Thermal barrier in welded joints of carbon steels

Abstract

When welding carbon steels, a part of the metal of the heat affected zone directly next to the weld bath undergoes austenitic transformation, which is characterized by a combination of minimal thermal conductivity and high thermal capacity. This zone represents a thermal barrier and prevents heat transfer from the weld bath to the base metal. In addition, this zone is able to accumulate and retain a significant amount of heat for a certain period of time. In the heating phase, this barrier has a positive effect on the formation of welded joints, and in the cooling phase it causes a negative effect the formation of hot or cold cracks, overheating and brittleness of the metal. The negative influence of the thermal barrier on the metal of welded joints increases with the increase of carbon content and alloying elements in steel, and also with the increase of heat input into the welded joint. Currently, an effective means of reducing the negative impact of the thermal barrier on the metal of welded joints is to reduce the heat input to the welded joints and their periodic cooling. Maximum efficiency is achieved in the case of a combination of these two techniques.