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Old 21st December 2017, 12:39 AM   #63
Timo Nieminen
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Originally Posted by A. G. Maisey
For instance, there used to be a gentleman named Mike Peterson who did a smelt once a year. Mike has passed on now but he lived on the South Coast of NSW. In technical terms he probably did not really smelt, what he did was to collect a lot of various kinds of iron and steel, stack with charcoal and produce a bloom. Or maybe Mike did "melt with smelting", as you have noted. I have a piece of one of the blooms he produced, and have worked with this material. It requires quite gentle initial welding, not dissimilar to welding meteorite. It makes very good blades.

Yes, technically not smelting. This is a traditional process for steel-making, starting with iron. It's one of the 4 ancient steel-making methods (make steel directly in a bloomery furnace during the smelting process, make iron in a smelter and then carburise in a second step, make cast iron in a smelter (a blast furnace rather than a bloomery) and decarburise the cast iron, and crucible steel).

The goal is to carburise the iron to produce steel, and done right it can make excellent steel. The diffusion of the carbon into the iron is the same as what happens when you make steel directly in a bloomery. You don't want it to melt, since you want high-carbon steel, not cast iron, so you get a bloom. I guess (but it's only a guess) that the bloom would be much cleaner than the bloom from a bloomery smelter, since if you just put in iron and charcoal, you should get a bloom full of slag.

Steel made this way is called oroshigane by the Japanese, and it's still done for swordmaking.

For those interested, video showing this kind of thing:

I've heard of people doing similar things with forge scale, which is smelting (since it's an oxide).

Originally Posted by A. G. Maisey
Yes when limonite does carry nickel, the content is quite low, I think something like 1%-2% ?

I know nothing about laterite ores, I've heard the name, but only in connection with soil and with building materials.

The only limonite I know anything of the chemistry of is bog iron, which AFAIK has only trace amounts of nickel. So time to learn more.

[A pause, to go away and learn more.]

OK, the deal with laterites is that "laterite" is a very broad category, and includes rocks that are iron ores and rocks that aren't iron ores. If they are iron ores, the iron is usually in the form of limonite. 70% of laterites contain limonite.

Anatolian laterites have a Nickel:Iron ratio of about 1:30. If you made nickel-iron from them with 100% efficiency, you'd get about 3-4% nickel in the iron. Some laterites have more nickel than that, which is why (a) 8% (rather than 4%) is often considered a good rule of thumb to distinguish between ancient smelted nickel-iron and meteoric iron, and (b) people look at the nickel:cobalt ratio because that tends to be different for terrestrial vs meteoric (and Jambon has some nice graphs showing this (but his data doesn't include Anatolian ores)).
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