Fine spheroidite vs coarse spheroidite

[DevinT]

There are a few posts on multiple quenches and normalizing.

Many steel producers anneal by heating a batch of rolled steel above Ac3 and turn off the furnace. The furnace cools at a slow rate down to somewhere below 1000'f. This is a cycle anneal and produces coarse spheroidite.

Fine spheroidite is produced by quenching from just above Ac3 and then doing a sub-critical anneal. Ac1 is the critical temperature. Heating to a temp just below Ac1, maybe 75-100f below, and holding for several hours is a sub-critical anneal.

The finer and more evenly distributed the spheroidite is, the finer the grain in the final quench.

Coarse spheroidite is sometimes slow to disolve and requires longer soak times and higher temps.

Those that I know doing tripple quenches, also are doing some normalizing steps before mutiple quenching.

In my testing, some steels benifit from mutiple quenches. All steels benifit from having fine spheroidite.

Hoss

 

[Shipshores]

So you quench from Ac3, then do the sub-critical annealing followed by normalizing and then final quench? Did I understand that right?

 

[DevinT]

Quench from just above Ac3, sub-critical anneal, full aus quench. Normalize before this whole sequence.

Hoss

 

[Shipshores]

Got it, thanks.

 

[Jeremie H-W]

Juste to be sure, Ac3 is three times the critical temperature (Ac1)?

 

[DevinT]

There is usually 100'f difference, or did you just say a funny?

Hoss

 

[stezann]

Hi Hoss, if you quench from above Ac3 (normalizing temperature, where you have all the carbon in solution) don't you risk filling the steel with microcracking of plate martensite? Or are you specifically talking about hypoeutectoid steels?
I do your procedure, but if i do the quench before spheroidization i do from around my final austenitizing temperature (eutectoid carbon range in solution) for the fear of cracks. Do you think am i overthinking on this concerns?

 

[DevinT]

Just above Ac3 is lower than full aus temp and lower than normalizing temp. 52100 Ac1 temp is 1390f and Ac3 is 1445f, other carbon steels have lower temps. A2 steel Ac1 is ~1460f and Ac3 is ~1550f.

Hoss

 

[Jeremie H-W]

There is usually 100'f difference, or did you just say a funny?

Hoss

Thank you for the precision Hoss. Sorry for my lack of knowledge, I am barely starting to scrach the surface on Metallurgy, wich is why I find these kind of threads really interesting. The Ac# temprature was just not a concept I was familiar with.

P.S.: I checked out your work and I just have to tell you that you make beautiful pieces. Especialy the feather pattern dasmascus, witch has always been my favorite pattern.

 

[DevinT]

Thank you for the precision Hoss. Sorry for my lack of knowledge, I am barely starting to scrach the surface on Metallurgy, wich is why I find these kind of threads really interesting. The Ac# temprature was just not a concept I was familiar with.

P.S.: I checked out your work and I just have to tell you that you make beautiful pieces. Especialy the feather pattern dasmascus, witch has always been my favorite pattern.

Good job asking questions and doing your home work.

Hoss

 

[stezann]

Ac3 (or Acm) is the name given to the temperature at which we have dissolved all the carbon and got full austenite. Just above that is where i go with normalization.
It take into account hysteresis and alloy effects, for 52100 it is not the same as A3 in the pure iron carbon diagram in equilibrium conditions.
Where did you find that reference for 52100?