Abstract
Oxide scale formation during short‐term annealing and electrolytic pickling behavior of ferritic EN 1.4622 and austenitic EN 1.4828 stainless steels are investigated. The annealing is performed at temperatures between 1000 and 1100 °C for ferritic and 1100 and 1200 °C for austenitic steel grade under humid atmospheres in simulated industrial process. Neutral electrolytic pickling, also referred to as neutral electrochemical pickling or the Ruthner Neolyte Process, is performed in Na2SO4 electrolyte, and pickling efficiency is evaluated visually and by image analysis of pickled surfaces. The results show that annealing conditions have a more impactful effect on the structure and the composition of the resulting oxide in the austenitic grade within the studied condition range. The thicknesses of the ferritic scales are mainly less than 0.4 μm, while almost all austenitic scales are thicker than it. In addition, the amount of silicon oxide formation inside the steel matrix of the austenitic and ferritic grades is highly different. Longer exposure times and higher temperatures promote scale growth during annealing, resulting in inefficient electrolytic pickling for the ferritic grade. For the austenitic grade, almost all steel surfaces are still covered with oxide scale after electrolytic pickling.
Highlights
Introduction behavior of ferriticEN 1.4622 and austenitic EN 1.4828 stainless steels are investigated
Silicon oxide is formed below the metal–oxide interface penetrating toward the steel matrix which is seen in the micrographs as a light gray tonality
The observed amount of silicon oxide was significantly lower in the ferritic grade, and a continuous silicon oxide was located under the thicker chromium-rich oxide, but it was not observed inside the steel matrix as it was in the austenitic grade
Summary
Introduction behavior of ferriticEN 1.4622 and austenitic EN 1.4828 stainless steels are investigated. The annealing is performed at temperatures between 1000 and 1100 C for ferritic and 1100 and 1200 C for austenitic steel grade under humid atmospheres in simulated industrial process. The amount of silicon oxide formation inside the steel tion, residential, chemical, and petroleum industries.[1] Austenitic stainless steel grades are widely used in high-temperature applications. Nickel-free ferritic stainless steel has lower thermal expansion coefficient and is cheaper as a material. As such, it has been developed especially for matrix of the austenitic and ferritic grades is highly different. Almost all steel surfaces are still covered with oxide scale after electrolytic pickling
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