The title asks it all.
Doesn’t forged mean somethings beaten into shape, and cast means it’s formed from a mold?
Having just researched it rapidly: I’m right, so forget about the interrogation mark in my previous post.
Forged:
To form (metal, for example) by heating in a forge and beating or hammering into shape.
To form (metal) by a mechanical or hydraulic press.
Cast:
To form (liquid metal, for example) into a particular shape by pouring into a mold.
That’s what I thought. I’m assuming casting is easier (once you have the mold, that is).
Amazing things, dictionaries are.
sar·casm (särkzm)
n.
A cutting, often ironic remark intended to wound.
A form of wit that is marked by the use of sarcastic language and is intended to make its victim the butt of contempt or ridicule.
How true.
Well, Mr. Blue Sky, whether one is easier or not is not always relevant. You get vastly different metalurgical qualities from the same metal, depending on whether it was cast or forged. I’m not a metalurgist but a resistance welding expert, so this may be B.S.: casting seems weak to me, that is, you get “foamy” material that’s not as strong as forged metal. Forged metal, though, is strong but brittle, and subject to shattering that cast material may not be. In a way, resistance welding is a forging process as far as the joint is concerned. I’d think Silicon Bronze or MiG would be kind of a moldless casting, and they both kind of behave like I’ve just stated.
If you want non-dictionary differces:
Forging is generally stronger and more expensive than casting.
Casting can be essentially any shape you can imagine, given the right casting process (lost-wax). Forging shapes are much more limited, although often you can often forge a simpler shape then CNC out the bits you don’t want.
Eh? I don’t understand this bit, I always thought cast metal is brittle, like cast iron is very brittle when compared to forged iron (like in iron railings, horse shoes, etc) And cast steel is more brittle than forged steel, e.g. wrenches/spanners are usually drop-forged and can be bent (if you apply enough force!) You usually cannot bend a casting.
Then again, the type of casting also plays a major role: investment casting usually produces a very strong material, e.g turbine blades are very intricate investment castings, and are immensely strong to withstand the forces acting on a turbine. I doubt you’d be able to forge a turbine blade. Another example is rifle actions: many modern actions use investment casting techniques instead of the machining down of forged steel into the required shape. Investment casting is a lot cheaper and faster and produces almost the same strength actions.
How about cast iron engine blocks? They have to withstand quite a lot of heat.
I’m with venterap. Forged steel is very much more flexible than cast. This is why mass produced swords suck.
From my hazy, mad-cap dash through 2nd year metalurgy:
Forged items tend to be a lot more tougher than cast. By beating the crap out of it you change the microstructure of the metal, particularly in alloys. A lot of the aluminium alloy used in aeronautical application are forged via ball peening (hitting them with ball bearings), making them much tougher. Likewise with swords, the process of forging makes them less prone to brittle failure while still being able to hold an edge.
Cast metals tend to be harder and more brittle. By a process of heat treatment, you can make extremely hard components. A classic example is engine blocks; of course a problem is that it they’re so hard it becomes difficult to machine. As mentioned before, they tend to be the cheaper route for mass production.
Actually, it’s a trade-off.
Cast metal is brittle and relatively soft because it is made of a ‘foam’ of fat (crudely spheroidal) randomly shaped regions of crystalization formed as the material cooled. Impurities and defects tend to be pushed to the boundaries of the crystals, so the boundaries are mechanically weak. The interior of these fat crystals are relatively unstressed, so the metal tends to be more ductile (it has fewer crystal deformities to start with, so you can deform it more) Of course the conditions of casting and cooling can have a big effect.
“Wrought metal” is cast metal that has been “worked” (‘wrought’ is an old word for ‘worked’) It’s stronger and tougher than cast iron. If you work the metal more, you get forged metal, which is harder and stronger becase the crystals have been flattened, stressed and aligned a fair amount. However, while cast iron is soft and brittle like cheap concrete (lots of tiny bits crudely glued together), heavily worked or overworked forged metal can be very hard and brittle like glass (which is usually harder but more brittle than steel) In other words, cast iron cracks, heavily worked iron can shatter.
Worked metal is often tempered: heated for a long time to allow the internal defects to resolve (which can soften the metal) and cooled either slowly (for toughness) or quickly to freeze the crytals in small and irregular shapes (making it harder but more brittle). Alas, the same word “temper” means to soften, toughen, harden, or even to lose the benefits of the tempering process. Look it up in a dictionary, and be completely confused. It has even more meanings in cooking, for unique crystal effects in foods like honey, candy and chocolate.
Metalworking and metalurgy are complex. I hope my skim helped, but don’t kid yourself into thinking it tells you more than it does
I guess by “brittle” I don’t mean like peanut brittle where it’s likely to spontaneously fall apart. Like I said, I’m not a metallurgist, so I mayn’t be using the right technology. I guess i mean if you take a sharp force at a cast object vs a forged object, the cast object is more likely to not break, whereas the forged object could shatter. The cast thing is molecularly misaligned, while the forged thing is more crystaline. So there’s more room for movement in the cast item. Kind of like you won’t break a steak dropping it on the tile floor if it’s thawed, but it could shatter when it’s frozen. So what’s better: Strong like a tree or flexible like a reed?
I presume we are talking cast iron here. The problem with most cast metals is that they shrink so much on cooling that the moulding deforms etc. Cast iron contains alot of carbon (ca. 4%). As the iron cools the carbon comes out as graphite which is a lot less dense, and hence cast iron does not shrink much on cooling, preserving the shape better. however, the high carbon content means that the metal is hard and brittle due to trapping of disclinations etc.
Cast iron engine blocks have excellent machineability, forged steel crankshaft are used for strength and durability, used with heavy duty trucks and racing applications.