The Fundamental Factors Incluencing the Behaviour of Welded Structures under Conditions of Multiaxial Stress, and Variations of Temperature, Stress Concentration, and Rates of Strain

摘要

An investigation was made to determine the dependence of zones of low ductility in weldments upon the steel and upon the welding conditions and heat treatment. The ductility was evaluated by means of eccentric notch-bar tension tests conducted at various low temperatures. A zone of low ductility was found in two low carbon ship plate steels at a distance of 0.3 - 0.4 in from the weld centerline when the weldments were made with 100F preheat and interpass temperature. A 400F preheat and interpass temperature improved the ductility in the critical zone, lowering the transition temperature from -20F to -45F. A 1100F postheat practically eliminated the zone of lowered ductility, the transition temperature being lowered to -70F. Temperature measurements made during welding showed that the embrittled region was not heated above the lower critical temperature. No change in microstructure could be noted between the critical zone and the unaffected base plate. Microhardness tests showed only slight hardening in the embrittled region. The occurrence of the embrittled region is thought to be due to some subcritical temperature phenomena which may be the supersaturation and precipitation of carbon or carbides from the alpha phase. (Author)