Recrystallization temperature for annealing

[Salvatio]

Dear all,

Is the a possible method to calculate the "ideal" recrystallization temperature for any steel grade? I read through some articles..a 10degC difference could bring the annealling time additional 1 hour.
Recently the Product Developement team brought us some new steel grade for testing. The given temperature is rather low, and also a longer cycle. I dont think they really calculated the annealling cycle for some reasons. So, is there actually anyway to calculate the best temperature?

Thanks..

 

[metengr]

Salvatio;
Just to be clear, are you referring to recrystallization annealing or a full anneal?

Recrystallization annealing is performed by holding material below the lower critical transformation temperature Ae₁ for some period of time. The recrystallization temperature is dependent on prior processing (cold working). I have not seen an empirical equation to estimate this temperature other than by experimentation.


To predict the actual austenitizing temperature of steel for full annealing, there are several empirical equations that are based on the chemical composition of the steel. An example of one equation is below to calculate the minimum value of Ae₃;

For 0.3-0.6%C low alloy steel
Ae₃ (deg C) = 854-179C-13.9Mn-17.8Cu-1.7Ni+44.4Si

(Elements are in weight percent amounts)

 

[EdStainless]

You can use Larson-Miller relationship to make the trade off between time and temp, as long as you stay within the correct temperature range.
This gets real spooky with some microallyed grades since they have all sorts of critical temperature rnages that you need to avoid.

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Rust never sleeps
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[Matlsguy]

Salvatio,

Why is so important that the annealing time be calculated if you can directly measure the material condition? What condition do you want to test the material in? Fully annealed? If you arn't sure if the material is fully annealed condition ask your development dept. to provide you with samples annealed at different times. Doing a Vickers test at those different times. If the hardness starts to flatten. You can be sure that the material is fully annealed.

Matlsguy

 

[Salvatio]

Matlsguy:

The material,4ft wide x 20mt flat product coil, is going through recrystallization annealing. The importance of annealing time is because it will greatly affect our production output, approximately 100mt/hr.

 

[TVP]

Is the process continuous annealing of coil? If so, then the time at temperature has a significant effect compared to batch annealing.

 

[Salvatio]

dear all,
the process is a batch annealing of coils. currently we have SPCC-1C coils to heat-treat. it was found that the quality was too good after annealing; required was CQ, but we've achieved DDQ. Ofcourse, we did this is a relatively high temperature, slow heating, and long cooling hours; with additional furnace cooling.

 

[Salvatio]

there another thing that's been bothering me about the temperature. with strip thickness less than 0.6mm (spcc-1c), after our normal heat treatment cycle, several cases of strip layers sticking together were reported. I've seen cases like this before, but is there any better remedy for this?

 

[EdStainless]

To prevent sticking you must control the furnace atmosphere. You can be too dry and clean. Using a slightly lower temp will help a lot also.

An issue with batch anneal of coils is that the heat transfer within the coil is dependenent on how tightly the coil is wound. A coil that is not very tight will not heat like a tight one.

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Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[NickE]

Also be sure to make sure teh carbon isn't leached out of the outer laps. I once had a huge issue with some steel bought directly from a "very large mill" that the two outer laps of each master had carbon below the minimum for the grade.



Nick
I love materials science!

 

[Salvatio]

yeah...some of our consultant also say it was too clean, as we have a cleaning line before the annealing line. but to what extend of "cleanliness"...we're still trying to figure out. So, now we're trying to use lower temperature. but as far as a i know, some steel mills use the same temperature as ours, however, their sticking problem occurs at much thicker strip, in which we have never encounter before. And so, i was wondering, would it be the heating rate and the cooling rate? p.s. the steel mill i referred to starts atmoshperic cooling bout 120dC (outside furnace). but ofcourse, they didnt let us see much bout their heating and soaking cycle.