The paper aims to avoid premature failure of slide valve, flapper valve and slurry backflush system for fluid catalytic cracking unit due to slurry abrasive wear by depositing Ni-Cr-Mo-W alloy on 304 austenitic stainless steel using synergic pulsed gas metal arc welding. An average coating thickness was obtained in the range of 2.41 mm to 2.78 mm and dilution level varied from 17% to 26.74%. The microstructure revealed that hypoeutectic Ni-FCC dendrites and interdendritic region with MC, M23C6 and M6C carbides were present. The formation of carbides was directly related to dilution level of the coating, since dilution level influenced the proportional amount of carbon and carbide forming alloying elements. Slurry abrasive wear resistance initially increased with an increase in dilution level up to 23.88% of dilution, later on it started to decrease due to reduction in solid solution alloying elements and carbide fraction. Slurry abrasive wear resistance of the coated surface was found up to 3.5 times higher than that of the substrate. The mechanism of abrasive wear under the operation of microcuttings, pits formation and ploughing with a little plastic deformation was witnessed on the worn-out surfaces.
The control of Fe dilution and carbide dissolution plays a vital role on the performance of metal matrix composite hardfacings. In this paper, the NiCrBSi–WC composite hardfacing is deposited on 304 austenitic stainless steel by plasma transferred arc hardfacing at 120[Formula: see text]A (specimen 1) and 140[Formula: see text]A (specimen 2) transferred arc current values to obtain different levels of Fe dilution and W dissolution for comparative investigations. The Fe dilution examined by scanning electron microscopy for specimen 1 was 24.54% and for specimen 2 was 33.09%. The microstructural investigations revealed higher W dissolution for specimen 2 due to higher heat input which led to significant reduction in the amount of WC and W2C hard phases. The slurry abrasive wear test performed as per ASTM G105 showed two times reduction in abrasive wear resistance of specimen 2 as compared to specimen 1. The significant reduction in the performance of specimen 2 is mainly due to higher Fe dilution and higher W dissolution caused due to higher heat input. Hence, selection of appropriate process parameters is vital to control Fe dilution and carbide dissolution in order to achieve superior performance of composite hardfacings.
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