professor, what if we use liquid nitrogen for cooling? will we see any change in microstructure different from martensite? thankyou for removing my fear for material sc.
Sir I have one doubt that whether Bainite structure is available at room temperature or not because in diagram (Austempering Heat treatment) we hold at temperature above Ms(Martensite start temperature).
It forms above Ms and below the nose. But once formed, it can be retained to room temperature. It will not transform to martensite. Thus if Bainite is cooled below the Ms no martensite forms. Only when austenite is cooled below Ms it transforms to martensite.
Sir if pearlite is formed by equilibrium rate means its the most stable form possible then how can if we hold a pearlite for 1 day it turns in spherodite?
Well the phases alpha and Fe3C are the stable phase but the microstructure of pearlite is not stable. Peralite microstructure has a lot of alpha/Fe3C interfaces. So a large interfacial energy. This interfacial energy is reduced when it transforms to spheroidite.
@@rajeshprasad101 thanx a lot sir🙏,but if spherodite is the most stable form and we can get it by very slow cooling(even more slow cooled than pearlite) from stable gamma,then in phase dia shoudnt we show spherodite instead of pearlite?
We need to distinguish between equilibrium phases and microstructure. The phase diagram. by definition, gives the equilibrium phases. The equilibrium phases here are alpha and cementite. Thus phase diagram indicates that equilibrium phases are alpha and cementite. It does not tell us whether these two phases appear as pearlite or spheroidite. This we interpret depending upon other conditions. Thus under normal cooling of austenite, these phases form alternating lamellae called pearlite. But if it is heated below the eutectoid temperature, the microstructure changes to spheroidite: spherical cementite in alpha matrix. The phases are still alpha and cementite, their distribution and shapes have changed.
Sir, Could you please explain why there is a difference in properties of bainite and pearlite, I mean how does it occur because of the microstructure, I want to know what is happening at the atomic level during the heat treatment process.
Although both are mixture of ferrite and pearlite, the difference is in there distribution. Pearlte consists of alternating plates of ferrite and cementite. Bainite consists of a matrix of ferrite with fine ditribution of cementite particles.
The isothermal experiment is not done in the air. It is done in a constant temperature bath. One uses molten salt or molten metal to maintain a constant temperature. It is like, you can use boiling water to maintain a temperature of 100°C.
The concepts are very useful and very clear explanation. I have never found like these on internet... Thank you very much sir
professor, what if we use liquid nitrogen for cooling? will we see any change in microstructure different from martensite? thankyou for removing my fear for material sc.
Sir,What are the alloying additions those can stabilize the bainite?
Thanks for making this videos, are really helpful, and you explained the topics really clear!
sir, explain the formation of bainite microstructure?? what causes fine needles??
Sir I have one doubt that whether Bainite structure is available at room temperature or not because in diagram (Austempering Heat treatment) we hold at temperature above Ms(Martensite start temperature).
It forms above Ms and below the nose. But once formed, it can be retained to room temperature. It will not transform to martensite. Thus if Bainite is cooled below the Ms no martensite forms. Only when austenite is cooled below Ms it transforms to martensite.
Thank you SIR ji
Sir your explanation is just incredible!!!!
Sir, will you tell some specific applications of Bainite?
Rolling element and ball bearings
Sir, u are extremely genius
Sir if pearlite is formed by equilibrium rate means its the most stable form possible then how can if we hold a pearlite for 1 day it turns in spherodite?
Well the phases alpha and Fe3C are the stable phase but the microstructure of pearlite is not stable. Peralite microstructure has a lot of alpha/Fe3C interfaces. So a large interfacial energy. This interfacial energy is reduced when it transforms to spheroidite.
@@rajeshprasad101 thanx a lot sir🙏,but if spherodite is the most stable form and we can get it by very slow cooling(even more slow cooled than pearlite) from stable gamma,then in phase dia shoudnt we show spherodite instead of pearlite?
We need to distinguish between equilibrium phases and microstructure. The phase diagram. by definition, gives the equilibrium phases. The equilibrium phases here are alpha and cementite. Thus phase diagram indicates that equilibrium phases are alpha and cementite. It does not tell us whether these two phases appear as pearlite or spheroidite. This we interpret depending upon other conditions. Thus under normal cooling of austenite, these phases form alternating lamellae called pearlite. But if it is heated below the eutectoid temperature, the microstructure changes to spheroidite: spherical cementite in alpha matrix. The phases are still alpha and cementite, their distribution and shapes have changed.
@@rajeshprasad101 ok sir got it,thanx a lot🙏
simply superb sir☺true reapect from us
many many thanks!
Nice to learn
respect
at 2 am and a night before exam...i am much more relieved now.. thank you so much
Material technology paper?
Same but at 3:30
@@hamza_ME_ all the best 👍
@@yashmalik8348 It's done... :')
Professor, your videos are just awesome!!!!!
Sir, Could you please explain why there is a difference in properties of bainite and pearlite, I mean how does it occur because of the microstructure, I want to know what is happening at the atomic level during the heat treatment process.
Although both are mixture of ferrite and pearlite, the difference is in there distribution. Pearlte consists of alternating plates of ferrite and cementite. Bainite consists of a matrix of ferrite with fine ditribution of cementite particles.
Super explanation Sir...tq
Sir can we have TTT diagram for other points also like for Eutectic and peritectic points?
Yes, it is possible.
@@introductiontomaterialsscience Thank you sir for the reply.
Thank you so much govt of India for digital teaching lecture free
best lecture
excellent
sir could you explain how scientist could able to cool isothermally for such long time in the air ??
The isothermal experiment is not done in the air. It is done in a constant temperature bath. One uses molten salt or molten metal to maintain a constant temperature. It is like, you can use boiling water to maintain a temperature of 100°C.
I think sir there is no bainite finish??
Why?
@@introductiontomaterialsscience cause morphology of lower bainite is similar to martensite and it's hard to maintain Bf tempreture
Sir, how can we hold the Gama Austenite without changing it's temprature ? Whether we give heat to remain the temperature same or not?
There are techniques for holding tempearture constant. For example you can submerge it in a liquid bath of constant temerature.
@@introductiontomaterialsscience Thank You respected sir.
Thank you Prof. you are really helping me a lot.