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Cyclic oxidation of 304L and 316L stainless steel coated and uncoated with Cr3C2–NiCr at elevated temperatures

Kumar Naveen, Alam Md Sarfaraz, Mishra Nagendra Kumar, Kumar Sujeet, Giri Jayant, Aly Ayman A., Gupta Gaurav Kumar

Materials Science Poland

2025

Vol. 43, No. 1

103--114

Failure of the boiler, gas turbine, incinerator, and other power-producing machines is mainly caused by the metals’ oxidation and alloys at high temperature service environment. It is a common practice to apply thermal barrier coating to increase the resistance to oxidation of metal alloys when subjected to high temperatures. In the current research, an effort has been made to apply a coating of Cr3C2–NiCr using the detonation gun (D-gun) technique on stainless steel (SS) 304L and SS 316L. The characteristics of coatings have been studied at 750 and 850°C. A cyclic oxidation process was carried out in a muffle furnace for 50 cycles. For each cycle, 304L and 316L SS, both bare and coated, are heated for 1 h in a muffle furnace and cooled for 20 min in ambient air. Under the investigated conditions, the Cr3C2–NiCr coating sprayed with a D-gun exhibited outstanding adhesion to the substrate alloy. A weight change/area versus the number of cycles plot has been drawn to understand the kinetics of oxidation. SS 304L coating has shown approximately 26.54 and 21.93% improvement in oxidation resistance at 850 and 750°C, respectively. For SS, 316L coating has shown approximately 27.67 and 25.92% improvement in the oxidation resistance, respectively, at 850 and 750°C. The oxide-scale-generated Cr3C2 phase demonstrated notable resistance to oxidation throughout the 50 cycles of cyclic oxidation at 750 and 850°C. The weight change/area shows that 316L has much better oxidation resistance than 304L at both temperatures of 750 and 850°C. The application of such coatings at high temperatures may reduce the formation of oxide scale which attacks and corrodes exhaust valves, turbocharger nozzles, and blade.

Evaluation of microstructural and mechanical qualities in optimised TIG-welded SDSS 2507 joints

Kumar Sujeet, Srinivas Madugula Naveen, Kumar Naveen, Giri Jayant, Fatehmulla Amanullah

Materials Science Poland

2024

Vol. 42, No. 4

163--179

Super duplex stainless steel (SDSS) is gaining attraction owing to its excellent mechanical strength and superior corrosion resistance. In this study, tungsten inert gas (TIG) was implemented for welding the SDSS thin sheet. The Taguchi method and analysis of variance (ANOVA) were carried out by selecting L25 orthogonal arrays. The optimum TIG parameters were a welding current of 75 A, an arc potential of 15 V, a welding rate of 120 mm/min, and an argon gas consumption rate of 12 L/min. An ANOVA study found that welding current (46.95%) was the largest contributor in producing the excellent welded joint. The microstructural research indicated increased grain size in the heat-affected zone (HAZ) and fusion zone (FZ), represented by distinct grain boundary layers, intragranulars, and Widmanstätten austenite. This was due to heat input and rapid cooling inclusion as well as re-crystallisation of the ferrite matrix. The elemental mapping analysis showed that chromium must be present to generate a shielding oxide layer, which decreased from 25.50% in the parent material to 23.40% in the TIG welded joint. The tensile test found that TIG welds had an ultimate tensile strength (UTS) of 789 MPa. This value was equivalent to the base metal UTS value of 800 MPa. The micro-hardness test of the TIG welded joint confirmed that the HAZ (350 HV) and FZ (325 HV) were higher than that of the base metal (305 HV). The hardness value near the FZ boundary experienced a significant increase due to the development of hard microscopic components and element migration during the TIG process.