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Assume you have two blades (of whatever design you wish) made from identical starting steel (in fact, we can assume that the two starting ingots are sisters from the same mill run). One is shaped by manual hot-forging, while the other is shaped by a single-blow, closed-die hot forging process. After shaping, they are identically heat-treated and machined to final dimensions.

How would the two blades be different, and how would this difference manifest itself in practical usage as a tool or a weapon, both initially and over a long period of time?

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  • $\begingroup$ Look up about die-cast (kitchen) knives. Wosthof has info, I recall. It has to do with the stress patterns frozen into the material. It might be moot if you then do heat treatment hardening. $\endgroup$ – JDługosz Dec 29 '16 at 2:35
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    $\begingroup$ Would this be a better fit on Engineering.SE? $\endgroup$ – Shalvenay Dec 29 '16 at 2:36
  • $\begingroup$ A way to find out is to look at their tags and search for questions on similar subjects. You can always ask on their Meta site, pointing to this Q. $\endgroup$ – JDługosz Dec 29 '16 at 2:39
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    $\begingroup$ What kind of blade is important something long and thin like a sword is going to react differently than a camp knife. on a sword drop forging in a single strike will be full of stress fractures. On the other hand as long as you can keep the metal hot you can press forge almost any shape. Normal drop forging will produce better results than smith forging, it is the one strike thing that makes it difficult. $\endgroup$ – John Dec 29 '16 at 4:17
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    $\begingroup$ @James Seems like I'm years late to remind you, but you was supposed to answer this. By the way, both techniques of forging swords, machetes etc are used today so one could buy and compare ;) $\endgroup$ – Mołot Jan 9 at 9:29
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Assume you have two blades (of whatever design you wish) made from identical starting steel (in fact, we can assume that the two starting ingots are sisters from the same mill run). One is shaped by manual hot-forging, while the other is shaped by a single-blow, closed-die hot forging process. After shaping, they are identically heat-treated and machined to final dimensions.

Ok so this is pretty straight forward, but there are some caveats you should consider.

  • Steel quality. Pre-modern steel and the steel we use today are very different.

Pre-modern steel had its problems. The quality was inconsistent though getting your ingots from the same run eliminates the related variance for your specific scenario. Contaminants were also a problem, steel today is very precisely manufactured and certain grades of steel are required for various applications...this depth of metallurgy didn't exist previously.

  • Tools versus blades. The process for creating tools and the best steel for creating them vary greatly. For example if you are creating a hammer or tongs you want to use a softer steel. Repeated blows from a hammer crafted like a blade wouldn't last all that long. Softer steel is ok for tools...not so much for blades.

When it comes to blades in particular, the forging process helped mitigate the problems with early steel, either by adding the necessary carbon to give steel its extra hardness vs iron or low carbon steel, or by folding the steel to remove and even out contaminants/impurities.


How would the two blades be different, and how would this difference manifest itself in practical usage as a tool or a weapon, both initially and over a long period of time?

Pre-Modern Steel

The standard vs one big hit blades would vary greatly, mostly depending on the steel that was used in the first place. There are a couple common problems that both pre and modern steel will share...Ill get to that. The traditionally forged blade would be better in this scenario. The process was refined specifically to improve quality based on the steel that was available at the time, with the drop forge process you lose all of that.

The drop forge blade would be more likely to break due to the shortened forging process.

Modern Steel

Modern steel, well... if I'm honest you don't even need to forge it to make an amazing blade. Given you complete the heat treating steps properly a blade cut out of a sheet and ground to shape will be just as effective, and significantly easier to make, when compared to a forged blade. Strictly speaking forging is just the shaping of the steel, then you have a whole bunch of heat treating and grinding/polishing steps after you finish forging.

The general forging process, though I left out the all the finishing steps (grinding polishing, handles etc...)

  • Forge to shape. Make the steel hot, smash it with a hammer until you get your shape
  • Normalize the steel (heat to 1300F, 1000F, 800F letting it cool to room temperature between each heating. This takes tiny fractures out of the steel from the forging process, think of it as a healing bath for broken microscopic steel bones. I don't know if this step can cope with the amount of stress a single really hard blow would put on the steel.
  • Hardening. Heat to critical (generally yellow hot) the steel will be non-magnetic. Quench, you can use water, but we use a mix of motor oil and antifreeze. This makes the steel very hard, if you drop it at this point it can shatter. (SAD Blacksmith)
  • Tempering. Re-heat the spine and tang of the blade while keeping the cutting edge cold. This process softens the spine and tang so they can take more stress and bend better while the cutting edge stays sharp and hard. You're literally giving a single piece of steel varying toughness vs hardness.

The drop forge idea could work fine, though I see potential issues when you start getting to larger sized blades. The larger the blade the larger the billet will need to be. To move the steel that effectively in one single shot you will have to make it hotter than you would traditionally get it when hand forging at least that is my assumption, I have not tried to make a blade in a single strike before.

The additional force required to move all that steel at once could also potentially have problems. I could see the edges of the steel tearing/ripping even when heated to a bright glowing yellow and if you get any hotter you are getting to the point where it liquifies and then you have to cast it...but cast iron does not work at all for blades, it is very brittle.

  • 2000°F Bright yellow - 1093°C
  • 1300°F Medium red - 704°C
  • 1200°F Dull red - 649°C
  • 1100°F Slight red - 593°C
  • 1000°F Very slight red, mostly grey - 538°C

In short, extra heat and force could cause tearing or change the nature of the steel in a way that I am not aware of...I can see it being possible but I'd have to do more research, I just don't deal with that in my forge.

Common problem with the drop forge

Old or modern steel I can see one problem coming up...when you forge a blade the traditional way you have to take care to strike the blade evenly on both sides. As the steel stretches from the blows it curves, and if you don't keep your blows balanced odds are the blade will warp when it goes through the hardening process...which is super frustrating for the record.

With a single blow, to only one side odds are you are going to get pretty significant warping when you heat treat the blade. You can selectively heat portions and straighten a blade that this happens to, but each bend and twist of a blade that you don't heat up fully adds stress to the structure creating weak points...and if the warping is severe enough you have to reheat the whole thing and start the heat treating process over.


Summary:

  • Traditional forging will get you a better blade with pre-modern steel
  • The easiest method with modern steel would be to not forge the steel at all
  • I'd need to research more, but even with modern steel the stress of all the steel moving in one shot could cause problems
  • A blade struck on only one side will warp when it is heat treated

Could you do it...yeah probably, with modern steel and modern tech. Should you do it...I have my doubts that it would make a better blade, it would be faster, but honestly the forging step of the process is usually the shortest. I can have a short blade forged to shape in under an hour. The rest of the steps...which you can't skip take longer.

Short versus long term...I don't think it really matters. The point is that steel behaves in certain ways under certain temperatures and certain stresses. If you don't forge properly you add to the likelihood that the blade will fail in some way in the future, the exact nature and timing of that failure will depend on the composition and structure of the particular blade/steel.

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  • $\begingroup$ Point of minor clarification -- by "tools" in the OP, I was referring to edged tools (vs. edged weapons). $\endgroup$ – Shalvenay Jan 9 at 23:31
  • $\begingroup$ For real life drop forged swords one should look for \$60 forged sword that would usually cost \$600. With meaningful lack of "hand" word next to "forged" and probably made in China. These swords are pretty ok when used as machetes, cutting practice with tatami etc. Don't know if they would survive swordfight. In modern times I don't think anybody tries. Biggest benefit is cost —drop forge wastes no material and is fast. $\endgroup$ – Mołot Jan 10 at 7:12
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So assuming a sword and assuming you are starting with decent steel.

If multiple strikes are allowed a drop forged blade will have fewer stress points, flaws, and other anomalies than smith forging. Thus it will be less likely to fail in the long run. But the benefits compared to a master-smith's work will be small, especially with proper heat treating.

If single strike is important press forging produces the best result, roughly the same as multi-hit drop forging.

A single strike drop-forged sword will be full of cracks and weaknesses, unless you have already shaped your ingot to a roughly sword shape by other means. It will be lucky to survive finishing much less use you are just moving the steel too much at once, moving steel cools it, move it to much and no matter how fast you do it it will get too cold during the process.

Your biggest difference is with consistency with quality, drop and press forging produce more consistent results so if well made will produce good results all the time, where a smiths quality can vary. The other big benefit is speed, drop forging is much much faster than hand forging.

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Bragging rights, mostly. When your sword was made by Thor himself in one strike of Mjolnir, people tend to buy you drinks.

It depends heavily on the original steel itself. The Japanese Katanas had to be forged many times to get the strength needed because their steel was poor. Modern tool steel fares well vs. Katanas despite not being forged in such a way.

If you forge a modern tool steel too much, you can actually negate much of the careful metallurgy that went into it and ruin the steel by introducing contaminants.

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    $\begingroup$ "people tend to buy you drinks" and run away when you draw your sword... $\endgroup$ – RonJohn Aug 6 '18 at 1:22
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The one that's forged will have less carbon in it and therefore become a different alloy of steel.

The one that's die cast will remain closer to the properties of the original ingot. It depends on those properties as to whether either is ultimately better for any given purpose.

If your ingot has an undesirably high amount of carbon, it'd be better if you banged on it a bunch, and vice versa.

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protected by L.Dutch Jan 9 at 9:10

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