The Research Of Acoustic Emission Signals Characteristic From Martensitic Transformation Process In45Steel

Martensite is a kind of quenching structure, which can make steel harden andenhanced. It is required after cooling rapidly when it is heated to a certain temperature.It is the most important stage from austenitic to martensite transformation, becausethis is a technology key to acquire hardened steel. So the research on the materialmartensite transformation process is of great significance. Acoustic emissiontechnology is a kind of dynamic testing technology, which is widely used in variousindustrial fields. This paper is mainly based on45steel, and its martensitetransformation process using acoustic emission technology was deeply discussed.First of all, the theory calculation method of thermodynamic simulation wasanalyzed. Considering the influence from latent heat of phase change to thedistribution of temperature field, we choose the heat transfer equation of transienttemperature field which based on equivalent heat capacity method to simulate. Andset up the2-D finite element model of the axis symmetric figure, getting thesimulation data under continuous cooling from different quenching mediums. Second,in this paper, the martensite transformation process under different quenchingmediums was studied with acoustic emission tests, and acquired the characteristics ofacoustic emission parameters, in the same time, got the start time point of martensitetransformation accurately. On the basis of statistical probability learning, the acousticemission signals extracted from test were further integrated. Using the theoryknowledge of the Gibbs probability entropy, the signals were quantized in timedomain to obtain the entropy curve of quenching process. Combined with thecharacteristic entropy value extracted from wavelet spectrum entropy, the signals werequantized in frequency domain, consequently realized the comprehensive descriptionand extraction to the system characteristics and made the martensite transformationprocess more objective and comprehensive. Based on the dynamics theory oftemperature-changed martensite transformation, this paper put forward a new methodto characterize the conversion rate of martensite volume fraction with the acousticemission RMS, and used the curve of acoustic emission characteristic parametersduring transformation process to analysis the dynamic characteristics and establisheda formula to calculate the conversion rate, realized the quantitative analysis for martensite volume fraction.