Nondestructive evaluation of temper embrittlement of Cr-Mo-V cast steels by electrochemical method using calcium nitrate solution

Quantitative evaluation of temper embrittlement of turbine casing material by anodic polarization behavior in calcium nitrate solution was investigated. A nondestructive electrochemical method for detection and evaluation of temper embrittlement was developed. Intergranular corrosion (IGC) occurs only on temper embrittled samples during anodic polarization in calcium nitrate solution. In polarization curves measured at 60°C, the increases in current density at passive potential range and in passivation potential attributable to IGC have a correlation with shifts in FATT caused by temper embrittlement. In polarization curves measured at 30°C, increases in current density of the second peak current attributable to IGC have a correlation with shifts in FATT.