Microstructure and Mechanical Properties in the Simulated Heat-Affected Zone of Non-Quenched and Tempered Steel

In this work, the microstructure evolution and its effects on mechanical properties in the weld heat-affected zone (HAZ) of non-quenched and tempered (NQT) steel with the composition of Fe-0.28C-0.97Si-1.61Mn-0.14V were investigated. To this end, HAZ samples of NQT steel were prepared by Gleeble simulation. Here we changed the welding conditions of heat input and peak temperature to simulate the HAZs. The microstructures of base metal and simulated HAZs were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), and electron back-scattered diffraction (EBSD) observations. The base metal consisted of typical ferrite and pearlite microstructure. The HAZs were composed of martensite, bainite, and ferrite, and then martensite fraction decreased and ferrite fraction increased with increasing heat input and decreasing peak temperature. In addition, the prior austenite grain size (PAGS) in HAZs increased with increasing heat input and peak temperature. The mechanical properties of simulated HAZs were evaluated through the Vickers hardness and Charpy U-notch impact tests, indicating that the strength and impact property decreased as the PAGS and the ferrite fraction increased.