A Short-Time Creep Rupture Study of the Synthetic Weld Heat-Affected Zone in a High Strength Steel

Abstract

A short-time creep rupture test has been carried out on the synthetic weld HAZ specimen in a 80 kg/mm² high strength steel. An effect of weld thermal cycle is investigated and there is some discussion with the results of the fractographic study on the fracture surface.
In this study, to observe the creep rupture tendency of specimens especially during heating, a tensile loading is started at the beginning of heating.
First, rupture strength and creep time to rupture of the coarse-grained HAZ specimens of 1, 380°C peak temperature are both lowered with increasing testing temperature, while the elongation to failure is improved distinguishly.
In comparison with the effect of cooling rate from 1, 380°C peak temperature, rupture strength and time to rupture are lowered in a rapid cooling than in a slow cooling.
Second, the results on the effect of which varied the peak temperatures showed that rupture strength, time and elongation to rupture are increased remarkably with decreasing peak temperature.
From the results of the effect of second thermal cycle after being 1, 380°C peak temperature, creep rupture properties of the reproduced HAZ are improved conspicuously in case of 900°C second peak temperature, but did not be affected in the least in case of 600°C.
In the fractographic study, it was found that an intergranular brittle fracture was mainly observed when tested below 700°C, and on the other hand, an intergranular ductile fracture above it. However, the fracture surface is almost affected to the original austenite grain boundary produced by a first thermal cycle regardless of brittle or ductile fracture.
According to the prolonged heating time, rupture stress was decreased markedly with increasing heating time in higher stress conditions, and when a heating time was increased extremely, some specimen was broken during heating before reaching to the fixed temperature.