Modeling Heating Effects in the Heat-Affected Zone of High-Strength Pipe Steel K70 with Double-Pass Submerged Arc Welding

Abstract

Simulation modeling is used in order to study metal structure in a heat-affected zone (HAZ) during submerged-arc welding. A correlation is established between low values of impact energy observed and features of HAZ structure formation during submerged-arc welding of low-alloy steel of strength category K70. It is shown that the appearance of brittle precipitates with an increase in content of the main alloying elements at large grain boundaries is a reason for low impact energy in the area of large HAZ grains during steel K70 welding. Development of these areas is connected with repeated heating (simulating a second pass during rolling) in a temperature range somewhat lower than the Ac 1 point. A reduction in cooling rate in the first heating cycle (which corresponds to an increase in linear energy during welding) facilitates precipitate enlargement over grain boundaries. Multipass welding and a reduction in pass linear energy are recommended in order to exclude the formation of these areas and to improve and stabilize impact energy in a welded joint HAZ.