Study of Reheat Cracking in Weldment (Part 3)

Abstract

It was already shown that a reheat cracking was a grain boundary cracking occurring at high temperature and there were some relationships between the cracking susceptibility and a strength of HAZ at high temperature. But the strength of HAZ that is one of the factors influencing the susceptibility was not sufficient to explain the phenomenon thoroughly.
In this paper another factor was quantitatively examined. Experiments were made with a apparatus that could simulate a practical stress relief heat treatment using a small specimen. of weldment.
It was found out that the cracking susceptibilities of weldment could be expressed with two factors, the strength of HAZ and the stress relaxation characteristics of base material.
The results obtained from the experiments of the present paper are summarized as follows;
(1) Weldment which has high susceptibility to the cracking shows a little stress decrement during stress relief heat treatment and non-susceptible weldment shows a large stress decrement. The relaxation characteristics of weldment is mainly controlled with that of base material. Base material of a weldment that is more susceptible to the cracking shows a less stress decrement than that of a weldment that is less susceptible to the cracking. This characteristics of base material is another factor controlling the cracking susceptibility.
(2) The cracking susceptibility can be expressed with two factors in one figure, one is the stress relaxation characteristics of base material at high temperature and the other is the strength of HAZ at high temperature.