Blister steel

[crockett]

I am starting a new thread that is branching off of a pc knife. I read some of the internet info on steel making but I am still confused. From what I understand blister steel was used for low grade knives. I am learning here but it sounds like bars of wrought iron were stacked with charcoal inbetween them and cooked for a week in stone/brick containers. This forced carbon into the iron and made steel. There was a greater proportion of carbon in the outer surface area.
I am familar with case hardening and I think Kasnit claims you can get a .10" depth if you heat for a long time. In any event- I think my problem is that I am visualizing a wrought iron bar with a skin of carbon steel- if that bar gets pounded or forged into a knife with the skin still outside then fine but if the blister steel is ground, etc- then what I am thinking is all the carbon steel skin got lost and all that is left is the soft inner core- and that would make a poor knife.
Where I may be going wrong is if the cementation process forced the carbon a lot deeper into the wrought iron than I am assuming. Or, maybe the edge was forged first- to insure the carbon steel portion was in the edge area.
In any event any help appreciated.

 

[LRB]

I have read the wrought iron was cooked from a few days, to as much as a few weeks. May have depended on the thickness. I may be wrong, but I would assume the carbon penetrated all the way, or it would have been worthless as blade material, unless folded and welded many times. Take a look here http://www.youtube.com/watch?v=3gSU4kx_fqc

 

[Andrew smith]

This is definitely something new for me. It's kinda interesting.

Wick, thanks for the link.

 

[crockett]

Thanks Wick. I do a very small amount of case hardening and so far have used the quick and easy method with Kasenit- dip the steel in the mix- looks like bone meal to me- heat cherry red and quench. The Kasenit people list another method that gets the carbon in deeper, I think .1"so if you had steel 1/4" thick that ought to just about get carbon through the entire thing. Given the long soak on the Blister I was figuring the carbon must have gotten in much deeper- I just didn't know.
Strange thing is, and I'm just thinking here- a sophmore- if a piece of blister steel had a higher carbon exterior and a lower carbon interior and the bar was struck and forged so the edge was formed with the exterior portion with high carbon- the remaining parts ground away, then you would end up with the ideal situation of an edge capable of a hard temper but a soft core/back which makes for a tough tool- as I understand it. I wonder if anyone today actually works with blister steel.

 

[LaBonte]

Strange thing is, and I'm just thinking here- a sophmore- if a piece of blister steel had a higher carbon exterior and a lower carbon interior and the bar was struck and forged so the edge was formed with the exterior portion with high carbon- the remaining parts ground away, then you would end up with the ideal situation of an edge capable of a hard temper but a soft core/back which makes for a tough tool- as I understand it. I wonder if anyone today actually works with blister steel.

Dave it doesn't work that way. When you heat/forge blister steel - which is not a simple casehardened blank, but rather a piece of steel made via the cementation process - you get carbon migration. Carbon migrates from the areas with the high concentration to areas of low concentration, thus you get a more homogenized piece of steel.
This is in fact the methodology behind shear steel, although shear steel was made in large billets formed of many cutoffs from the blister stock rather than forging froma single bar.
On the other hand blister steel (and other types) did vary in quality considerably and that's well documented.
To get a sft back on a knife (not actually that good of an idea on thin blades like trade blades) there are basically two process:
1) Diffierential heat treating wherein the back is either not hardened during the heat treat via a controlled quench or fully hardened and then the back drawn back using a torch or similar tool.
2) Welding a steel edge to an iron back - either via a direct weld like the Vikings did or via the sandwich method like the Japanese San Mai or the Swedish layered steels.

Here's a bit of info on the three main types of steel used from 1745 through the 1850 period. After 1863 or so the Bessemer process made these three types obsolescent, but not completely obsolete until after WW 1. There is an online book via Google on the cementation of steel which gives more info on times and heats used in making blister steel- I believe it's this one... http://books.google.com/books?hl=e...=X&oi=book_result&resnum=10&ct=result#PPR5,M1

Very briefly, the cementation process involves placing alternating layers of iron bars and charcoal into refractory chests, which are subsequently sealed, or cemented, closed. This prevents the charcoal from igniting. The chests sit in a large furnace, which is then fired for a period of a week to ten days. The firing is monitored to maintain a temperature below the melting point of the iron bars, while carbon from the charcoal diffuses into the iron bars. These bars tend to have a blistered, or scaled, appearance when they emerge from the process - hence the term, blister steel.

1) Blister-steel: Steel formed by roasting wrought iron bars in contact with carbon in a cementing furnace. It is so called from the blistered appearance of it's outer skin. To improve the quality, it was subjected to two subsequent processes, which converted it into shear-steel and cast-steel.
Blister steel was NOT a one off method for individual blades, but rather a method of making large amounts of steel - this method was developed circa the 1500's. James Hanson mentions in his Fur Trade Cutlery Sketch Book, that the bars of wrought iron used for making blister steel could be as large as 1/ 2" x 4" x 20 feet.

2) Shear-steel: Blister-steel was sheared into shorter, manageable lengths, heated, and tilt hammered to homogenize the steel which improved the quality. Several bars are welded together and drawn out. The bar is sometimes cut, fagoted, reheated, and again tilted. This may be repeated. The terms single shear and double shear indicate the extent to which the process is carried. It was widely used for blades of all types through the end of the 19th Century.

3) Cast-steel (aka crucible steel): Blister steel which has been broken up, fused in a crucible, cast into ingots, and rolled. The blocks of steel are melted in crucibles of re fractory clay, and the molten metal is poured into ingot-molds of cast-iron. These are opened, to let out the red-hot ingot, which is then passed to the rolls.
The process of making cast/crucible steel was developed by Benjamin Huntsman, of Sheffield, England, circa 1745. Oddly, crucible steel at first was not greeted well by the Sheffield makers while the French cutlers soon recognized it's qualities. The Sheffield makers even went so far as to ask the government for an embargo on the raw steel.
By 1840 the English had developed the cast steel method to the point that English steel made in this way became 40% (about 20,000 tons a year - up from the 200 tons a year produced by the English using all previous methods) of all steel produced in Europe. Other steel centers of note during the period were: Germany (manganese and other trace minerals in the local ore made it a better than normal alloy), Spain, and Sweden). A few years later, in the 1850's, the Bessemer process was developed which increased steel production immensely.

There is also documentation to show that pattern welded Damascus was being produced in Europe at the time as well as in Inda and otehr eastern countries. Not only were gun barrels and other parts being made of Damascus by the late 18th century, you can see via the link below Jean Jacques Perret's 1771 treatise on the Art of the Cutler for the process used in making blades of said material. Perret also mentions in his treatise that what is now commonly knwon as San Mai - essentially a sandwich of a steel core wrapped in a blanket of iron or low grade steel. His recommended steel for the core was German, which was made from an ore which includes manganese.
http://damascus.free.fr/f_damas/f_hist/perret.htm

I find the Perret treatise interesting:
1) It not only shows that such pattern welded steel was being made in Europe at the time (the methods for pattern welding blades were NEVER lost as is often touted)
2) Perret notes that "true Damascus" aka wootz, an ancient cast steel was a different product than pattern welded.
3) Perret notes that even then selling folks on higher quality items was a problem
4) Perret also gives the technique for making sandwich/laminated blades - the Japanese version is known as San Mai, a term often used today to designate this type blade.
5) And perhaps most interesting, to me anyway, is that Perret discusses the problem of "fake" Damascus - implying that the quality of Damascus blades was well known enough that folks were in fact faking it - nothing new under the sun!

And yes the are folks making blister and shear steel today - the man to talk with is Rick Furrer of http://www.doorcountyforgeworks.com/Welcome.html

He holds regular workshops for making blister and shear steel in smaller quantities.
Here's a page with several videos by Rick http://www.doorcountyforgeworks.com/Steel_Making.html

 

[William O.]

That was fascinating, thanks for posting those links as well as your explaination. :thumbsup:

 

[crockett]

Yes Indeed. Thanks Chuck. Really appreciate it.

 

[gmarc]

Blister steel was uneven in quality and supplanted by Huntsman process crucible steel promptly. This process was introduced around 1745 AD.

You can produce blister steel, but it is intensive in labor, materials and time.

 

[LRB]

Done as in the video, it only requires a bar of low carb steel or wrought iron, some carbon, and and heat for a few hours. Where is the intense labor?

 

[crockett]

Wick, it is said Shear steel is better. Probably on a sort of damascus principle but on the blister steel- how good were the knives? Was it sort of potluck whereas cast steel was more dependable?

 

[LaBonte]

Wick -
Both wrought iron and blister steel were labor intensive as built in the past and the end product was heavily affected by the raw materials (iron, charcoal, etc.) as well as the laborers know how, both making quality control of blister steel an issue. But then again in the past blister steel was as noted above made in large quantities and not in the small batches seen so often today - a big difference in labor intensity.

Dave - blister steel quality varied considerably as noted in the following, which is just one of many documented period complaints.

"A blacksmith named Newton, at LaPointe Wisconsin in 1836 complained that it was impossible to warrant the half axes and tomahawks because of the blister steel being so bad."quote is from the book, "Indian Tomahawks & Frontiersmen Belt Axes" by Hartzler & Knowles and he asked for cast steel to be sent.

Also somewhere I've got documentation of a complaint by the local Indians (IIRC in Canada) when knives made from crucible steel were first introduced in the last half of the 18th century - they stated they were "too" hard to sharpen. Incongrously enough the Sheffield Knifemakers also fussed about the "new" cast steel being too hard to work with in comparison with their normal blister and shear steel stock. It was the French using cast steel for knives which usually created a superior product that finally caused the Sheffield makers to start using it in larger quantities. So with all due respect cast steel was not taken up promptly by all makers, especially in England

The Sheffield cutlers refused to work with his steel which was harder than that which they were used to. Huntsman then turned his attention to the French who were quick to take advantage of the new steel and bought all his produce.

When the Sheffield cutlers found that their markets were being lost to the superior quality French cutlery, they tried to obtain a government order to prevent Huntsman exporting his crucible steel. Forunately for Sheffield's development, they were unsuccessful in this attempt. Just as Huntsman was contemplating a move to Birmingham, the Sheffield cutlers abandoned their moves to block his steel making business and started using his steel to make their own products (note: this was IIRC around 1763)

The demand for Huntsman's steel increased rapidly and in 1770, he moved his factory to a new site in Attercliffe in the Don Valley. This area later became the main location for the huge special-steel making industry of Sheffield.

http://www.muzzleloadingforum.com/fusionbb/editpost.php?pid/1020743/

 

[crockett]

I think that's what I recall reading, that in England at least the cast steel was first used in clock making- for springs, etc and then later in cutlery, that for much of our target period shear steel might have been the most common.
And interesting insight on the blister- obviously not all knives were made in Sheffield. Has anyone ever come up with a percentage of how many knives in the U. S. were made here versus imported from Sheffield? For the fur trade with the larger companies, the proportion of Sheffield knives would seem to have been more than say the Longhunter who lived in a frontier town and went out on shorter expeditions.

 

[gmarc]

Wick

Producing blister steel in large quantities is very labor intensive in the handling of the materials.

In the crucible process, the operation takes place in much less time, and in the crucible from which it is teemed.

 

[gmarc]

I had heard that crucible steel was most promptly adapted for use in the production of small-arms barrels and bayonets, vs. edged cutlery.

 

[gmarc]

It was crucible steel springs that made marine chronometers possible. In fact, the Crown offered a prize to the first maker to produce a chronometer, which made calculating latitude easier.

This prize went to, I think, a man named Harrison, who used crucible steel springs in his clock. Crucible steel was the first product reliable enough for long-wearing spring applications. Its amazing to think of an age where reliable steel was NOT readily available.

 

[LaBonte]

I had heard that crucible steel was most promptly adapted for use in the production of small-arms barrels and bayonets, vs. edged cutlery.

With all due respect cast aka crucible steel barrels do not show up in the historical record until the 1830's - almost a hundred years after it's development. It went hand in hand with the development of deep hole drilling. It may have been used earlier in conjunction with iron to make damascus barrels, but I have seen no evidence for that - then again I'm always willing to learn....
Everything I have read regarding cast steel has it being used at first for springs, Huntsman was a clock maker originally, and then for cutlery of all kinds. But again documentation shows it was not widley used by the English cutlers until the 1760's. Trade list from that era on through the late 1800's era show knives being supplied to the Americas in both "regular" steel and in cast steel.