Suppose I get a structure with Martensite and Bainite. I tempered it . Now how can i differentiate between the tempered martensite and bainite as both looks same however the mechanism of formation is different.
I think that the main diffesrence could be connected with the fact, that in lower bainite "cementite precipitates on the {011} habit plane of ferrite. In tempered martensite, many internal twins form in the tempered martensite plate and the cementite precipitatespreferentially on the {112} twin planes" - this main conclusion comes from http://www.sciencedirect.com/science/article/pii/S0254058407005081
I hope that this lecture will be very useful.
for better understanding you can go through book Bainite in steels. The major difference is during bainite formation, there is carbide precipitation within or along the sheave take place depending on the bainite that is formed. so there is autotempering taking place. whereas, in martensite there is carbon entrapped in the lattice. which on tempering forms ferrite + carbide. The carbides changes its composition during tempering at various temperature. which is not the case with tempering a bainite. if you temper bainite the coarse carbides (fe3C) formed remains through out tempering unless some secondary hardening takes place in the steel. Also tempering bainite at high temperatures lead to recrystallization of ferrite and dissolution of bainitic carbides which is contrast to tempering martensite where coarsening of carbides take place.
Hope this information is sufficient.
The simplest way to differentiate between tempered martensite and lower Bainite is to observe the carbide precipitates in the following manner: If the ferritic plates have carbide precipitation within themselves that lies in two different axis, then you are looking at a tempered martensitic plate. If, however, the carbide ppts lie only in one axis (which is at about 60 degree to the long axis of the ferritic plates) you are looking at a lower Bainitic plate. On the other hand, the difference between upper Bainite and tempered martensite is too obvious, as upper Bainite will not have cementite ppts within the ferritic plates.
Good question… Please check references below.. hope it will be helpful for you…
Regards…
http://www.fem.unicamp.br/~sergio1/pos-graduacao/IM324/AULAS/Aula4/Bainita-Tenacidade.pdf
https://hal.archives-ouvertes.fr/jpa-00255655/document
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