Microstructure of steel according to the TTT diagramm
Microstructure of steel according to the TTT diagramm
(OP)
Hi every body
Just a help
I want to perform this heat treatement
1 - Cooling to 350 °C from 850 °
2- Holding at 350 °C four 4H hours
3 - Air coling
What is the final microstructure ?
Thanks in advance
Just a help
I want to perform this heat treatement
1 - Cooling to 350 °C from 850 °
2- Holding at 350 °C four 4H hours
3 - Air coling
What is the final microstructure ?
Thanks in advance





RE: Microstructure of steel according to the TTT diagramm
RE: Microstructure of steel according to the TTT diagramm
If you can get to below 650C in under 3.5 minutes, you can probably get nearly 100% bainite.
rp
RE: Microstructure of steel according to the TTT diagramm
However, what is it that you are aiming at,let us know too.
I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
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RE: Microstructure of steel according to the TTT diagramm
thanks
redpiceker, yes the time betwen 850 and 350 is about 5.5 hours
My questions for both :
1- How you can know the propotion of each phase, this is not à CCT diagram ?
2- Is this TTT diagram accepatable for the big thickness parts > 600 mm ?
RE: Microstructure of steel according to the TTT diagramm
RE: Microstructure of steel according to the TTT diagramm
Perhaps you need to introduce thermocouples at different section thicknesses to understand clearly the expected microstructure.
I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
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RE: Microstructure of steel according to the TTT diagramm
I would try to locate a CCT diagram for a more accurate depiction during slow cooling. This is a common material for CCT diagrams. The TTT diagram shows austenite reformation at around 530-550 deg C, where the curve displaces to the right for a considerable time interval.
RE: Microstructure of steel according to the TTT diagramm
It's acceptable for isothermal transformation. At slow cooling rates, you approach isothermal transformation, so you can approximate.
For example, on the cooling curve you drew, you hit 650 C at around the 1 hour mark. Your microstructure at that point isn't going to be much different than if you cooled rapidly to 650C and held it there for an hour. Since the only transformation product is ferrite, it's safe to say that you'd be just a little behind equlibrium with continuous cooling at that rate for this steel composition.
But, as metengr points out, CCT diagrams for 4340 are pretty common, so if you need a more exact evalutation, google a bit and you can probably run across one.
rp
RE: Microstructure of steel according to the TTT diagramm
Arunmarao :
Thanks for your advice for thermocouples, my aim was to avoid quench cracking during air cooling for the thikness part > 600 mm
Again Thanks all