CORROSION BEHAVIOUR OF TEMPERED 42CrMo4 STEEL

Low-alloy 42CrMo4 steel (AISI 4140) is a medium carbon steel, commonly used as a quenched and tempered steel. Because of its good mechanical properties, high tensile strength and toughness, 42CrMo4 is one of the widely used and investigated steels. In order to increase ductility even more, in addition to standard quenching and tempering, steel is often hardened by double quenching and tempering and austempering. The aim of this paper was to investigate the corrosion behaviour of 42CrMo4 steel after quenching and tempering, double quenching and tempering and austempering. For this purpose, microstructural characterization and electrochemical investigation after different hardening processes were performed. Microstructure of specimens was observed using optical microscopy and scanning electron microscopy. Open circuit potential and potentiodynamic polarization measurements of tempered specimens were carried out using computer-controlled potentiostat with three electrode set-up in 0.6 M NaCl naturally aerated solution. It was concluded that applied heat treatment processes increase the corrosion resistance of 42CrMo4 steel in comparison to normalized steel. In comparison to quenched and tempered steel, double quenching and tempering, as well as austempering, do not significantly change corrosion resistance of steel.

Wear Resistance of Medium Carbon Steel with Different Microstructures

In this research, the tribological properties of different microstructures of medium carbon steel produced by either an austempered process or quenched-tempered process are investigated. The as-received samples with annealed microstructure (spherodized) are austempered to obtain a bainite microstructure or quenched-tempered to obtain a tempered martensite microstructure. The tribological performance of these microstructures was studied using a ball-on-disk UMT3 tribometer. The results indicated that both bainite microstructures and tempered-martensite microstructures produced better wear resistance than pearlite microstructures. At the same hardness level, the austempered disk specimens have less cracking due to higher fracture toughness compared to quenched and tempered steel. For the disks, tempered martensite microstructures produced more plastic deformation compared with bainite microstructures. Mild abrasive wear was observed on the harder disks, however, smearing wear was observed on the softer disks. Adhered debris particles were observed on the balls.