TTT Diagram of Alloy Steel

[@samirrathod768]

Thank you sir for provide such information by very effective way of presanting it. Generally in an industries peoples are quenching a steel within a 60 sec, so how the chemical composition effect the quenching time or it is not affected ?

[@rushishwargattu5154]

Sir,among Mn,Cr,Mo,Ni at a fixed temperature which element will diffuse in the iron at a faster rate?does it depend on the crystal structure of the element?

[@eylulZZ]

Sir, I have one question - why Carbide forming alloying elements like V, W etc also shifts the TTT curve towards right;it should shift towards left as those Carbides will act as nucleation centers, increasing nucleation rate as well as transformation rate.?

[@introductiontomaterialsscience]

These carbide forming elements are substitutional solutes. Thus to form carbides they have to diffuse by substitutional mechanism (vacancy assisted) which is much slower than the diffusion of C which happens by interstitial mechanism.

[@Adityasinghm26v]

​@@introductiontomaterialsscience sir, can you please explain that how these carbides forming elements form finer grains and are called grain size refiners?

[@Adityasinghm26v]

Sir, if the same cooling rate is given in two cases 1) without alloying elements 2) with alloying elements The transformation will begin earlier in case (1) and at a higher temperature than in case (2) .Hence , the finer grains will be formed in case (2) because the transformation has started at lower temperature with alloying elements and growth rate is also lower than that of case (1). Are these the ressons why these elements are called grains size refiners? If not, how does these elements restrict grain growth? Please answer 🙏

[@dhananjaysingh991]

What an explanation sir, thanks

[@janakirampanchireddy3413]

Loved this presentation sir. But i didn't understand why alloy steels got 2 noses in their TTT curve? Transformation rate however wil be higer at one place, how can it will be faster at 2 regions?

[@introductiontomaterialsscience]

Actually, there are two kinds of transformation, austenite->pearlite and austenite->bainite. Both have their own C-curve and their noses are at different temperatures. T

[@janakirampanchireddy3413]

@@introductiontomaterialsscience sir,why particularly rate of transformation for bainite is faster than the pearlitic one in tat curve??

[@introductiontomaterialsscience]

@@janakirampanchireddy3413 Bainite is a much finer distribution of ferrite and cementite. Thus the diffusion distances are much shorter requiring less time for transformation.

[@zeeshanahmed9719]

SIR if we further cool along the "RED" curve in alloy steel TTT diagram ( which gives Bainite on continuous cooling) upto room temperatures can we get Martensite in that can also?

[@rajeshprasad101]

NO, once austenite has transformed to some other microconstutuent, no further transformation is expected. All transformation curves relate only to untransformed austenite.

[@zeeshanahmed9719]

Rajesh Prasad Thank you Thank you SIR JI

[@udaykumarkondaveeti7698]

Sir even the austenitic and ferritic stabilizer can effectively chance the Fe-Fe3C diagram so the TTT diagram changes abruptly. If possible please explain the TTT diagram with effects of austenitic and ferritic stabilizers point of view.

[@lifi-sp]

Sir thanks 👍 Explaination is excellent in the video.

[@mr.chindo8570]

In second point sir said that the substitution is slow hence transformation is slow! Does he mean that alloying and phase transformations are being performed during the same process?

[@introductiontomaterialsscience]

What I meant was that diffusion of substitutional element is slower in comparison of diffusion of C. This reduces the transformation rates in alloy steel compared to that of plain C steels.

[@prakharbhalla9461]

Sir does CCT curve also shifts rightwards from TTT curve as for eutectoid steel or both are same for alloy steel

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[@emersonsaint8164]

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[@pailasaisravan5423]

sir please tell what i understood is right or not . once we cross the start curve to the right side and enter into complete pearlite region above the nose and then even though we further cool we cannot form even 1% of martensite

[@introductiontomaterialsscience]

That's right. All the transformation lines (Start C-curve, finish C-curve, Ms and Mf) are applicable only to untransformed austenite. Once austenite is transformed they are ineffective.

[@shrikantthakare9569]

What can say is just Greattttt !!!

[@rink47]

Sir, Why do we get 2 curve for Pearlite and Bainite?

[@introductiontomaterialsscience]

Please see reply to Janakiram.

[@nirmal148]

Normalising is faster cooling in air......so it may produce fine pearlite....but when cooling proceeds further will a portion convert to martensite?......you may say NO it will not since the phase has already trasnformed to pearlite......i kind of understand that logic.....but then how do we draw the cooling curve?.....because logically if we continue with same rate of cooling, we should come out of the nose area that we reached during normalising and should move down into the alpha+bainite zone and then move further down into the martensite zone.......will this happen or is it that once a transformation happens, say from austenite to fine pearlite then the TTT diagram is different?

[@introductiontomaterialsscience]

Mohammad Zee Sham had similar confusion and I had replied to that. All transformation curves, C-curves as well as martensite start and finish horizontals apply to only untransformed austenite. Thus is untraformed austenite crosses these boundaries appropriate transformations happen. But if austenite is already transformed then there is no relevance of these boundaries and crossing them causes no transformation.

[@nirmal148]

@@introductiontomaterialsscience Thank you

[@sivasakthi5661]

Solution annealing duplex stainless steel class

[@bestcakesdesign]

Less time more conceptual