Research On Measurement Methods Of Retained Austenite In Magnetic Metal Materials

The physical and mechanical properties of metallic materials are affected by residual austenite,such as hardness,wear resistance and contact fatigue.When residual austenite under the action of external stress and friction,phase change would be occurred,serious accidents such as material failure may be caused.In order to ensure the quality of metal materials and understand the service state of metal materials,the residual austenite content in metal materials should be measured.As a promising non-contact measurement method,magnetic measurement has the advantages of low cost,short cycle and no damage to the material.In this paper,based on the analysis of the residual austenite content measured by the magnetic method at China and abroad,the measurement of residual austenite content of the metal in the AC magnetization method is studied,mainly include:1.A new magnetic sensor of nine foots structure is designed for measuring residual austenite content.Moreover,the finite element electromagnetic simulation software ANSYS Maxwell is used to model the nine foots magnetic sensor,studied the effect of magnetic sensor structure parameters,coil parameters,excitation parameters and air gap on the nine foots magnetic sensor output signal and magnetic properties.Finally,based on the principle of optimization,the parameters of nine foots magnetic sensor are determined2.Based on the principle of magnetic measurement,the relationship between the content of retained austenite and the AC magnetic permeability is deduced.Moreover,by introducing the concept of the effective value of AC magnetic permeability of the material,the calculation model of the effective value of the residual austenite content of the metal material and the magnetic permeability of the material in the nine leg magnetic sensor is established.The theoretical basis is provided for measuring the residual austenite content of metal materials in the process of AC magnetization.3.Based on the calculation model of residual austenite content in metal material,the residual austenite content measurement system of metal material was designed and fabricated.The influence of the temperature variation of the nine foots magnetic sensor and the residual magnetization of the sample on the measurement results of the system is studied.The results show that the temperature change and the residual magnetization of the sample have a significant influence on the measurement results.Therefore,in order to ensure the accuracy of the measurement results and the repeatability of the system,it is necessary to carry out the demagnetization operation before the measurement of the residual austenite content of the material and the preheating operation of the magnetic sensor with no less than 150s.4.In this paper,the measurement of residual austenite content in low carbon steel Q325 was carried out by the measurement system designed in this paper.The measurement results of the system were compared with the results of X ray diffractometer(standard method).The results show that the system designed in this paper and X ray diffractometer have a high consistency,the correctness of the calculation model of residual austenite in the process of AC magnetization and the validity of the measurement system were proved.