That is, the workpiece is immersed in a salt bath enriched in [N][C] medium, and the nascent [N][C] atoms in the salt bath are permeated and diffused into the interior of the workpiece, and a compound layer is formed on the surface layer of the workpiece. The sub-layer forms a low-temperature, environmentally-friendly chemical heat treatment process of the diffusion layer. According to different requirements of customers, different processes can be selected, including SW, SQ, SQP, QPQ, QPQP and so on.

(1) Process definition

Setting: The processed parts are placed on the jig in a regular manner.

Preheating: 1 Dry the moisture remaining on the processed parts to prevent the water from vaporizing during the furnace to splash the molten salt. 2 Reduce the temperature difference when the processed part is introduced into the furnace to reduce the deformation due to thermal stress.

TF-1: Refers to salt bath soft nitriding.

AB-1: refers to an oxidizing salt bath, which has two functions of isothermal cooling and oxide film formation. The color and thickness of the produced oxide film are deepened and dense with an increase or extension of temperature and time.

Post-treatment: The purpose is to remove the ash and dirt generated on the surface after soft nitriding, and at the same time have the effect of smoothing the surface. Existing post-processing methods include: vibration grinding, telecentric grinding, centerless grinding, cloth wheel polishing, dry (liquid) sand blasting, iron powder and stainless steel shot blasting, etc.

(2) Process performance and application

After the salt bath soft nitriding treatment, a layer of Fe and N compound is obtained on the surface of the workpiece. The layer has high hardness and good wear resistance and corrosion resistance. Due to the presence of this compound layer, residual compression occurs on the surface of the workpiece. The stress can significantly increase the fatigue strength of the workpiece, and as the cooling rate of the soft nitriding increases, other properties (such as bending strength) also increase.

After the soft nitriding treatment of the salt bath, if it is treated by the oxidizing salt bath, a black oxide film mainly composed of Fe3O4 is formed on the surface of the workpiece, which not only improves the corrosion resistance of the workpiece, but also greatly reduces the workpiece. The friction coefficient of the surface has strong lubricity. The salt bath soft nitriding process is suitable for carbon steel, low, medium and high alloy steel, stainless steel, cast iron and iron powder metallurgy materials. Therefore, it is widely used in wear parts, work and molds with thin layers, small load and strict deformation requirements.