Nowadays flow-forming has become a desired near net shape manufacturing method as it provides excellent mechanical properties with improved surface finish and significant manufacturing cost reduction. However, the material is subjected to excessive plastic deformation during flow-forming process, generating a very fine and complex microstructure. In addition, the intense dislocation density and residual stress that is generated in the component during processing makes the microstructure characterisation using conventional micro-analytical tools challenging. Thus, the microstructure/property relationship study in such a material is rather difficult. In the present study a flow-formed Cr–Mo–V steel nanostructure and crystallographic texture were characterised by means of Transmission Kikuchi Diffraction (TKD). Here, TKD is shown to be a powerful technique in revealing very fine martensite laths within an austenite matrix. Moreover, fine precipitates in the order of 20–70 nm on the martensite lath boundaries were clearly imaged and characterised. This greatly assisted in understanding the preferable site formation of the carbides in such a complex microstructure. The results showed that the actual TKD spatial resolution was in the range of 5–10 nm using 25 kV for flow-formed Cr–Mo–V steel.
S. Biroscaa, R. Dingb , S. Ooic, R. Buckinghama, C. Colemana, K. Dicksd
a. Materials Research Centre, College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP, UK
b. School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
c. Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK
d. Oxford Instruments NanoAnalysis, Halifax Road, High Wycombe, Buckinghamshire HP12 3SE, UK
Ultramicroscopy, 2015, Vol. 153, Pages 1–8, doi:10.1016/j.ultramic.2015.02.001