Great teaching skills. Directly printed to the brain. However I still have one doubt. As discussed in the lecture austenite have the highest density and it gets expanded upon cooling. 1) But in casting we have solidification shrinkage which shows as we decrease temperature from solidification temperature to room temperature material contracts. To avoid this shrinkage allowance are provided. 2) also in strength of material in thermal stressing, it shows the upon heating iron get expanded and if we resist this expansion thermal stresses are generated. So material science theory tells material expands with cooling and casting and som theory shows materials contracts with cooling. quite contradicting. So my doubts are : 1) Is this theory only applicable to austenite to martensite transformation or it is applicable to austenite to any transformation in TTT diagram? 2) If it is applicable to all transformation of austenite what is the concept behind above mentioned contradiction? Thank you for this amazing course.
There are two types of volume change involved: volume change due to temperature change and volume change due to transformation. Cooling usually leads to contraction when there is no transformation. Iron in your strength of materials lab is an example. Water below 4 deg C is a counterexample as it expands on cooling. Volume change during transformation can be either expansion or contraction. Thus most metals contract during liquid-> solid transformation. This is the case of casting where you provide shrinkage allowance. But water is again a counterexample as it expands on freezing. Austenite to martensite is solid-to-solid phase transformation where also you observe an expansion. I hope this clarifies.
Thank you sir. I have a doubt. There will be residual stresses whenever we quench from austenitic range..that means quench crack is an inherent mechanism associated with quenching practice of steel??
The magnitude of residual stress depends upon the tempearture differential between different parts (different distances from the surface) of the piece being quenched, This in turn depends upon the cooling rate. Higher the cooling rate, higher the differential in temperature and higher the residual stresses. Thus the propensity of quench crack depends upon cooling rate and can be reduced by reducing the cooling rate. Obviously, one cannot reduce the cooling rate below the critical rate. But there is no need to go for much higher cooling rate than required.
Thank your sir. I have a question. Quenching produces Martensite, does that mean every time we heat Martensite above Eutectoid temperature it will transform from Body centred tetragonal(Martensite) to FCC(Austenite) or it will form a new crystal structure.
Carburizing is a method of increasing the surface hardness by heating the metal in the presence of Carbonaceous material. It is entirely different from tempering.
![STEEL HEAT TREATING CLOSEUP - WATER VS OIL [Trollsky Knifemaking]](/img/n.gif)
never thought someone will make this subject so interesting, thank you sir
@Ignacio Jasper don't have girl friend bro
Great teaching skills. Directly printed to the brain.
However I still have one doubt.
As discussed in the lecture austenite have the highest density and it gets expanded upon cooling.
1) But in casting we have solidification shrinkage which shows as we decrease temperature from solidification temperature to room temperature material contracts. To avoid this shrinkage allowance are provided.
2) also in strength of material in thermal stressing, it shows the upon heating iron get expanded and if we resist this expansion thermal stresses are generated.
So material science theory tells material expands with cooling and casting and som theory shows materials contracts with cooling. quite contradicting.
So my doubts are :
1) Is this theory only applicable to austenite to martensite transformation or it is applicable to austenite to any transformation in TTT diagram?
2) If it is applicable to all transformation of austenite what is the concept behind above mentioned contradiction?
Thank you for this amazing course.
There are two types of volume change involved: volume change due to temperature change and volume change due to transformation.
Cooling usually leads to contraction when there is no transformation. Iron in your strength of materials lab is an example. Water below 4 deg C is a counterexample as it expands on cooling.
Volume change during transformation can be either expansion or contraction. Thus most metals contract during liquid-> solid transformation. This is the case of casting where you provide shrinkage allowance. But water is again a counterexample as it expands on freezing.
Austenite to martensite is solid-to-solid phase transformation where also you observe an expansion.
I hope this clarifies.
You make this subject to easy and interesting..I am so thankful to you 🙏🙏
Thanks for ur videos sir these are very helpful for me to understand the concepts very clearly
Thank you sir.
I have a doubt. There will be residual stresses whenever we quench from austenitic range..that means quench crack is an inherent mechanism associated with quenching practice of steel??
The magnitude of residual stress depends upon the tempearture differential between different parts (different distances from the surface) of the piece being quenched, This in turn depends upon the cooling rate. Higher the cooling rate, higher the differential in temperature and higher the residual stresses. Thus the propensity of quench crack depends upon cooling rate and can be reduced by reducing the cooling rate. Obviously, one cannot reduce the cooling rate below the critical rate. But there is no need to go for much higher cooling rate than required.
@@introductiontomaterialsscience Thank you sir for the explanatory answer.
Thank you sir....all doubts cleared😀🙏
Most welcome 😊
Thank your sir. I have a question. Quenching produces Martensite, does that mean every time we heat Martensite above Eutectoid temperature it will transform from Body centred tetragonal(Martensite) to FCC(Austenite) or it will form a new crystal structure.
Above eutectoid temperature, a eutectoid steel will transform to austenite.
@@introductiontomaterialsscience thank you Sir for clarifying
What a masterpiece it was!!! completed 100 lectures in a go. Now onwards, material science is my strength.
Hi can u tell how is your material science strong
We need more teachers like him... More of em... They are great magicians... Mazaa aa gya.... Feel aa gayi..
Thank you so much Sir.
Why engines loses their hardness when we pour water after a long run
Excellent description.
Thank you very much
Great video thank you
awesome lectures sir, thank you very much, may you live long
Sir, i want to make material science strong as you. How to do ?
Thank You Sir for this wonderful explaination
superbly explained
If quench cracks happen inside the material .then what I can do for regain its crackless structure.
Once it has cracked, you have cannot get the crack free state back.
That's why we do carborising????
Carburizing is a method of increasing the surface hardness by heating the metal in the presence of Carbonaceous material. It is entirely different from tempering.
Sir how can we produce single Crystals?
same research is going on in Turbine blade. Read related research papers