Fig. 1. Metallographic organization images with 100 times magnification of samples with different grain sizes
(a): at level 9.5; (b): at level 10.0; (c): at level 10.5;(d): at level 11.0; (e): at level 11.5

Fig. 2. A schematic diagram of LIBS system

Fig. 3. LIBS spectra of Fe, Cr, Mo and Co of 5 samples
(a): the wavelength range of 402~406 nm; (b): the wavelength range of 423~427 nm;(c): the wavelength range of 384~388 nm; (d): the wavelength range of 239~243 nm

Fig. 4. Modelling results of PLS-DA based on full band spectral intensities pretreated by SNN
(a): Training set; (b): Prediction set

Fig. 5. CARS wavelength screening process

Fig. 6. Wavelength screening process of SPA

Fig. 7. CARS-SPA wavelength screening process