STRUCTURE OF HIGH-CARBON STEEL AFTER WELDING WITH RAPID COOLING

Abstract

In this paper the effect of rapid cooling during arc welding on the structure of fusion layer and heat affected zone (HAZ) of high-carbon low alloyed steel have been studied. The main idea was that despite of high carbon content (1.2%) it is necessary to achieve quenching in HAZ. Due to proper chemical composition of welded steel martensite start temperature Ms is about 20 ^oC, therefore austenitic structure of quenched metal is preserved after rapid cooling. Exposition of HAZ to excessive heat during welding cycle leads to local precipitation of carbides from austenite and thus raising of Ms. In this case some amount of martensite was present in structure after cooling along with austenite and carbides. Microstructure, microhardness and chemical composition of remelted electrode metal, fusion zone and HAZ were studied by means of optical microscopy, SEM, EDX and microhardness testing.