The tribological properties of high speed steel based composites

Marcin Madej, Jan Leżański Akademia Górniczo-Hutnicza, Wydział Inżynierii Metali i Informatyki Przemysłowej, al. Mickiewicza 30, 30-059 Kraków, Poland

Quarterly No. 1, 2008 pages 87-92

DOI:

keywords: high speed steel, composites, infiltration, wear quality, friction coefficient

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abstract High hardness, mechanical strength, heat resistance and wear resistance of M3/2 high speed steel (HSS) make it an attractive material for manufacture of valve train components such as valve seat inserts and valve guides. Since technological and economical considerations are equally important, infiltration of high-speed steel skeleton with liquid cooper has proved to be a suitable technique whereby fully dense material is produced at low cost. Attempts have been made to describe the influence of the production process parameters and additions of powders: copper, graphite, iron and tungsten carbide on the tribological properties of copper infiltrated HSS based composites. The compositions of powder mixtures were M3, M3+7.5Cu, M3+0.3C, M3+20Fe, M3+50Fe, M3+10WC and M3+30WC. The powder mixtures were prepared by mixing for 30 minutes in the 3-D pendulum motion Turbula® T2C mixer. Then the powders were cold pressed in a rigid cylindrical die at 800 MPa. The infiltration process was carried out in vacuum better than 103 Pa. Both green compacts and compacts pre-sintered for 60 minutes at 1150C in vacuum were contact infiltrated with copper. Carefully pre-weighed performs of copper were placed on top of the rigid skeletons of predetermined porosity, heated to 1150C, held at temperature for 15 minutes, and cooled down with the furnace to the room temperature. From the analysis of the obtained results it may be concluded that the mechanical properties is mainly affected by the manufacturing route and powders characteristics (M3/2 HSS, Höganäs iron, tungsten carbide WC) and powder composition of porous skeleton for infiltration. From it is evident that the as-infiltrated properties of the investigated composites are a complex function of the manufacturing route and tungsten carbide content. The molten copper is drawn into the interconnected pores of the skeleton, through a capillary action, and fills virtually the entire pore volume to yield final densities exceeding 97% of the theoretical value. Wear quality of the as-infiltrated composites increases with the increased content of tungsten carbide, whereas the bending strength seems to be adversely affected by the addition of the tungsten carbide powder. Considerable differences in hardness between the mat- erials obtained from the two infiltration routes have been observed, with higher wear quality numbers achieved with direct infiltration of green compacts. As can be seen, the additions of iron didn’t worse wear quality of composites obtained from infiltration of green compacts.