Fig. 1. Hardness detection points using QNESS 10A high-precision micro-hardness tester

Fig. 2. Schematic diagram of LIBS system

Fig. 3. Relationships between the spectral line strengths of matrix elements and alloy elements and the hardness of 8 samples

Fig. 4. Correlations between the strength ratio of ion lines to atomic lines of matrix elements and alloying elements and sample hardness
(a): Correlation between the strength ratio of Fe Ⅱ 238.203 8 nm to Fe Ⅰ 404.581 3 nm and sample hardness; (b): Correlation between the strength ratio of Cr Ⅱ 276.258 nm to Cr Ⅰ 425.433 1 nm and sample hardness

Fig. 5. Correlation between the spectral line strength ratio of alloying elements to matrix elements and sample hardness
(a): Correlation between the strength ratio of Mo Ⅰ 313.259 4 nm to Fe Ⅰ 358.119 3 nm and sample hardness; (b): Correlation between the strength ratio of W Ⅰ 283.138 nm to Fe Ⅰ 358.119 3 nm and sample hardness

Fig. 6. The prediction results of the model established using the full-band spectral line intensities after SNV pretreatment

Fig. 7. Prediction results of the model established by combining the original data of spectral line intensity with the spectral line intensity ratio

Table 1. Main chemical components of HS7 steel (Wt%)

Table 2. Measured vickers hardness values of the samples

Table 3. Evaluation index results of the model

Table 4. Spectral lines of manually selected matrix elements and alloy elements

Table 5. Spectral lines used to calculate spectral line intensity ratios

Table 6. Evaluation index results of the model