1989 Volume 75 Issue 2 Pages 353-360
Prolonging annealing treatment below the critical temperature is carried in order to relieve residual stress due to welding and to improve toughness of weld heat affected zone in the fabrication of pressure vessels. It has been known that this treatment named stress relief (SR) annealing decreases strength and toughness of base metals. Thus, the effects of microstructure and alloying elements on this decrease in mechanical properties were investigated in carbon-manganese, manganese-molybdenum and chromium-molybdenum steels for pressure vessels.
The decreasing amount of strength and toughness due to SR annealing was the largest in martensite structure and next in bainite structure. These was little change in strength and toughness in ferrite-pear-lite structure. Good toughness was obtained by SR treatment at high temperature and for short time in comparison with that of low temperature and long time at a certain strength. The start of decreasing toughness was delayed by an increase in {1/5 (Mn(%)+ Cr(%))+Mo(%)} content.
Applied stress equivalent to residual stress level in SR treatment did not affect mechanical properties. The amount of temper embrittlement due to slow cooling in SR treatment decreased with prolonging SR treatment.
