Forging temps/ carbon loss?

[sunny_2_75]

Hello everyone. I have a question. I am not a forger, however everything I have read about heat treating high carbon steel says to get it to the critical point, soak for a bit and imediatly get it quenched. They say to do this because the carbon is attracted to oxogen and they like to take off together.So....what happens to the carbon when forging...do you loose a fair amount?...confused!

 

[thompsonblades]

Yes, you do loose carbon, but that also helps to make the metal softer to shape. There some tricks to putting the carbon back in though, one you've got the shape you want. I like to quench in used motor oil.

 

[sunshadow]

you will always lose carbon at the skin of the piece. Iron will oxidize faster than carbon will diffuse out, so I forge hot and scale off iron oxide faster than the decarb zone

-Page

 

[SShepherd]

Yes, you do loose carbon, but that also helps to make the metal softer to shape. There some tricks to putting the carbon back in though, one you've got the shape you want. I like to quench in used motor oil.

oh boy

only worry about it if you overheat the steel and it starts "throwing sparks".

You can not add carbon back to steel by quenching in used motor oil, charcoal mud, or the bones of a dead saint.

 

[Don Hanson III]

Very little, if any carbon is lost when forging properly.

 

[sunny_2_75]

Thanks, I am still abit confused. All the material removal makers I have seen have there quench tank right next to there oven or gas forge so they can quench immediatly so as to not lose temp and for carbon loss. The forgers have there still up to temp over and over while they are forging there blade. So I gather it is just to quench at crital temp and not to let it drop....not so much the carbon loss...right?

 

[SBuzek]

Right,getting the temp. down during the quench is the important part.As in 1095 having only a second to get below 900 deg . The carbon loss is not that much.
Stan

 

[Justin King]

Hello everyone. I have a question. I am not a forger, however everything I have read about heat treating high carbon steel says to get it to the critical point, soak for a bit and imediatly get it quenched. They say to do this because the carbon is attracted to oxogen and they like to take off together.So....what happens to the carbon when forging...do you loose a fair amount?...confused!

Some steels have such a narrow hardening window that even a few seconds delay in going from the forge to the quench can prevent the steel from hardening properly. This is may be the original logic behind what you have read. This is true mostly of shallow-hardening low-alloy steels such as 10-series.
Carbon loss from forging is generally not considered to be a huge issue, the effect should be only on the surface of the workpiece and this affected material is usually ground off after heat treat, at least from the edge area.

 

[delbert ealy]

Forget about the carbon loss, like has been said above, the only carbon loss in at the very surface of the steel and when forging that layer flakes off as scale.

The reason for haste when heat treating is that for most steels that are forged you have only a short period of time to get the blade cool. It has nothing to do with carbon loss.
Del

 

[Bruce Bump]

oh boy

only worry about it if you overheat the steel and it starts "throwing sparks".

You can not add carbon back to steel by quenching in used motor oil, charcoal mud, or the bones of a dead saint.

If you experience the 4th of July sparkler its too late and that blade is ruined. Just keep the heat down when forging and thermal cycle to normalize (reduce grain size) and anneal (soften and stress relieve). When re heating to quench (harden) just bring the steel up hot enough to be nonmagnetic (about 1500f) and no hotter or else the grain will grow again and quickly quench. The quench oil is near the heat source because you only have a second or two before too much heat loss. This all works best if you can see the colors. If you are forging in the sunlight its nearly impossible to tell what is happening. Forge in the dark or in the shade.

 

[Matthew Gregory]

Forget about the carbon loss, like has been said above, the only carbon loss in at the very surface of the steel and when forging that layer flakes off as scale.

There it is, right there. Unless you're like me, and your forging skills suck so badly that it takes you two hours of heating and banging to come up with a banana shaped object that you can grind into a knife!
Also, the size of the scale has nothing to do with it - scale is carbon loss, regardless of how big it is - and the longer you work it, the more there will be. Proper forge atmosphere will certainly help reduce it, though...

The reason for haste when heat treating is that for most steels that are forged you have only a short period of time to get the blade cool. It has nothing to do with carbon loss.
Del

Again, Del's nailed it. No type of quenching is going to increase carbon content to offset the losses during forging. Get it hot, move it around quickly and efficiently, and normalize. It's just that simple!

 

[deker]

Also, the size of the scale has nothing to do with it - scale is carbon loss, !

I'm going to disagree with you on this one Matt. Scale doesn't contain carbon. Scale is iron oxide (FeO2)...it's just really advanced rust. We all know that iron likes oxygen, and when it gets some, it makes rust. Now, scale is just what happens when you accelerate this reaction by adding a lot of energy into the system. So, iron at the surface of your steel, at high temperatures, with oxygen present precipitates iron oxide on the surface of your steel. So, the only thing you lose to scale is iron.

So, where does the carbon go? Why doesn't a piece of 1050, scaled to death become 1070 or 1095? If I understand it correctly (after chatting with Delbert about this) Carbon also has an affinity for oxygen. So, when some of that spare carbon at the surface enters a hot, oxygenated atmosphere, it attaches to oxygen atoms and becomes...carbon dioxide (CO2).

I don't know the rates of these reactions, but the chemistry of it all makes sense. I know it's a picky point, but the "scale is carbon" thing just drives me nuts for some reason.

-d

 

[White Rabbit]

I'm going to disagree with you on this one Matt. Scale doesn't contain carbon. Scale is iron oxide (FeO2)...it's just really advanced rust.
-d

I believe what he was saying is that the scale is an indicator of carbon loss in that carbon is obviously lost when the iron oxidizes.

 

[Nebulae]

I believe the rate of carbon loss is something like .6-.8 mm/h depending on the original C content of the steel and the forge atmosphere.

I also think (correct me if I am wrong) that part of the reason decarb is not such an issue is that most forgers use a carbon heat source. Indeed it is actually possible to add C to the steel if left in charcole, or something of the sort for a long period of time.

this is also the reason for vacume, or inert gas heat treating kilns, because for large industrial tools, in steels that require long very soak times may suffer from decarburization

 

[Stacy E. Apelt - Bladesmith]

decker is correct - Scale is iron oxide. There is little or no carbon in it.

The carbon was bonded to the iron, and as it heated up above 1500F, they became so disassociated that the carbon combined with the oxygen in the air, making a stronger bond than the iron had.This new molecule was carbon dioxide, and floated away as a hot gas. At the same time the super-heated iron was combining with the oxygen in the air,too. This made a very stable iron compound called iron oxide ( actually forge scale is closer to hematite- Fe/2-O/3. Rust is hydrated Fe/2-O/3+H/2-O ). We just call it scale. The scale is collected from the anvil pan by smiths in many parts of the world ,and ground down into a fine abrasive - rouge.

Unless the bar of steel was greatly over-heated in the forging, or the air blast/supply to the forge was way too high, the amount of iron and carbon loss is fairly equal (99% iron and 1% carbon). With proper forging technique, forge atmosphere regulation, and the grinding/filing/sanding of the outer surface after forging and HT, the finished blade should be nearly the same carbon content as the original bar of stock.

And as said before, unless the blade is carburized in a metallurgical special oven, there is no way to add carbon or special elements to the blade.....not by quenching in blood, or charcoal, Quaker State, or anything.

Stacy

 

[delbert ealy]

I believe the rate of carbon loss is something like .6-.8 mm/h depending on the original C content of the steel and the forge atmosphere.

I also think (correct me if I am wrong) that part of the reason decarb is not such an issue is that most forgers use a carbon heat source. Indeed it is actually possible to add C to the steel if left in charcole, or something of the sort for a long period of time.

this is also the reason for vacume, or inert gas heat treating kilns, because for large industrial tools, in steels that require long very soak times may suffer from decarburization

The only way that carbon gets into steel in a solid state is through either carbon monoxide or carbon dioxide, and the only atmosphere that is right to add is a charcoal fire, no other. Any other fire doesn't create the right atmosphere. Even then it takes a lot higher temp to infuse carbon in any quantity and although it can be done at lower temps (case hardening) this only applies to the very surface of the steel, and it takes much more time.
In any forge open to the atmosphere the rate of production of forge scale is much higher than any infusion of carbon.

Like I said earlier, except under very special circumstances carbon loss or gain in forging is a non-issue.

Del

 

[sunshadow]

My experience and what I've seen under the microscope backs up what Del said.
The short of it, if you heat at medium low temperatures to try to minimize scaling you will have visible decarb. If you forge hot enough that you get moderate scaling, you will peel off scale at about the same pace as you get decarb. No issues. You cannot put carbon in a steel with quenching. period.
Diffusing carbon into iron to make blister steel in the olden days involved placing the iron in a sealed vessel with finely ground charcoal and heating the entire vessel for a week. Carbon does diffuse in a solid state but very slowly

-Page

 

[Matthew Gregory]

I believe what he was saying is that the scale is an indicator of carbon loss in that carbon is obviously lost when the iron oxidizes.

True, however it should have been said the way Deker said it, as that is the right answer, and not the dumbed down answer. Thanks, Dek!
I should have thought further on it before posting, and maintained full clarity. My bad.

 

[deker]

True, however it should have been said the way Deker said it, as that is the right answer, and not the dumbed down answer. Thanks, Dek!
I should have thought further on it before posting, and maintained full clarity. My bad.

Don't feel bad, it took me hours of thinking about it and conversing with Del about it to make sure I had my ducks in a row. Even then Stacy beat me up on the chemistry of it...I was thinking FeO2, not Fe2O3...

-d

 

[Ed Fowler]

Your thoughts are right on the money! Rex shot a chemistry on a 5 1/2 inch round bar, Doc forged it to a 3 X 3 inch bar and send it to me, I forged that bar down at low temps, (1625 f.) to blades using flat dies, many normalizing cycles. After multiple quench and tempering there was no measurable carbon loss from the first sample.