Meysam Hoseini Vahed - M.Sc Student of Materials Engineering, Karaj Branch, Islamic Azad University, Karaj, Iran
Hamed Sabet - Associate Professor, Department of Materials Engineering, Karaj Branch, Islamic Azad University,Karaj, Iran

In this study, the effect of GTAW heat input on the microstructure of Heat Affected Zone in AISI D2 steel has been reviewed. For this purpose, parts of D2 steel were prepared and welded by GTAW. The variable parameters in this study are the number of welding passes and the intensity of the welding current. After welding the specimens, an optical microscope (OM) as well as a vegetative electron microscope (SEM) equipped with EDS analysis were used to examine the microstructure of the heat affected zone (HAZ). The micro-hardness test was also performed to check the hardness of different areas. Microstructural studies have shown that as the welding heat input increase, the width of the affected area, the grain size and carbides size in this area increases. The major phase formed in the samples was M7C3 carbide. The hardness test results showed that the HAZ has the highest hardness, by increasing the heat input of welding martensite has increased and also the uniform distribution of carbide at the grain boundary has increased the hardness of this region. Also reduce the hardness by PWHT due to decreasing the density of deformations and residual stresses.

GTAW, AISI D2 Steel,Welding Heat Input, HAZ.