A study on Rupture properties of Large Welded Specimens of HT70 Steel for Nuclear Pressure Vessels (Report 1)

Comparison with Results of Large and Small Welded Specimens

Abstract

Creep rupture properties at 400, 450 and 500°C of Mn-Cr-Mo-B alloy HT 70 quenched and tempered steel were investigated of large welded specimens, having the shape as welded. Test steel, 30mm thick, was produced experimentally for nuclear pressure vessels and welded joints were made with covered electrodes. The results of creep rupture properties of large welded specimens were compared with those of usual small welded specimens, cut off from the welded joint.
The results are;
(1) The creep rupture elongations and strengths of large welded specimens were generally inferior to those of usual small welded specimens. This seems to be caused by formal and metal-lurgical stress concentration.
(2) The creep rupture configuration of large welded specimens was very different from that of small welded specimens. The initiation of cracking in rupture occurred at the toe of weld metal and the intersection of the bonds of both side weld metal. The cracking propagated along the grain boundary of austenite of bond in the heat-affected-zone of base metal.