24 replies to this topic

[Robert Simmons]

I had heard that if you pack red hot steel into charcoal and let it slowly cool that it will take in carbon during the annealing process. If that is true then if you do it enough it stands to reason that it would turn low carbon steel to high carbon steel. Is this true?

If not, then is there a way to add carbon to steel in the home shop without melting it down?

Finally, is there a way that someone in a home shop could determine the exact carbon content of a piece of steel?

[edge9001]

I've heard somethign similar, although from what I've read. you put your steel in a nearly sealed(vents for pressure to escape) can of charcoal powder and then heat it. although, I think the two processes should yield similar results, if it's true.

as for telling the carbon content, I've not heard of a way to accuratly tell, other than a spark test, which I'm not too familiar with yet.

[Timothy Miller]

http://en.wikipedia....ntation_process

[Phil Krankowski]

Blister steel is well described in that link, Thomas Powers has mentioned he made some in a steel can in his propane forge, and got a little higher on the carbon content than he intended.

Another way is using a solid fuel fire to place the iron in the carburizing portion of the fire (above the hottest part) and several minutes at welding temperature in this portion of the fire should impart a carbon increase to about 1/16 deep, possibly all the way through if you are using a flat profile you may get the carbon all the way through in one go.

Yet another way is to take a thin piece of cast iron and heat the part to welding temperature and the cast iron to near melting temperature and "crayon" the CI onto the mild to get a hard face with higher carbon content.

I haven't tried any of these methods yet.

Phil

[arftist]

Possible? Yes. Practical? No.

The miniscule amount which could be absorbed during the cooling process is not worth discussing. To build a thick, hard case would take days and days of heating above critical to build even a shallow case. .050" per twenty four hours at best. Now, all you have is a mild steel bar with a carbon rich outer case. Hardly practical in todays world of free medium to high carbon steel in every repair shop and junkyard.

Spring steel is a good all around source of medium carbon steel, and is suitable for most uses you could think of.(knives, blades, tools, and springs). Most spring steel is between .6-.8 percent carbon.

To do a spark test, find a bit of known steel, and in a dark room, grind the bar and note the shape and length of the forks cast off. Compare a file(1-1.2 percent carbon to a leaf spring, to a soft bolt or peice of flat bar or chanel. To get even more precise, down load a spark test chart or find one in a metalworking book.

If you want to get real specific, order some tool steel in whatever alloy you desire. Plain carbon steel is sold as 1040, 1060, etc. with the last two digits representing the decimal of a percent of carbon.

[Phil Krankowski]

arftist, on 09 August 2010 - 01:56 PM, said:

Possible? Yes. Practical? No.

In a general sense, and in most cases that I have need of higher carbon content, I agree with you, but not for all cases. Where's the fun in that?
Phil

[ThomasPowers]

Days and Days? 30 hours packed in a tube of powdered charcoal in my gas forge got me too close to cast iron to use. The next batch will be only 10 and 20 hours. I was starting with wrought iron too.

To know exactly how much carbon is in it would take an analysis either chemical or spark spectroscopy (and you could probably buy new steel for your life for the cost involved of owning your own set up.)

May I again commend "Steelmaking before Bessemer, Vol 1, Blister Steel" to all interested in this topic.

[arftist]

ThomasPowers, on 09 August 2010 - 03:43 PM, said:

Days and Days? 30 hours packed in a tube of powdered charcoal in my gas forge got me too close to cast iron to use. The next batch will be only 10 and 20 hours. I was starting with wrought iron too.

To know exactly how much carbon is in it would take an analysis either chemical or spark spectroscopy (and you could probably buy new steel for your life for the cost involved of owning your own set up.)

May I again commend "Steelmaking before Bessemer, Vol 1, Blister Steel" to all interested in this topic.

How thick was the stock you started with?

[ThomasPowers]

As I recall it was about 5/16" to 3/8 I can dig out the mate and measure it when I get home.

When we usually get this question it's WRT blademaking so fairly thin stock is involved.

The piece we did was to make the edges of an early medieval spearpoint the center of which was a twisted patternwelded billet. Unfortunately it was so high in carbon we could not weld it to the core as it fell apart just like cast iron does at high temps in the forge.

It's time to get another set up to be ready for cooler temps in the fall to try again. I soapstoned the start and finish times on the side of my propane forge to keep a record of how much time at temp it had.

[arftist]

Thirty hours for 3/8" likely put you right through. I tend to think in terms of round stock for some reason, not much of a bladesmith.

[Robert Simmons]

ThomasPowers, on 09 August 2010 - 05:08 PM, said:

As I recall it was about 5/16" to 3/8 I can dig out the mate and measure it when I get home.

When we usually get this question it's WRT blademaking so fairly thin stock is involved.

The piece we did was to make the edges of an early medieval spearpoint the center of which was a twisted patternwelded billet. Unfortunately it was so high in carbon we could not weld it to the core as it fell apart just like cast iron does at high temps in the forge.

It's time to get another set up to be ready for cooler temps in the fall to try again. I soapstoned the start and finish times on the side of my propane forge to keep a record of how much time at temp it had.

I am not so interested in swords and knives as I am in making tooling. Thanks for all the great information.

[thingmaker3]

Rate of carbon diffusion in steel is proportional to the square of the Kelvin temperature. Translation: pack carburization would take days & days at dull heats, hours & hours at medium heats, and a few hours at brighter heats.

Note also: the "case" is not just a well-defined layer where the carbon content drops off at the edge like some underwater cliff. There is a gradient.

Try an internet search on "Ficke's Second Law of Diffusion." Don't get bogged down in the math examples, but do study the graphs.

[evfreek]

thingmaker3, on 10 August 2010 - 09:23 AM, said:

...
Try an internet search on "Ficke's Second Law of Diffusion." Don't get bogged down in the math examples, but do study the graphs.

If you really want to get scientific, the characteristic time is inversely proportional to the square of the thickness, so half the thickness means 4 x faster.

Also, the addition of a small amount of "accelerant" will boost the rate considerably over that observed for the ancient process.

[Robert Simmons]

thingmaker3, on 10 August 2010 - 09:23 AM, said:

Try an internet search on "Ficke's Second Law of Diffusion." Don't get bogged down in the math examples, but do study the graphs.

Is there any graph in particular you are referring to? Do you know one for diffusion into steel?

[ThomasPowers]

carbon diffusion is both time and temperature dependent so you would need 3 axis graph: time temp and carbon content/thickness.

However there is a book on "The Cementation of Iron and Steel" Giolitti, Federico that goes into excruciating detail on the subject (cementation was an old name for the process)

As far as making tooling material it would be probably cheaper and easier to buy higher C stock at the scrap yard than to spend the fuel to make it from lower carbon stuff.

I play around with it as part of my historical processes experiments.

[thingmaker3]

The full equation requires at least four axis, Mr. P. We have to account for initial carbon concentrations, and the presence of things like nickel or silicon.

Robert Simmons, on 10 August 2010 - 12:05 PM, said:

Is there any graph in particular you are referring to? Do you know one for diffusion into steel?

What I had in mind was something like I have in a couple of my books: set of graphs showing carbon content x millimeters below surface after y hours at z heat for a specific steel of uniform size.

I can dig out some titles later in the week if you wish... might find them in your local university library...

[Robert Simmons]

thingmaker3, on 10 August 2010 - 02:37 PM, said:

The full equation requires at least four axis, Mr. P. We have to account for initial carbon concentrations, and the presence of things like nickel or silicon.What I had in mind was something like I have in a couple of my books: set of graphs showing carbon content x millimeters below surface after y hours at z heat for a specific steel of uniform size.

I can dig out some titles later in the week if you wish... might find them in your local university library...

Honestly I wouldnt know where to look in the Library. I have a masters in Computer Science, not mechanical engineeing (these days I think that is unfortunate)

[ThomasPowers]

I have degrees in Geology and Computer Science and have worked in both fields. What I have learned about metallurgy is because I was interested in the subject and researched it on my own!

Where you would go is to the Materials Science section not MechE. Old school would be Metallography or Metallurgy. Or just look up the book I mentioned and look around it for other titles that look interesting...would work in my study! (of course my interests tend toward the 1900's and earlier...)

[Richard Furrer]

Or, if I may be so bold, wait till December and get this video by this guy on blister steel:
http://www.doorcount...eel_Making.html

adding carbon can be very rapid if you do not mind grain growth or are reforging the material after.

Thomas...I think your areas of interest are wide afield and deep. Your iron will show prominently in the video.

Ric

[ThomasPowers]

Makes me happy I shipped so much of it to NM when I moved!