2000 Volume 18 Issue 1 Pages 87-94
According to previous reports, columnar grain boundary embrittlement caused by bismuth is responsible for the reheat cracking of Type 308 FCAW weld metal. It is necessary to quantitatively evaluate the reheat cracking sensitivity for comprehension of the reheat cracking mechanism. It is considered that grain boundary cracking at elevated temperatures occurred when the strain due to creep deformation caused by residual stress in the relaxation process reached a critical value in the neighborhood of the grain boundary. Therefore it can be said that this critical strain represents the reheat cracking sensitivity of the weld metal.
In this report, a constant load tensile test using a notched specimen is performed and the reheat cracking sensitivity of weld metal is quantitatively evaluated by crack opening displacement (Φc) which corresponds to the critical strain of a grain boundary fracture. The results show that Φc is reduced with increasing bismuth content and increasing test temperature. At temperatures above 1100 K, Φc is remarkably decreased in the bismuth-containing weld metal whose fractured surface shows signs of requation. Φc shows a good relation with the cracking ratio of the y-groove self restraint cracking test. Therefore, Φc quantitatively represents the reheat cracking sensitivity of the weld metal.
