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Jpnine

Can you forge previously cast metals?

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I'm very very new to the topic of metalworking. During my research, I've seen the two main methods of casting and forging. Casting seems simple, you melt the metal in a crucible and pour it into the mold for the shape you want. And with forging, you can have it cold or hot and shape it while it's in the solid state. As I was looking at those techniques, I saw somewhere that you can't really forge with cast iron. But I was thinking you would cast iron into bars so you could use them for forging later on. If not, then what is the process of getting metal from the ground so it can be used for forging? Is there a way to make cast metals usable for forging? Is this only an issue with iron? I'll likely be using aluminum first so I can cheaply make a smelter/forge and practice with it, so I'd like to know if I can move between casting and forging the same piece of metal.

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Welcome aboard... Since you posted this in the Non-ferrous Metal Working section I assume you are not thinking of melting steel. Casting is far from simple and a very hazardous undertaking. I have worked in a foundry and can state for sure it is not for novices. The process of getting metal (ore) from the ground is called smelting. Moving between casting and forging depends upon the metal.

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Welcome aboard Jpnine, glad to have you. If you'll put your general location in the header yo'll be surprised how many members live within visiting distance and a LOT of information is location specific. 

Where have you been "researching"? While major methods of working metals, casting and forging are hardly the main methods, fabrication maybe outweighs both put together. Technically casting/forging is required for all modern steels but that's producing the steel. The steel mill melts scrap or processed iron from the smelter, molten steel is adjusted for analysis and goes from the melter to the continuous caster which produces a continuous bar of steel which is then allowed to cool below solidus cut to length and then is sent through a series of roll mills where it is roll forged into desired shapes and sizes. So YES casting and forging are by default THE main ways of working steel. . . Sort of. I think digging comes first though.

Not being able to forge cast iron is a metallurgy issue. Cast iron has too much carbon to be forgeable, it's too brittle even at very high temperatures. 

Other metals can be cast in forgeable alloys.

Frosty The Lucky.

 

 

 

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Dear Jpnine,

Whether you can forge cast metal is dependent on the metallurgy/chemistry of the cast metal.  For example, cast iron cannot be forged because it is too high in Carbon.  Generally, brass cannot be forged because most brass alloys contain lead which makes it better for machining but weakens it at high temperature so that if you attempt to forge it it will crumble.

However, the converse is not true.  You can generally melt down and cast anything that has been forged.

This is a sermon that many of us preach but be VERY careful about melting and casting metals, even those with fairly low melting points such as pewter and aluminum.  A small mistake can result in molten metal flying around and being hit by it can result in a life changing injury.  I'm not saying don't do it but be sure that you have the proper tools, techniques, knowledge, and personal protective equipment.  A healthy amount of fear and respect is good to keep around hot metal, solid or liquid. 

"By hammer and hand all arts do stand." 

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10 hours ago, Jpnine said:

I'll likely be using aluminum first so I can cheaply make a smelter/forge and practice with it

I doubt very much you will build a smelter.  Bauxite is hard to come by and its not easy to extract the metal from it, and there is nothing cheap about it.  I am unaware of any combination unit of smelter and forge.

Melting can be done in a forge, but is more practical to be done in a furnace.

Perhaps you need to better understand the definitions of the words you use,

SMELTING is the extraction of metals from an ore

MELTING is liquefying a metal, commonly for casting

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Ok a bit of confusion on terminology: all steel is now cast as part of it's original processing and the resulting ingots/shapes can be heated and worked. Prior to the 1850's and the rise of the Bessemer/Kelly process this was not the case.  Real Wrought Iron---the material---could be made by smelting using the Direct Process where the metal never really melted or the indirect process where cast iron was made from the ore and then processed, (see the Puddling process), to remove excess carbon leaving real Wrought Iron.  (The Byers process of taking molten steel and adding back in ferrous silicate slag and mixing the result is only mentioned as a curiosity.)

The Bessemer/Kelly process took molten cast iron and burnt out the carbon by blowing air (later oxygen in the BOF) through it turning it into molten steel that was then cast and then could be forged or rolled to various shapes.

So: cast iron, >2% Carbon, crumbles when you try to forge it---or *splashes* if you heat it high enough.

Steel can be cast to shapes that then can be forged.  (The pre Bessemer/Kelly "cast steel" was made by melting real wrought iron and then casting  it into ingots, (aka "teeming"), that were then forged/worked.  It was not used to cast to final shapes as the grain structure would be horrible!) 

Modern Steels can be cast as part of the smelting process or scrap can be melted and cast as part of a remelt process.  Once solid it can be forged/rolled if needed.  The issues with grain structure can be addressed by proper alloying and Thermal processing. (Two of the huge breakthroughs in modern metallurgy!)

Cast iron can be remelted and cast multiple times; example using a cupola furnace, and is always known as cast iron.

Cast Wrought Iron derived steels are actually old style "Cast Steel"  (see wikipedia on the Huntsman Process).

Modern steels can be remelted and cast and are still known as steel.

If you are interested in casting; Aluminum is a good place to start to learn the process and the safety tips before moving on to the higher temp metals of which steel is probably the hottest and most dangerous of the common metals to cast and few hobbyists do it!  (Cast iron is much simpler and cheaper to cast.)

There are a number of people smelting iron from ore usually using the direct process; more for bragging rights or historical replication than for better materials! (Many more using the direct, "Bloomery process", than the indirect processes like puddling.

Now just to confuse people there are "traditional" names still used for various items like a "Tin Roof" which is made from galvanized iron (which is actually galvanized *steel* and not cast iron or wrought iron!)

So when you get to talking with folks be SURE that you are using the same terminology!

Now if you really want to get into learning about the old school ways; may I commend to your attention: "Steelmaking before Bessemer: vol 1 Blister steel, Vol 2 Crucible steel"  Kenneth Charles Barraclough

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