| Q245R steel is a low-alloy high-strength steel widely used in the petrochemical industry and pressure vessel manufacturing industry.It has the advantages of high strength,good plasticity and corrosion resistance.In engineering applications,most pressure vessels and other mechanical equipment are under high pressure,high temperature,high load and other environments,and damage will inevitably occur.The microstructure of the material,especially the grain size,is very sensitive to the performance characteristics of the material.At present,the conventional nondestructive testing methods for in-service equipment are not accurate enough for the analysis and testing of some polycrystalline materials.In order to ensure that the microstructure of the material is studied in time without affecting the normal operation of the equipment in service,scholars at home and abroad have found that nonlinear ultrasound technology can be used as an effective research method for non-destructive testing of equipment in service.This article takes Q245 R steel as the research object and uses nonlinear ultrasonic detection technology to perform nonlinear ultrasonic characteristics experiments on Q245 R steel specimens with different grain sizes.By analyzing the nonlinear ultrasonic characteristic parameters obtained during the experiment,the nonlinear characteristics are established The quantitative relationship between the parameters and the grain size of the material,and the establishment of a quantitative formula to achieve the purpose of using nonlinear ultrasonic characteristics to characterize the grain size of the material.At the same time,the Vickers hardness test was carried out on the Q245 R steel specimens with different grain sizes,and the Vickers hardness was quantitatively analyzed with the nonlinear characteristicparameters as the characteristic parameters.Grain size levels and mechanical properties provide an effective method.The main research contents are as follows::(1)Introduced the research status of nonlinear ultrasound technology by scholars at home and abroad.In-depth study of the process and principle of using RITEC RAM-5000 SNAP instrument to carry out nonlinear ultrasonic experiments on materials.The effects of the material grain level on the mechanical properties are analyzed.(2)Considering that the research object of this subject is Q245 R steel materials with different grain sizes,in order to achieve the purpose of comparative analysis,a nonlinear ultrasonic experiment is performed on the Q245 R steel specimen in the initial state,and the nonlinear ultrasonic characteristics of the Q245 R steel specimen are calculated.(3)Combining the knowledge of heat treatment of metal materials and the theoretical basis of metallurgical method for observing the grain size,four groups of Q245 R steel specimens with different grain sizes are obtained through heat treatment,relying on metallurgical microscope to observe the grain size of each group of materials,Use the area method to calculate the grain size of each group of test pieces.(4)Non-linear ultrasonic characteristic experiments were carried out on four groups of Q245 R steel specimens.By comparing the nonlinear ultrasonic characteristic parameters in the initial state,it was found that the second-order nonlinear coefficient ? and attenuation coefficient ? of Q245 R steel with the material grain size Changes produce different trends.The two sets of experimental data show that as the grain size of the material increases,the attenuation coefficient increases first.After the grain size reaches 5,the attenuation coefficient begins to decrease;as the grain size increases,the second-order non-linear The linear coefficient gradually decreases.At the same time,it is found that there is no obvious relationship between the sound speed of the material and the level of grain size.(5)Select the attenuation coefficient ? and the second-order nonlinear coefficient ? as the characteristic parameters,analyze the relationship between the two parameters with the grain size of the material,and establish the quantitativerelationship formula with Q245 R steel grain size.(6)Quantitative analysis of the Vickers hardness HV of Q245 R steel with different grain sizes measured by the Vickers hardness tester to establish a quantitative relationship formula between the Vickers hardness HV and the material grain size level.Combined with the second-order nonlinear coefficient formula,the second-order nonlinear coefficient ? is further used to characterize the material Vickers hardness HV,which provide an effective characterization method for non-linear ultrasonic characteristics to judge the grain size level and mechanical properties of Q245 R steel materials. |
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