So, ok. You want to make a steel stabbing weapon. The movies have the smiths pouring molten steel into sword shaped molds and hammering on it.
As I understand it, modern manufacture of anything high strength metal, you start with plates or bars made by a foundry who does the recipe just right. CNC machines carve the resulting metal product out of the blanks and you treat the surface chemically as needed.
Well, what if you wanted to make a crapton of swords? Could you cast sword blanks using the same recipes used to make plate or bar blanks, and then cut the final blades out from them?
Hollywood likes the visually exciting. It’s very exciting to watch molten metal flow into a sword-shaped mold. It’s much less exciting to see the smith take a bunch of iron rods and forge them into a blank.
No, swords are not made from cast blanks. Except in bad fantasy productions.
Frankly, anyone who makes a sword or knife from indifferent crap iron or steel, or by forging it, is more about the renfair image and effort than an optimum product. Modern blades are made from blanks of very select steel - often special aerospace alloys - and ground to shape.
I’ll put one of the 134CM steel blades I made a while back against just about anything sweat-n-hammr forged, and see which one survives.
You could do this with copper or bronze weapons, but I don’t think cast iron would be the best thing for a weapon. Generally real sword smiths get a billet of iron (or, if you are going old school Japanese, you get lumps of low quality iron that you heat and beat eventually into a billet) and then pound that into the shape of a sword (or whatever tool they are trying to make).
You could do this today. You’d make a sheet of sword grade steel and then use a press to stamp out the shape you wanted (or you could use a water or plasma cutter to cut it out), then basically grind the edge. You wouldn’t get the best quality sword, as the body and blade would be basically the same thing, but you could make a lot of them this way. You couldn’t do this back in the days where swords were actually useful though.
(Today you could use a lot of automated tools…hydraulic hammers, high performance furnaces, computer controlled alloy mixers for making optimal steel alloys and grinders and such…to make a real sword that would be a lot less work than in the bad old days and still make a sword every bit as good, but not mass production, which would give you a lot of poor to medium quality swords)
Not even modern casting methods can make a workable sword blank. Grains are too fine at the surface and too large in the center. Even powder steel has to be rolled several times to prduce even layers and alighment of grains.
You would cast a large volume of steel and roll it into a thin sheet. Then you cut it into many appropriately-sized bars and mill each into a blade, which needs to be heat treated.
If you are making a real ‘crapton’, you’d stamp out the blanks, which would dramatically cut down on milling time.
Ok, what I was thinking the problem was, was “you have to follow an empircally developed recipe just right to get metal alloy with a grain structure that is strong enough to compete”.
And, since you can cut almost anything out of rolled or tubular pieces of metal, that’s what you use.
In actuality, the geometry of a sheet or a tube is different, and the forces on the metal from the mold are different, which is why you have to do the seemingly counterproductive thing of making bar/tube/sheet pieces of steel and then cutting the sword blade laboriously out with a milling machine.
The phase of the steel is determined by the way it’s cooled and the chemical composition. In the modern age where cutting steel by machine is relatively easy, the distribution of phases in the metal can be more easily controlled with a simpler shape, that is a rectangular billet will cool more evenly from outside to inside across it’s surface, whereas a sword cast would be thinner and thicker in different areas and would alter the phase structure because of it. Before the invention of the blast furnace, all iron (or steel, if it could be managed) was smelted as a solid bloom and forged into shape, with no casting involved. With the mechanization of blacksmithing and the ability to melt iron and steel, casting became more common. It’s false to say that just because something has been poured into a mold that it is “cast iron”. Cast iron is usually considered to be synonymous with pig iron, or a very high carbon iron. It’s hard and brittle, and the initial product produced by a blast furnace before the reduction process that would result in steel. If you are looking to make a reproduction of an older blade, using the cast-forge or bloom-forge method will give you a product that is more accurate to the specifications and attributes of the original. If you’re looking to make as strong and durable a product as you can in an older style, using a modern technique is probably better. Really, it depends what you’re looking for.