Oxide scale formation of stainless steel in transition of annealing and reheating towards fossil-free methods
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
University of Oulu, Linnanmaa, Timjami (5D105)
Topic of the dissertation
Oxide scale formation of stainless steel in transition of annealing and reheating towards fossil-free methods
Doctoral candidate
Master of Science (Technology) Susanna Airaksinen
Faculty and unit
University of Oulu Graduate School, Faculty of Technology, Process Metallurgy
Subject of study
Process engineering
Opponent
Associate professor Daniel Lindberg, Aalto University
Custos
Professor Timo Fabritius, University of Oulu
Oxidation of stainless steel in the process furnaces in transition towards fossil-free methods
The hydrogen transition enables a significant reduction of industrial carbon dioxide emissions by replacing carbon with hydrogen as reducing agent and fossil fuels as an energy source. In the steel industry, fossil fuels, such as natural gas, are used as a heat source in the process furnaces, in which the steel temperatures are raised over a thousand degrees. Combustion of fossil fuels produces carbon dioxide, but when hydrogen is used as a fuel, only water vapor is formed. The completely carbon-neutral combustion process uses hydrogen produced with renewable sources, but its energy-efficient production still requires development.
Annealing and reheating furnaces are used in stainless steel production. In the heating of furnaces, fuel gas combustion is carried out using excess air, producing an oxidizing furnace gas atmosphere. Atmosphere combined with high temperatures causes oxidation on the steel surface, which is called oxide scale formation. The removal of oxide scale layer is required to produce a clean and corrosion-resistant surface for the steel product.
In this study, the effects of different simulated heating methods and conditions were compared on the oxidation of stainless steel surface. Changes in the structure, composition, and amount of the oxide scale were studied and their effects on the efficiency of removal process were evaluated. The transition in heating towards hydrogen combustion with oxygen promotes the decomposition of the first formed protective oxide scale layer, continuing with rapid progressing breakaway oxidation under conditions of both annealing and reheating. The results showed that the differences between steel grades are significant in the suitability of the heating method change. The changes in the oxidation of ferritic steel grades remain significantly smaller, but reheating of austenitic steel grades can produce oxide scale multiple times in transition from the current natural gas combustion with air to hydrogen combustion with oxygen.
Annealing and reheating furnaces are used in stainless steel production. In the heating of furnaces, fuel gas combustion is carried out using excess air, producing an oxidizing furnace gas atmosphere. Atmosphere combined with high temperatures causes oxidation on the steel surface, which is called oxide scale formation. The removal of oxide scale layer is required to produce a clean and corrosion-resistant surface for the steel product.
In this study, the effects of different simulated heating methods and conditions were compared on the oxidation of stainless steel surface. Changes in the structure, composition, and amount of the oxide scale were studied and their effects on the efficiency of removal process were evaluated. The transition in heating towards hydrogen combustion with oxygen promotes the decomposition of the first formed protective oxide scale layer, continuing with rapid progressing breakaway oxidation under conditions of both annealing and reheating. The results showed that the differences between steel grades are significant in the suitability of the heating method change. The changes in the oxidation of ferritic steel grades remain significantly smaller, but reheating of austenitic steel grades can produce oxide scale multiple times in transition from the current natural gas combustion with air to hydrogen combustion with oxygen.
Last updated: 29.8.2024