The effect of chloride ion mass concentration(0

1

20 mg/L) on stress corrosion cracking of Inconel 740H

a candidate nickel based alloy for high parameter ultra-supercritical units at 630～700 ℃

were investigated by slow strain rate tensile testing and stress corrosion crack propagation testing. Moreover

the relevant mechanism of high mass concentration chloride ions promoting the initiation and propagation of stress corrosion cracks was explored. The results showed that

high mass concentration of chloride ions promoted the stress corrosion cracking of 740H alloy

and the stress corrosion sensitivity index Iscc(δ) of the alloy increased with the chloride ion mass concentration. When the mass concentration of chloride ions increased to 20 mg/L

both the middle and edge of the fracture exhibited intergranular brittle fracture characteristics

with a large number of secondary intergranular cracks near the fracture. At this point

the alloy experienced stress corrosion cracking. The average crack propagation rate in a 20 mg/L chloride ion water environment reached 1.15×10~(–6) mm/s

which is 111.7 times the average crack propagation rate in high-purity water.