Estimation and analysis of surface heat flux during gas quenching through IHC method

Gas Quenching is a process of quenching steel components with a gas quenchant. This process, due to its several advantages is being extensively used now a days. This work studies the effect of the variation of gas jet pressure and the standoff distance (SOD), which is the distance between the quench probe and the tip of the nozzle on the quenching heat transfer during gas quenching. A gas quenching chamber of octagonal cross-section of side 100 mm was used for quenching experiments, in which an array of nozzles was fixed. The cylindrical workpieces of 20 mm diameter and 50 mm length were machined from stainless steel 304L and K-type thermocouples were fixed at the selected locations inside the workpiece to read the temperature during quenching. Compressed air as the quenchant at different pressures of 4 bar, 6 bar and 8 bar and different SOD of 9 cm, 10 cm and 11 cm were used to study the effect of these two parameters on the quenching heat transfer rates. Surface heat flux computations were made using Inverse Heat Conduction (IHC) method using the measured time–temperature data as input. It was found out that as the pressure increased, the cooling rate and the peak surface heat flux increased and as the nozzle standoff distance was increased, the cooling rate and the peak surface heat flux dropped. The effect of increasing the nozzle SOD by 1 cm was more than the reduction of gas jet pressure by 2 bar.