Electroless Nickel Plating Spring Steel Mechanical Properties

Electroless plating has the advantages of easy operation and simple technology, the coating has uniform thickness, higher hardness, better wear-resistance and corrosion resistance, therefore, it is applied in many areas. In this paper, the effects of electroless nickel plating on hydrogen brittleness, internal stress and fatigue property were studied using 70 spring steel as base material. By means of slowly-tensile tests, the hydrogen brittleness of specimens was measured; By applying the thin film flexural method, the Internal stress of electroless nickel plating was measured; By three-points bending comparative fatigue tests, the fatigue property of specimens was obtained. Combining with micro-morphology observing of break, the main and valuable conclusions are as follows: 1. The specimens show hydrogen brittleness because of intermingle-hydrogen; The heat-treatment is a method of eliminating hydrogen brittleness. After deposition, the specimens must be heat-treated immediately. No matter dehydrogenization heat-treatment or crystallization heat-treatment , the hydrogen brittleness both can be weakened. There is no evident difference on the results of slowly-stretching tests between the specimens before and after acid-washing . 2. When the pH value of plating solution in 3.8～4.1 and 4.4～4.6,the internal stress of coating is compression stress, but when the pH value in 4.8～5.1,it turn tension stress; By the heat treatment at 200℃×1h, the internal stress of coating at the pH value in 3.8～4.1 and 4.4～4.6 is compression stress also, but the numerical value are decrease, and the internal stress of coating at the pH value in 4.8～5.1 is tension stress , but the numerical value is decrease, too. By the heat treatments at 400℃×1h and 600℃×1h, the internal stress of coating at the three pH values are tension stress, further more the numerical value are increase evidently. 3. The fatigue life-span of base materials is the longest, and the fatigue life-span of plated specimens is shorter comparing with that of the base materials, which is caused by hydrogen brittleness; The fatigue life-spans of specimens after dehydrogenization heat treatment and crystallization heat treatment are all decreased observably, which is caused by the tension internal stress.