Metals and Alloys, lecture 6, Recovery and Recrystallisation

[@TheJiordano]

Thank you Prof Bhadesia. Your lecture is very fruitful for understanding heat treatment mechanism associated with dislocation interaction, stored energy during deformation and its consumption for triggering recrystallization.

[@zarathustra498]

Wow, thanks for the lectures! The concepts are explained clearly and coherently. I don't even work in the field and watch it to study for fun. The grain recrystallization looks very similar to Oswald ripening of emulsions, I guess they can be considered in some ways analogous

[@bhadeshia123]

Thank you. Some teaching resources on this are available on www.phase-trans.msm.cam.ac.uk/teaching.html

[@TheUnderdog6]

method of presenting information is flawless, thank you professor

[@kodumudiprabhakaran]

Special thanks to Prof. Bhadeshia. An excellent lecture and most importantly I learned a lot.

[@bhadeshia123]

Glad you enjoyed it.

[@materialscience7138]

This lecture video is nothing less than a blessing. Dream to attend a live lecture.

[@bhadeshia123]

Really pleased you like it. There are more freely available resources on www.phase-trans.msm.cam.ac.uk/teaching.html

[@materialscience7138]

Thank you so much Prof. Bhadeshia! I could access the portal.

[@bhadeshia123]

Small particles may be more effective when the comparison is made at constant volume fraction, but large particles and large volume fraction would clearly be more effective in pinning.

[@prasadmlp3]

hello sir. lots of large particles of higher fraction to get best pinning? I couldn't get that since in precipitation hardening (example) we desire smaller size precipitates for pinning, and the moment precipitate grows, we say it has lost its strengthening effect. Please help me.

[@n.bouliez941]

Thank you for your precious knowledge. There is a question I've been mulling over though. Addition of fine particles, such as the oxides you talked about, are often called inclusions with harmful répercussion on mechanical properties including toughness. When you look at a fractography with SEM for a sample to look for the origin of surprisingly low ductility, you could pinpoint an oxide inclusion such as Al2O3 as the origin of crack initiation. So the question is how to make a choice ? On the one hand you increase toughness with lower grain size thanks to small inclusions but on the other hand you add lattice incoherence (I guess) with these inclusions leading to sooner cracks and lower toughness. Maybe you could enlighten me. Thank you

[@bhadeshia123]

Yes, you are right. The particles involved in thermomechanically processed steels are, however, not harmful. They are fine carbo-nitrides with a level of coherency with the matrix. The gain from the resulting grain refinement far exceeds any consequences on ductile void nucleation.

[@n.bouliez941]

@@bhadeshia123 Thank you for your answer. So it depends on the compound that is formed and on its size to maintain a certain coherency. If not the pile-up of dislocation brings about the decohesion from the matrix I think. Thus the compounds to add up can't be chosen at random

[@smithgeorge6979]

Does the recrystallization new grain inherit the defect density of the low-density grain from which new grain grow? Thank you.

[@bhadeshia123]

Smith George No, destruction of defects is the driving force for recyrstallisation

[@abdulmalikmemon3668]

Dear Professor, if we making the grain size finer, does that means we are infusing the more grain boundaries into the material? Which further lead to the high diffusion at low temperature? Many Thanks

[@bhadeshia123]

Yes, a finer grain size leads to more grain surface per unit volume and a higher net diffusion coefficient. See page 10 of www.phase-trans.msm.cam.ac.uk/abstracts/L1-2.pdf

[@abdulmalikmemon3668]

bhadeshia123 Thank you, Professor. I would like to ask that, we are working on the weldability of high strength structural steel with low strength filler weld material then base material at TU Dresden Germany. I have seen your lectures on Metals and alloys and if you could recommend me which lectures I should I follow further to have a better understanding of my current topic. Many Thanks.

[@kishorkumar-ef9fo]

I unable to search lecture 7 ...could you please help me

[@kathirvelan4918]

How the reduction in grain size improves the toughness?

[@bhadeshia123]

Two effects. The first is that a propagating cleavage crack is more frequently deflected as it encounters discontinuities at a grain boundary. Secondly, in steels, the size of cementite particles decreases as the grain size is reduced (see Curry and Knott, Metal Science 12 (1978) 511-514)

[@RaviKumar-iu8ws]

has recovery been explained in this lecture?

[@bidhanpandey4020]

is it not so that recrystallization occurs below melting point? then how does nucleation occurs in the solid state as i believe it occurs during solidification as liquid cools?or is the term nucleation of re-crystallization different to the term nucleation ? plz help

[@bhadeshia123]

+Bidhan Pandey Recrystallisation is a solid state process. www.msm.cam.ac.uk/phase-trans/2005/growth.html

[@bobstevens7028]

What is the driving force for Re-X if the material has already recovered prior to Re-X occurring. Doesn't recovery exist solely to reduce the driving force for Re-X to occur in the first place. If the material has recovered, the driving force for Re-X should be lowered or gone.

[@bhadeshia123]

I presume that "Re-X" means recovery and recrystallisation. If recovery reduces the driving force sufficiently, recrystallisation may not occur, though recovery cannot change the shape of the deformed grain structure.

[@bobstevens7028]

@@bhadeshia123 Thanks, by "Re-X", I meant recrystallization exclusively. Since recovery always precedes recrystallization, I am surprised that recrystallization ever occurs.

[@bhadeshia123]

Indeed it has in the series of three lectures

[@pradeepbkt1]

I am working on Avrami model and grain size measurement after re-crystallization. Where do i get detail information regarding Avrami model..?

[@bhadeshia123]

Please see www.msm.cam.ac.uk/phase-trans/teaching.html

[@pradeepbkt1]

bhadeshia123 Thanks a lot.

[@bspatil7400]

Sir,I want information about Feltham and Hillert model-drift model.

[@bhadeshia123]

P. FELTHAM, ActaMet. 5 (1957) 97. 5. M. HILLERT, ibid 13 (1965) 227

[@bspatil7400]

thank you sir

[@jitendarkumar3433]

how could I lower the recrystallization temperature of a BCC structure material?

[@bhadeshia123]

Add precipitates to pin boundaries etc.

[@jitendarkumar3433]

thank you Sir

[@barbaraf0]

If precipitation of Nb occurs at interface of MnS, the pinning effect would be limited and the grain would growth more. But why MnS inclusion attract Niobium and another inclusions not?

[@bhadeshia123]

I am afraid I don't have specific knowledge of why MnS acts as a heterogeneous nucleation site for NbC, but the latter does tend to form on other phases such as TiC or TiN

[@barbaraf0]

@@bhadeshia123 According to the reasons proposed for intragranular nucleation of acicular ferrite, I was thinking that heterogeneous nucleation of Nb in MnS could be stimulated by the difference between thermal expansion coefficients of MnS and delta ferrite. Today I found this: "this phenomenon (segregation of Nb rich phases on MnS) is related to the higher thermal expansion coefficients of MnS compared to the steel matrix (delta ferrite) during the solidification process, which could take place in such low carbon/peritectic steels. Subsequent stress fields and debonded areas at the interface of MnS and matrix are able to stimulate the formation of large Nb-rich phases (with high formation temperature) around this particle. It should be mentioned that due to removal of these phases (MnS and Nb-rich phases) during the sample preparation" TORKAMANI, Hadi et al. Contributions of Rare Earth Element ( La , Ce ) Addition to the Impact Toughness of Low Carbon Cast Niobium Microalloyed Steels. Metals and Materials International , 2018. .0123456789.

[@barbaraf0]

@@bhadeshia123 Loder, D.; Michelic, S. K.; Bernhard, C. (2016) Acicular Ferrite Formation and Its Influencing Factors - A Review. Journal of Materials Science Research, 6(1): 24-43 www.ccsenet.org/journal/index.php/jmsr/article/download/64338/35400

[@bhadeshia123]

@@barbaraf0 Thank you for this.

[@pzhu9047]

IS Recrystallisation nucleation that the less defect regions grow? form your vedios ,it looks like many new grains form and grow.

[@fishindudas3205]

beautiful lecture!

[@bhadeshia123]

Thank you.

[@knowledgezone8748]

treasure of knowledge thanku a lot

[@engineermistructe3768]

excellent

[@bhadeshia123]

This is too complicated to answer in general because both processes play a role.

[@bhadeshia123]

You are welcome

[@aaneisk]

nice