Journal of Failure Analysis and Prevention

, Volume 13, Issue 3, pp 368–376 | Cite as

Superplastic HSLA Steels: Microstructure and Failure

  • Sara Fernandez
  • María José Quintana
  • José Ovidio García
  • Luis Felipe Verdeja
  • Roberto González
  • José Ignacio Verdeja
Technical Article---Peer-Reviewed
  • 200 Downloads

Abstract

Certain materials can show superplasticity when traction tested at temperatures higher than 50% of their melting point and with low strain rates (\( \dot{\varepsilon } \) < 10−2 s−1), showing very high elongations (>100%) without localized necking and mainly intergranular fractures. This behavior requires that the starting grain size is small (<10 μm) so the flow of matter can be non-homogeneous (sliding and rotating of the grain boundaries, accommodated by diffusion). This work presents the superplastic characteristic of shipbuilding steel deformed at 800 °C and a strain rate slower than 10−3 s−1. The fine grain size (5 μm) is obtained when using Nb as a microalloying element and manufactured by controlled rolling processes (three stages). After the superplastic deformation, the steel presents mixed fractures: by decohesion of the hard (pearlite and carbides) and ductile (ferrite) phases and by intergranular sliding of ferrite/ferrite and ferrite/pearlite, just as it happens in stage III of the creep behavior. This is confirmed through the Ashby–Verrall model, according to which the dislocation creep (power-law creep) and diffusion creep (linear-viscous creep) occur simultaneously.

Keywords

Superplasticity Ultrafine grained Strain rate m coefficient Boundary sliding High-strength low-alloy steels (HSLA steels) 

Notes

Acknowledgments

The authors thank the Department of Metal Sheet and Hot Coil of Mittal Arcelor of Gijón–Avilés (Asturias, Spain) for providing samples for this research. Also, thanks to T. Iglesias and B. Mendieta for the preparation of images and figures.

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Copyright information

© ASM International 2013

Authors and Affiliations

  • Sara Fernandez
    • 1
  • María José Quintana
    • 2
  • José Ovidio García
    • 1
  • Luis Felipe Verdeja
    • 1
  • Roberto González
    • 2
  • José Ignacio Verdeja
    • 1
  1. 1.E.T.S.I.M.O.Universidad de OviedoOviedoSpain
  2. 2.School of EngineeringUniversidad PanamericanaMexicoMexico

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