A Study on Rupture Properties of Large Welded Specimens of HT 70 Steel for Nuclear Pressure Vessels (Report 3)

Influence of Heat Treatment on Creep Rupture Strength

Abstract

From the foregoing reports, it is known that the creep rupture strength of welded specimens is influenced by initial conditions of structure in the heat-affected zone. In this report, the influence of heat treatment after welding on the creep rupture strength of large size welded specimens is investigated. The specimens are made under the following three conditions of heat treatment after welding: (a) 550°C×2.5 hrs., furnace cooling, (b) 650°C×2.5 hrs., furnace cooling and (c) 900°C×2.5 hrs., furnace cooling.
The results are as follows;
(1) The creep rupture strengths of welded specimens, treated under 650°C×2.5 hrs., furnace cooling and 900°C×2.5 hrs., furnace cooling after welding, are superior to that of the as-welded one. The heat treatment under 550°C×2.5 hrs., furnace cooling seems to decrease the creep rupture strength.
(2) The welded specimens, treated under above conditions, arc ruptured at the heat-affected zone of base metal near the bond.