Stress corrosion cracking and temper brittleness: effect of phosphorus grain boundary segregation in a low-alloy steel

The presence of phosphorus at the grain boundaries of a low-alloy 2.25Cr-1Mo steel is shown to affect the intergranular stress corrosion cracking in ammonium nitrate solution. At grain boundary phosphorus levels of up to 20% monolayer, this segregation-induced stress corrosion effect is linear in terms of times to failure in constant strain rate tests. The levels of phosphorus to which stress corrosion is sensitive are much lower than the levels for temper brittleness, and immunity from this form of stress corrosion cannot, therefore, be assessed from temper embrittlement data. A lanthanum additive remedial treatment for temper embrittlement does, however, improve stress corrosion properties.