Mizuo Edamura1, Minoru Makimura1, Takashi Kajikawa1, K\=oichi Imai1, Satoshi Furuitsu1 and Satoru Kunise1
1Engine and Motorcycle Group, Kawasaki Heavy Industries Ltd., Akashi
In our previous report, it is shown that the growth rate of the compound layer in the ion-softnitrided S15C steel follows the linear law during the first one-half hour and then it nearly follows the parabolic law. In this report, the thickness of the compound layer in the ion-softnitrided S15C steel was investigated by optical microscopy by varying the current density, voltage, nitriding temperature and nitriding time. The main results obtained were as follows.
(1) Both the values of k and t0 were hardly affected by the current density but influenced by the voltage when the nitriding temperature and time were constant. Here k was the growth rate of the compound layer during the stage of the linear law, and t0 was the time when the stage changed from the linear law to the parabolic law. When the voltage was increased, the value of k was increased and the value of t0 was decreased.
(2) During the stage of the parabolic law, the activation energy for diffusion of nitrogen in the compound layer showed a nearly almost constant value, which was hardly affected by the current density and voltage.
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