Experimental Study On Milling Surface Integrity Of Nuclear Power Cast Steel

With the dramatically increased demand of energy, nuclear power hasbecome an important energy industry. Nuclear power units are huge, usuallyusing the cast alloy steels, improve the accuracy and surface roughness of thecast steel and coating the machined parts with a layer of stainless, that theupper and lower half seal combination does not penetrate, can meet the needof application. Nuclear material working condition is quite wet, the positionswhere the steam flow direction changes and steam leakage bind surfaces areeasy to suffer from severe water erosion. The corrosion pits under thecommon action of stress and corrosion grow up to cracks, culminating in theformation of stress corrosion damage.Nuclear material failure will lead veryserious consequences, not only affects the safety of nuclear power plants, buteven affect the public and environmental safety, endangering the sustainabledevelopment of the national economy. So the study of cast steel millingsurface quality of nuclear power is very important.The studied materials here are G17CrMoV5-10(low alloy steel) andGX4CrNi13-4(martensitic stainless steel) of one million kilowatts nuclearpower unit. The coating cyclone blade GC1025 and IC908 have been selectedas the milling experiment tools. Orthogonal test and single factor testmethods are used. Choose cutting speed, feed rate, cutting depth and cuttingwidth, cutting tool nose radius and flank wear as the changing parameters,with the surface roughness (Ra and Rz) as the test target, surface roughnessof the feed direction and vertical direction of feed are studied, and roughnessRz and Ra values in the two directions are basically the same . Theoptimal cutting parameters were obtained, GC1025 blade can get a smallersurface rough, the Rz value is 0.792μm. As for GX4CrNi13-4, the largestinfluencing factors of roughness are cutting speed and feed rate. The tip arcradius Rεof 1.2mm can get minimum roughness.At the same time, the effectsof materials heat treatment on surface properties are analyzed.In addition, machining surface hardening, microstructure changes andresidual stress are selected as three main indicators of cast steel millingsurface metamorphic layer. By changing the cutting speed and feed rate, theprocessing of surface degenerating layer is studied. Hardening is minimum in feed rate 0.1mm/r, with the feed increasing, the metamorphic layer becomescritical, and then gradually disappears; the maximum compressive residualstress in the depth direction is increased.At the same time different radius ofthe cutter tip and tool wear effects is also analyzed. For GX4CrNi13-4, at adistance from surface about 28μm, the maximum compressive residual stressup to 432MPa, the affected depth is around 100μm.This paper obtained the optimized cutting parameters and toolparameters which meets the need of the surface quality, improve workreliability, efficiency and the processing cost is reduced too. And providereference for similar materials'processing.