1972 Volume 41 Issue 9 Pages 1094-1108
Recently two main types of high temperature weld cracking have been recognized. One is liquation cracking which is associated with microsegregation leading to intergranular films, the other ductility-clip cracking which occurs at newly migrated grain-boundaries free from films.
An investigation has been carried out using a high temperature microscope and an electron probe X-ray microanalyser to obtain a basic understanding of the grain-boundary liquation cracking in the weld heat-affected zone of steels.
In this paper, Type 310 and Type 304 stainless steels were used. The main results obtained are as follows.
1) For Type 310 steel which seems to be comparatively susceptible to hot cracking, low-melting point liquation of grain boundary was observed at about 1355°C-1360°C in rapid heating (heating rate about 140°C/sec). This temperature was extremely lower than the solidus temperature (about 1420°C) in rapid heating.
2) It was demonstrated how the phenomenon presented above was caused by segregation of low-melting point compositions and how such grain-boundary segregation, was induced only when both grain-boundary migration accompanied with heating and solute-rich zone were in simultaneous exsistence.
3) It was presumed that the most important factor to cause hot liquation cracking of Type 310 steel was the low-melting point eutectic reaction beween Cr and Ni which had been enriched to grain-boundary simultaneously.
4) The reasons why Type 304 steel is less susceptible to hot cracking in HAZ than Type 310 steel are as follows.
a) As a great deal of Cr element dissolves into δ-ferrite, Cr is separated from Ni element, the low-melting eutectic reaction between them is suppressed.
b) The grain-boundary migration on heating is apt to be interrupted by δ-ferrite, so it becomes difficult for solute atoms to be swept up to the grain-boundary.
