Strengthening of the NKV Type Centrifugal Pump’s Shaft by Chemical-Thermocycling Treatment

2021 
The paper is devoted to studying the process of nitrocementation with cycling heating compared to nitrocementation with isothermal heating. The purpose of thermocycling nitrocementation is to grind the base’s structure and the surface layer of steel type AISI 5140, which produces the centrifugal pump’s shaft. The metallographic analysis showed that the grain score after isothermal and after thermocycling nitrocementation varies from № 5–6 to № 9 in the core and № 5–6 to № 10 in the diffusion layer (respectively). The thickness of the protective layer after thermocycling nitrocementation is 1.50 more than isothermal nitrocementation, which indicates a positive effect of thermal cycling on the saturation rate of the steel matrix. The depth of the protective layer obtained during nitrocementation and surface hardness are the criteria for assessing the shaft’s serviceability. It is established that thermocycling nitrocementation in comparison with isothermal leads to increase cavitation resistance by 0.6–1.5 times. The use of chemical-thermocycling treatment leads to reduced time, grinding of grain, and improved mechanical properties of constructional steel.
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