Fig. 1. The microstructure of 6 samples for group 1
(a): Martensite in as-cast; (b): Pearlite+ferrite; (c): Martensite in quenching; (d): Martensite in tempering; (e): Tempered troostite+tempering

Fig. 2. The experimental setup of LIBS for the detection of D2 steel

Fig. 3. Typical LIBS spectrum of sample 1

Fig. 4. Spectral line intensities of Fe, Mn element for 6 samples

Fig. 5. Spectral line intensities of Fe, Mn elements for 6 samples versus hardness

Fig. 6. Ferrum Ionic to atomic intensity ratio versus the surface hardness of D2 steel

Fig. 7. Boltzmann plots of the studied samples

Fig. 8. Plasma excitation temperatures versus sample hardness

Fig. 9. The hardness and LIBS spectrum versus different increment of manganese samples