Effect of length of vapor blanket duration in quenching oil on mechanical property and distortion of steels

The effect of length of vapor blanket duration when the steels, which were carbon steel JIS-S45C and low-alloy steel JIS-SCM435, quenched in quenching oil on the surface and internal hardness and the distortion of steel was investigated. The heat treatment was accompanied by phase transformation, which caused bending in the direction of the keyway. The quenching oil with the longest length of vapor blanket duration showed the smallest distortion, and the quenching oil with the shortest length of vapor blanket duration showed the largest distortion. It is assumed that this is proportional to the time taken from the temperature of 900°C at the start of quenching to 352°C, the Ms point at which phase transformation from austenite to martensite occurs. The larger the temperature difference between the keyway, which is the low temperature side, and the thick wall, which is the high temperature side, below the Ms point, the larger the distortion. The longer the cooling time from 800°C to the Ms point, the smaller the temperature difference between the low and high temperature sides, and the smaller the distortion.