PSI - Issue 36

Pavlo Prysyazhnyuk et al. / Procedia Structural Integrity 36 (2022) 130–136 Pavlo Prysyazhnyuk et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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carbide phases, represented by the white areas. Such elements redistribution caused by formation only single dominant carbide phase crystalizing from a melt at high temperatures.

Fig. 2. Microstructure of the fusion zone between EMH hardfacing and base metal and corresponding results of the EDS line scan analysis.

Microstructural investigations of top hardfaced layers (Fig. 3a) show, that carbide phase precipitate in form of uniformly distributed in austenitic matrix, faceted equiaxial grains with average size of 2 µm. Some of carbide inclusions are dispersed in the interdendritic space without the formation a continuous carbide network. According to the results of EDS analysis for a randomly selected carbide grain (Fig. 3b), its chemical composition is not fully homogenous. The core regions of carbide grain are mainly enriched with Ti and V, while its periphery zones are characterized by increased amounts of Nb and Mo, despite the observed concentration inhomogeneity, the presence of all carbide-forming elements in significant amounts was detected in carbide grain. In the general case, such type of structure formation can be classified as a multicore/rim structure, which provides increasing of crack resistance by crack closure and deflection around the grain cores. The total amount of reinforcing multicomponent carbide phase in hardfaced layer is approximately 12% by volume, that provides the hardness value of 46 HRC in as deposited state and 57 HRC after work-hardening, while hardfacings hardness, deposited using serial hardfacing electrodes which can be reached during work hardening does not exceed 45 – 47 HRC. Such increased work-hardening rate in hardfacings, reinforced by multicomponent carbide phase caused by superposition of deformation hardening inside austenite grains due to twining mechanism and dispersion hardening, as a result of dislocation motion blocking by complex carbide phase fine precipitations.

Fig. 3. EMH hardfacing microstructure (a) and results of the EDS analysis across the carbide grain (b).

Figure 4 shows the relationship between hardness and impact-wear resistance for tested hardfacings as well as for HSS steel and St. 45 steel. As can be seen from Fig. 4, increasing in hardness leads to an increasing in impact-wear