Embrittlement of welded joints and materials of pressure vessels at operating temperatures

An analysis is made of causes of thermal embrittlement and the decrease in notch toughness of Cr-Mo type steel for reactor pressure vessels and their welding joints. The effect was monitored of the basic chemical composition and interaction of elements (especially Mn, Si and trace admixtures of P and Sn) and their combinations. In this connection the effect was assessed of grain size and various patterns were studied of heat treatment of basic material and welds prior to exploitation within the range of temperatures between 400 and 600 degC. Also monitored was the effect of heat input during welding, of electrode and flux coating, of welding technology and with it the related shape of weld beads. (B.S.)