The characteristics of blackening of unlocking bolt

What are the advantages of stainless steel bolts after blackening treatment? Hongsheng screw standard small make up to give you a careful analysis.

Appearance characteristics

Austenitic stainless steel screw after blackening the appearance of access characteristics can be seen that the surface is evenly plated with a black film layer. In order to investigate the uniformity of the film layer, the batch production was carried out specially, and the results proved that there was no color noise between the screws inside each screw, which had good uniformity.

After blackening the austenitic stainless steel screw, it can be seen that the outermost layer is black oxide layer, the inner layer is nitriding layer, the white area is the matrix, and the total depth of the layer is 28 m. The wear resistance and hardness of the film layer are determined by the nitride layer. Because the nitride layer has certain cavity and porosity, and the substrate is chrome-poor after nitride, the corrosion resistance is reduced. After nitriding, oxidation treatment was carried out. Due to the oxidation treatment, a black FeO film with anti-salt-alkali corrosion was formed on the surface of the nitriding layer, and this oxide film was filled with the porosity and cavity after nitriding, resulting in the surface enrichment of oxygen, which greatly improved the corrosion resistance of the surface.

The surface hardness

The surface hardness of austenitic stainless steel screw after blackening is shown in table 1 (press load 51g) (slightly). The hardness decreases gradually along the depth of the permeable layer, which corresponds to the concentration gradient distribution of nitrogen atoms in the permeable layer.

The corrosion resistance

After the austenitic stainless steel screws were blackened by nitriding, the neutral salt spray test was carried out on the neutral salt spray test machine manufactured in west Germany. The test specifications refer to iso3768-1976. The intermittent spray method was adopted. 24h is one cycle, and five cycles are performed. The results showed that the surface of the screw was intact without corrosion after five cycles of test.

All kinds of parts after stainless steel blackening passivation, with higher hardness, good alkali resistance, wear resistance, acid resistance, and color uniform and beautiful. It has been put into batch production in fastener industry in guangdong and achieved good results. In addition, it has been successfully applied in plastic mould, die casting mould, hydraulic parts, mineral body and other parts. Therefore, it has a broad market prospect and good economic and social benefits.