Why is this happening!??? (forging)

[Mike Turner]

All great advice here. When I started I was using my shoeing forge (NC Whisper Mama) and quickly found out the way your burner comes into your forge can also cause problems. As with the NC Whisper Mama the burners blast right onto your work and it also has the wrong atmosphere. Once I made my own forge with the burner on a tangent I no longer had the pitting.

 

[Alarion]

In fact when using Tamahagane (japanese steel) to make the billet for a sword, the smelted part rich in carbon is then mixed with lower carbon parts and forged repeatedly to make it homogeneous and bring the carbon content down to the level desired by the smith.

 

[Troop]

Those blades show classic signs of oxidation in forging. When I was teaching it would invariably show up on blades when students had the air blast too extreme or took too long to forge the knife. Both conditions expose the steel to oxygen long enough for large bits of steel to be turned into iron oxide and leave the blade, and also gets pounded back into the surface making pits which then oxidize deeper on subsequent heats.

There are two things that can happen to hot blade steel in the atmosphere, you can have the air take carbon - decarburization, or you can have the air take iron- scaling. Many confuse scaling with decarb when it is oxidized iron. Heavy scaling will give you things like this, while light scaling can actually help a little to fight decarb by removing iron from the decarburizing surface and maintaining a better ratio of the two. Carpenter steel did studies that involved heating steels in very oxidizing atmospheres which resulted in steels that had a higher concentration of carbon on the surfaces. This seemed insane, as everybody knows you must use a carburizing flame to carburize steel, until you stopped to think that there was no carbon added but instead iron was removed until the iron/carbon ratio was skewed in favor of carbon.

Why is a "reducing" atmosphere called that? Because it works very well in smelting to reduce iron oxide to pure iron. Atmosphere rich in carbon monoxide with an empty space hungry for another oxygen atom will strip it from iron oxide to form carbon dioxide and take it out the top of the furnace leaving purer iron behind. It is this funny balancing act that makes carburizing so tricky in anything other than an entirely closed atmosphere, and why the vast majority of claims of adding carbon to steel while forging is absolute bunk put forward by people that obviously have a very limited understanding of the complex chemistry involved. It’s complexity became very clear to me when I started messing with bloomery smelting and saw the chemical processes at work.

For many years now, all the scholars writing all the books stated that in ancient times only soft iron was made in the direct bloomery process, which then had to be cut up and carefully made into steel by carburizing in the forging process…wrong. The reality is quite the opposite. Steel and even cast iron is quite easy to make in a bloomery hearth and the forging process is much more often a matter of reducing the carbon content and evenly distributing it

…. I have wandered quite far from pock marks in blades, haven’t I?

Thank you for the explanation, Mr. Cashen. I believe that that is exactly what is happening; I'm sure my messy work habits ref. scale on my anvil is part of the problem, but I think I'm getting my forge much too hot, to the point where you mentioned that I'm turning my steel into, ehhh...."something not good."
I ordered some soft firebrick today to close off one of the side portals of my Forgemaster. That should reduce some O2 concentration inside the forge, right? Which will help to prevent all these bad things from happening???
- Thanks again.

 

[Troop]

All great advice here. When I started I was using my shoeing forge (NC Whisper Mama) and quickly found out the way your burner comes into your forge can also cause problems. As with the NC Whisper Mama the burners blast right onto your work and it also has the wrong atmosphere. Once I made my own forge with the burner on a tangent I no longer had the pitting.

Hey Mike,
Yup. My Forgemaster has two jets that literally blast flame down right on top of my work. I gotta reduce that pressure down from 10 lbs., it looks like.
- Thanks

 

[Troop]

In fact when using Tamahagane (japanese steel) to make the billet for a sword, the smelted part rich in carbon is then mixed with lower carbon parts and forged repeatedly to make it homogeneous and bring the carbon content down to the level desired by the smith.

Alarion, thanks, but, this smith will be happy just to not ruin his steel.

 

[Teknition]

I'm not sure how many "openings" you have in your forge but you only really need 2. One opening is to put your steel in the forge and the other is the choked opening for the burner. With only 2 openings you will find it easier to control the atmosphere in your forge. Light your forge and adjust your gas pressure to something suitable for forging (in the 5 psi range), then adjust the choke on your burner so you have a bit of flame (dragon's breath)coming out the opening that you put your steel in.

If you run your forge with a bit of flame coming out the opening, you will have attained a reducing atmosphere (all the gas isn't getting consumed inside the forge and has to find oxygen outside the forge to finish the burn).

Be careful when putting steel in and pulling it out of the forge- the dragons breath can be hard to see in some lighting conditions.

You may also find it helpful to move the steel off to the side a bit in the forge so the blast from the burner isn't directly on your blade. Let the radiant heat inside the forge bring your blade up to temperature.

Brad

 

[fitzo]

A fuel-rich reducing atmosphere will have an orange-yellow flame coming out of the forge 3-4" minimum. This is fuel finally burning as it finds oxygen in the air outside the forge. Blue flame exiting the forge is undesirable and indicates excess oxygen.

Adeed: Not being a wiseguy, but your forge is not the best design for bladesmithing. You are going to have to learn to carefully adjust it to get a proper balance.

 

[Troop]

Thanks, Brad. I think closing off one of the side portals with the firebrick should help. Also, like you mentioned, I'll put my steel in off to the side so it doesn't have the flame blasting right on top of it.
I guess you could say that I have five openings in my forge. Two jets, (coming down from up top,) two side portals (square openings, one on each side of the forge, approx. 4" x 3"), and a big, front door that swings open....a lot of "holes."

- Thanks again.

 

[Troop]

A fuel-rich reducing atmosphere will have an orange-yellow flame coming out of the forge 3-4" minimum. This is fuel finally burning as it finds oxygen in the air outside the forge. Blue flame exiting the forge is undesirable and indicates excess oxygen.

Mike, As my forge is right now (before I close off one of the portals with firebrick), I have orange-colored flame busting out of both ends approx. 8".
Is this O.K.?
- Thanks

 

[fitzo]

Orange is good. I agree with what everyone has said about learning to throttle it back some. Those damned burner blasts are probably frying your steel. Try and keep the flame off the blade in there if there's room.

Another thing is to not overheat the steel. Here is something you might try to teach you to read temp: get a box of 20MuleTeam Borax. Sprinkle a small amount (onto a spot your steel) and stick it in the forge. Watch (with polycarbonate safety shades on) until you notice the flux start to bubble. This will tell you that the blade is right around 1900. Forge now. Eventually you get used to the color that you should forge at. It's best to learn to forge in the dark or in deep shade.

Hope that helps.

 

[Troop]

Orange is good. I agree with what everyone has said about learning to throttle it back some. Those damned burner blasts are probably frying your steel. Try and keep the flame off the blade in there if there's room.

Another thing is to not overheat the steel. Here is something you might try to teach you to read temp: get a box of 20MuleTeam Borax. Sprinkle a small amount onto your steel (small amount) and stick it in the forge. Watch (with polycarbonate safety shades on) until you notice the flux start to bubble. This will tell you that the blade is right around 1900. Forge now. Eventually you get used to the color that you should forge at. It's best to learn to forge in the dark or in deep shade.

Hope that helps.

Wow... thanks, Mike, for the temperature reading trick, until I develop enough "know-how" to learn to read the steel. :thumbup:

 

[GlennM]

I started out on a similar forge and found I could reduce the air intake with small pieces of steel wool packed around the air intake where the gas tube crosses the venturis. Made it manageable but nothing like the forced air I'm using now.You will notice better gas mileage.Play with it till you get it tuned to your liken.

 

[Troop]

I started out on a similar forge and found I could reduce the air intake with small pieces of steel wool packed around the air intake where the gas tube crosses the venturis. Made it manageable but nothing like the forced air I'm using now.You will notice better gas mileage.Play with it till you get it tuned to your liken.

Thanks, Glenn,...it looks like I'm going to have to mod the heck out of this thing in order to make it work for bladesmithing.

 

[SteelSlaver]

I don't think you are going to have to modify it that much. Jut a learning curve on running it. You could get a small chunk of kao wool and play with closing off the air ducts no real mods untill you see what is needed. If you have problems keeping your work out of the path of the flame you could use a baffle. Get a piece of open ended stainless pipe and set it in your forge so that your work lays inside the pipe and it defects the blast. Also makes the heat more even on the work piece. There was a thread on doing this for ht a while back. Jim

 

[Troop]

I don't think you are going to have to modify it that much. Jut a learning curve on running it. You could get a small chunk of kao wool and play with closing off the air ducts no real mods untill you see what is needed. If you have problems keeping your work out of the path of the flame you could use a baffle. Get a piece of open ended stainless pipe and set it in your forge so that your work lays inside the pipe and it defects the blast. Also makes the heat more even on the work piece. There was a thread on doing this for ht a while back. Jim

Jim, Thanks for the great idea!!! :thumbup:
I would never have thought of that! Does the blade need to rest "flat"? So, I'd have to flatten the bottom of the SS pipe out? Any ideas on where I can get a wide (large diameter) SS pipe?
- Thanks again, Bro'.
P.S. I paid a lot of money for the forge, so if I can do something to make it work, that would be great.

 

[Raymond Richard]

The pipe in the forge works good for heat treat but your work will take much longer to heat up.

You also mentioned you were having trouble forging A-2. Not a steel I would advise to forge starting out since its air hardening.

 

[Troop]

The pipe in the forge works good for heat treat but your work will take much longer to heat up.

You also mentioned you were having trouble forging A-2. Not a steel I would advise to forge starting out since its air hardening.

Ray, let me tell you something.....it's seems like after every heat, the A2 would get harder! I'm not kidding. Felt like I was forging Kryptonite or something! Holy Mole...was that frustrating! I was going in circles. I'm not doing that again anytime soon. What a waste of steel.

 

[Raymond Richard]

The thing with A-2 the second you remove it from the heat it will start to harden up. It needs to be done at much higher heat than the 1095. D-2 is even worse. Leave the air hardening steels alone.

 

[Troop]

The thing with A-2 the second you remove it from the heat it will start to harden up. It needs to be done at much higher heat than the 1095. D-2 is even worse. Leave the air hardening steels alone.

Best advice I've heard all day. Thanks.

 

[Donald Babcock]

Here are a couple of questions for you that might help clear things up a bit.

What temp are you working your steel at? You can base this by the color of the metal when it comes out of the forge as long as your shop isn't to brightly lit. Most blacksmith shops were dimly lit so the smith could see the color of the metal. Most steels (at least the ones that I am familiar with for blacksmithing) are worked around 1800 degrees which would be a bright orange color. If the metal is more of a yellow color then you are getting the steel closer to 2000 degrees and the metal will oxidize more at that tempurature. If it is a dull orange/bright red then it is around 1500 degrees and wont move as easily

Are you wiping the scale off your anvil when you put the steel back in the forge? If any of the scale is left on the anvil when you start forging again then it will leave "dents" in the hot metal that will have to be ground out later (I learned this the hard way).

How much scale are you noticing on your steel when it comes out of the forge? If there is a lot of scale that comes off with the first few hammer blows then your forge is too hot and you are causing the metal to oxidize to much.

I might be on the wrong track with this, but it seems to me that you are getting the steel to hot and causing to much oxidation resulting in a lot of scale that is leaving those dents in the metal. Either that or you just have crappy steel that has impurities in it that are forming voids when they burn out.