Steels 2022: martensite, Lecture 1 of 11

The characteristics of martensite in steels, are explored in some depth, beginning with a scheme that quantitatively defines the temperature and driving force domains where reconstructive and displacive transformations are expected. The martensite-start temperature, the plate shape, observation of the shape deformation, the consequences of the shape deformation, the irrational habit plane, the irrational orientation relationship, the athermal and isothermal transformation behaviours etc. It ends with some difficulties, that are resolved in the lecture that follows.
This series of lectures is organised by Professor Fabio Miani of the University of Udine in Italy.
Associated teaching materials can be found on:
www.phase-trans...
H. K. D. H. Bhadeshia

[@florianh.5763]

I am extremely happy that you continue to upload your lectures and interesting presentations. In combination with your publications/books, this channel greatly facilitates the understanding of metallurgy; you have helped me a lot over the past years! Since this is the first video as Prof at QMUL, I wish you all the best and a good start in London! I am very much looking forward to your future uploads 😊 Thanks for all!!

[@bhadeshia123]

That is incredibly nice - makes me happy, so thank you, Florian.

[@anibaldiluch9897]

Dear Prof. There are a couple of questions I would like to ask if I may...
1) I have read in a book by W. Hosford that the reason why martensite in steels is athermal is the following: “Each platelet that forms decreases the possible size of the next Platelet. With a smaller radius, the next disc requires greater cooling below the Ms temperature to form. This decrease of the radius of the next platelet requires greater cooling below the Ms temperatures” (Iron and Steel/page #132). I wonder if you agree with this thought.
2) Taking into account martensite and bainite formation are quite similar (both displasive), why martensite formation is athermal and in the case of bainite it is possible to form it isothermically?
I hope I made myself clear.
Hopefully, I will attend your last lecture on Friday!
Thanks in advance.
Best regards.

[@bhadeshia123]

Martensite is not strictly athermal, but in many materials happens rapidly, thus giving the impression of being athermal. Yes, it is correct that the plate size decreases as the austenite grain is geometrically partitioned. However, the plates that form later are thinner so there may not be a requirement for greater undercooling. The theory is that easy nucleation sites are used first, with greater undercooling to stimulate more nucleation. Both martensite and bainite can form isothermally - i think i presented a TTT diagram with C-curves for martensite when the latter forms at cryogenic temperatures. However, there are consequences when bainite forms at low driving forces, discussed in my lecture on bainite.

[@anibaldiluch9897]

@@bhadeshia123 many thanks Professor!

[@anibaldiluch9897]

Thank you so much Sir for sharing your passion with us!

[@bhadeshia123]

Thank you, it is my pleasure.

[@jianhaochen9527]

Thank you so much Prof.

[@bhadeshia123]

You are very welcome, thank you.

[@purnimachakravarty5516]

These videos are a blessing for learners who do not get an opportunity to sit in a classroom. thank you very much, Prof. Bhadeshia! 🙏

[@bhadeshia123]

You may also find useful, the materials that are available freely on my teaching web site
www.phase-trans.msm.cam.ac.uk/teaching.html

[@purnimachakravarty5516]

Dear Prof. Bhadeshia, I have checked the material on your website. Thank you very much!

[@SandeepKumar-ux8pg]

Thank you sir ❤️

[@bhadeshia123]

You are very welcome.