Enhanced cavitation erosion resistance of GX40CrNiSi25-20 cast stainless steels by surface TIG re-melting

Abstract

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.