Influence of product type on stress corrosion cracking of alloy 600

Grain-boundary carbide coverage obtained from metallographic replications has been considered as an estimation of SCC susceptibility of alloy 600 components in pressurized-water reactor (PWR) primary water. Stress corrosion cracking (SCC) initiation tests were carried out on alloy 600 (UNS N06600) in primary water at 325 C and 360 C and in steam with hydrogen at 400 C to gain some insight into the SCC behavior of different alloy 600 products. Forged bars, thick-walled tubes (cold-worked and hot-worked), and steam generator (SG) tubing with different thermomechanical histories were tested. As expected, materials with a high density of intergranular carbide were more resistant to cracking in high-temperature water than materials with few carbides in the grain boundary. However, materials with similar microstructures but different thermomechanical histories presented different SCC susceptibilities. In general, forged bars were more resistant than thick-walled materials with similar grain-boundary carbide coverage. Cold-worked materials (thick-walled tubes and SG tubing) presented similar behaviors. However, appearance of intergranular fractures at high magnification seemed to be related to the SCC behavior of alloy 600 in steam and in primary water. More resistant materials exhibited pseudointergranular fractures