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Air Quenching is employed when slower and uniform cooling is required in the workpiece such as high alloy steels. Still, air or compressed air can be used to cool the workpiece though care must be taken that cooling is uniform to prevent cracking or deformation. The air stream must also be free of moisture.Air quenching is used as a means to limit the residual stresses as well as the brittleness that occurs during the quenching process. Rapid quenching also has a tendency to create distortions due to the stresses, especially if the cooling is non-uniform over the surface of the part, air quenching may be used to remedy this. For improving fatigue life some residual stress can be advantageous and can be achieved through the comparatively slower cooling rate of air quenching. Cooling rate is governed by the Heat Transfer coefficient (HTC), which is a function of the heat flux and the temperature gradient. Since the HTC is the critical factor for achieving desired material properties while air quenching, understanding some of its influences is a necessity. Some of these influences include, size and material to be quenched, air velocity, air temperature, type of gas being used for quenching, surface quality (machined, cast, etc.), and the orientation of the material in the stream of air. Factors proving to be relatively insignificant are the relative humidity and the airtemperature however they do still have an effect. Orientation of the part presumably has significance, but its effects have yet to be studied in detail.