MICROSTRUCTURE AND WEAR BEHAVIOUR OF 17-4 PRECIPITATION HARDENING STAINLESS STEEL WITH VARIOUS Ti CONTENT

Abstract

In this study, the wear behaviour of aged 17-4 PH SS (precipitation hardening stainless steel) that contains 0.5, 1, 1.5, and 2% of Ti was examined. The mixed elemental powders (in wt.%: 17 Cr, 4 Cu, 4 Ni, 1 Mn, 1 Si, 0.3 Nb, 0.07 C, and Fe remaining) were cold-pressed (800 MPa), and the pre-formed 17-4 PH SS green compacts were sintered at 1300 °C for 60 min in a 0.1 Pa vacuum and at 4 °C/min heating rate and cooled down in furnace to room temperature. Alloys with different amounts of titanium were aged at 480 °C for 1, 4, and 8 h. Scanning electron microscopy, X-ray diffraction analysis, and density and hardness measurements were employed to characterize the aged alloys. The pin-on-disc apparatus was used for wear testing. The wear testing was performed under the sliding speed of 0.8 m/s, two various loads (of 30 and 45 N), and at five different sliding distances of 600, 1200, 1800, 2400, and 3000 m. Research results showed that in 17-4 PH SS, the weight loss and density decreases with a higher titanium content, while their hardness increase. Thus, a higher amount of Ti addition contributes to lower weight losses. The friction coefficient shows the highest value in the samples containing 0.5% Ti and the lowest in the alloy containing 2% Ti. M₂₃C₆ and M₃C carbides are formed in the microstructure of the material, as expected. From the SEM images of worn surfaces, the adhesive and oxidative wear mechanisms were determined as dominant. Due to the choice of composition with the highest hardness and corresponding sintering conditions, the wear resistance of alloys can be increased significantly.