Speaker
Description
Chromium pre-alloyed powder metallurgy (PM) steels are extensively used in high-performance applications due to their low costs, good recycling capabilities, and high hardenability. High density is one of the main pre-requisite properties for high-performance components. In this current study, water atomized pre-alloyed with 1.8 wt.% Cr is utilized and admixed with 0.3 wt.% UF-4 natural graphite and 2 wt.% Ni. Two mixes were prepared with and without Ni: Fe-1.8Cr-0.3C and Fe-1.8Cr-2Ni-0.3C. Cylindrical compacts and Impact energy samples were uni-axially pressed at 600 MPa. Sintering was then performed on the samples at 1120 °C and 1250 °C, in N2/H2 (90/10) atmosphere.
Shrinkage at different stages during sintering was studied based on the dilatometry curves. Chemical reactions during sintering such as reduction of surface oxides were studied using thermogravimetry analysis based on mass change. Microstructural analysis revealed ferritic-pearlitic microstructure in the components as well as inhomogeneous distribution of nickel in the admixed with Ni compacts. Nickel as an alloying element aids in achieving enhanced hardenability and is known to favor densification especially after high-temperature sintering. High hardness values were observed for Ni-containing compacts after high temperature sintering. The impact tests were performed after sintering and fracture surface was studied. Dilatometry and thermogravimetry analyses together with the microstructure and fractography studies revealed the importance of Ni when it comes to PM steel densification and enhancing the properties. The experimental characterization was coupled with modelling using JMatPro and Thermo-Calc to elucidate in particular on the role of nickel.
| Speaker Country | Sweden |
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