STUDY OF MICROSTRUCTURE AND WIDTH IN HEAT AFFECTED ZONE IN WELDING OF A 4130 HARDENED STEEL

Abstract

In present work, the width and microstructure behavior of the thermally affected zone (TAZ) was studied as a function of electrical current and preheating temperature in welding with a fused electrode and gaseous protection (GMAW) of a hardened 4130 steel. Current variation and preheating temperature, keeping the welding speed constant, was carried out based on a factorial experiments design. Metallographic analysis of a sample of base metal and samples extracted from the strands on sheet metal, obtained for each experimental condition, was carried out. The hardness profiles also were obtained for each test condition. From the hardness profiles the width of the TAZ was defined as the interval with low hardness values. As a result of the work, a quantitative relationship is established which shows that welding current increase and preheating temperature cause an increase in TAZ width, so that the best condition are lowest current and without preheating. It is also concluded that the TAZ presents three subzones with different microstructures.