| 摘要 |
PROBLEM TO BE SOLVED: To provide a soft nitriding treatment method which allows a soft nitriding treatment without a special pretreatment of the surface of a steel material prior to the soft nitriding treatment and retains or improves properties of the steel material, e.g. corrosion resistance.SOLUTION: A soft nitriding treatment method is based on heating urea in a nitriding treatment vessel 11 to decompose thermally and carrying out a soft nitriding treatment of a steel material with the decomposition gas of a soft nitriding treatment temperature. The lower limit of the soft nitriding treatment temperature is 400°C, and the upper limit of the soft nitriding treatment temperature is set to be decreased gradually from 440°C to 400°C. The upper limit of the soft nitriding treatment temperature is set to be decreased from 440°C to 400°C through at least two stages. For example, the lower limit of the soft nitriding treatment temperature is 400°C independent of the soft nitriding treatment time, and the upper limit of the soft nitriding treatment temperature is set to be 440°C for a total soft nitriding treatment time of 3-5 h and then set to be 420°C for a total soft nitriding treatment time of 6-10 h. |
