About the Bainite blog
For the blog I would like to discuss about metallurgy and science and related topics, and all the etc.
About Bainite the Microstructure
Bainite is a microstructure of steel that forms at temperatures intermediate between the formation of pearlite and martensite in many steels. First discovered by Davenport and Bain who conducted a series of isothermal transformation experiments.
Historically there has been much discussion in the literature about the mechanism of transformation of bainite, with opinions varying from it being very similar to pearlite, to it being similar to martensite. Results of Ko and Cottrell showed that bainite exhibited a surface relief consistant with a martensitic transformation mechanism. Shortly after Matas and Hehemann introduced the concept of a sub-unit mechanism to explain the apparant inconsistancy between the slow speed of transformation and the high speed the interface would be expected to move.
Microstructures formed as a result of continuous cooling or by welding are often very complex and this leads to lots of scope for errors in identification of microstructures. This leads to more confusion over the appearance of the microstructure an an urge to classify constituents by appearance rather than transformation mechanism.
Generally bainitic ferrite forms austenite as plates before carbon is partitioned to the austenite. Carbide precipitation can also take place either within the ferrite or between the plates of ferrite due to supersaturation. This distinguishes upper-bainite and lower-bainite.
If transformation occurs without the formation of carbides the volume fraction of bainite forming will be limited by thermodynamics. Once the carbon in the austenite reaches a concentration were any new bainite that formed would have the same energy as the parent austenite. This is the ‘incomplete transformation’ and ‘T-zero concept’.
You can find more information on the phase transformations and complex properties group’s page about bainite.
About the Author
I enjoy steel, computers and microscopes.
My name is Mathew Peet, I have a webpage at mathewpeet.org which has some more of my stuff.