how do i carburizing mild steel (case harden)

R

rons-aun@hotmail.com

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i have mild steel(low carbon) and need to add carbon.i have read to use oil? is there a readily available kind(at the auto store)? how many times should i quench? also,is there another method other than oil? a have a recipe for a super quench. is salt carbon? thanks
 
Welcome to forum.

Do you want the steel has a thin hi carbon layer outside? For this maybe you can find a HT company which also does vacuum, salt or plasma carburizing. If you have a forge you can also do it by placing it in a canister with some carbon in it (charcoal mainly). But this method requires a good heat for maybe 12 hours to a day or so... I dont think there is a "super" quench or something which can add carbon in it...
 
There is a commercial product called "Casenit," or "Kasenit."
Steel is heated to red and then submerged in the powder. It leaves a thin, grey, extremely hard surface.
 
Hi,

+1 for kasenit. I've used that stuff for years for quick and dirty case jobs. I can generally drive the case .020 to .030 deep with multiple dredgings.

dalee
 
Are you trying to make a knife or cutting tool out of mild steel? If this is the case, save yourself a lot of trouble and unsatisfactory results and go get some high carbon steel. These are the proper materials to quench in oil for hardness. Easy materials to start with are coil or leaf springs, lawnmower blades, large saw blades, or old files. I suspect, reading your post, that you are referring to simply quenching mild steel to harden it. This does not add carbon and will not work on mild steel. Case hardening can add carbon to the very surface of mild steel, but is not satisfactory for a knife as you will erase the hardened skin right off the soft core after a couple sharpenings. The "super quench" is the one made up by Robb Gunter, right? It will have some effect on mild steel, but will only really harden it to the low Rockwell 40s or so. (Not suitable for anything but perhaps a throwing knife). It does not add carbon, but forces the absolute most results from what little carbon is already in mild steel. The Shaklee "Basic I" in the recipe (which can be replaced by Calgon or JetDry) is a surfactant, which breaks down water surface tension, allowing a more complete coverage of the steel by the brine. Salt is not carbon, it is sodium cloride; it lowers the boiling point of water which quickens water's quenching speed. These are in no way intended to be complete or authoritative statements and are just pointers to get you started in the right direction. As you learn more about metallurgy and heat treatment you will find out how complex it can be. And, if this answer was way off base, if you really are just trying to case harden, or if I just told you a bunch of things that you already know, my apologies...
 
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always put that extra info in, vorpal, someone here wants it!!!!!

thanks for the stuff about super fast quenchants
 
Grandpa lived on a ranch in the White Mountains of Arizona. He used to get snowed-in 15 miles down a dirt road and had to make do with what was in the barn. (His activities became my education for the day...) He Case-hardened completely shaped mild steel small parts by chucking them up in a pliars wrapped with a spring or wet leather thong, held in a vise. He heated the part with an oxyacetylene cutting torch with a long carbon feather till red to orange-red. then turned off the oxygen, keeping the acetylene flow over the part (which would briefly flash "wet-looking" and coated with a bit of visible soot which burned off until the part cooled below carburizing temperature (whereupon the soot formed a coating to signify temperature low enough to quench). The wet appearance was carbon being absorbed and lowering the melting temperature of the now carburized iron surface by a couple hundred degrees F. and the soot formation kept the surface from oxidizing and flaking off during the quench. When the part was barely dark blood red, he removed the pliars and part (wearing welders glove) from the vise and dredged it in tepid (not warm or cold) water til cool enough to handle. Then he would polish the part bright and shiney and draw it straw yellow with a small neutral oxyacetylene flame (or the electric burner element of a kitchen stovetop), allowing it to air cool afterwards. (Polishing makes the drawing/anneal color easier to see). I saw this done with home made firing pins, mower blade cutting edges and the like. This works for mild steel only -- Do this starting with hi carbon steel and it will surely crack from the quench (the carburized layer of formerly mild steel will now be 1 to 3 percent carbon at the surface, decreasing with depth -- starting with high carbon stock will spoil the high carbon by adding too much carbon)! (Remember never hit the OXYGEN cutting lever even slightly, the cutting torch was used because it has more gas orfices.)
Try this on mild steel scrap first, but I think you will be impressed. Prior comments about best materials give best results apply, but this does work, particularly for the financially challenged. if you make a "hawk" of mild steel, just do the cutting edge after shaping! Not fine but serviceable, I've used this method a few times myself. -Bob Flowers (old retired guy)
 
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Bob Flowers said:
Grandpa lived on a ranch in the White Mountains of Arizona. He used to get snowed-in 15 miles down a dirt road and had to make do with what was in the barn. (His activities became my education for the day...) He Case-hardened completely shaped mild steel small parts by chucking them up in a pliars wrapped with a spring or wet leather thong, held in a vise. He heated the part with an oxyacetylene cutting torch with a long carbon feather till red to orange-red. then turned off the oxygen, keeping the acetylene flow over the part (which would briefly flash "wet-looking" and coated with a bit of visible soot which burned off until the part cooled below carburizing temperature (whereupon the soot formed a coating to signify temperature low enough to quench). The wet appearance was carbon being absorbed and lowering the melting temperature of the now carburized iron surface by a couple hundred degrees F. and the soot formation kept the surface from oxidizing and flaking off during the quench. When the part was barely dark blood red, he removed the pliars and part (wearing welders glove) from the vise and dredged it in tepid (not warm or cold) water til cool enough to handle. Then he would polish the part bright and shiney and draw it straw yellow with a small neutral oxyacetylene flame (or the electric burner element of a kitchen stovetop), allowing it to air cool afterwards. (Polishing makes the drawing/anneal color easier to see). I saw this done with home made firing pins, mower blade cutting edges and the like. This works for mild steel only -- Do this starting with hi carbon steel and it will surely crack from the quench (the carburized layer of formerly mild steel will now be 1 to 3 percent carbon at the surface, decreasing with depth -- starting with high carbon stock will spoil the high carbon by adding too much carbon)! (Remember never hit the OXYGEN cutting lever even slightly, the cutting torch was used because it has more gas orfices.)
Try this on mild steel scrap first, but I think you will be impressed. Prior comments about best materials give best results apply, but this does work, particularly for the financially challenged. if you make a "hawk" of mild steel, just do the cutting edge after shaping! Not fine but serviceable, I've used this method a few times myself. -Bob Flowers (old retired guy)
Click to expand...

This is great information Bob. Particularly for small parts. How was he able to keep the long edge of a lawn mower blade from, at least part of it, oxidizing?
 
Bo T:
He carburized it it 3-4 inches at a time, with the previously done parts mostly buried in a bucket of dry sand. He would heat the entire part when done for the quench. He only quenched it once. He referred to this as "cowboy engineering". (And yes, he also had a pretty good blacksmith forge, which was his preferred technique. Sometimes not everything was in working order, like the hand crank blower. I also remember he would use the local Manzanita wood when he was out of coal or coke. It burned hot enough to melt the bottom out of a sheep herder stove made of sheet metal, but so do other hardwoods.)
Modern machine tool makers use a continuous technique known as "Flame-Hardening" to case harden rails of long milling machines and lathes in one pass. A thick section of steel is exposed to a single pass of very carbon rich oxyacetylene flame. It self quenches the surface as the flame moves on. Only low Rockwell 40 hardening results, and there is danger of warping the rail, but it is a common technique nontheless. - Bob
 
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Thanks. Just one point, when you resurrect an old thread (this one is 5 years old) many of the original posters may not be on board any more. So it might be better to start a new thread to judge if there is current interest in the subject.
 
OK, I am not trying to start a flame war or even bash here. And I am not trying to pick on a new member of the forum, and welcome Bob! We are a very open forum where all are encouraged to speak their mind. It is through these discussions that we all learn. And I am not trying to be blunt, or sound that way (as I am sometimes accused) so read the below like it was said across a coffee table in the comfort of a lounge...

Also not trying to keep a necropost rolling... Figured Stacy would have hung the shackles on this one by now... lol.

This is my take on the above, and if completely wrong, hang me. :)

Carburizing to case harden and flame hardening are two different things. Flame hardening is done with steel which already has a high enough carbon content to create martensite. .30-.65%Cish. It is heated to critical with an open flame and then quenched rapidly. This creates a jacket of martensite at the surface of the steel, and extends as deeply as the heat zone reached in the steel. Carburizing is done to case harden mild steel. Still only reaching a few thousandth's thick. A lawnmower blade, if already a blade, would not benefit from either process as it should have already been hardened and tempered back to a proper hardness for cutting without being overly brittle. Mower blades are typically 1050ish I am told. Heating it in such a manner would create a hard but brittle face on an overly tempered parent steel core I would think. And doing so on a precision manufactured thing like a large mill or lathe bed after it has been milled to final tolerances would make me cringe...

The overall carbon content of our steel was closely controlled at the foundry. Are there ways to heat, beat and fold to introduce more carbon to the steel with a forge and anvil? Yes. But, what we are talking about in this thread and the other areas of the web where this fix is usually mentioned is taking a finished, formed to shape item and making it harder. If that thing is a blade, this just won't work worth a toot, at least not very long. If you have ever seen the dynamic forces at work in a foundry, even thinking some surface treatment, no matter how prolonged, is way off the grid. Always seemed to me like the old belief you could learn calculus by sleeping with your head on a math book.


-Eric
 
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This may not be exactly what you want to achieve, but it does give some good background information on the process. Good luck!

[video=youtube;3gSU4kx_fqc]http://www.youtube.com/watch?v=3gSU4kx_fqc[/video]
 
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