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I'm asking the question to figure out the effects of what will happen when a substance is cut by a heated blade, lets say of a dagger's length, not a blade made of literal fire or heat. Steel that has been heated to high 1370 C (2500 F) will melt so imagine the blade being heated to 800 - 900 c. I'm looking for the process of how the blade interacts when slicing into a few different things with the equivalent force to slice meat.

  • Flesh
  • Bone
  • Scales

  • other steel blades both heated to the same degrees and cooled to normal temperatures.

    Imagine the blade staying at the same temperature.

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  • $\begingroup$ Worth noting that if the cut is sufficiently fast, the fact that the blade is hot would be nearly unnoticeable (thanks to things like the Leidenfrost effect). For a slower cut... think cooking. $\endgroup$ – NPSF3000 Feb 2 '16 at 0:39
  • $\begingroup$ A swift cut would likely cause some amount of cauterization, if the blade is hot enough. $\endgroup$ – user16492 Feb 2 '16 at 2:00
  • $\begingroup$ How hot, what cutting force, and also how much thermal mass in your cutting surface? The result can be different if the blade is able to maintain its temperature throughout the duration of the cut as opposed to rapidly transferring all of its thermal energy to the substance being cut and quickly cooling down to an equilibrium temperature. $\endgroup$ – aroth Feb 2 '16 at 4:08
  • $\begingroup$ Also, "what's the area of contact of the heated surface?" $\endgroup$ – The Nate Feb 2 '16 at 6:15
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    $\begingroup$ Weapons are on-topic, but asking about real-world effects of physical interactions between objects (such as a heated metal object, and human flesh) IMO is not within the realm of worldbuilding. That would probably have been better asked on Biology or possibly Physics depending on the focus sought in answers. Maybe even Martial Arts. $\endgroup$ – a CVn♦ Jun 7 '16 at 14:31
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You burn them, then you die

If you try to duel someone with a sword that is heated to 800°C, and you manage to get the first hit, what will happen is that...

  1. you will cause a nasty burn wound on someone
  2. you will die, because your blade will bend... and while you are reeling from surprise, the enemy will sucker-punch you and kill you

Steel at 650°C has lost 2/3 of its strength. At 800°C it is down by 80-90%, or more. That is so low that any impact, stab or other exertion of force on it, will cause it to deform. And of course it will not keep any kind of edge.

Strength of different metals, over temperature

You would have known this a long time ago, because on the first impact against cold steel or a training dummy, you would have seen this instantly. A sword heated to those temperatures will deform as soon as you try to use it, leaving it bent or badly dented. And of course the blacksmith will let you know this because they are intimately familiar with how iron and steel soften with temperature.

As a side-note: this is what brought down the World Trade Center towers in 2001. The fires did not melt the steel cores of the towers, but the cores did get heated enough to lose their strength, leaving them unable to carry the weight of the towers above the impact zones. This meant that the outer skin was left to carry the entire weight. With one side of the outer skin smashed by the planes, and the floor beams starting to sag (for the same reason: losing strength from heating) and pull on the skin from the inside, the outer skin eventually gave out and the collapse started.

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  • $\begingroup$ This is exactly it. Heated steel gets softer. That is bad for weapons... $\endgroup$ – James♦ Jun 7 '16 at 13:32
  • $\begingroup$ "Heated steel gets softer." Tell that to the structural steel at 400 F. Or the wrought iron at 550-600 F. I'm not saying this answer is wrong, but even at those temperatures, the OP might be able to get some use out of it. $\endgroup$ – a CVn♦ Jun 7 '16 at 14:28
  • $\begingroup$ @MichaelKjörling Fair enough... heat the blade to "only" 250 degrees C and it will be harder. It won't add much damage though. 250 degrees will more likely cauterize the wounds which is a boon for the victim, lessening the risk of infection. :D $\endgroup$ – MichaelK Jun 7 '16 at 14:37
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I once put my naked thumb on a 1800°F (982°C) piece of ceramic (a glove with a hole in it). There was a hiss and my print melted flat with no char or blackening.

Let's make that the temperature. You would have no bleeding and it would still be a bit numb 20 years down the road.

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    $\begingroup$ Ouch! Put that under lessons learned by experience. $\endgroup$ – Jim2B Feb 2 '16 at 1:27
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    $\begingroup$ Once when doing glasswork in chemistry class I touched a piece of molten glass. The result was similar; a hissing sound, skin turned to fine white ash, and no pain until some time afterwards. Left a nice fingerprint-like impression in the glass, too. $\endgroup$ – aroth Feb 2 '16 at 4:05
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Heating a blade is kind-of at odds with itself. Heat transfer is an inherently slow process. You may not think burning yourself on a stove is slow, but compared to a cut, heat transfer is actually quite slow. A case study is the famous science class experiment where the teacher pours molten lead over their hand. Very little heat actually transfers because a layer of steam forms keeping the molten lead from actually touching (at least until you get used to this, and are no longer scared. Then you don't sweat as much and bad things happen!) In combat, you could actually force the metal to touch, but it just shows how long it takes to do damage with heat.

The one use for it would be if you ever got in a locked position where you could hold the blade near your opponent to irritate them with the radiating heat. However, as a general rule, these positions are hard to come by. (I believe I read that they almost never actually happen outside of the movies, but I'll bow to any contrary opinions by a SCA sword master!)

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