Effect of surface treatments on stress corrosion cracking of alloy 800 in alkaline solutions

The effect of surface treatment such as shot peening on stress corrosion cracking (SCC) of Alloy 800 in high temperature alkaline solutions was investigated. Both U-bend and C-ring specimens were stressed after surface treatment. The controlled potential experiments were carried out in the boiling 50% NaOH+0.3% SiO2 solutions, and autoclave tests were carried out in the 10% NaOH solutions at 593 K. Alloy 800 specimens were cracked in boiling alkaline solutions at the potential range of -100 to 0 mV. Controlled potential experiments at this potential range revealed that shot peened specimens cracked more easily than annealed specimens and the susceptibility to SCC increased with increasing the coverage of peening and the surface roughness. The steel ball shots more enhanced cracking than alumina sand did. The autoclave test results of U-bend specimens were approximately same as those of the controlled potential tests, whereas C-ring specimens did not occur to crack under any surface condition.