Articles written in Sadhana
Volume 46 All articles Published: 28 April 2021 Article ID 0088
In the present work, continuous cooling transformation (CCT) of coarse-grained heat-affected zone (CGHAZ) and simulation of Charpy-sized impact specimens were performed using a Gleeble 3800 thermomechanical simulator. Results obtained from the dilation studies show significant effect of cooling rates onmicrostructure and low-temperature (–20 ΟC) Charpy impact toughness. Phase transformation temperatures (Ar3 and Ar1) and impact toughness decreased while hardness and amount of bainite increased with increasing coolingrates. At slow cooling condition (\ 5 ΟCs-1) quasi-polygonal ferrite and pearlite phases were observed in the microstructure. At medium cooling rate (5–25 ΟCs-1), bainite and quasi-polygonal ferrite were obtained in the microstructure. For still faster cooling rates, microstructure was completely bainitic in nature. Themicrostructures were confirmed by hardness measurement where the hardness value for lower, medium and high cooling rates were 191–196, 213–214 and 234–253 HV, respectively. Charpy impact toughness increased with decrease in cooling rate due to the presence of softer ferrite phase.
Volume 47 All articles Published: 7 June 2022 Article ID 0108
Flash butt weld failure due to oxide entrapment is one of the primary causes of wheel rim failures. The welding process parameter plays a critical role in eliminating the oxides from the bond line. Experimental investigations to understand the effect of initial jaw distance (IJD) and the number of preheating pulses (NP) on the upsetting length (UL) were studied. It was observed that IJD and NP played a critical role in altering the peak temperature achieved at the interface. Higher peak temperature at the interface helped achieve a larger upset length, forming a defect-free weld. Failure analysis of the flash butt welded fractured surface revealed the presence of penetrators/cold spots and oxide inclusion. The study suggested that a sufficient upset length was necessary to expel oxides/cold spots formed during welding for obtaining defect-free joints. Furthermore, increasing the preheating pulses smoothened the abutting edges and significantly reduced the defects. The presence of Goss, Rotated Goss, and Cube textures at the fusion zone of flash butt weld were found to be theenabler for crack propagation during post-weld forming operations once the crack has been initiated.