1095

[MCoughlin]

all this talk about 1095...I'm currently on my 3rd try for a particular knife I'm working on for my brother in law. My first 2 attempts have gone to s%$t but I'm doing my third try tonight once it gets dark. I'm also using water and as a related question...it has been mentioned that with a 1/4" thick blade of 1095 fully hardening can be a problem when quenching in oil...Is it right to assume that water would be the opposite end of the spectrum and causes the steel to harden almost tooo fast causing cracking,warping etc? I have experienced both in the past. I think water quenching is a bit of an art in itself....
Mike

 

[fitzo]

For anyone who wants to read a bit about the complexities of decarburization, check out the section starting on page 306 of this Google book:Steel Heat Treatment, by George Totten
It's no wonder Robert didn't want to get into numbers.

 

[Mike Krall]

I don't want to get into numbers ! Scale is iron oxide, decarb is a layer of steel near the surface that has reduced carbon content. Off hand I don't have a photo of decarb, perhaps Kevin does. In any case there is a carbon gradient dependant on a number of variables. If the carbon in the atmosphere is richer than that of the steel, carbon will be added to the steel [carburizing] .If the carbon in the atmoshpere is less than that of the steel, carbon will be removed from the steel [decarburization].

Mete, I can feel one of those tail chasing things I seem to get into coming on... and OK, no numbers... even though I'm seriously curious about the percentage carbon loss.

Iron Oxide as scale... so though a forge may have a reducing atmosphere, there is still enough oxygen to oxidize the iron in the steel.

The rate of decarburization is reduced by having a reducing atmosphere in the forge ... more fuel than oxygen... but the unburned gas (is it mostly as carbon and carbon monoxide?) hasn't got a high enough carbon content to add carbon to the steel, but it is high enough to significantly reduce the carbon loss (decarb.)?

I better quit while I'm still able to convince myself I'm marginally ahead...

Mike

 

[Mike Krall]

For anyone who wants to read a bit about the complexities of decarburization, check out the chapter starting on page 306 of this Google book:Steel Heat Treatment, by George Totten
It's no wonder Robert didn't want to get into numbers.

Thank you Fitzo... you may have saved me. One of the best things in the world for me to do when I start with numbers is total immersion... after a while I have to stop, and it feels so good...

Mike

 

[Stacy E. Apelt - Bladesmith]

Mike, while your math may be right, the argument is specious.
The math you used is based on the just carbon content. We are not forging a pile of carbon , but a piece of steel with .89% carbon. The loss to the carbon may be 5.6%, but the loss to the steel is only .05%. It is the steel we are making a blade from, not the carbon.

You are correct that the loss increases with more high heat time and higher heats. The forge may be balanced for a reducing atmosphere when forging, but when you remove the blade for forging, the oxygen in the air is higher.You are also correct that the balanced or slightly rich forge chamber is not rich enough, nor is the blade in there long enough, for carburization to happen.

When making damascus there is a higher degree of carbon loss, which is one reason for a power hammer or press. More heats = lower carbon content. If you lost a lot of carbon making damascus from 1084 and 15N20, the total carbon content may fall to .60% . Properly heat treated and tempered, this will produce a superb knife.

Too much emphasis is put on carbon content most of the time.
When making tamahagane, having a mix of carbon content from 0.00% to as much as 3.00% is important, and the smith knows how to fold and blend them for a final carbon content of .50-.60%

Scale, decarb....all add up to loss of carbon - which is unavoidable - but can be reduced to a certain degree, and compensated to a certain amount.

Glad to see folks thinking about what is happening in the steel.
Stacy

 

[Tai Goo]

Yes, a full quench is putting the entire blade immediately in the tank.
A differential temper is when (after tempering the whole blade) you use a small torch ( brazing tip or similar little flame) and slowly heat the spine up. The blade edge is usually sitting in a shallow pan with about 1/4-1/2" of water in it. The blade is rocked constantly to keep the tip cooled down, too. As the spine and main blade body heat up, the temper colors will "walk" down the blade surface (you have to sand the scale off the blade to clean metal first, of course) first showing a golden yellow, then pale peacock, the darker blue. When the darker blue is on the spine, the yellow should be down toward the edge area at the waterline. Just lay the blade over in the pan and let it cool, once you have drawn the spine down to the degree you want. This will often show a nice temper line when you polish and etch the blade. The spine will be softened much more than the edge (differential) and the whole blade will be tougher for it. It would be nearly impossible to break the blade from the spine while pounding it while splitting wood ,or with severe abuse. The edge might chip if you hit a rock,it might get stuck while chopping down a tree, but the blade won't bream without a lot of abuse and bending
Stacy.

I think you are better off if you bake the blade in an oven first, to get the temper just right along the edge, nice and even around 450,... give or take depending what you want, rather than trying to "walk" the temper down to the edge with a torch. Then after it cools, draw the spine down with a torch using water to protect the edge.

 

[Stacy E. Apelt - Bladesmith]

That is what I said to do -
A differential temper is when ( after tempering the whole blade))..............
Stacy

 

[Mike Krall]

Mike, while your math may be right, the argument is specious.
The math you used is based on the just carbon content. We are not forging a pile of carbon , but a piece of steel with .89% carbon. The loss to the carbon may be 5.6%, but the loss to the steel is only .05%. It is the steel we are making a blade from, not the carbon.

You are correct that the loss increases with more high heat time and higher heats. The forge may be balanced for a reducing atmosphere when forging, but when you remove the blade for forging, the oxygen in the air is higher.You are also correct that the balanced or slightly rich forge chamber is not rich enough, nor is the blade in there long enough, for carburization to happen.

When making damascus there is a higher degree of carbon loss, which is one reason for a power hammer or press. More heats = lower carbon content. If you lost a lot of carbon making damascus from 1084 and 15N20, the total carbon content may fall to .60% . Properly heat treated and tempered, this will produce a superb knife.

Too much emphasis is put on carbon content most of the time.
When making tamahagane, having a mix of carbon content from 0.00% to as much as 3.00% is important, and the smith knows how to fold and blend them for a final carbon content of .50-.60%

Scale, decarb....all add up to loss of carbon - which is unavoidable - but can be reduced to a certain degree, and compensated to a certain amount.

Glad to see folks thinking about what is happening in the steel.
Stacy

I get a lot of what you are talking about but I don't understand it well. It's why I'm in this.

My whole point of reference is trying to understand relative carbon loss. To me, your reference to 1089 losing 5 points of carbon through forging and process before quench implies I should be heat treating for 1084, not 1089. I would try to deal with those two steels differently.

Mike

 

[mete]

Good forging and HT practices will minimize carbon loss. The only way to find out how much carbon is lost is to have chemical analysis which not too many do.This is where the "art" of 'smithing comes in. Do some experimenting with the materials and proceedures that you use to find what's best.

 

[Stacy E. Apelt - Bladesmith]

Mike,
It is good for a smith to think about things like carbon loss. That way you will use good forging skills. There is the temptation to over-think it, though. The HT for any simple carbon steel ( 10XX steels) is an average of all the parameters of the steel, and all the things that were done to it prior to HT. Everything affects the steel to some degree. The actual carbon percentage in steel can vary a good bit,+/- 5% ( of the total carbon, as you calculated it. In the case of 1089,thus from .95 to .84) It doesn't really make all that much difference in the final results, because that variable is figured into the average. However if the temperature was off 5% that would make a 1525F soak run at anything from 1450F to 1600F. That would make more difference in the final results in the blade than the carbon content variance.

The point I'm making is that with good forging skills, and a controlled HT, you can get the most from the steel.

Starting with a steel of a known constitution is a plus. Aldo's steel is made under good conditions and analyzed for exact content. If you forge it in the right atmosphere, austenitize it properly, quench it in the right oil, and temper it to the right degree.........it will make a good blade. Any other steel of known content will, too. It is the Heat Treatment that makes a good blade, not the carbon content variance.

Some areas where smiths can try to limit their carbon loss are:

Annealing - Use a neutral to slightly reducing atmosphere in the forge. Cool in an oxygen restricting environment (closed container of vermiculite/lime). Avoid overheating the steel. This is one of those places where "nonmagnetic plus a bit" is good enough. The annealing temperature of simple steels is the same as the hardening temperature.

Forging - Use a slightly reducing atmosphere in the forge. Know the forging range of the steel you are working ( No, they all don't forge at Red Hot ). Run the forge in the temperature range that you plan to forge at, thus avoiding overheating the steel. Plan each heat while the steel is heating up, to maximize the hammer time per heat, and minimize the number of heats. heat only as much of the blade as you need to for each forging cycle. For example - No need to heat the entire blade to forge out the tang.

Normalizing - Use the proper temperatures in as controlled an environment as your equipment can deliver. If using a forge, a slightly neutral to reducing atmosphere is desired. Again, avoid overheating. Many smiths drop the temperature about 25-50F each cycle for three cycles.

Austenitization - This is where the soft steel becomes a hard blade. The more control over the conditions and fluctuations - the better the results. If using a HT oven, this is not much of a problem. If using a forge, you have to have as much control as possible for best results. Keep the atmosphere balanced. Most forges are at their lower end at austenitization temps, so the air/gas mix may need to be adjusted. A PID controlled forge can be controlled to stay within the desired temperature range. Coating of the blade with something to block oxygen and flame contact is a plus here (Turco, PBC,thin layer of clay, etc.). Allow the steel to come up to austenitizaton temperature, and hold at that temp for the desired time ( time does not start when you stick the blade in the forge/oven). While soak time should be kept to the minimum needed to fully dissolve and disperse the carbon/carbides, remember that overheating is the enemy, not oversoaking.

Stacy

 

[Tai Goo]

That is what I said to do -
A differential temper is when ( after tempering the whole blade))..............
Stacy

By golly, you sure did,… guess my speed reading needs a little work.

Carry on...

 

[Mike Krall]

That's a nice lick, Stacy...

Mike

 

[J.S. Carter]

I don't want to get into numbers ! Scale is iron oxide, decarb is a layer of steel near the surface that has reduced carbon content. Off hand I don't have a photo of decarb, perhaps Kevin does. In any case there is a carbon gradient dependant on a number of variables. If the carbon in the atmosphere is richer than that of the steel, carbon will be added to the steel [carburizing] .If the carbon in the atmoshpere is less than that of the steel, carbon will be removed from the steel [decarburization].

So if I burried my blade in my coal forge and brought it up to temp and soaked it since it's surrounded by burning carbon, would this be considered a "carburizing" environment?

 

[Aldo Bruno]

Stacy,
I love when you talk about my steel this way.

 

[mete]

J.S.Carter, yes that would be a carburizing atmosphere. When you take a blade out for forging you will immediately change to a decarburizing atmosphere. Also the higher the temperature [as in forging ] the greater the carburizing or decarburizing tendency.
It all depends on time , temperature , and atmosphere.

 

[sharpeknives]

I personally love 1080/1084. Its very forgiveing. Also easy to work. I use a simple method : Take to critical and do a full quinch or an edge quinch, if I do an edge quinch once the blade scales I submurge the intire blade. Temper at 450 for 1.5 hrs,cool in a brine then retemper again.
I love the people here and am learning alot every day. I do think we all tend to overwhelm the beginner with info.
My advice would be to choose a metal, 1080 or any 10xx is not too expensive , learn that steel, play with different temper temps and hardenig methods. In the beggining keep it simple. Make a good knife and make each that follows a little better. When you are comfortable with 1080 (or whatever you choose)move to something else and learn it.
This is not a race, have fun at it.