Influence of thermal cycles of repair electroslag welding on the structure and mechanical properties of joints of cast medium carbon steels

Abstract

The results of the study of the effect of thermal cycles during multi-pass electroslag welding on mechanical properties of the weld metal and the heat affected zone (HAZ) are presented. It is shown that one of the ways to approximate the mechanical properties of the welded joint to the properties of the base metal without high-temperature heat treatment is to perform electroslag welding not in one but in several passes, when the heat released during each adjacent pass affects the previously welded sections, producing their partial heat treatment, improving the mechanical properties. Analysis of thermal cycles showed that the cooling rate of the metal HAZ of each weld within the temperature range 600...500°C (w6/5) does not exceed critical values for 35L steel type, and also decreases with the welds overlapping, i.e., the danger of martensite formation in this zone is absent. It has been established that the effect of automatic heat treatment of welds results in the structure recrystallization, contributing to grain refinement in the overheating area of the heat transfer zone and weld metal and significant improvement of the mechanical properties. The results of impact bending tests (KCU) of the welded joints showed that the toughness impact in the areas of the weld metal, which have undergone the accompanying heat treatment, exceeds that one of the base metal, as well as the regulatory requirements, by 2...4 times.