Characterization of Austenitic Stainless Steels Deformed at Elevated Temperature
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INTRODUCTION
FOR sustainable energy production, renewable energy resources with high efficiency are needed.[1–3] One way to achieve a higher efficiency in sustainable energy production is to increase the temperature and pressure in the boiler section[4] of, for instance, biomass-fuelled power plants.[1] Higher temperature and pressure will increase the demand for improved high-temperature properties of the materials that operate in high-efficiency power plants. For the components in the boiler section, resistance to fireside corrosion and steamside oxidation, creep–rupture strength and fabricability are the most important material requirements.[1,4–6] Austenitic stainless steels are commonly used for components within the energy-producing industry[1,4–6] due to their high corrosion resistance, good creep resistance and excellent ductility, formability and toughness.[6–8] Advanced austenitic stainless steels are designed to withstand temperatures up to 923 K (650 C) or even 973 K (700 C).
MATTIAS CALMUNGER, STEN JOHANSSON, and JOHAN J. MOVERARE are with the Division of Engineering Materials, Department of Management and Engineering, Linko¨ping University, 58183 Linko¨ping, Sweden. Contact e-mail: [email protected] GUOCAI CHAI is with the Division of Engineering Materials, Department of Management and Engineering, Linko¨ping University, and also with the AB Sandvik Materials Technology R&D Center, 81181 Sandviken, Sweden. ROBERT ERIKSSON is with the Division of Solid Mechanics, Department of Management and Engineering, Linko¨ping University, 58183 Linko¨ping, Sweden. Manuscript submitted September 30, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
At higher temperatures, the recovery phenomena of dynamic recrystallization (DRX) occurs. DRX is associated with recrystallized grains in the microstructure.[9] At higher temperatures, 973 K (700 C) and above, nickel-based superalloys are often used.[4] It has been reported that mechanical properties, like strength, may be significantly changed due to dynamic strain aging (DSA).[10,11] DSA can lead to an increase in flow stress and strain hardening rate.[12,13] Austenitic stainless steels show DSA in a temperature range from 473 K to 1073 K (200 C to 800 C),[14–16] which includes both the operating temperatures of today’s power plants and the elevated operating temperatures for future power plants.[5] DSA originates from interaction between solute atoms and dislocations during plastic deformation. Under plastic flow, dislocations are gliding until they come across an obstacle where they are stationary until the obstacles are surmounted. When the dislocations are stationary, solute atoms can diffuse towards the dislocations which results in an increase in the activation energy for further slip and, consequently, also an increase in the stress needed for overcoming the obstacle.[15,17–20] At temperatures below 623 K (350 C), carbon is proposed to be responsible for DSA while nitrogen and/or substitutional chromium atoms are proposed to be responsible at higher te
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