Study On High Temperature Manganese Phosphating Of Alloy Steel 25Cr2Ni4W And 30CrNi3

As two kinds of high performance alloy materials, 30CrNi3 and 25Cr2Ni4W are widely used to produce the machine parts and other parts. However, owing to many alloy elements, they are difficult to be phosphated which seriously affects their application in actual production. Thus, this paper took 30CrNi3 and 25Cr2Ni4W as the experimental objects, and made a large amount of experimental researches on the phosphate orthogonal test of manganese phosphating under high temperature, the relationship between the properties of the phosphating coating and the phosphating conditions. The phosphating mechanism of alloy steel 30CrNi3 and 25Cr2Ni4W are theoretically analyzed and discussed, and the optimum phosphating parameter range of 30CrNi3 and 25Cr2Ni4W had been proposed, which had been recommended to be applied to actual production.By selecting the five factors of total acidity, the ratio of total acidity to free acidity, ferrous ion concentration, active time and phosphate time, we choose the orthogonal tables L16(45) and L27(313) for alloy steel 30CrNi3 and 25Cr2Ni4W respectively to investigate the influence of the phosphating parameters upon coating weight and anticorrosion property. It is found that: (1) For alloy steel 30CrNi3:â‘ The factors which influenced the coating weight were listed by the importance as follows: total acidity, phosphate time, active time, the ratio of total acidity to free acidity and ferrous ion concentration. The parameters which can get the heaviest coating are: total acidity 140 point, the ratio of total acidity to free acidity 4.9, ferrous ion concentration 1g/L, active time 40s, phosphating time 20min.â‘¡The factors which influenced the anticorrosion property were listed by the importance as follows: phosphate time, the ratio of total acidity to free acidity, ferrous ion concentration, total acidity and active time. The parameters which can get the best anticorrosion property are: total acidity 100 point, the ratio of total acidity to free acidity 6.3, ferrous ion concentration 0.5g/L, active time 40s, phosphating time 15min. (2) For alloy steel 25Cr2Ni4W:â‘ The factors which influenced the coating weight were listed by the importance as follows: total acidity, the ratio of total acidity to free acidity, ferrous ion concentration, phosphate time and active time,. The parameters which can get the heaviest coating are: total acidity 130 point, the ratio of total acidity to free acidity 7.0, ferrous ion concentration 1.8g/L, active time 40s, phosphating time 20min.â‘¡The factors which influenced the anticorrosion property were listed by the importance as follows: phosphate time, the ratio of total acidity to free acidity, total acidity, active time and ferrous ion concentration. The parameters which can get the best anticorrosion property are: total acidity 110 point, the ratio of total acidity to free acidity 60, ferrous ion concentration 0.6g/L, active time 20s, phosphating time 20min.According to the optimum phosphating parameters of the orthogonal experiments and analysis from experiments, the optimum phosphating parameters of alloy steels 30CrNi3 and 25Cr2Ni4W were extended to a certain range, and experiments were carried out to verify the phosphating range, finally the phosphating parameter range were identified, using these technology, the anticorrosion property of phosphating coating which tested by neutral salt spray test could reach more than 1.5h.This paper employed SEM to observe the phosphating coating growth process. The coating growth process was divided into three main stages: corrosion of the substrate, creation and growth of phosphate crystal nucleus and thickening of phosphate coating. Then the mechanism of phosphatization was discussed.