Case hardening bad experience

[evfreek]

Hi. I love fiddling around and trying to make do with less. So, when I surfed around the Internet, I noticed lots of references to using sugar for case hardening mild steel. Apparently, the legend is that POW's used this method to harden homemade wire cutter jaws. The sugar would melt and coat the steel, allowing the carbon to diffuse in at a bright heat. So, the other night I tried this out on a piece that was a little too precious for an untested process. Not such a good idea . Also, having watched sugar burn, I should have realized that this was not going to work.

After heating the piece to a good red heat (starting to scale), it was dipped into a mixture of charcoal powder, sugar and baking soda. The stuff ignited, fluffed up really badly, and did not really stick. Talk about candy-coating the subject! Anyway, sugar shell coating works at candy-making temperatures, not steel hardening temperatures. I should know better, since I scratch-make candy. Internet searches do turn up failures, including those of commercially made compounds containing sugar. These have become displaced by things like Cherry Heat and Kasenit. But, I couldn't find any of those at the local store.

Anyway, the tool failed. By the way, Cherry Heat and Kasenit both work. I have seen successful application of both at demo's. I just don't want to buy a whole can, and anyway, it is much more fun to experiment. These homemade mixtures seem much more suitable for pack case hardening. I would recommend dispensing with the sugar, because it fluffs up too much.

[thecelticforge]

When my Grandfar would case harden stuff, he would make a "box" out of clay and pack it with shavings off of a horse's foot and the piece to be hardened. I seem to remember he kept it bright red all night and then quenched it. I was the one that got to get the clay from the creek and make the box.

[ThomasPowers]

Time and temp make a difference; we did a pack carbonization experiment by packing pieces of wrought iron into a piece of steel pipe (1.5" dia IIRC) filled with powdered charcoal with one end welded up and then we folded the other end over to make a semi air tight system. Rolled it to the side of the gas forge and then kept track of how many hours at temp by soapstone on the forge shell. (rolled the pipe over every now and then)

Our first attempt was 30 hours---got cast iron carbon amounts---oops! The week long soaks described in making blister steel were in a much larger system and running at lower temps.

(BTW "The Cementation of Iron and Steel" and "Steelmaking before Bessemer, vol 1 Blister Steel" are commended reading on this topic...)

[edge9001]

sugar charcoal and baking soda...sounds like a messed up gunpowder mixture....becareful adding sugar to anything that will touch red hot metal, especially since sugar combined in equal amounts with potassium nitrate otherwise known as saltpetre is a military grade smoke mixture. I can attest from personal experience a large tablespoon of this mix will fill a small room with some until barely visible.
I would be careful with the sugar and baking soda mix, especially adding anything else.

[John B]

Are you sure you should have used sugar?

One old time recipe was to use a mixture of wholemeal flour (1spoon) and salt (2spoons), and clean water, mixed to a paste, apply that warm when it will stick to the metal surface to be hardene, then heat to brifght red and quench in clean water.

Or you could just apply salt directly to the surface to be treated at a red heat until it sticks, then bring up to a bright red heat (the salt becomes molten) and quench,

Both these methods will appreciably harden the surface where it is coated.

[maddog]

Or you could just apply salt directly to the surface to be treated at a red heat until it sticks, then bring up to a bright red heat (the salt becomes molten) and quench,
Both these methods will appreciably harden the surface where it is coated.

How does salt alone harden the steel? Don't you need some carbon?

[evfreek]

Hi. Thanks for all the comments. I am sure all of these methods will work. The one with the salt and flour sounds particularly promising. Thomas' suggestion of making blister steel is a good one if I need to make steel out of wrought iron, but it will not work for my application, hardening a threading tap. The reason I know this is that I saw Phillip Baldwin demonstrate exactly this process at a blacksmith conference. He used bars of old wrought iron from a shipwreck, and pack carburized them with charcoal for about 12 hours. This made blister steel, which would have been disastrous for my tap. The blister steel was weak at the blisters, and needed to be "refined" by welding it together in order to homogenize the inclusions. Fortunately, the tap survived one use, which was all I needed it for, but it got goofed up pretty badly.

[Frank Turley]

I don't think the wheat/salt method is going to impart carbon. H. Holford in his book* says that it will protect thin edges on a tool such as a knife steel or on rasp teeth, so that they don't get scaled and dulled at hardening heat on high carbon steel.

* "The 20th Century Toolsmith and Steelworker"

http://www.turleyforge.com Granddaddy of Blacksmith Schools

[John B]

How does salt alone harden the steel? Don't you need some carbon?

The short answer is I don't know, but it seems to when tried, I have used it on MS dies for tooling for many years. As do some other non logical methods in other situations, I put it down to the magic of smithing.

[Nakedanvil - Grant Sarver]

Salt can improve the quench. It protects the surface from scaling which inhibits the quench. It also comes off as soon as you put it in the quench and gives some of the benefit of brine.

[MOONY]

Hi all this Moony here the carburizing of mild steel or wrpought iron is not a simple avent i heatreat a lot of bevel gears used in slashers to cut feilds, i pack the gears in a steel box about 1/4 '' thick wall all the gears have a peice of wire tired to them so you can fetch them from the box, the items wishing to be case carburizing is packed in the box with charcoal crystals about 10mm dia not dust , with a full covering over the items, when the box if full with items and charcoal fit a lid that you can make leak proof [sealed] with a mixture of fire clay and sand 50 50 , when dry put the box into the furnace and take to tempreture 900c hold at this temp for many hours about 5 hour will give you about 20thou of an inch , longer will go deeper but a 1'' thick piece will take many 10s of hours to get full carburizing if you can!!! , this method is only used to put a case [surface hardness ] of about 1=2mm at most on the items that need the wear resistance , and if you want only some areas case carburized you pant benternite clay on to the un case carburizing area then heat as normal , then after you have soaked the items in the box ,open it quickly drag the piece out with a hook to grab the wire then quench is the medium , [brine , water] or the medium that the steel designed for , but you usually only do case carb on soft steels . like mild steel os case hardening steels only have fun its not a quick thing to do

[bmazingo]

I am pretty new to blacksmithing but I have been working on engines for a while. I thought it interesting how different methods were used for case hardening. The automotive parts industry case-hardens camshafts in a similar fashion to painting on clay. Some actually coat the areas that are not hardened with a coating containing copper, Mopar used a purple paint-like chemical. Just thought it was a neat comparision.