Blacksmith Jim

Hardening Mild Steel

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OK.. So I've heard that people make disposable (or limited use) tools out of mild steel, maybe a drift or something I guess. And I've heard people talk about hardening mild steel with things like SuperQuench. But my understanding was that in order to really harden metal, it takes carbon. And mild steel just doesn't have much carbon. I always wrote it off. Earlier I made a few tools from what I assume was mild hex bar. They bent or deformed when used on the one project I used them form. I may have let them get too hot without quenching (I honestly don't recall how much I quenched them while using) but to me, I wrote it off to them being made out of mild steel. Now I make my tools out of coil spring mainly.

Then, the other day I burnt the end of a bar I had just started working on. When I pulled it out it was sparkling and spitting, so just for fun, I submerged it straight into the quench tub. I thought maybe it would crack, and I hadn't seen that before. When it was cool, I figured I would cut off the end and start over. So I threw the end in my band saw. The saw barely scratched it. It removed the surface layer, then wasn't cutting beyond that. So it seems like the quench hardened the mild steel. So now I'm confused..

Can mild steel harden? Is it just that mild steel does not stay hard once it is hardened?

Thanks for any enlightenment!

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First off, to my knowledge (and I could be wrong), hex bar is tool steel, not mild. But to your primary question, yes mild steel can be hardened. Anything with carbon in it can be hardened. It's just the question of how hard. And the properties of the metal also depends solely on the rest of the chemical composition. Does it have nickel? Lithium? Vanadium? Columbium? Any other elements make a big difference. But just plain old mild steel, that I know of, will not get hard enough where a band saw won't cut through it.

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Also keep in mind that modern mild steel is recylced many times over and usualy has much more alloying elements in it than older mild steel did. This can cause new mild steel to be harder (and harder to work) than much of the older stuff which was closer to a pure iron with limited carbon.

Mild steel (and even wrought iron) will work harden as well

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You can harden mild steel. By quenching it at high temperature you are making all the molecules that are racing around freeze up all of a sudden and almost crystalize....funny story. Early in my smithing life I made up a triangle dinner bell for a friend as a wedding gift. When she picked it up and rang it for everyone to see it fell into 2 pieces....looking back after I got over the embarrasment I quenched that corner of the triangle for one reason or another making it really brittle instead of throwing it down and letting it air dry.

I have also case hardened mild steel using Casenit(I think I spelled it wrong). With this stuff you just heat it up and rub this junk all over it and heat it again and then quench it. I think all this stuff is made up of is mostly ground up bone...not sure. I do know that thing is extremely hard. I have made several nails with that header and it is holding up just fine.

A neat disposable tool I have been told about is forging out your punch or drift, etc....and heating up some cast iron and rubbing it ff on the mild steel while they are both hot(in the fire)...then quench it. I have been told by a guy that has done this it will last up to 6 uses depending on what you are doing with it.

well.....I know there are several out there with better answers than this one. So I will let them get to it!

Peyton

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Mild steel can be either case hardened ( a thin layer of carbon will be absorbed by the steel and it will make for a hard case with mild steel inside - hence the term) and WORK hardening. . .which is done by beating the steel until you compress the molecules together and it;s a bit harder than before. . .quenching undoes this. . .
Hex bars are often tool steel. And Vanadium, chromium and manganese CAN affect the hardenability of steel.

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The hex bar I used was from the inside of rollers. It didn't really spark that hard. I made two eye punches. Both bent pretty quickly at first use, though I didn't harden them.

Thanks for the feed back all.

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you can buy hex stock in ledloy 12L14 OR 1018 so all hex is not tool steel
here is a link for heat treating Special menu bar
look under rob gunters super quench , there are many testimonials about his super quench that he can harden 1018 steel to cut itself
i heard he forged parts for nasa .
chuck
but as far as what i do i use the product casenite very succesfully

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Hi. I have "hardened" mild steel. It was a failed forge weld that got burnt. It completely defeated a file (Rc 60+). I later learned from a more experienced smith that burning metal causes it to leaf or string out, with very hard scale between the layers. This composite is very wear resistant but weak. It is useless as a tool. A grinder made quick work of the burnt end. A hot rasp will also work

If you want to make emergency tools, I would highly recommend "qualified" rebar. One of my students brought in a piece of new store bought rebar (it was cheaper than the steel from the big box rack). I spark tested it for him right next to a sample of A-36. The difference was striking. It was burstier than truck axle; looked like 1050 or better. It was also red hard, and made that characteristic "clank" noise below a high orange. We made a chisel, tempered one step to bronze, and it was hard. You could tell just by tapping the end. This stuff is cheap! And if it is no good, use it for bottle openers, or hooks or something. Another student made a really nice spring fuller out of rebar. He forgot to qualify it, then he forgot to temper it. It shattered on him. I made one out of "qualified" rebar, and it has fullered a lot of candleholders, letter openers, S-7 tools (careful, keep it hot), etc. Looks just fine.

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I have been working on a machete made of mild steel and plan on trying the Super Quench. I will report my results when done.

I've seen the standard response to this, "why not use carbon steel?"
2 reasons. I haven't located a carbon steel supplier yet and since this is my first "knife" I don't want to ruin an expensive piece of steel.

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And my stock two answers: you should be able to get car leaf or coil springs for free---unless you actually live somewhere where there are no cars and so have a cheap piece of decent knife steel to ruin!

If you learn on low carbon steel your habits will be set for low carbon steel. if you want to be a knifemaker best to get your habits set for high carbon steel and then have problems working mild steel...takes an act of will for me to work wrought iron at a yellow heat as my habits are screaming that I'm burning the steel!

I have just been given some re-bar from a major power plant construction site that I want to check out vs the WKW rebar I've scrounged and don't use for anything but snakes and stakes.

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I live in an area that everyone seems to think used items need to bring new prices. But honestly I haven't really looked for any free or inexpensive leaf spring. The leaf wouldn't have done me any good for this project because I'm not forging, just grinding. I needed 4 inch wide and don't know if I could find any that big.

And I have no illusions of being a knifemaker. Just trying to make a few neat things.

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Log truck or semi truck or large flat bed trailers etc, have leaf spring that is 4 inches wide or more. Can be an inch thick or more too. A friend of mine made a few pieces for a fellow who worked at a log truck repair shop (i think) and he gave him a few HUGE sets of leaf spring. Most of it will probably end up as dies or other tools. I've had OK luck getting coil spring cheap off of craigslist.

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Leaf spring would be a bear to make a machete from strictly stock removal. Much better would be some of the giant bandsaw blade used for sawing tree's at a saw mill, about the right thickness to start and good steel to boot. I sometimes see pieces a couple of feet long and 9" or so wide for sale at hammer-ins.

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For a start, hello to all! RegionalChaos, sounds to me like you carbonized the mild-steel. I'm presuming that you burnt the end in a coal forge and not a gas forge, remember that coal is a form of carbon and it can migrate to the steel / iron. If you divide your pile of burning coal in to three horizontal levels, the bottom layer ( closest to the air grate ) is the Oxidizing Area. the middle is Neutral and the top layer is the Carbonizing Area! It would take a while to carbonize the bar all the way through but you could quite have easely have hardened the outside enough to notice it on the bandsaw. Note that modern case hardening powders have replaced this very old form of carbonizing steel/iron!!

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To harden mild steel or iron we need to first carborize it in a few steps

Prep:

Powder all ingredients

6 parts charcoal

4 parts table salt

3 parts wheat flower

Enough water to make a paste

Coat:

Coat steel to be hardened with generous layer of char-paste and allow to fully dry. It should resemble a corn dog.

When dry apply a 1/4 inch jacket of clay and allow to set up and then fire red hot for 20-80 minutes. Depending on the depth of desired carborization you may need to expiriment on heat times. 

Once complete quickly remove from forge and gently break away the clay and quench in your desired quenching solution. 

Now you have a blade with a core of mild steel or A36 and an outside layer of hard crystalline martensite or tool steel. 

This is an ancient and fool proof way to create high carbon steel with a variable depth of penetration. You can fully harden the steel all the way through or just the surface based on how long you hold a red hot temp.

 PhotoGrid_1507736714929.thumb.jpg.b415833ff77f199d326d14f34339e3c3.jpg

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look up Blister Steel   (A good source would be "Steelmaking before Bessemer, vol 1 Blister steel"  Theophilus also provided instructions about 1120 A.S. in "Divers Arts".)

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16 hours ago, DarkHorseArmory said:

To harden mild steel or iron we need to first carborize it in a few steps

Prep:

Powder all ingredients

6 parts charcoal

4 parts table salt

3 parts wheat flower

Enough water to make a paste

Any idea as to the purpose of the table salt?  Chlorides are notorious contributors to stress corrosion cracking (even in stainless steel), so I'm a bit puzzled as to why it would be included in the recipe.

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