Microstructure and Mechanical Properties in Friction Welded Joint of Non-Quenched and Tempered Steel

In this work, we investigate the microstructure and mechanical properties in friction welded joint of V-microalloyed non-quenched and tempered steel. To this end, NQT steel was bonded with S45C high carbon steel by friction welding. The microstructures of welded joint were observed by optical microscopy (OM) and scanning electron microscopy (SEM) analyses, and their effective grain size were measured by electron backscattered diffraction (EBSD) analyses. Welded joint consists of bond line, thermomechanically affected zone (TMAZ), and heat-affected zone (HAZ). The TMAZ and HAZ of S45C high carbon steel are composed of grain boundary ferrite and pearlite microstructure, and the TMAZ then has larger grain size and higher fraction of pearlite compared to the HAZ. The TMAZ and HAZ of NQT steel are composed of grain boundary ferrite, acicular ferrite, and bainite microstructure, and the grain size of the HAZ is then smaller than the TMAZ. The mechanical properties of welded joint were evaluated by tensile, Charpy U-notch impact, and Vickers hardness tests. In both NQT steel and S45C high carbon steel, the hardness decreases with increase in the distance from the bond line by increasing the fraction of ferrite.