Study on the evaluation of the aging grade for the industrial heat-resistant steel by laser-induced breakdown spectroscopy

Heat-resistant steel is widely used in various industrial pressure-bearing equipment, and the change of metallographic structure and properties of steel is of great importance for the equipment function and safety. In this work, laser-induced breakdown spectroscopy (LIBS) was applied to estimate the aging grade of industrial heat-resistant steel. Firstly, the laser spectroscopy tomography was proposed to obtain the representative spectra from the metal matrix of industrial pipe and the effects of surface oxides on the matrix plasma parameters were studied and compared. The results indicated that the correlation analysis of emission intensities along the radial direction can accurately identify the boundary between surface oxide and matrix. The presence of surface oxides would decrease the plasma temperature and increase the electron density. Secondly, multiple scattering correction (MSC) was applied to correct the interference of surface oxides, and K-fold-support vector machine-recursive feature elimination (K-SVM-RFE) was exploited to select the optimal spectral feature subset. Finally, the estimation of aging grade model was established based on support vector machine (SVM) and the optimal feature subsets. The estimation accuracy of validation set after spectral correction was improved from 80.56 % to 84.72 %, and the model performed similar capability on the industrial pipe and the corresponding samples with mechanical polishing eliminate surface oxides. This work demonstrates that LIBS would be well-suited for fast safety assessment in industrial field.