A new test method to characterize heat transfer coefficient distribution in industrial gas quenching systems

Gas quenching is widely used in aerospace industry when quenching medium or high hardenability steels. High pressure and high velocity gas flow induce complex flow pattern in the furnace. The heat transfer coefficient distribution is localized and affect the cooling rate, microstructure and mechanical properties of the parts. In this paper, a method using bars with proper geometry and steel grades to evaluate heat transfer coefficient distribution in gas quench furnace is proposed. The relationship of the measured hardness at the core of the samples and the outside HTC was investigated by the authors previously. Using this relationship, by simply measuring the core hardness, the HTC distribution in the gas quench furnace can be mapped. It was verified that 0.5” diameter and 4” length AISI 4340 bar can be used to evaluate 2bar nitrogen gas quench furnace. An attempt to measure 20bar helium gas quench furnace was made as well. A basic test procedure was proposed.