ORIGINAL ARTICLE Cyclic Oxidation Behavior of the Super Austenitic Stainless Steel 904L in Air at 500–650 °C Manishkumar K. Singh 1 • Sharvan Kumar 1 • Om Prakash Sinha 1 • Vakil Singh 1 • Girija Shankar Mahobia 1 Received: 9 October 2019 / Accepted: 10 March 2020 Ó The Indian Institute of Metals - IIM 2020 Abstract Cyclic oxidation behavior of the super austenitic stainless steel 904L was studied for 100 h over the inter- mediate temperature range from 500 to 650 °C in air. The oxidized surfaces and cross sections of the oxidized sam- ples were examined by scanning electron microscope (SEM–EDS), X-ray diffractometer and electron probe micro analyzer. The weight gain was found to follow nearly parabolic rate law. At 500 and 550 °C, there was rapid weight gain up to the initial 5 h of exposure, whereas the rapid weight gain at 600 and 650 °C was up to 10 and 25 h of exposure, respectively. The weight gain was drastically reduced during the later stage of exposure. Since the formed scales were thin, strong peaks of austenite (c)- matrix were observed in all the exposed samples. There was formation of thin layer of Cr 2 O 3 on the specimens exposed at 500 and 550 °C. Also, there was heterogeneous formation of iron oxides in some regions. The exposure at higher temperatures of 600 and 650 °C led to the formation of different spinels of oxides such as FeCr 2 O 4 , NiCr 2 O 4 , FeNi 2 O 4 and others, along with Cr 2 O 3 and Fe 2 O 3 oxides. Keywords Super austenitic 904L Á Oxidation kinetics Á XRD Á SEM–EDS Á EPMA analysis 1 Introduction Super austenitic stainless steels (SASS) possess outstand- ing oxidation and corrosion resistance over a wide range of temperature. These high-performance steels differ sub- stantially from the conventional grades of stainless steel with respect of their high content of alloying elements Cr, Ni, Mo, Cu, Mn and a small amount of Si which enhances their strength as well as oxidation resistance at elevated temperatures [1]. These steels are known as Fe–Ni–Cr grade [2] and rely on the formation of a protective chro- mium-rich oxide scale with very low porosity, good adherence, high mechanical as well as thermodynamic stability and slow growth rate [3]. The most commonly used super austenitic stainless steels include 904L, 254 SMO, 654 SMO, AL-6XN, SANICRO-25 and 28, etc [4]. Earlier studies on majority of SASS have focused mainly on high-temperature deformation/precipitation behavior between 650 and 1000 °C[5]. The 904L steel is a SASS, designed for an intermediate level of oxidation and corrosion resistance up to 480 °C[6]. It contains a high level of Cr and Ni, in addition to Mo and Cu which provide corrosion resistance in certain media. The 904L steel is used widely in situations where corrosion resistance of the AISI 317L and 316L stainless steels is not up to the mark [7–9]. Some major uses of the SASS 904L include wiring in electrostatic precipitators, oil refinery components, gas scrubbing plants, seawater cooling devices, pulp, and paper processing industries, sulfuric, phosphoric and acetic acid processing plants owing to its good corrosion resistance, excellent stability, high strength, and weldability [4]. The standard heat treatment of the SASS 904L is solutionizing at 1050–1150 °C and water quenching. Cao and Norell [10] compared oxidation behavior of the 304L and 904L stainless steels in humid air over the & Manishkumar K. Singh manishkumarksingh@gmail.com 1 Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi, India 123 Trans Indian Inst Met https://doi.org/10.1007/s12666-020-01949-1