2. Experimental details
2.1. Material
AISI 4140 steel plate with a thickness of 6.5 mm in the annealed condition was used for this study. The typical nominal chemical composition of the material is 0.37–0.44 C, 0.10–0.35 Si, 0.65–1.10 Mn, 0.75–1.20 Cr, 0.15–0.35 Mo, ≤0.040 P, ≤0.040 S, and Bal–Fe. Flat test specimens prepared under the annealed condition are designed as the baseline. Test samples were also fabricated from 4140 that is hardened by conventional heat treatment procedure. These samples were austenitized at 840 °C and water quenched – designated HT in the present study. Flat samples were also prepared from material from FSP treatment and designated FSP accordingly.