Abstract
The paper presents research results on the quality of hardfacing layers made during the renovation of unheated mold surfaces designed for injection of aluminum alloys using the plasma transferred arc (PTA) technology. As mold material, the medium alloy steel X38CrMoV5-1 (H11) was used. For the formation of functional layers, three types of additives in the form of powder were applied: two types on an iron basis with the designation HSS 23 and HSS 30 and one type on a nickel basis with the designation DEW Nibasit 625-P. The hardfacing layers were made on a 120 × 350 × 50 mm plate in two layers on the plasma hardfacing machine PPC 250 R6. The quality of the layers was evaluated by means of nondestructive and destructive tests. The surface integrity of the layers was assessed using visual and capillary tests. The samples passed these tests. The impact of the parameters used and the mixing of the hardfacing metal with base material, as well as the structure analysis, were assessed by means of light and electron microscopy (SEM). The chemical composition of the elements was determined by energy-dispersive X-ray spectroscopy (EDX) analysis using a SEM microscope. The hardness of the individual layers was evaluated. Since, during operation, molds are subjected to significant wear due to friction, the friction coefficients for selected temperatures were determined by the equipment for the evaluation of tribology properties. Based on the experiments conducted, all three types of additives can be used for renovation. However, from a tribology perspective, the additive DEW Nibasit 625-P on a nickel alloy basis is recommended for renovation.
Highlights
high-speed steels (HSSs) are produced by the plastic deformation of cast ingots or semifinished products made by sintering of powders while achieving reduction to ensure that the homogenization of alloys reaches up to 98%
For the hardfacing layers HSS 23 and HSS 30, cracks are visible in the hardface, separating the hardface from the base material
The DEW Nibasit 625-P hardfacing layer is free of microscopically visible defects
Summary
Intense plastic deformation disrupts the interdendritic network of eutectic carbides, leading to the increased toughness and strength of HSSs at elevated temperatures. Plastic deformation can lead to an uneven distribution of damaged eutectic carbides, which results in the anisotropy of mechanical properties [4,5]. The larger the cross section of the forged bar, the higher the microstructural heterogeneity and the more pronounced the anisotropy of carbides, and the worse the toughness and strength of the steel. The large reduction required in hot plastic deformation increases the production costs of hot-formed HSSs. In addition, machining bars into the desired shape turns a large amount of expensive forged material (up to 30–50% and more) into waste [6,7,8]
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