Thread: forge ideas

I've seen photos somewhere on the web from a guy who made his forge by stacking four to six 4x4x8" firebricks into a chamber. Like Mike mentioned, you can reposition them as needed.

I'm far from an expert on physics, but it seems like the main considerations when building a forge are: size of the chamber relative to the size of your burner, the shape of the chamber, the heat-reflecting/absorbing properties of your forge liner, and the mass of the forge liner.

- To a point, smaller is better when working with a small heat source like the JTH7 torch. A one-brick forge with a 1 1/2" round chamber will let me hit forge-welding temps on a 4" section of steel. In a two-brick forge with a 4" round chamber, I can't get it above a nice forging temperature, except maybe if I let the flame hit the steel directly for a few minutes.

- If the chamber is too small, though, it will prevent the air from moving around the steel, and you'll only get heat where the flame makes contact.

- I've heard round chambers allow for the heat to swirl around better and even things out. I haven't tried a square one, so I'm not sure from experience...

- Too much mass in the liner and it will take a long time to absorb heat and get up to temperature. That's why the hard firebricks don't work very well.

You'll probably build several forges before you get one you really like, so keep at it. Or you could do what I chose to do and get a ready-made one.

Josh

Originally Posted by bg42

I made forge out of an 18 wheeler brake drum,an angle grinder, mig welder and some pipe . the air supply is from an old reversible vacuum cleaner
It will melt steel if you don`t keep an eye on it
kind regards Peter

here are the pics as promised ,the first is a general set up ,you can see the vacuum cleaner hose, this will be changed in the near future ,I have a blower and a small 1/4 horse electric moltor, the second is air input and the leaver on the side lets the ash and clinkers from the air supply pipe the third is the top with bricks ,I usually position those each side of the air supply and fill the area with coke or coal , there is coke in there at the moment, notice the slots cut out from the side to allow for long pieces ,at the bottom of the forge under the coke there is a cast iron drain grate to stop the coke from falling through .
Once the materials were together it only took a couple of hours to knock up ,like I said ,nothing fancey but it will melt hardened steel

Originally Posted by spazola

The blue stuff is layout dye, It makes it easier to scribe lines on metal.

Thanks, thats what I thought after posting, haha. Why no use a sharpie?

Peter,

Thanks for the pictures of your brake drum forge. It looks like it is all business to me.

Tjiscooler,

A sharpie works, but the layout dye works better it does not rub off as easy.


Charlie

To get the most out of your blade you need to fully harden it. When hardening steel the temperature is first raised above the critical temperature (CT) this forms austenite inside the austenite are the carbon atoms. If the steel is then cooled quickly enough the carbon is trapped inside a new hard crystal structure called martensite. This has a lot of stress in it which is relieved by tempering, which turns some martensite into bainite. A steel without enough carbon in it will not harden enough, and a blade cooled too slowly (a water cooled steel in oil/ an oil cooled steel in very thick oil) will not produce the most amount of martensite it is capable of.
To heat treat efficiently you need to understand metallurgy. The better your understanding, the better you can choose a method of hardening your blades. Recipes can provide results when followed properly, but without the physics you have no explanation or starting point to understand what went wrong. Nor can you teach someone unless you know what is happening. That being said...

Simple carbon steels, and the W series tool steel harden in water. Thin sections (under 3/32) can crack. That is when you quench in something a little thicker. Too much insulation will not form martensite, which is what we are after.

O1, 51xx and others are Oil quenched because of their chemical makeup they generate too much stress in the rapid cooling water gives them.

D2 is an air hardening steel used in tools and dies, it could be considered stainless because of its high chromium content, because of its makeup even thick as hell motor oil/engine sludge could potentially crack it. quench this baby in water and it will pretty much explode.

My advice to anyone, if you are serious about making quality blades, go to the library and in the reference section dust off a copy of The American Machinery's Handbook or The Machinist's Handbook (you might be the first person to look for it in a while). Open it up to steel and read everything from simple steel's composition to the alloys you might use, then read everything regarding to heat treating it will tell you exactly what is happening in your steel and how it's doing it.

Good luck, lets see some amazing steel!

Originally Posted by bg42

here are the pics as promised ,the first is a general set up ,you can see the vacuum cleaner hose, this will be changed in the near future ,I have a blower and a small 1/4 horse electric moltor, the second is air input and the leaver on the side lets the ash and clinkers from the air supply pipe the third is the top with bricks ,I usually position those each side of the air supply and fill the area with coke or coal , there is coke in there at the moment, notice the slots cut out from the side to allow for long pieces ,at the bottom of the forge under the coke there is a cast iron drain grate to stop the coke from falling through .
Once the materials were together it only took a couple of hours to knock up ,like I said ,nothing fancey but it will melt hardened steel

If you use coal, how do you light it?

Originally Posted by Twalsh341

To get the most out of your blade you need to fully harden it. ...

Do you need to do this for every blade? The ABS spends a good deal of energy specifying a differentially hardened blade in their testing criteria. There are a lot of folks making Japanese style hamon on their blades. By definition, those are not fully hardened. Some steels do not through harden and others do. Which of those are best for razors?

... This has a lot of stress in it which is relieved by tempering, which turns some martensite into bainite. ...

I agree that you are better off understanding metallurgy when heat treating, but I want to know how tempering produces bainite. And explain the difference between tempered martensite and bainite. Why is one better or worse than the other? How does this play into the world of razors?

I throw some kindling between the bricks with a fire lighter light it up and turn on the air put some more kindling on till its going pretty good then slowly start adding the coal or coke, once that starts to light add more then a cup of kerro add more coal as it begins to light once you have a good amount of coal going fill the space between the two rows of bricks with coal then go and do something else for 20 min,buy that time its raging and ready to go
kind regards Peter

Originally Posted by Mike Blue

Do you need to do this for every blade? The ABS spends a good deal of energy specifying a differentially hardened blade in their testing criteria. There are a lot of folks making Japanese style hamon on their blades. By definition, those are not fully hardened. Some steels do not through harden and others do. Which of those are best for razors?

I agree that you are better off understanding metallurgy when heat treating, but I want to know how tempering produces bainite. And explain the difference between tempered martensite and bainite. Why is one better or worse than the other? How does this play into the world of razors?

Differentially hardened blades are technically fully hardened, the part of the blade that is hardened (under the hammon) needs to be fully hardened like any other blade, on one of these though there is a boundary where a softer steel structure comes into play. the came thing goes for case hardened blades. the cutting part needs to be fully hardened, if it is connected to a piece of softer steel that is okay, as long as the soft steel is not your cutting edge.

Yes some steels harden to different depths, that is mostly with case hardened steels relative to amount of carbon that penetrates the steel during carburization; the other case is when thick sections are hardened where internal heat can temper out the quench from the inside/cool too slowly. Razors are so thin that any of these issues become irrelevant, unless you were differentially heating a 4/8ths razor with a huge spine I don't think you could cause those types of problems. Something else would be preventing the blade from hardening. Martensite is a very hard crystal structure formed from rapid cooling of austenite, the carbon gets trapped in the martensite.

Originally Posted by Twalsh341

... With the thinness of razors a very hard blade is more likely to crack due to the small cross section our friend bainite prevents this from happening.

Then what's different between the tempering cycles for martensite and bainite? All you've explained up to now is that bainite is a degradation structure between martensite and pearlite, not that there is anything special about it.

How can you tell you have bainite instead of martensite?

Why do we not see more bainitic razors then if this is such a great structure to have in the steel?