terms of HE resistance. This could be associated with the presence of numerous strong traps such as reverted austenite in the over-aged structures to retard hydrogen diffusion to the highly strained region. Conversely, the lack of strong hydrogen traps in the under-aged specimens caused an enhanced susceptibility to HE. It was also noted that the laser welds were susceptible to HE, while the steel plates were insensitive to hydrogen in the peak-aged condition. Apparently, the existence of coarse columnar grains was responsible for a higher NTS loss in hydrogen of peak-aged welds. Fractographic observations generally correlated well with the NTS loss of specimens, i.e. greater NTS losses corresponded to a greater amount of brittle fracture in specimens tested in hydrogen.