Microstructural and mechanical characterisation of some sinter hardening alloys and comparisons with heat treated PM steels

Abstract

Four grades of sinter hardening materials have been compared, using industrial equipment. Three powder types were completely prealloyed; the last one was a hybrid, combining prealloying and diffusion bonding. Different amounts of Cu have been added by mixing. The lubricated mixes, containing 0 . 6% graphite, have been compacted at different pressures, to form gears at green densities >7 . 0 g cm 23 ; the compacts have been sintered at 1120uC, under endogas from methane and fast cooled (at least 7 K s 21 within the range 850-400uC). The final step has been stress relieving, at 180uC, for 1 h. Material properties have been investigated, focusing on porosity, pore shape, hardness, microhardness, microstructure, local chemical composition and mechanical properties. For comparison, other gears, compacted in the same tool and at the same density level, but manufactured according to a more conventional cycle, i.e. starting from less alloyed powders and adding carbonitriding, quenching and stress relieving, have been used. The analysis of the different experimental results enabled the authors to find out and outline some criteria suitable for selecting sinter hardening materials and for choosing more reliable manufacturing conditions to fulfill specific application requirements.

Microstructural Aspects and Wear Behavior of Sinter Hardened Distaloy HP

“…The rapid development of the automotive industry and focus on production costs presents a great increase in the application of high performance powder metallurgy (PM) parts and exploits a great market of iron‐based PM materials. The main differences between PM and fully dense materials are the presence of porosity and, in many cases, the typical heterogeneity of chemical compositions 1. The sliding friction and wear characteristics of sintered steels were reported by many investigators 2–8.…”

Homogenization Study of Molybdenum and Copper in P/M Steel

“…Mo in P/M steels may be added in form of pure elemental, partially or fully prealloyed and diffusion bonded powders (Danninger, 1992, Bocchini et. al., 2004, Yilmaz et.…”

Effects of sinter hardening technology on homogeneous and heterogeneous microstructures

“…6 To optimise manufacturing costs and performance of sinter hardened parts, the combined effects of alloying elements, their content and the base powder on compressibility and hardenability must be properly analysed and balanced. 7 Many sinter hardenable powder metallurgy materials [8][9][10] have been developed over the past few decades and commonly used Fe-Cu-Ni-Mo-C system, which has exhibited good dynamic and static properties. [10][11][12][13] By controlling the post-sintering cooling rate, the microstructure can be manipulated to form the required amount of martensite to obtain the desired mechanical properties.…”

“…Chromium base materials have also shown good sinter hardening characteristics 6. To optimise manufacturing costs and performance of sinter hardened parts, the combined effects of alloying elements, their content and the base powder on compressibility and hardenability must be properly analysed and balanced 7. Many sinter hardenable powder metallurgy materials8 – 10 have been developed over the past few decades and commonly used Fe–Cu–Ni–Mo–C system, which has exhibited good dynamic and static properties 10 –.…”