Weld heat-affected zone of austenitic stainless steel is susceptible to intergranular corrosion for the grain-boundary carbides precipitated by the thermal cycles during welding. In the previous paper the influence of the peak temperatures of thermal cycles on the susceptibility to corrosion
and the precipitation of carbide particles was investigated. In this paper the relationship between the corrosion resistance and the behaviour of carbide particles was investigated on all of the specimens given thermal cycles between the room temperature and the temperature of 650°or 800°C after solution treatment at 1050°C for various holding times up to 2 hr. The results obtained were as follows :
(1) It was recognized that the amount of carbide particles precipitated during thermal cycles decreased with increasing holding time of solution treatment. The remarkable precipitation of carbide particles was observed in the specimens given twenty cycles at the peak temperature of 800°C after solution treatment for the shortest holding time and the precipitates were continuously formed along grain boundaries.
(2) Boiled 65% nitric acid tests on the specimens given thermal cycles showed that in the same peak temperature and number of thermal cycle, the susceptibility to corrosion decreased with longer holding time of solution treatment.
(3) Intergranular corrosion tests by Strauss solution showed that etching occurred on all of boundaries precipitating carbide particles. There was a direct correspondence between the degree of etching and the amount of precipitates. The etching increased with increasing amount of precipitates and was very severe for the specimen given twenty cycles at the peak temperature of 800°C after solution treatment for the shortest holding time.
(4) In the electron microscopic observation of the carbide particles extracted from the specimens given thermal cycles after solution treatment, a numerous of fine carbide particles and a few dendritic carbide particles were observed around grain boundaries.
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