Idea: Case alloying steel

[White Nomad]

Ok, so most of you would be familiar with the process of case hardening mild steel/iron to form high carbon steel. I had a thought (and we all know how dangerous that is) to use the case hardening technique to adjust the levels of alloying elements in steel.

So here's my rough outline of the process that I'm thinking of:
1) Let a piece of steel (any kind, preferably scrap. would be easiest in bar form) sit in a normal camp fire for a good few hours, possibly repeat the process multiple times. I've found that when I have done that, a lot of scale is formed on the surface which when chipped and scraped away, leaves a very black, malleable piece of what I'm assuming is wrought iron. This is used to remove any pre-existing carbon and alloying elements in the steel. (This step can be skipped by just starting with wrought iron bars).
2) Use rough sand paper to scratch the surface of the bar. This increases the surface area of the metal which in theory should allow for a faster reaction (My grade 11 chemistry coming into play)
3) Collect the alloying elements you desire to use, if you're unsure of what you need to make a certain type of steel, you can google the steel composition and elements for the respective steel online. 
4) Sand down the alloying elements and collect the filings. You will need the small particles to increase the surface area of the mixture. Depending on the size of the iron bar, you will need quite a lot of filings. This step can be skipped by buying the alloying elements in granulated form, generally pottery stores and firework supply stores will sell metal powders for glazing and firework stars.
5) Measure out the alloying powders by weight for the respective steel you wish to make, then mix the powders with non-raising flour, salt and water. This will create a gooey slurry.
6) Cover the iron bar with the mixture and let it dry. Then once the paste is dry, cover with clay and let that dry. 
7) Place in your furnace/forge to heat up. I'm not sure for how long, maybe a few hours once it's red hot. You want the iron bar in the core to heat up a lot. 
8) Take the clay pod out once it's finished heating and break out the iron. Quench the new bar in either water or oil or brine, whichever you want. 

The theory behind this idea is that as the clay pod heats up, the iron will heat to a white/bright orange and the alloy metals will melt and mix onto the semi liquid iron bar. However, this process would only affect the outer layer of the iron bar, so you would either need to use a thinner piece to get full penetration, or you could draw out the bar, fold it over itself and then forge weld it together, like making a Damascus billet. This would result in the alloyed outer layer being mixed in throughout the final bar. 

So what do you guys think? Would this work, or is it a pipe dream? 
Also if anyone has a similar process mentioned in the past please feel free to direct me to it to read over. 
Thanks for your time
- White Nomad

[Frosty]

5 minutes ago, White Nomad said:

So what do you guys think?

Maybe talk to your 11th. grade chemistry teacher?

Carbon migrates in iron so it's possible to pack iron in carbon, heat it to near melting temps and have the carbon migrate into the iron. Afterwards it requires folding and welding to sort of even the % throughout the bar.

Migration doesn't apply to other alloying metals. Perhaps a few though I don't believe so. I'll leave that to someone in the gang with a materials science and or metallurgy degree. I wouldn't be surprised if they didn't have to look it up but they'd have a much better chance of: finding,  understanding and explaining what they found. 

Also, you're confusing "Case hardening" with Blister or wootz steel. Case hardening is literally causing a thin layer with higher carbon content on the outside of the treated steel, encasing it, literally. Case hardening is typically only a couple thousandths of an inch deep and usually for wear resistance. It does nothing at depth so a case hardened mild steel bar would: dent, bend, twist, tear, shear, crush, just like mild steel. What it wouldn't do is wear through abrasive action like mild. Utterly useless for blades, sharpening would eliminate the case. 

If you want to make your own alloy steel why not collect drill or lathe swarf of the desired metals and seal them in a suitably refractory container with your iron swarf and heating it to melting temp? 

Frosty The Lucky.

[White Nomad]

Yes, I understand what case hardening is. The method I was modifying is the one ClickSpring used in his file making video on youtube. The idea is that will industrial steel production is that the alloy metals are added to the molten steel and mixed around, thus causing the other metals to join into the crystal structure of the final steel billet. My idea is to seal a bar of iron in a container that won't allow for the alloy metals to run out and away from the iron, and the lightly melt the surface of the iron, causing only the outer layer of iron to alloy, as it's in a semi liquid state. Would that not be the case?

[Frosty]

My mistake, what you're describing sounds like case hardening and lots of folk confuse it with other processes.

Different metals have different specific gravities how are you going to combine them without mixing? On the other hand I don't really know. I suppose it'd depend a lot on how readily your new ingredient alloys with steel. It's over my head.

Frosty The Lucky.

[White Nomad]

Yeah fair point. I might experiment around with this idea this weekend. If I find anything interesting I'll post it on here somewhere

[Frosty]

I'll keep my eye pealed, I'm always into new things. 

I just realized why I thought you were confusing case hardening with alloying when I read the subject. 

Frosty The Lucky. 

[White Nomad]

All good

[Frazer]

I'll start by saying that if it's over Frosty's head it's way over mine. However, I'll add my 1.5 cents nonetheless.

1. leaving a piece of steel in a camp fire will not result in wrought iron.. WI has it's characteristic properties due to it's low carbon content and slag inclusions within the bar itself. Perhaps you have a bar of annealed decarburized steel, but it's not wrought.

2. It kind of sounds like (at least the theory of your approach) sintered powdered metal parts (it's most often used in gears and brass bushings). But I don't think it would work the way you describe. You need a mold (your clay) to keep everything in place and some pressure to fuse the grains of the materials.

3. Why flour? Flour ~= flux as far as I'm aware. (please pardon my ignorance if I am wrong about this, but I have never heard of such a thing)

Again, I am very likely outside of my area of understanding, but I don't see any reason why this would work.

Why not just do canister damascus? Fill up some square tube with powdered metal and a mild steel core and forge weld yourself a billet, then you have your heat and your pressure and a contained vessel for it all to stay put in (ish).

I haven't seen ClickSpring's video(s), but I do know GreenBeetle has a lot of videos of him making canister damascus out of all sorts of different things. Yes, he usually makes knives afterward, but the general approach is the same.

 

[Chris Williams]

Forget the camp fire removing alloying elements part; it doesn't work like that.

As for packing alloying elements around an iron/steel bar, encasing it in clay, and heating it up high enough for long enough, you have two possible mechanisms that could credibly create the "case" that you seek. 

If you are able to control melting to only include the very outside of the bar (i.e., through careful control of temperature AND time, or some creative measurement or observation scheme), then it could work like I (think) you envision it. How well it works would depend in part on the melting points of your alloying elements and their solubility in the steel. Alternatively, you can perhaps select alloying elements that have lower melting points than the steel, and which would then dissolve the steel into the melt. In either case, heating too high or low for too short or long would yield a disappointing result.

The second mechanism is diffusion, and is the same mechanism that causes carbon diffusion into steel during case hardening. Time and temperature will determine the result here, along with selection of both a starting steel composition and alloying elements that will readily promote diffusion. 

You would likely have some degree of both mechanisms occurring depending on a myriad of factors. The flour or other carbon source would help prevent oxidation and therefore promote diffusion (including of carbon) into the bar, but I don't know how it would behave with molten materials. I suspect that it may prevent your metal powders from consolidating with the bar or each other. 

This is far too open ended and vague of a question for me to go into much depth, but the bottom line is that your idea can be made to work with at least some materials, and likely quite a bit of experimentation. I have a number of ideas, but would likely just weld a cladding material onto a piece that I wanted some different property in rather than trying do it through diffusion or carefully controlled (non-welding) melting. Frazer also brings up a good point about canister Damascus, in that you may be able to make much more controlled materials that way. Now doing it just to do it... I could get behind that! 

[ThomasPowers]

I asked this question back in MatSci class at Cornell University: As I recall, Chromium will diffuse into steel; it will take around 30 years to get the same depth as carbon migrates in 30 minutes *and* you have to keep it at the same high temp the entire time.  Which of course will do wonders for the grain size of your base material.

Other elements will also diffuse, and at differing rates but Carbon is the "top fuel dragster" of the useful ones.

So possible; but not a good idea.

Now way back when over at Sword Forum there was a guy making some interesting alloys using thermite to produce molten steel.  He stopped suddenly when his Dr told him that even using the expensive PPE he had he was going blind.

If you really want to play around with steel chemistry look into an induction furnace, either vacuum or inert atmosphere as melting in air you don't get exactly what you start out with...

As for surface cladding: why not solid state welding or explosive welding?  (They do a lot of explosive welding here at EMRTC--Energetic Materials Research and Training Center.  Energetic Materials == BOOM!)

[Steve Sells]

I remember the star furnace he built, so sad he lost some eyesight doing it, he came up with some cool rare earth (rhodium?)  experiments while it lasted

[ThomasPowers]

Yes I thought he should have been in a good MatSci program doing PhD research with proper equipment as his experiments were great fun!

[Frosty]

Were I doing surface cladding I'd use spray deposition, I already have the oxy propane torch, all I'd need is the attachment. 

Now I have to search out the star furnace, sounds like fun. As a lay tip, do NOT look at the burning thermite!

Frosty The Lucky.

[patrick]

Case hardening or case carburizing where carbon is added to the surface of an item through diffusion processes can have widely varying depths depending on the time and temperature used. In industrial practice I have seen things like rail road bearings with effective case depths of 0.100 inches. 

Another method of increasing surface hardness is to expose the item to a high nitrogen environment. Usually that is done with steels having about 1% aluminum. The aluminum reacts with the nitrogen to form a uniform aluminum nitride coating. This coating is generally only about 0.010 inches thick but can have a hardness of about HRC 70. 

Intentionally adding alloying elements to just the surface of steel is generally not done because it is not practical. If you attempted to melt just the surface to allow alloying elements to get into the steel you'd be left with an as-cast structure on the steel surface which may not be be what you want, especially if you have already forged the part. If you will forge after alloying addition is made, that likely will be lost due to oxidation.

If you attempt to add alloying elements via diffusion processes as with carburizing, you will be there a very long time. That is because the alloying elements in question have fairly large atomic radii and very slow diffusion rates in iron. Only those elements with very small atomic radii, such as carbon and nitrogen, are suitable for difussion based surface alloying.

 

[FisherPriceAnvil]

I'd have to dig into my materials science books or look at literature to see if there is some feasibility of diffusing alloying metals into a steel bar. As ThomasPowers stated though I'm guessing the diffusion rate is not worth it. The easiest way to visualize this is that carbon atoms are smaller than alloying metals, so that's why carbon and nitrogen are used in these case-hardening processes.

However with your crude procedure I see issues with using sandpaper to get the particle size you want. That sandpaper is going to produce contaminants.

Using the flour and salt would also likely add contaminants.

If you want to change the surface composition of your steel, I think forge welding, spray deposition, or electrochemical processes would result in more consistency and a better product. If you really want to use powders in your garage, I think the best way is to mix them around your part and consolidate via forge welding with a jacket technique or otherwise sinter them together with specialized tooling.

[ThomasPowers]

If I recall correctly  my MatSci prof said that the diffusion of chromium into steel at high temps would take around 35 years to get to the same depths as you could do in 35 minutes with carbon at the same temps. Of course the cost of heating the steel for 35 years; not to mention the issues like grain growth; makes it pretty much a nonstarter.