The stress corrosion cracking (SCC) behavior of Inconel X-750 in high-temperature water has been examined in relation to aging conditions. SCC susceptibility for the two-step (solutioning + aging), heat-treated alloy (SA) varied with its aging condition, and the aging conditions that gave a high yield strength also gave a high SCC susceptibility. Wide chromium depletion produced by the formation of M23C6 along the grain boundary during aging was identified by energy dispersive x-ray analysis (EDXA) to be a cause of intergranular stress corrosion cracking (IGSCC) susceptibility for SA. The three-step (solutioning + stabilizing + aging), heat-treated alloy (SSA) was more susceptible to IGSCC than the SA alloy, in spite of the smaller corrosion rate in a modified ASTM(1) Standard G-28 test. EDXA revealed titanium segregation and formation of titanium-rich phases along the grain boundary, and it is speculated that the poor resistance to IGSCC following a SSA treatment might be caused by formation of a local cell between the grain boundary and the matrix.

Subject
Carbides, Intergranular stress corrosion cracking, Nickel based alloys, Chromium, Transmission electron microscopy, Titanium, Titanium alloys, Grain boundary, Alloys, Heat treatment, Yield strength, Stress corrosion cracking, Aging
National Association of Corrosion Engineers
1988
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