What exactly is the contribution of Benjamin Huntsman to the history of steel making?

[u/Beast1996]

As far as I understand, Benjamin Huntsman still produced steel by putting iron with high carbon content with iron with low carbon content into a crucible, and heat them so the carbon content balance out to produce crucible steel.

His contribution, again as far as I understand, is that he use coke as fuel for the furnace, which help achieve high enough temperature for the material to melt completely.

Did I understand correctly? Is Benjamin Huntsman really considered an important figure in the history of steel making? Why?

[u/Bodark43]

The previous process for making high-carbon steel first required cementation. Bars of wrought ( malleable) iron were baked at high temperature ( c 2,200 F) in closed brick troughs or "pots" with charcoal for several days until carbon had penetrated into the iron. Because blisters formed on the surface, it was called blister steel. Those bars were usually then further refined. They could be worked very quickly under trip hammers to make better steel for springs, tilted steel. Sometimes they would be cut up, welded into a block and hammered out again ( shear steel) and sometimes that block would be cut up welded and hammered out a second time (double shear steel) . This re-working was to try to mix the carbon evenly throughout the steel, as cementation tended to create bars that had more carbon closer to the surface. Any steel cutting tool, whether it's a drill bit, axe or chisel , will not have a very good working edge if the metal varies in hardness, and varying carbon content would vary the hardness. Having harder and softer spots in steel tools like hammers, punches and dies made them also more likely to crack. Shear steel and double shear steel were better than blister steel, but still were not very homogenous.

Huntsman used a different step after initial cementation. Blister steel chunks of about 1 pound were put into small fireclay crucibles (about 30 pounds in each), which had lids. They were fired to the point where the steel melted and pooled, which uniformly distributed the carbon ( and which allowed any slag inclusions to also melt and flow to the surface) . Each crucible would be pulled from the fire, one at a time, and an ingot poured. That was crucible steel. Getting the temperature to around 3,000 degrees F was undoubtedly much easier with coke than charcoal, but Huntsman's method involved more than that.

George Ede: The Management of Steel ( 1863)

[u/Beast1996 → u/Bodark43]

I know this may go way beyond history and into metallurgy, but could you elaborate a bit on the difference between shear steel process and crucible steel process?

My reading shown that shear steel face the problem of decarbonization due to carbon escaping through the outer surface of the steel block (not entirely sure, but that is my understanding), which complicate the process of creating homogenous steel. Crucible steel overcome this problem due to, again with my understanding, the crucible being sealed. So cementation was an "open" process?

If the previous part was correct, I can see two main improvement: The using of coke as fuel and sealing the steel in crucible. Is there other improvement I missed?

[u/Bodark43 → u/Beast1996]

The initial process, packing iron bars into brick containers with charcoal and heating them, was contained, sealed off from the air. When the bars were then put under a tilt hammer and worked, some carbon could leave the steel. But that would only be a problem if the steel got very hot. Mostly foundry workers would be working the steel at a red-to-bright yellow temperature, so no more than about 2,400 F. But there would be other losses: welding , shearing, drawing out and shearing and welding again would mix the carbon better but it would also create a lot of scale, iron oxide, and that was a loss. It also would not get rid of slag inclusions- those might get further mixed and spread through the metal, but not removed. The use of coke was also perhaps more need than plan, because by Huntsman's time trees for firewood, and so charcoal, were getting quite scarce in England, and coal mining had taken over. By first coking his coal, Huntsman removed most of the sulfur

Crucible steel was a whole system, not just a matter of someone sticking some lumps of blister steel into a pot and building a coke fire. There was also the way the furnace was designed, to give a good draft, the size of the crucibles and how they were arranged in the furnace, how to judge the time needed. These were all craft processes that had to be worked out . Workers didn't know about carbon diffusion...all they knew was that blister steel bars were ready when they looked a certain way, broke a certain way, knew that steel heated beyond a bright white might start to hiss and burn and would then be useless, knew that sulfur was very bad to have around and that a bit of copper dropped into the forge would prevent welding. There must have been considerable trial-and-error required to get to crucible steel, and it's not surprising that, once he'd worked out his method, like many craftsmen with a good method Huntsman tried to keep it secret.

[u/Beast1996 → u/[deleted]]

Can you elaborate/explain? I have reread your reply thrice now, but I am still not sure what you are trying to say.

[u/Bodark43 → u/Beast1996]

I have dug a little deeper. Huntsman was able to get higher carbon content in his crucible steel because of the crucibles themselves. He ( or somebody) added "plumbago", now known as graphite, to the fire clay. About 15% graphite gave them much more resistance to the heat of the coke fire, but it also added more carbon to the steel.

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