Metal Finishing Guide Book

2012-2013

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Page 349 of 903

Fig. 4. Variation in elongation, tensile strength, and hardness with temperature. Watts bath pH 3 and 495 A/m2 (46 A/ft2). resistant to neutral and alkaline solutions, but not to most of the mineral acids. Corrosion resistance in engineering applications is controlled by optimizing nickel thickness. The thickness of the nickel is dependent on the severity of the corrosive environment. The more corrosive the service conditions the greater the thickness of nickel required. Thickness generally exceeds 0.003 in. (75 ��m) in engineering applications. Nickel Plating and Fatigue Life Thick nickel deposits applied to steel may cause significant reductions in the composite fatigue strength in cyclical stress loading. The reduction in fatigue strength is influenced by the hardness and strength of the steel and the thickness and internal stress of the deposits. Lowering the internal stress of the deposits lowers the degree of reduction in fatigue life; compressively stressed nickel deposits are beneficial. Fatigue life is enhanced by increasing the hardness and strength of the steel and by specifying the minimum deposit thickness consistent with design criteria. Shot peening the steel prior to plating helps minimize reduction in fatigue life upon cyclical stress loading. Hydrogen Embrittlement Highly stressed, high-strength steels are susceptible to hydrogen embrittlement 342

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