The Development Of New Steel Non-toxic Blackening Corrosion Resistance

The blackening solution of traditional iron and steel materials has limitations of high toxicity and low stability. The resulting blackening film has poor corrosion resistance. And the traditional blackening processes have the defects of high energy consumption and complex processes. In order to overcome the above mentioned, corrosion resistance experiments and morphology analysis of blackening film of A3 steel sheet (40mm×25mm×1mm) were carried out and the optimal formula and process conditions of high temperature nontoxic blackening solution, room temperature nontoxic blackening solution and room temperature nontoxic "4 in 1" blackening solution were investigated and determined, respectively.Based on the previous research works, basic compositions of blackening solution have been screened out and suitable experimental conditions were discovered from single factor experiments. The optimum formula and process were obtained from orthogonal test and verification experiments.The experimental results show that the optimal formula of high temperature nontoxic blackening solution non-toxic blackening solution was determined: aluminum chloride 8.5g/L, citric acid 14g/L, sodium m-nitrobenzene sulfonate 9g/L, zinc dihydrogen phosphate 9g/L, sodium 3g/L and the optimal process conditions were: temperature 70℃, pH value of 4, the processing time 20 minutes. The optimal formula of room temperature nontoxic blackening solution was determined: copper sulfate 3g/L, zinc dihydrogen phosphate 6g/L, citric acid 3g/L, sodium metavanadate 2g/L, sodium nitrate 3g/L and its optimal process conditions were: room temperature (about 20℃), pH value of 4, the processing time 14 minutes. The optimal formula of room temperature nontoxic "4 in 1" blackening solution was determined: Sodium lauryl polyoxyethylene ether sulfate (AES) 5g/L, sodium lauryl benzenesulfate 5g/L alcohol 7.5g/L, phosphoric acid 310ml/L, zinc oxide 14g/L, zinc nitrate 26g/L, potassium chlorate g/L, sodium fluoride 8g/L, nickel nitrate 6g/L, copper nitrate 0.03 g/L and its process conditions were: the steel surface were uniformly smeared with the blackening solution by means of wiping or short time dipping at room temperature.Three experiments were performed to demonstrate the performance of the blackening film, respectively. The corrosion resistance of blackening film has good reliability through the test of copper sulfate intravenous drip. The results of SEM analysis show that the blackening film was uniform and compact. Moreover, the results of Tafel polarization indicate that the blackening film can effectively improve the corrosion potential of steel A3 and then have higher corrosion resistance. These experimental results confirmed that new non-toxic steel blackening solution can fully meet the steel processing requirement.The experimental research provided an effective method to investigate and develop metal blackening solution.