Abstract
Abstract In powder metallurgy (PM), there are several ways of introducing alloying elements into a PM material in order to adjust a certain alloying element content. Each alloying route has its advantages and disadvantages. Master alloys (MA), powders with a high content of typically several alloying elements, can be added in small amounts to a base powder, especially to introduce oxygen sensitive elements such as Cr, Mn, and Si. In addition, the master alloy can be designed in such a way that a liquid phase is formed intermediately during the sintering process to improve the distribution of alloying elements in the material and to accelerate homogenization. In this study, such master alloys were combined with pre-alloyed base powders to form hybrid alloyed mixtures with the aim of improving the material‘s sinter hardenability. The hybrid alloys were compared with mixtures of master alloy and plain Fe as reference material. The sinter hardenability of all materials was determined by generating CCT diagrams recorded with 13 different cooling rates. These were verified by metallographic cross-sections of specimens treated at common cooling rates of 3 and 1.5 K/s and subsequent hardness measurements of the microhardness (HV 0.1) of the microstructural constituents and the apparent hardness (HV 30). ◼
Highlights
Ferrous powder metallurgy precision parts are manufactured for a wide range of applications, their main benefits being excellent reproducibility of dimensions and properties and efficient utilization of material and energy
Whereas classical powder metallurgy (PM) steels for precision parts are usually alloyed with Cu sometimes combined with Ni and/or Mo, today more cost-efficient alloy elements such as Cr, Mn and Si are being investigated for sintered steels, where the high oxygen affinity of these elements is much more critical than in the case of wrought steels
This results in cooling rates of typically 2–3 K/s in a fully loaded furnace and significantly slower than e. g. oil quenching. This is a much cleaner process, since the parts are not contaminated with oil, which is important regarding the open porosity of virtually all PM precision parts
Summary
Ferrous powder metallurgy precision parts are manufactured for a wide range of applications, their main benefits being excellent reproducibility of dimensions and properties and efficient utilization of material and energy. G. high pressure water atomization, fine MA powders containing Fe, Si, C, Cr and/or Mn with low oxygen content can be produced today [11] These MAs were further modified to improve liquid phase formation, infiltration behaviour and alloying element content compared to previous studies [12]. CCT diagrams of all hybrid alloyed mixes (MA with pre-alloyed base powder) and the reference material (MA + plain Fe) were generated and compared with regard to hardenability and microstructure in order to optimize the combination of alloying elements and alloying routes (hybrid alloying) with regard to sinter hardening response of the material. Daher wurden in der vorliegenden Studie sowohl die MAs als auch die Sinterbedingungen so gewählt, dass sie einen ausreichend homogenen Werkstoff ergeben
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