How can black appear on the gas soft nitriding surface?

1. Soft nitriding: scientific name' nitrocarburizing', which translated the liquid method of the Soviet Union (Russia) into' low temperature cyanidation' in the early days. At present, gas method, non-toxic (low) liquid method and ion method are popular in China. Nitrogen is the main element infiltrating into the steel surface, and carbon is added at the same time. The addition of carbon can improve the formation and properties of the surface compound layer (white bright layer) to some extent, even obviously. What needs to be emphasized here is that the difference from nitriding is that nitrocarburizing focuses on obtaining a certain thickness (generally 10 ~ 20μm, but it is also required to be more than 20μm. At present, the thickness of carbon steel that has been achieved in the laboratory is said to be 1 10μm), with high hardness, little brittleness and no or little looseness. Nitrocarburizing is widely used, covering almost all commonly used steel grades and cast iron. Taking carbon steel as an example, according to the temperature of nitrocarburizing treatment, it can be divided into ferritic nitrocarburizing (520 ~ 590℃) and austenitic nitrocarburizing (600 ~ 720℃), and the treatment time is generally 2 ~ 6 hours. The white layer obtained by the former is iron-nitrogen compound, and the latter has a layer under the iron-nitrogen compound layer after rapid cooling. In order to enhance and improve the performance of white bright layer, Chinese heat treatment workers have added boron, oxygen, sulfur, rare earth and other elements separately or in combination while nitriding, and have done a lot of work, most of which have achieved visible results to varying degrees. This kind of exploration is still in the ascendant, and it is one of the hot spots pursued by heat treatment workers.

2.' Soft nitriding' means not that the hardness obtained is lower than the so-called' hard nitriding', but that it is simple, convenient and low in cost.

Nitriding treatment technology Nitriding, as an important treatment technology in heat treatment, has many forms.

Each process corresponds to different performance characteristics. I hope everyone can talk about their experiences and views here and improve together. There are six kinds of nitriding treatments commonly used in our unit, including compound nitriding technology. Composite nitriding -Qpq

This nitriding treatment is characterized by high wear resistance and high oxidation resistance. It mainly overcomes friction and wear, and has strong bite resistance, which is close to the effect after adding sulfur. Concept: (Soft) nitriding is the process of nitrogen atoms infiltrating into the steel surface, aiming at improving the surface hardness and wear resistance, as well as fatigue strength and corrosion resistance.

It uses ammonia gas or organic liquid containing nitrogen atoms to decompose active nitrogen atoms in the heating process, which is absorbed by steel, forms a nitride layer on its surface and diffuses to the center at the same time.

Nitriding is usually carried out with special equipment or well carbonizer. Suitable for all kinds of high-speed transmission precision gears, machine tool spindles (such as boring bars and grinder spindles), high-speed diesel engine crankshafts, valves, tools, etc.

The technological route of nitriding workpiece: forging-annealing-rough machining-tempering-finishing-stress relieving-rough grinding-nitriding-fine grinding or grinding (generally used directly after nitriding).

Because the nitrided layer is thin and brittle, it needs a high-strength core structure, so it needs to be tempered first to obtain tempered sorbite, improve the mechanical properties of the core and ensure the quality of the nitrided layer.

After nitriding, steel has high surface hardness and wear resistance without quenching. Nitriding treatment has low temperature and small deformation, which is much smaller than carburizing and induction surface quenching.

Soft nitriding of steel: also known as nitrocarburizing; Nitrocarburizing is the process of simultaneously infiltrating carbon and nitrogen into the steel surface, also known as cyanidation. At present, gas nitrocarburizing (gas soft nitriding) is widely used. Its main purpose is to improve the hardness, wear resistance, fatigue strength and resistance to common defects of occlusal nitriding (soft nitriding) of steel.