lyuv

What makes a good forging iron?

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Suppose I can be picky with my iron(/steel). Are there guidelines as to which is more "blacksmith friendly"? That is, easier to move, at lower temperatures. Less prone to breakage ect.

I"m talking about differances that are actualy felt by the blacksmith, rather than theoretical.

I heard that stainless steel is a xxxxx. But what about low carbon construction iron? steel salvaged from hand tools (like wrenches), machinery and springs? How significant is the carbon content (or other properties)?

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As a rough guide, the higher the carbon content, the more difficult to work. This is in relation to actual force required to move as well as a narrower working temperature range. For the majority of blacksmithing (other than blades and tools) A36 or mild steel is more than adequate.

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Also, remember that, generally speaking, the properties of the finished piece are more important than the working characteristics of the material. Yes, high-carbon steel is tougher to forge than low-carbon, but if you're making knives or punches, low-carbon is definitely not the way to go.

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Extremely low carbon steels are a delight to forge for ornamental work. I'm talking about 1005 and lower, the "4 Ought" steel. Stuff that won't harden even if quenched in ice water or super quench. They are also hard to source and expensive.  You can do amazing things with them; but pretty much nobody will pay for it when you can get by with 1018 or 1020.  A-36 is pretty much the standard steel you buy hot rolled but it is prone to hardening and cracking if you don't take care.

Stainless is a pain to work with; but can be great as the customer does not have to maintain it as much, (look up electropolishing too)

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I must wonder - the "academic" resources state that pure iron's melting temperature is HIGHER than when carbon is added. From that, I would expect that pure iron would get softer at HIGHER temperature. And adding carbon would reduce that temperature (along the melting temp).

I don't question the reality. Just wonder where my logic goes wrong.

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lyuv, what you say is true, but its not just temp that dictates the ease of forging. A good coal or charcoal forge would get plenty hot enough to melt both mild and tool steel. 

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The melting temperature is not that relevant. You are not casting the stuff.

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I'm sorry but can you state your "logic" I don't see you making any statement save that of the academics.

The extremely low carbon steels can be worked both hotter and colder than higher carbon steels with no issues---the forging RANGE is greater and for some alloys MUCH greater than for some other alloys.  At hotter temps they are softer under the hammer; but they are also softer at equivalent temps making for easier forging.

In this way they mimic a lot of the real wrought iron that was forged at temps where modern steels are often burning!

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You need to get off the attempts to "understand" things academically. Academics make a career out of Studying things and rarely have a real understanding. Not in my experience anyway, I know a few guys who'd qualify as academics but they apply the knowledge or study as a pursuit. 

Have you seen diagrams of what iron and steel would look like if we could see atoms and molecules? Iron molecules are sort of smooth and rounded and so slip past each other with "Relatively" little force. Carbon atoms and molecules have more free electrons so they're sticky and fill the gaps between iron molecules but stick to more than one. The more carbon molecules the more the iron molecule are stuck together. BUT in an annealed state many if not most of the carbon molecules are bound within the iron molecules so it does't glue so many iron molecules to each other. 

The hotter it gets the more the iron molecules expand and the carbon  becomes more fluid the carbon gets squeezed out of the iron molecule to between them. If you allow it to cool slowly the carbon returns to the centers. Shill it quickly and the carbon is trapped between the iron molecules and bonds them together.

Okay, I know that's not necessarily correct but it draws a decent mental picture of how it works. If you think of carbon like cement in concrete and heat like the water you'll have an okay working handle on what happens. They're not metallurgically correct but it's a usable working handle on what's happening.

Frosty The Lucky.

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Funny i have a friend who is a Metallurgy Professor at a local University; guess who got called in when his young son was having problems forging a gladius of real wrought iron to take into school as a project.  I ask him a lot of questions but when it comes to hammer on wrought iron or steel I excel the PhD!

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