Investigation of the effects of pre-annealing on the microstructure and hardness at arc welding of steels

m INVESTIGATION OF THE EFFECTS OF PRE-ANNEALING ON THE MICROSTRUCTURE AND HARDNESS AT ARC WELDING OF STEELS (M.Sc. Thesis) Mürsel Osman MOR GAZI UNIVERSITY INSTITUTE OF.SCIENCE AND TECHNOLOGY JULY 2001 ABSTRACT In this work, the effects of pre-heating on microstructure and hardness on the welding of construction steel has been investigated. The sapmles of 200x80x10 mm have been welded by manuel arc and MAG welding methods. The welding are carried out at room temperature ancMOO, 200, 350 °C as pre-heating temperatures. In the manuel arc welding, rutil and basik electrodes were used. On the other hand, in the MAG welding, SG2 welding wire was used. The microstructure of the welded specimens were investigated and their hardness were measured. No change in hardness of HAZ at 0.20%C steel has been observed, but the HAZ hardness of 0.42%C steel which was pre-heated over 100 C was decreased to less than 350 VH. The HAZ hardness at 0,84%C steels was not decreasing under 350 VH. The cracks at HAZ were observed as carbon content increased. The cracks were decreased at welding zone on pre-heating specimens basik elektrodes led toIV a lower hardness at welding zone compared to the other electrodes and methods. It was observed from microstructure examination of the all specimens, the grain size was reduced considerably while HAZ getting larger. Science Code : 225.04.01 Key words : Arc welding, MAG welding, Primary annealing Page number : 102 Supervisor : Assist. Prof. Behçet GÜLENÇ