Ｆｅ‐３６％Ｎｉ合金（インバ）溶接金属の延性低下割れに関する研究 ＩＩ 再現高温延性試験法による低延性特性の検討

Abstract

Simulated hot ductility test was done to establish the correlation with reheated weld hot cracking test of Fe-36%Ni alloy and to reveal the mechanism of reheated hot crack. Cross lines were drawn with a sharp razor on specimen surface electropolished to study the effects of grain boundary sliding, grain boundary migration, recrystallization and so on. Main conclusions are as follows: 1) There was ductility trough between about 600°C and 1000°C in reheated weld metal, and minimum ductility was located arround 900°C. These behaviors agreed well with those in the actual reheated weld hot cracking test. 2) There was good correlation between brittleness temperature range or minimum ductility evaluated by hot ductility test and total crack length in Cross-head tensile hot cracking test. 3) Grain boundary sliding together with grain boundary precipitates and/or grain boundary serration seems to cause the ductility trough and thus reheated ductility-dip crack by cavity formation process. The grain boundary precipitates contained Al and S. 4) Recovery of dutcility at about 1100°C was associated with active grain boundary migration and recrystallization.