In order to shorten the nitriding cycle and make the nitriding process not limited by steel grades, two new nitriding processes, soft nitriding and ion nitriding, have been developed in recent years on the basis of the original nitriding process. In essence, soft nitriding is low temperature nitrocarburizing, mainly nitriding. When nitrogen atoms of steel penetrate, a small amount of carbon atoms penetrate. Compared with ordinary gas nitriding, the hardness of the nitrided layer is lower and the brittleness is smaller, so it is called soft nitriding.

Soft nitriding methods include gas soft nitriding, liquid soft nitriding and solid soft nitriding. Gas soft nitriding is the most widely used in domestic production. Gas soft nitriding refers to low temperature nitrocarburizing in an atmosphere containing active nitrogen and carbon atoms. Common eutectonizing media include urea, formamide, ammonia and triethanolamine, which undergo thermal decomposition reaction at soft nitriding temperature to produce active nitrogen and carbon atoms. The active nitrogen and carbon atoms are absorbed by the surface of the workpiece, and penetrate into the surface of the workpiece through diffusion, so as to obtain a nitrocarburizing layer dominated by nitrogen. The gas soft nitriding temperature is usually 560~570 ℃, because the hardness of the nitriding layer is the highest at this temperature. The nitriding time is usually 2~3h, because over 3h, the nitriding layer depth increases slowly with time. Structure of soft nitriding layer: after soft nitriding, the outermost layer of steel can obtain a white layer of several microns to tens of microns ε Phase γ` Phase and nitrogenous cementite Fe3 (C, N), the secondary layer is the diffusion layer, mainly composed of γ` Phase harmony ε Phase composition. Soft nitriding has the following characteristics:

(1) The processing temperature is low, the time is short, and the workpiece deformation is small;

(2) It is not limited by the steel type, and carbon steel, low alloy steel, tool and die steel, stainless steel, cast iron and iron base powder unmetallic materials can be treated;

(3) The surface hardness of the workpiece after soft nitriding is related to the nitriding process and materials;

(4) It can significantly improve the fatigue strength, wear resistance and corrosion resistance of the workpiece, and also has the properties of anti scratch and anti seizure under dry friction conditions;

(5) Because there is no brittleness ξ Therefore, the nitriding layer is hard and has certain toughness, and is not easy to peel off.

Soft nitriding has been widely used in the treatment of wear-resistant workpieces such as molds, measuring tools, tools (such as high-speed steel tools), crankshafts, gears, cylinder liners, and mechanical structures.