Severe Tempering of Bainite Generated at Low Transformation Temperatures

These are some pictures of the beautiful microstructure of super-bainite. The fine structure of bainite plates and austenite thin films is formed by isothermal transformation at 200°C (or alternatively 473.15 K, or 392 F). With this fine microstructure (or more accurately nanostructure) it is possible to reach very high strength in steel (more than 2 GPa ultimate tensile strength).

Before

Super Bainite Before Tempering (as transformed at 200°C)

Super Bainite Before Tempering (as transformed at 200°C), as seen in transmission electron microscope

Super bainite as transformed at 200°C, as seen in scanning electron microscope.

Super bainite as transformed at 200°C, as seen in scanning electron microscope.

After

'Super bainite' after severe tempering.

‘Super bainite’ after severe tempering.

This is what happens if you attempt to temper at the highest possible temperature. As expected the microstructure approches equilibrium and coarsens. We found that the temperature calculated using thermodynamic software is not applicable to this heat treatment. Rather than an equilibrium structure of ferrite and carbides as we expected at this temperature, austenite, ferrite and carbide phases were all stable. On cooling, the austenite transformed, usually to pearlite as seen here, but in some cases bainite and martensite were also observed.

Read more: Severe tempering of bainite generated at low transformation temperatures (mathewpeet.org) or Severe tempering of bainite generated at low transformation temperatures (phase transformations)

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