Blister

[44-henry]

After last weeks conversation about blister steel I decided to go ahead and make some. As you can see in the lower photo the 1/16" plates came out with some interesting colors and also a fair number of the so called blisters.

These plates were carburized in a wood/bone charcoal mixture for 3 hours at 2000 degrees F. The material seems to harden fine and breaks clean with a nice uniform structure. I made a small spring for a test piece and it seemed to work fine as well.

So, I went ahead and made a penny knife out of it. Not as fancy as Wick's, but seems to have come out OK.

The handle is about 4.25 long and is turned out of a scrap of rosewood I had lying around.

 

[Nifeman]

Very nice :hatsoff: ...Bud

 

[lonehunter]

Looks good.
How hard is the blade, Did you test it?

 

[44-henry]

I didn't do a Rockwell test on it, but it seems plenty hard. Here are a couple photos of the test piece I made. After hardening it broke cleanly with as can be seen in the photos. The structure along the break was plenty clean and you certainly couldn't touch it with a file.

I don't have the photos, but I did make a spring out of one that seemed to work fine. All in all I think it makes a usable knife. It certainly isn't the equal of even the most basic modern tool steel, nor was that my intent. I just wanted to see if I could make a knife from "mild steel" and have it perform reasonably well.

I probably will have my students build these in the future as there are a number of good skills that can be picked up from this project, including the blister steel aspect.

 

[lonehunter]

Cool project! :thumbsup:

 

[LRB]

A truly beautiful piece, and excellent workmanship. :thumbsup:

 

[tallbear]

Very Nice!!!!!!!!!!!! I like it :thumbsup:

Mitch Yates

 

[M. De Land]

Nice work on the knife Alexander and particularly interesting test on the blister steel.
Did the carbon penetrate the whole thickness at 2000 degrees.
At 1550 on some mild sheet steel I worked with it would only penetrate a couple thousands, maybe .005 even from half a dozen cycles, from what I could see when I purposely cracked it to get an idea how deep the case was. The core was still soft on .060 sheeting. MD

 

[44-henry]

One thing you have to remember is that temperature is very critical in this process. When I color case harden I keep the temperature of the pack around 1450 degrees, any hotter and the colors start to diminish. This is not really a good temperature for general case hardening and the penetration is not very good. Industrial carburizing typically takes place at much higher temperatures 1650 degrees F+. With simple charcoal mixtures the charcoal is only mildly active at those temperatures and doesn't really start to perform until it reaches about 1800 degrees F. Pushing it up to 2000 degrees + and the action is much faster.

There are of course other factors that need to be taken into consideration and some of these get very technical.

I do believe that I achieved full penetration of carbon, how evenly distributed it is I have no idea.

 

[crockett]

Did you make a barstock of blister steel and then grind out a blade? If you did it that way then the edge is from the center of the bar and the carbon must have penetrated all the way if the edge is good. If you ground out a blade and then case hardened it, the carbon might have only gone through the edge area.
What I was thinking on the second method- make a second "test" blade and keep grinding it back to see how much can be ground off and still have a hard edge. Let's say you had to grind off 3/16" before a soft core was encountered- that's more wear than most knives will ever have so the case hardening would seem viable- if that makes sense.
If anyone has already tried this- please share the information.

 

[44-henry]

This particular blade was made from barstock that was carburized. Since the thickness was only 1/16" the carbon easily penetrated through the work piece. It would be interesting to try a shaped blade, my only fear is the difference in cross section could result in too much carbon in the thinner sections.

Still, it is an interesting concept and one I will probably play with later on. I do have access to some pretty good test equipment at the university and since I will be using this as a student project I can justify its use for this purpose. When I have some free time in the summer I will try to do some of this testing and report back.

 

[crockett]

I had no idea you could get that depth of carbon in just a few hours. On the other approach (that is-grind out a blade from mild steel and then case harden), my thinking is this: the ideal situation on most knives is to draw the temper so that the edge area is hard while the back is soft. The idea is that this makes a tough knife. If mild steel is used and case hardened and the carbon only penetrates a little into the steel, in the edge area the steel is so thin that the carbon ought to go entirely through in the edge area but towards the top of the blade (back- spine) the steel is thicker so the carbon is just in the surface and doesn't reach the interior in that portion of the blade and Voila- you have a hard edge and soft spine. If that makes sense.
If it does work why don't knife makers do it that way??? Probably because cutlery steels are alloys with lots more than just carbon- still- it would be an interesting experiment.

 

[LRB]

Although you might have some control over the depth of carbon penetration, you won't have control over the amount absorbed, nor it's degree of uniform absorption. Were it that easy, cast steel would not have been necessary to make dependable springs for the chronometer, which if you recall allowed for accurate longitude readings in navigation in the 18th c.

 

[crockett]

I agree you really can't get a consistent type steel but I thought it would take a lot longer than 3 hours however the only thing I had read before had a much lower temperature.
On the Kasenit I use, I use the directions about heat to a red and dip in the stuff and I think you reheat to red and quench.I've often wondered about the quality of that method since the company also gives instructions for a deeper carbon coating/case that (if I recall) used a sealed pipe, etc.
On parts that wear and are case hardened. Off hand it would seem a deeper case would be desirable.
Now that Kasenit is gone I'm wondering what to use when my supply runs out.

 

[LRB]

I believe there are other products that do the same, but if not, I guess one would have to pack harden, or do a part like the blister.

 

[RushCC]

Very nice work, indeed! You people amaze me with your great talent. (And time :surrender: ) :hatsoff:

 

[44-henry]

I think it would be possible to get a much more accurate distribution of carbon and a much better control over the content using today's technology, this would have been a problem in the past. I doubt there was any kind of furnace in the 18th century that could compete with the one that I used for the above experiment in terms of accuracy over long periods of time. Period sources show that temperature control was a problem for sure and this would have had a huge impact in the quality of the output.

As far as the lack of Kasenit, I believe that Cherry Red is a new substitute that works similarly. If you have a furnace there is no shortage of carbon containing materials that can be used for the pack hardening process.

 

[crockett]

A. J. I did a little reading on this. At the time I think stacks of wrought iron (Swedish) and charcoal were put in sealed stone vessels and "cooked" for about a week at around 1200 degrees to produce blister steel but it had to be inferior as to the even distribution of the carbon or they probably would not have gone to the trouble of making shear or double shear steel, so....yes. What you have done probably produces a superior blister steel but still...I can't see how it could compair with today's state of the art cutlery alloy steels.
But....if you can make blister steel without much fuss- I would think some of us history nuts would buy some just to be PC. As I said, I had no idea it could be done in only 3 hours.