PROCESSING AND PROPERTIES OF SINTER-FORGED Fe-2Cu-0.7C-xMo ALLOYS

Abstract

Iron-Copper-Carbon (Fe-Cu-C) is widely used alloy system in the ferrous powder industry and is extensively used in many mass manufactured P/M components of automobiles such as connecting rods, planetary gear carriers and variable valve timing components etc. Molybdenum provides soild solution strengthening enhances hardenability and has thus been used to improve properties of ferrous alloys significantly. The present investigation deals with the effect of varying Mo (0wt%-3wt%) content on the properties of sinter-forged Fe-2Cu-0.7C alloys. Powder compositions were processed by mixing of elemental powders followed by sintering and forging at 1150oC in N2-10%H2 atmosphere. Sinter-forged compositions were reforged and homogenized to ensure almost full density as well as complete dissolution of alloying elements. Alloys were then subjected to various heat treatment (annealing, normalising, quenching and quench plus tempering) conditions. Mechanical and tribological properties with microstructural changes were determined. Further, the hardenability response of these alloys was also ascertained by Jominy end quench test. A separate study the expansion behaviour during sintering of Fe-Cu-C alloy was also investigated. Mechanical properties were significantly influenced by the addition of Mo as well as with heat treatment conditions. Strength was found to increase with Mo addition as well as with severity of quench while ductility contrasted strength. Addition of 1.5 wt% Mo in quench plus temper heat treatment resulted in best combination of strength and ductility. Attainment of significant amount of ductility accompained with high strength is one of the marked features of the present work. A profound effect of Mo addition on hardness and strength under normalised condition was also noted and indicates the ability of these alloys for sinter-hardening applications. Combination of Cu and Mo addition improved the hardenability response of Fe-0.7C alloy which Increased with increasing Mo content. Significant increase in hardenability of Fe-2Cu-0.7C alloy was observed with 1.5 wt% or higher amount of Mo addition where specimen got through hardened. Study of wear behaviour delineates a complex mechanism of wear (delamination, abrasion and oxidation) in Fe-2Cu-0.7C-xMo alloy depending of the amount of Mo added as well as on heat treatment conditions. Among all the compositions studied, 3wt% Mo composition under noramlised condition was found to undergo minimum wear loss during dry sliding test and corresponding frictional coefficient was lower. Quenched specimens exhibited higher wear rates which indicates hard martensitic structure does not supports wear in these alloys. Study of dimensional change during sintering of Fe-Cu-C alloys indicated that green density of pellets, copper particle size and carbon content are the decisive parameters for the expansion behaviour of these alloys.