Study On Residual Stress And Microstructure Of Ultra High Strength Steel In High Speed Milling

16Co14Ni10Cr2Mo is a kind of secondary hardened ultra-high strength steel.It is widely used in the manufacture of industrial heavy-duty equipment such as aircraft,submarine and rocket due to its high strength,toughness,heat and corrosion resistance.With the continuous improvement of new technologies and processes in the manufacturing industry,the processing efficiency and product life requirements for difficult-to-machine materials are gradually increasing.The high-strength steel 16Co14Ni10Cr2Mo has poor processing properties,and the surface quality after processing is extremely difficult to control,so the fatigue life of the parts is difficult to meet the requirements.Therefore,the research on the residual stress and microstructure of ultra-high-strength steel in high-speed milling has a very important significance and application value in ensuring the processing efficiency while improving the surface quality.In this thesis,the mechanism of the residual stress and microstructure of the cutting process is analyzed.The surface is milled to test the different processing strengths.Through the stripping corrosion and microstructural test specimen preparation,the distribution of residual stress in the depth direction of different strengths along the depth direction and the influence on the microhardness of the surface layer are analyzed,the detection of microstructure reveals the nature of the processing of ultra-high strength steel.Based on the finite element software Deform,the milling simulation model is established.The variation law of residual stress along the depth direction is studied,and the correctness of the test residual stress law is verified.The end-milling and side-milling single factor test of 16Co14Ni10Cr2Mo ultra-high strength steel is carried out to determine the influence of cutting factors on surface integrity and the variation law.The milling speed is continuously improved under the condition of stable tool.The effects of milling speed,feed per tooth and milling width on surface roughness,residual stress and microhardness is studied.The orthogonal test of low-speed and high-speed milling conditions is designed.The optimum cutting parameters of low speed and high speed were determined by range analysis,and the empirical formula model of surface roughness and cutting force is established.The results show that the ultra-high-strength steel 16Co14Ni10Cr2Mo has a small difference in the surface roughness between the side milling and the end milling when the milling amount is small.The change of the cutting speed has little effect on the roughness.As the cutting speed increases to high speed,the side milling roughness increases first,then decreases and then increases,the roughness is minimum when the cutting speed is 401.92m/min and high-speed milling is beneficial to obtain smaller surface roughness.The end-milling surface has residual compressive stress,and the compressive stress increases with the increase of milling speed.When the side milling is at low speed,the surface has residual compressive stress,but it is smaller than the compressive stress during end milling,and gradually turns to pull with the increase of milling speed.The stress continues to increase with the milling speed.At a speed of 226.08 m/min,the tensile stress reaches the limit and is no longer affected by the speed.At the speed of 401.92m/min,the residual tensile stress is the smallest.When the cutting speed is very low,the surface microhardness will increase significantly with the milling speed.After reaching the high speed state,the microhardness will increase slightly compared with the hardness of the substrate,and will no longer show regularity with speed.When the speed reaches 100.48m/min,the surface hardness gradually dec reases with the milling speed.The feed per tooth has the greatest influence on roughness and residual stress,and has little effect on microhardness.The change of the cutting width and the depth of cut at low speed hardly affects the roughness.At higher speeds,the roughness decreases slowly with the cutting width,and the cutting width has little effect on the residual stress and microhardness.Therefore,a higher cutting speed and a lower feed per tooth can be used to obtain a better milling surface.