The difference between bluing and blackening

The surface blackening treatment of metal bluing steel products is also called bluing The commonly used methods of blackening treatment are the traditional basic heating blackening and the later room temperature blackening But the effect of blackening at room temperature on low carbon steel is not good A3 steel blackened better with alkali Alkaline blackening is subdivided, and there is another blackening and two blackening difference The main components of hair black liquor are sodium hydroxide and sodium nitrite The tolerance of the temperature required for blackening is relatively large A good surface can be obtained between 135 ° C and 155 ° C, but it only takes a little time In practical operation, it is necessary to pay attention to the quality of rust removal and oil removal before blackening, as well as passivation and oil immersion after blackening The quality of blackening often changes due to these processes The metal "bluing" solution adopts alkaline oxidation or acid oxidation method to form a layer of oxide film on the metal surface to prevent the metal surface from corrosion This treatment process is called "bluing" The oxide film formed on the surface of ferrous metal after "bluing" treatment is mainly composed of ferric oxide on the outer layer and ferrous oxide on the inner layer 1、 Basic oxidation "bluing" solution 1 Formula: sodium nitrate 50-100g, sodium hydroxide 600-700g, sodium nitrite 100-200g, water 1000g 2 Preparation method: after measuring according to the formula, under the stirring condition, add each material in turn, dissolve it, and mix evenly 3 Notes: (1) the metal surface must be cleaned and dried before "hair basket" treatment (2) the "bluing" treatment conditions of metal devices are related to the carbon content in the metal The "bluing" solution temperature and the treatment time of metal devices can refer to the following table Carbon content in metal% working temperature (℃) treatment time (min) begins to terminate > 0.7135-13714310-300.5-0.7135-14015030-50 < 0.4142-145153-15540-60 alloy steel 142-145153-15560-90 (3) analyze the content of sodium nitrate, sodium nitrite and sodium hydroxide in the solution on a regular basis every other week or so, so as to supplement relevant components in time Generally, all solutions shall be replaced after half a year of use (4) after metal "bluing" treatment, it is better to rinse it with hot soapy water for several minutes, and then rinse it with cold water Then wash with hot water and blow 2、 Acid oxidation method "bluing" solution 1 Formula: phosphoric acid 3-10 g calcium nitrate 80-100 g manganese peroxide 10-15 g water 1000 g 2 Preparation method: after measuring according to the formula, under constant stirring conditions, successively add phosphoric acid, manganese peroxide and calcium nitrate into it, dissolve and mix evenly 3 Note: (1) the metal device can be "bluish" after being washed and dried (2) the protective film obtained by this method is black, and its main component is composed of calcium phosphate and iron oxide Its corrosion resistance and mechanical strength are higher than those obtained by the alkaline oxidation method 4 The working temperature of "bluing" is 100 ℃, and the processing time is 40-45 minutes In the treatment of carbon steel, the content of phosphoric acid in the solution is controlled at 3-5g / L; in the treatment of alloy steel or cast steel, the content of phosphoric acid is controlled at 5-10g / L It should be noted that the content of phosphoric acid in the solution should be analyzed regularly 5 The cleaning method of metal devices after "bluing" treatment is the same as above.