Research On The Effect Of Cryogenic Treatment Process On Residual Stress

Nowadays,it is well-known that the residual stress state of the mechanical parts could have extremely great affect at material mechanical properties like strength,fatigue,dimensional stability,corrosion resistance and so on.Thus,the performance and life of the parts are affected.Because the residual stress of the material is the result of the various effects of the stresses,its state is easily affected by external environmental factors.Therefore,it is of great significance to study the regulation technology of the residual stress of the material.Based on whether or not phase transformation occurs during the cryogenic treatment of materials,we selected M42 high speed steel and 2024 aluminum alloy as our research object.By the means of numerical simulation and experimental validation,the effect of cryogenic treatment on the residual stress of materials would be studied.Based on the simulation results,we utilized the orthogonal test method considering the cryogenic process parameters such as cryogenic temperature,holding time,times of cryogenic treatment and cooling rate to arrange the test scheme,whose target is to quest for the importance of each factors on the residual stress state of the material.Finally,a series of heat treatment process optimization parameter design scheme would be proposed,in which we selected the residual stress state after HT as the characteristic quantity.The paper conducted research on the following contents and conclusions:(1)Numerical simulation of coupling temperature field and stress field in heat treatment process.A thermal elasto-plastic finite element analysis model was established to simulate the HT process of M42 high speed steel and 2024 aluminum alloy.Firstly,we used the thermal analysis software to interpolate the relevant physical properties of the material;then operate the numerical simulation software ABAQUS 6.14 to perform thermodynamic analysis through sequential coupling and direct thermal coupling;high speed steel and 2024 aluminum alloy;subsequently,according to the simulation results: the deep-stressed M42 high-speed steel adjusts the tensile stress state of the quenched material surface to the compressive stress state.After the cryogenic treatment,the material distributes along the thickness direction as the “inverted V” distribution;after the solid solution and quenching treatment of 2024 aluminum alloy thick plate,residual compressive stress will remain on the surface,and an “inverted V” stress distribution will appear in the thickness direction.Through the cryogenic treatment,the residual stress can be largely eliminated,and the overall stress has been released.(2)Experimental study on effect of cryogenic treatment on residual stress of M42 high speed steel.The quenching process of M42 high speed steel specimens shall be uniformly treated(i.e.quenched in grade to 1200? plus hold for 2 hours),and then we selected the cryogenic temperature,holding time and times of cryogenic treatment as the independent variables,and utilized the orthogonal table L9(33)to determine the test scheme.The results showed that under certain residual compressive stress condition the best combination of cryogenic process parameters could be set as following :the cryogenic temperature of-150 ?,holding time of 1 hour and 2 times of cryogenic treatment.At the same time,the residual stress distribution along the thickness direction of the material after cryogenic treatment was obtained as “M-type distribution” by electrochemical stripping method,and the overall stress value decreased.(3)Experimental study on effect of cryogenic treatment on residual stress of2024 aluminum alloy.The HT process test scheme of 2024 aluminum alloy is as following: the samples shall be uniformly heat-treated to 495? and hold for 2 hours,and the water quench temperature was set as 25?.Next we selected the cryogenic temperature,holding time and cooling rate as the independent variables,and utilized the orthogonal table L9(33)to determine the test scheme.The results showed that cryogenic treatment can eliminate approximately 60% residual compressive stress after quenching of aluminum alloys,and also could be concluded that under certain residual compressive stress condition the best combination of cryogenic process parameters could be set as following :the cryogenic temperature of-150 ?,holding time of 1 hour and 2 degree per minute of cooling rate.(4)From the microscopic point of view,the change process of the internal structure of the material in cryogenic treatment would be analyzed.The martensitic transformation occurs in high-speed steel materials.At the same time,a large number of dislocations cause carbon atoms to be pinned near the dislocation line,and fine carbides are precipitated to uniformly distribute the internal structure,so that the internal stress of the material is released;eutectic transformation occurs inside the aluminum alloy material,and its volume contraction and grain turning effect will have an important influence on the stress distribution.