Austempered high silicon steel: investigation of wear
resistance in a carbide free microstructure

Abstract: The production of wood-pellets involves fractioning of the raw material,
e.g. the sawdust and cutter shavings, into a homogeneous particle size
before pressing through a ring die pelletizer. The fractioning takes place
in a hammer mill, where wear on the cutting knives is considered a problem.
The main material property requirements of the knives are high wear
resistance and toughness. This research project examines the suitability of
austempered high silicon steel to achieve these desirable properties. One
specific steel, 55Si7, has been austempered to obtain a carbide free
ausferritic microstructure and the mechanical properties, microstructure
and wear resistance of this steel have been characterized. Microscopy and x-
ray diffraction were used for microstructural characterization and
examination of the stress-induced transformation of retained austenite into
martensite. The mechanical properties were characterized via tensile
testing, Charpy V-notch impact testing and hardness measurements: and the
wear resistance has been investigated in a laboratory environment under non-
lubricated sliding wear conditions. The wear resistance of austempered high
silicon steel has been compared to other steels heat treated under
different conditions to obtain different microstructures. In addition, a
field test took place in a hammer mill for a direct comparison between the
wear on four austempered high silicon knives and commercial knives made of
case hardened low carbon steel. The austempered high silicon steel proved
to have a uniform and high hardness combined with good impact toughness,
plastic deformation before fracture, and high wear resistance. These
desirable properties were achieved by austempering at low temperatures,
resulting in a very fine microstructure and absence of carbides due to the
presence of silicon.