Reverse Martensitic Transformation and Resulting Microstructure in a Cold Rolled Metastable Austenitic Stainless Steel |
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Authors: | Axel Knutsson Peter Hedström Magnus Odén |
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Affiliation: | 1. Division of Engineering Materials, Lule? University of Technology, 971 87 Lule?, Sweden;2. Nanostructured Materials, Dept. Physics, Link?ping University, 58183 Link?ping, Sweden |
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Abstract: | The reverse martensitic transformation in cold‐rolled metastable austenitic stainless steel has been investigated via heat treatments performed for various temperatures and times. The microstructural evolution was evaluated by differential scanning calorimetry, X‐ray diffraction and microscopy. Upon heat treatment, both diffusionless and diffusion‐controlled mechanisms determine the final microstructure. The diffusion reversion from α′‐martensite to austenite was found to be activated at about 450°C and the shear reversion is activated at higher temperatures with Af′ ~600°C. The resulting microstructure for isothermal heat treatment at 650°C was austenitic, which inherits the α′‐martensite lath morphology and is highly faulted. For isothermal heat treatments at temperatures above 700°C the faulted austenite was able to recrystallize and new austenite grains with a low defect density were formed. In addition, carbo‐nitride precipitation was observed for samples heat treated at these temperatures, which leads to an increasing Ms‐temperature and new α′‐martensite formation upon cooling. |
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Keywords: | metastable austenitic stainless steel reverse martensitic phase transformation heat treatment microstructure |
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