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According to a variety of different heat-treated alloy steel transition phase structure organizational characteristics of the product, as well as the propagation of ultrasonic waves in which the use of ultrasonic velocity, attenuation coefficient, and the relative power spectral analysis of three methods, the three steel (40Cr, 38CrMoAl and GCr15SiMn) Different heat treatment (normalizing, quenching / annealing, quenching and tempering Ji quenching tempering) transformation products were ultrasound microstructure characterization. Compared three characterization methods to distinguish between different tissue sensitivity and characteristics, and proposed alloy microstructure ultrasonic nondestructive characterization methods should follow a multi, multi-parameter principle. Using the TI-40N-precision ultrasonic thickness gauge, ultrasonic studies on different kinds of steel, heat-treated transformation products in different ultrasonic velocity C 1 : 38CrMoAl steel hardened tissue C 1 min, after quenching 200 ℃ ~ 650 ℃ tempering treatment within the range, with the tempering temperature, C 1 gradually increased, HRC and C 1 good correlation between; normalizing organization C 1 between tempering after quenching and tempering in the product organization C 1 between. 40Cr steels of different microstructure C 1 38CrMoAl steel with similar variation. GCr15SiMn steel quenching and tempering organization C 1 is much larger than normalizing, annealing and quenching and tempering organization C 1 ; normalizing, annealing and quenching and tempering Organization The C 1 close. The elastic modulus of different microstructures differences may be the main cause of the experimental results. Ensure the specimen shape, size, surface finish, system parameters, the pressure applied to the probe and test conditions coupling layer thickness of the same circumstances, the use of cylindrical rods measuring the attenuation coefficient, respectively, and comparing said determined type of treatment sample relative attenuation coefficient changes, the experimental results obtained are: Ji 38CrMoAl for 40Cr steel, α tempering <α_ (quenching) <α tempering < α normalizing ; For GCr15SiMn steel, α tempering <α annealing <α tempering <α normalizing ; and as the frequency increases, the attenuation coefficient showed an increasing trend. Studies show that, by comparing the cylinder surface as measured relative attenuation coefficient, capable of multi-phase structure having a larger size for ultrasonic characterization of steel specimens. This method overcomes the absolute determination of the attenuation coefficient of the most demanding on the experimental conditions, less difficult to achieve, so that ultrasonic characterization engineering conditions closer, more practical value. The use of a narrowband signal spectrum analysis techniques highlight the advantages of high sensitivity, select a center frequency of 1MHz narrowband ultrasonic signals, different heat treatments on the above samples were ultrasonic power spectrum analysis, found that different heat-treated product in the main frequency power spectrum, peak characteristics (amplitude, quantity, distribution), etc., there are different degrees of difference. Thus suggested that ultrasound can be used for narrowband power spectrum technique heterogeneous structure steel ultrasonic characterization of the microstructure. Ultrasonic velocity, attenuation coefficient, and the relative power spectral analysis of three methods independently; Meanwhile, three methods have different sensitivities to distinguish between different organizations, the experimental results can complement each other. 38CrMoAl steel quenching and quenching and tempering organization, with main frequency sound velocity method and comparative law are difficult to distinguish, the best method is to compare power spectral peak characteristics (amplitude, quantity, distribution). As for the use of comparative spectral peak characteristics (amplitude, quantity, distribution) indistinguishable GCr15SiMn steel annealing and normalizing organization, you can take advantage of the relative attenuation coefficient method for comparison. Three methods of analysis of the findings that, for a variety of alloy phase structure of these materials should be integrated use of a variety of methods to extract multiple parameters, from different angles contrast characterization in order to obtain comprehensive and reliable conclusions.
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