Abstract
In order to improve wear resistance of cast steel, hard alloy powder layer was inserted by molten cast steel at 1843K. The vertical cross-section of the inserted layer was examined on the microstructure and the hardness. The results obtained are as follows. Sound inserted layer of 3mm in thickness was confirmed to be formed without any defects on the surface of cast steel.
A reaction layer with some lump shaped particles was formed in the interface between the inserted layer and the mother metal (cast steel). The lump shaped particles were identified to be Fe3W3C phase which had a cubic structure with a lattice constant of 11.1094×10-8cm. The particles were considered to be formed by a reaction between the Co bond phase dissolving WC in hard alloy powder and the molten iron dissolving low concentration of C in molten steel. The hardness of cast steel was about Hv300, while the inserted layer exihibited high hardness of Hv600 to 800.
Especially, the reaction layer showed peak hardness of Hv1800, but the layer was not brittle. The toughness of the reaction layer was considered to be due to a mixed structure of tough bainite and retained austenite around the hard Fe3W3C particles. The present method using the inserted hard alloy powder layer is therefore to be very effective one for local hard facing of cast steel.
