Research On Magneto-mechanical Effect Of Metal Magnetic Memory And Heat Treatment Quality Evaluation

Magnetic memory testing technology is a new nondestructive testing method,which based on the magneto-mechanical effect of ferromagnetic materials,it not only can detect the macro cracks of ferromagnetic materials,but also can be used to judge the stress concentration area of the material in the early stage to prevent sudden disaster.Now,the main research of magnetic memory testing is experimental research and exploratory applications of ferromagnetic material components whether exist macroscopic cracking or stress concentration,but less research on heat treatment evaluation.In this paper,first,that combined the theory of metal magnetic memory,by means of finite element analysis and the tensile test to explore the magneto-mechanical effect of ferromagnetic materials.Finally,metal magnetic memory technology was applied to the evaluation of the quality and performance of ferromagnetic materials after heat treatment.That is of great significance to promote the application of metal magnetic memory test technology in engineering.Taking Q235 for research objects,the static tensile tests were carried out on specimens with different notch characteristics(V-notch,semicircular-notch and double correlation notch).For observing stress distribution of the double correlation specimen,the finite element simulation analysis of the double correlation specimen was carried out.The influence of the internal stress on the magnetic memory signal was discussed in the geomagnetic field,then compared the experimental results with the simulation results.The tensile curve results show that the three notched specimens are occurred notched strengthening phenomenon,and the V-notch specimen notched strengthening phenomenon than the semicircular-notch specimen is obvious,and the double correlation notch specimen notched strengthening phenomenon is the most obvious.The magnetic memory curve results show that,the variation of magnetic memory signal curve of different notch specimen are consistent with the increase of the load,they both have nonlinear change of magnetic memory signal variation at stress concentration filed,and the amplitude of magnetic memory signal of V-notch is greater than the semicircular notch.The magnetic field value at the center of the double correlation notch specimen is similar to the superposition of the magnetic field value of the symmetrical two fixed points,and it is also similar to the superposition of the magnetic field value of the single notch specimen at the corresponding position.The test result is consistent with the simulation result.The stress distribution nephogram in simulation results shows that the V-notch stress concentration is larger than the semicircular notch,and there also have stress concentration phenomenon at the center of the double correlation notch.However,the gradient value k(y)of the normal component magnetic flux leakage field at the center stress concentration of the specimen does not reach the maximum value.So,it is no longer suitable for using the gradient value of the leakage magnetic field normal component to value the stress concentration.Taking 45 steel for research objects,the heat treatment experiments were carried out with different quenching methods(quenching temperature,cooling medium)and different tempering modes(tempering temperature),them the static tensile tests were carried out on different heat treatment specimens.The result show that the value of magnetic memory signal(35)B decreases with the increase of quenching temperature,decreases with the increase of cooling rate,and increases with the increase of tempering temperature.So,the quenching parameters(quenching temperature and cooling rate)and tempering parameters(tempering temperature)can evaluated by the signal characteristics of the magnetic memory(35)B value.According to the characteristic value of the magnetic memory signal(35)B,the relationship between the mechanical properties of ferromagnetic material and the magnetic memory signal after heat treatment is established,the smaller(35)B value,the greater the tensile strength,and the smaller the elongation.According to the changing characteristics of the gradient of magnetic memory signal under the action of ordered tensile stress,the heat treatment quality of the specimen that subjected to different quenching methods and different tempering methods can be evaluated,and the stress state and damage degree also can effectively evaluated.