Study of Reheat Cracking in Weldment (Part 2)

Abstract

Occurrence of reheat cracking is promoted by presence of elements which show a precipitation hardening phenomenon. It might be natural to consider the secondary hardening phenomenon, during stress relief heat treatment, is a factor controlling the tendency of the cracking behaviours.
In this report, investigations have shown that one of the materials, which were used to examine the phenomenon, namely Nb-Mo type 80 kg/mm² class steel—precipitation hardening steel—, showed very low susceptibility to the cracking comparing to T-1 type steel. Therefore it is neccessary to reconsider if there are relations or no relations between cracking susceptibility and secondary hardening phenomenon.
In this study, these phenomena were examined measuring the hardness and strength at high temperature of HAZ and the conclusions obtained were as follows;-
(1) There is no relationship between the second precipitation hardening and the susceptibility of the cracking and also it can be said that high hardness value of HAZ at high temperature does not correspond to high susceptibility of the cracking.
(2) It can be said that when the strength of HAZ at high temperature is high, the susceptibility of the cracking is low and when the strength is low, susceptibility is high. Therefore the strength of HAZ at high temperature, where the appearance of fractured surface has the typical grain boundary fractured one, plays very important role, in another expression, boundary strength of HAZ at high temperature is one of the main factor influencing the cracking.