Talk:Forge welding

Temperature

What temperature is required for forge welding mild steel? I talked with a blacksmith this weekend who implied he needed about 2000 °F to do it (which only one of his forges could supply). —Ben FrantzDale 14:03, 18 September 2006 (UTC)

Quote: "The temperature required to forge weld is typically 50 to 90 percent of the melting temperature". Percent temperature is meaningless unless one uses an absolute temperature scale. Biscuittin (talk) 19:30, 1 August 2015 (UTC)

Welding can take place when gamma iron changes into delta iron. For pure iron, this is ~ 2500 degrees F. The more carbon added, the lower this temperature becomes. For around 2% carbon it can be as low as 2100. The way to easily tell is that delta iron is non-magnetic, so it's ready to weld when a magnet no longer sticks to it. Zaereth (talk) 01:52, 2 October 2015 (UTC)

I added some more info to the temperature section, so I hope that helps. I'll work on some other sections in the near future. Zaereth (talk) 18:11, 5 April 2016 (UTC)

Hi @Zaereth! I removed your section about finding the right welding temperature using a magnet. It was incorrect. For context, I am helping with this article as I have been a blacksmithing who regularly forge welds for over a decade. The initial assessment from @BenFrantzDale is accurate. Forge welding happens at very high temperatures. A blacksmith has to act very quickly while the iron is hot enough. Using a magnet does not make any sense. A blacksmith assesses visually whether the temperature is hot enough. Sometimes you can look at the appearance of the flux to get a sense of the right temperature, e.g. it bubbles on the surface of the steel. Hope this helps. SonicSmithy (talk) 19:00, 29 April 2023 (UTC)

For the record, I've been blacksmithing and forge welding for nearly 4 decades. You should check the cited sources. Zaereth (talk) 19:19, 29 April 2023 (UTC)

@Zaereth That's awesome. How often do you use a magnet to check your forge welding temperatures? I don't know a single blacksmith who does that when forge welding. Would love to understand your process and time management for forge welding. SonicSmithy (talk) 19:24, 29 April 2023 (UTC)

I don't. That came from the cited source. Try it for yourself. When talking about allotropes of iron, alpha iron is magnetic, whereas gamma iron is not. That's a good way to tell when it's time to quench, especially for a beginner who doesn't really know the proper color temperature. It's also good if you're using a steel with an unknown carbon content and don't really know which color temp to look for. When gamma iron changes into delta iron, which for pure iron happens at about 2500 degrees (or approaching the melting point of steel) it becomes magnetic again. Of course, pure iron is something you only find in laboratories.

It's not practical to do that while forging, but it is a way to tell what the proper color temperature looks like, because it varies for different types of steel. For example, when forging a Japanese sword, you begin with steel with a carbon content of about 1.5%, and cast iron with a carbon content ranging from 2.0% to 2.5%. If you heat this to a yellow heat it will be hot short and will just crumble when you try to weld them together. You have to start out welding at more of an orange heat, which is vastly lower than that used for steel. As folding progresses the steel loses a lot of carbon from decarburization. To combat this you have to coat the steel in clay each and every time before you heat it and weld it together. Even so, you still lose carbon, so by the time you're nearly finished you're having to heat it to a yellow heat. Likewise, when forging the wrought iron for the core, you need to het that much hotter than steel, to nearly white heat. If you're unsure of the proper color temp to heat it to, you can easily test this out beforehand with a magnet, and if your magnet is on a long stick, you can even do this while it's still in the coals.

The thing about Wikipedia is, we're not supposed to use our own experience and expertise to write articles. See: WP:NOR Everything we put in articles needs to come from a reliable source. Zaereth (talk) 19:52, 29 April 2023 (UTC)

Thank you, @Zaereth! I appreciate your detailed response. I also agree that we should not do original research. That said, I did check the references, e.g. Titanium: A Technical Guide, 2nd Edition by Donachie does not support the sentence where it was used as reference. Similarly, there are no references in the article or elsewhere that support the assertion that you can forge weld at critical temperature. Maybe I am missing something. I would certainly appreciate to hear about your interpretation of the references.

NB: I have made tamahagane and forged Japanese-style swords; never used cast iron though - that's not a material you end up with in a bloomery process. SonicSmithy (talk) 20:08, 29 April 2023 (UTC)

An Iron Carbon/Cementite Phase diagram answers many of the questions that are in debate here. Specifically, once you reach the γ-austentite phase, it is non-magnetic. The next phase change is to γ-austentite/liquid iron or straight to liquid iron. There are no magnetic phases after that. SonicSmithy (talk) 20:25, 29 April 2023 (UTC)

first method?

It was first applied to iron, yet it's the first method used to join metal? so for about 2000 years previous to the discovery of iron, when only copper, tin, lead, and a couple others were known, nobody ever joined 2 pieces of metal? thats clearly wrong, one of those statements has got to go.70.70.136.240 09:24, 5 February 2007 (UTC)

Copper, bronze, and brass are rather difficult to forge weld due to the particular impurities they form, especially in a charcoal or coal forge. For forge welding to work, weld surfaces must be extremely clean, and in ancient times, good grade fluxes and neutral flames just weren't available. Small amounts of copper would greatly affect iron's ability to weld, so great care had to be taken to extract as much as possible during smelting, or poor welds were produced. (In contrast, copper has little effect on arc welds.) Electric welding of copper is typically impractical because a filler metal cannot be used, but the weld must be face to face, like a spot-weld. The best way to weld copper in the solid state is either cold welding, roll welding, or explosion welding. In ancient times, it was easier to just melt it down and recast a broken item.

With lead and tin, it's like, what's the point? The metals are so soft and have such a low melting temperature they had few practical applications except for as a solder. As far as I know, iron was the first metal to be welded, and that was very significant, because it was a leap in technology that allowed us to move out of the bronze age. Iron actually had to be forge welded just to manufacture it, because after smelting all you really have is sponge iron, which is so porous it has very little strength. Therefore, the sponge iron had to be welded into a single block to squeeze out air pockets and turn it into a solid block, because, unlike copper, the ancients had no way to melt it fully. (The ability to weld was so revered and mysterious that it seemed almost magical, and in many culture blacksmiths were actually used to perform wedding ceremonies because of it.) Zaereth (talk) 05:55, 2 October 2015 (UTC)

Famous applications?

I'm trying to rework the last paragraph of the main section. It isn't cited, and seems awkward. Any suggestions? I'm tempted to move it to this page, and let people work on it. --Talroth 17:07, 17 February 2007 (UTC)