Effect of Heat Treatment on Fatigue Strength of Gas-Chromized Cr-Mo Steel

Abstract

For the purpose of clarifying the effect of heat treatments on the fatigue strength of gas-chromized Cr-Mo steel, three kinds of samples of Cr-Mo steel SCM22, that is, one annealed, quenched and tempered, diffusion treatment after gas-chromizing with CrCl₂, and the other gas-chromized, quenched and tempered after a preliminary carburizing, have been subjected to a rotary bending test in the ambient atomosphere, and the results are as follows:
(1) Annealing after gas-chromizing provides a fatigue strength lower than that without gas-chromizing.
(2) Quenching and tempering after gas-chromizing provides a fatigue strength lower than that without gaschromizing.
(3) The lower fatigue strength of chromized samples is considered to be due to decarburized zone under the Cr diffusion layer.
(4) Therefore, through the diffusion treatment followed by the gas-chromizing, fatigue strength of the steel is improved.
(5) Furthermore, it has been confirmed that the gas-chromizing after carburizing have increased fatigue strength of the steel.