LOW TEMPERATURE CRACK PROPAGATION MECHANISM OF ALLOY 182 WELD

摘要

It is well-known that Alloys 182 and 82 welds aresusceptible to low temperature crack propagation(LTCP), leading to intergranular (IG) cracking duringfracture toughness tests in 54oC water but not in 338°Cwater. Nonetheless, the mechanism by which the LTCPoccurs remains elusive. To understand this, Alloy 182weld is taken from the Alloy 600/182 weld made bysubmerged arc welding and is subjected to differentialscanning calorimetry (DSC) tests. The results show thatheat evolution occurs in a low temperature range of RT to200°C, which is observed neither in water-quenched Alloy600 after solution annealing nor in furnace-cooled Alloy182 weld after heating to ～1000°C. This anomalous heatevolution for the Alloy 182 weld reveals the occurrence ofordering upon aging or deformation at low temperatures.Given our previous observations that heat evolutioncorresponds to ordering, causing lattice contraction ingrains and thereby IG cracking, LTCP of Alloys 182 andEN82H welds in low temperature water is determined byordering but not by a hydrogen-induced degradationmechanism despite the fact that ordering is promoted byhydrogen. Compelling evidence is provided by thecorrelations between heat evolution behavior and theLTCP resistance of Alloy 600 and Alloys 182 and EN82Hwelds. This work clearly confirms that IG cracking ofnickel alloys during SCC tests is driven by ordering orshort-range ordering.