Super Austenitic Stainless Steel with SiC Metal Matrix Composites for Nozzles In Harsh Environment

We investigated the possibility of developing super austenitic stainless steel Avecta SMO 254 X1NiCrMoCuN20-18-7 (EN 10088-4) and austenitic stainless steel X15CrNiSi25-21 (EN 10095) coated with SiC, resulting in the obtainment of a Metal Matrix Composite (MMC) by Additive Manufacturing (AM) for the upgrade of nozzles for sulphur recovery thermal reactors. One layer of the MMC targets the outer surface of the part that is in constant contact with the flame and the area is subjected to high friction erosion. The Directed Energy Deposition Laser (DED-LB) method has made it possible to produce a high strength-to-weight ratio. The aim is to engage lower-cost material with similar thermal stability and durability in extreme conditions. The robotic unit used for the application allowed for the computer control of the positioning, feeding of the SiC particles inside the shielding gas and deposition in the melted pool. After the solidification process, visual testing (VT) and ultrasonic testing (UT) were applied for the non-destructive evaluation, checking for disbonding and subsurface imperfections. Then, samples were tested with microhardness measurements, bond strength, microcracking detection, porosity, interface zone assessments and microstructural analysis. The process achieved 0.4 to 0.7 KJ/mm heat input with no defects and the intended nozzle surface passed UT and VT. Controlled parameters provided strong metallurgical bonding.

Funding: The author acknowledges support from project BG16RFPR002-1.014-0005.