The Effect of Hydrogen on Intergranular Stress Corrosion Cracking of Alloy X750 in High Temperature Pure Water

摘要

In order to clarify the mechanisms of intergranularstress corrosion cracking of Alloy X750 in high temperaturewater, the authors have studied the relationship between thedistribution of hydrogen and the microstructure of grainboundary precipitates by using electron micro autoradiographictechnique. Two types of Alloy X750 with different heattreatment history were prepared. The one is sensitive tothe stresscorrosion cracking in high temperature water, which hasincoherent precipitates other than M_(23)C_6 discretely exist atthe grain boundaries. The other has excellent resistance to thestress corrosion cracking and has coherent M_(23)C_6precipitates which semi-continuously exist at the grainboundaries. Tritium and hydrogen were charged into thesespecimens at room temperature by cathodic charging method.After the charging, specimens attached by the sensitive film(monolayer of fine silver bromide particles film) were kept in adark box for about 10 day. The distribution of silver particles onthe specimen was observed by electron probe microanalyzer andtransmission electron microscope. For the specimens which aresensitive to the stress corrosion cracking resistance, the silverparticles existed on the grain boundaries, however, for thespecimens which have excellent resistance to the stresscorrosion cracking, the silver particles were not found at thegrain boundaries. From this evidence, it seems that hydrogentrapping behavior at the grain boundaries affects the stresscorrosion cracking resistance.