Effects of Residual Impurities on Hydrogen Assisted Cracking in High Strength Steels. Part II.

Abstract : Intergranular brittle fracture in steels can be induced either by the segregation of certain solute elements to the grain boundaries or by the segregation of absorbed hydrogen under stress. Alloying elements in steel are generally added because of their beneficial effects on the mechanical properties. However, certain elements from groups IV, V and VI of the periodic table e.g. Sn, Sb, As, P, S, etc., when present in small quantities as impurities along with the usual alloying elements like Ni, Cr, Mn, Si, etc., can deteriorate the mechanical properties drastically by lowering the cohesion at the grain boundaries and thereby resulting in an intergranular brittle fracture along the prior austenite grain boundaries. These problems, often encountered in service, are generally known as 'temper embrittlement', (TME) tempered martensite embrittlement, (HE) hydrogen embrittlement, (SCC) stress corrosion cracking, etc. The purpose of the present investigation was to clarify the effects of these impurity elements in promoting TME and intergranular cracking in a hydrogen atmosphere at low stress intensity levels.