EMBRITTLEMENT OF AN AISI-8640 LOWER BAINITE STEEL

A study was performed to determine the cause of an abnormally low frac ture toughness of an AISI 8640 resulfurized steel. The embrittlement e ffects of phosphorus and arsenic on this steel heat-treated to a lower bainitic structure were studied by employing fracture toughness tests , Charpy impact tests, X-ray fluorescent spectroscopy, and scanning el ectron microscopy (SEM). The results showed that the steel was embritt led by phosphorus at prior austenite grain boundaries in a manner simi lar to the tempered martensite embrittlement (TME) phenomenon. Arsenic is also believed to be involved in the embrittlement effect, specific ally as related to producing a reduction in the upper shelf Charpy imp act energy. Embrittlement was manifested by a reduced fracture toughne ss, an increase in the Charpy transition temperature, and intergranula r fracture.