Effect of stress on microstructure of a medium-carbon ultrafine grain bainitic steel
The bainite transformation process is often affected by stress and/or strain,and its transformation kinetics and microstructure will undergo significant changes.The effect of stress on microstructure of a medium carbon ultrafine grain bainitic steel was studied by means of thermal simulation testing machines,scanning electron microscopy,transmission electron microscopy and electron backscatter diffraction techniques.The results show that the thickness of bainite lath first increases and then decreases with the increase of stress.The additional mechanical driving force provided by the stress leads to the coarsening of bainite lath,while the deformation of austenite is conducive to the refinement of bainite lath.The competition between the two causes the above phenomenon.In addition,by comparing the experimental and theoretical calculated pole figures,it is found that under the experimental conditions,the relationship between austenite and bainite is more in line with the Nishiyama-Wassermann(N-W)orientation relationship.After applying stress,the number of bainite variants significantly decreases,resulting in a significant selection of variants.
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