Reduced Coefficient of Friction of Laser Surface Hardened AISI 4130 Steel Substrates

Abstract

AISI 4130 steels have been used in several engineering applications, although presenting limited hardenability in conventional heat treatments. This contribution is aimed at determining the final hardness and reciprocating wear coefficient of friction (COF) after a given laser surface treatment (LST) with or without a carbon coating (C). The results indicated that the bare (B, without coating) condition produced a deeper case depth as a result of the carbon-rich plasma shielding. The observed microstructural features in the cases B and C showed martensite transformation and cementite formation; the latter is entirely in the C condition. Simple calculations using Rosenthal’s formalism indicate a high cooling rate, estimated as 32 ′ 280°C/s 40 μm below the irradiated surface and a heat-affected zone bounded by the austenite locus. The hardness near to the surface was higher in case C than in case B, but the overall final hardness is more pronounced when the surface is bare (B) due to plasma shielding. On the other hand, the final COF was very low in the C case (0.1) compared to the B condition (0.6).