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This study aimed to reduce cavitation erosion effects by improving the surface properties of high-alloyed steel cast parts using the tungsten inert gas (TIG) surface physical modification technique. Local surface melting was performed at different linear energies (El = 4080–8880 J/cm) by varying the current between 100 and 200 A at a constant voltage of 10.2–11.1 V. Hardness increased from 210 to 390 HV5 when a TIG current of 150 A with a linear energy of El = 6630 J/cm was implemented. Using this technique, a surface layer with increased resistance to cavitation erosion was formed. This new surface absorbed large amounts of impact energy owing to a favourable combination of microstructural changes, leading to improved elastic and plastic properties, work hardening, cracking, and failure response. The cavitation erosion performance of the re-melted surface layer was analysed using a piezoceramic vibrating device according to the ASTM G32–2016 standard. Following TIG surface re-melting, the average penetration depth of erosion and the cavitation erosion rate increased by approxmately 6.8 times. Based on optical and electronic metallographic analyses, hardness measurements, and X-ray diffraction, it was shown that the morphology of the surface layer following cavitation erosion tests was affected. Microcraters tended to develop at locations where carbide particles from the alloying elements were previously present. At a current of 150 A, the depth of the microcraters reached values of approximately 15 μm; however, microcrater depth reached 10 μm in the austenite matrix. Based on these investigations, an understanding of the mechanisms that result in the improvement of the resistance to erosion by cavitation of cast high-alloy steels whose surfaces were re-melted using the TIG technique is developed. • TIG surface re-melting of GX40CrNiSi25 - 20 cast stainless steel leads to improved cavitation erosion resistance. • Optimal TIG current was 150 A for a linear energy of 6300 J/cm. • More than six times improvement of the cavitation erosion resistance. • Micro-cracks initiated and developed on the austenite grain boundaries. [ABSTRACT FROM AUTHOR]

The paper analyses the effect of the surface microstructure effects on the cavitation erosion following rapid re-melting and solidification of gray cast iron parts with lamellar graphite and perlitic matrix. The heat source used was the electric arc generated between the tungsten electrode (via the TIG process) and the gray cast iron part. The local melting of the surface was performed at different linear energy values (E l = 3420–5400 J/cm) varying the current between 60 A and 90 A, at a constant voltage of 9.5–10 V. The results showed an increase of the surface hardness from 192 to 198 HV5 to 700–740 HV5 and an improvement of the cavitation erosion resistance, the mean penetration depth of the erosion decreasing by 2.4 times, and the erosion rate by 3.56 times. Optical and scanning electron microscope were used to characterize the microstructure and to identify the phases in the re-melted area. The results showed that the melting of the surface led to an almost complete dissolution of the graphite lamella; the fine microstructure after re-solidification was composed of dendrites of transformed austenite embedded in ledeburite, consisting of transformed austenite and cementite Fe 3 C. Austenite dendrites have a preferential orientation and martensite needles are formed inside some of them. • TIG surface re-melting of gray cast iron leads to a fine structure in the marginal layer. • Significant hardness increase observed as a function of TIG currents. • Two times improvement of the cavitation erosion resistance. • Cavitation localized at boundaries between acicular cementite and transformed austenite. [ABSTRACT FROM AUTHOR]