Nondestructive Evaluation of Temper Embrittlement in HY80 Steel

The problem of temper embrittlement has accompanied the use of alloy steels for a number of decades and has been thoroughly studied and documented [1,2,3,4]. Temper Embrittlement (used here to include the phenomenon of Stress Relief Embrittlement) is the decrease of impact toughness which occurs in susceptible commercial grade alloy steels when they are heated within or slowly cooled through the embrittling temperature range of approximately 371 to 599 degrees C (700 to 1110 degrees F). It is caused by migration of impurity elements such as sulphur, phosphorus, tin, antimony and arsenic to prior austenite grain boundaries and is primarily encountered during post-fabrication heat treatments such as those used to relieve residual stresses. Studies show that, although these embrittling elements are typically present in bulk weight percentage concentrations of 20 to 200 ppm, grain boundaries of embrittled steel can contain concentrations that are 1 to 2 orders of magnitude greater due to segregation during heat treatment. This is determined by using Auger electron spectroscopy of fracture surfaces of embrittled test samples broken and analyzed in vacuum. Approximately 500 angstroms of material are typically removed from the fracture surfaces by ion milling before the concentration returns to that of the bulk material.</p