Lower temper or different steel?

T

tr3yanderson

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Mar 6, 2017
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Hey ya'll, I'm still a newbie trying to learn as much as I can and recently I had a thought.

It appears that generally speaking, lower carbon steels are "tougher" than higher carbon steels. That is why I notice many larger chopping type blades, as well as swords are made with lower carbon steels like 1045, 1075, 1080, etc. So my question is. what's the difference from using a lower carbon steel such as these vs using a higher carbon content and just tempering much lower than you would for a smaller knife? Does that make sense? My understanding of metallurgy is very small right now, but I'd like to know why 1045 would be better for a sword instead of like O1 that was tempered to a very low RC.

Thanks
 
Carbides. More carbon, more carbides, less toughness.
 
I Don't think I'd call 1075 or 1084 'lower carbon steels' nor would I put them in the same category/class as 1045.

Just for clarification.
 
I'm not a metallurgist so perhaps one the steel nerds could chime in, but here's my take on it. Less than .6 carbon in solution leads to a largely lath martensite. Over .6 carbon in solution starts to develop plate martensite. Lots of carbon in solution will result in a highly tetragonal plate martensite. Tempering can relax this until the individual crystals looks more or less cubic, but the fundamental overall plate vs lath structure doesn't really change much.

Lath is tougher, more ductile. Plate tends to propagate fractures worse and has less elongation at yield so can fail more catastrophically but it does better with a crisp edge and can even seem more durable in use. Up until it fails. All of this is outside of the hardness.
 
It really comes down to stresses. The stresses that can be put onto a sword are insanely higher than those put on a knife in similar circumstances. Because humans cannot effectively use blades much heavier than 3 or so LBS, beefing up a sword to knife dimensions is impractical.

Forged in fire demonstrates this nicely. The judges abuse knives in ways that are pattently absurd. Hammering a knife through a railroad spike for example. Most of the time, they don't snap. WHen they do, it is almost universally attributable to austenitizing at far too hot a temperature, poor lamination, or a really poor geometric shape.

The final challenge, generally swords, are not abused nearly as much, but show breakage rates that are similar to the first couple stages. This is despite the greater controls on HT, geometry, construction that are afforded by a 5 day production period. This is generally because the momentum and energy of the blows is significantly out of proportion to the mass and geometry of the blades, when compared to a knife.

All that said, what Nathan mentioned is right on. If you want something that is going to take an insane amount of abuse and keep going, 1055 or similar is a good option in the simple steels. That all being said, a tough blade can be made out of nearly any decent blade steel with the proper heat treat. Because steel, when properly HTed, is ridiculously strong, tough, and durable.
 
5160 will probably be tougher than 1045. It just won't take a hamon or behave like the simple steels in traditional swords. Probably doesn't forge or weld as well either (I don't know, I'm not a smith). But in moderation certain alloying such as chrome and molly can improve toughness, it's not just about carbon content. And, while vanadium doesn't improve toughness directly, it can help with grain refinement which does improve toughness. So, while simple steels can be very tough, they aren't the end-all-be-all.

However alloying like nickel, which improves toughness, increases RA and decreases edge stability. So, while "tougher", it would also be more fragile in a knife, if that makes any sense.
 
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Nathan the Machinist said:
I'm not a metallurgist so perhaps one the steel nerds could chime in, but here's my take on it. Less than .6 carbon in solution leads to a largely lath martensite. Over .6 carbon in solution starts to develop plate martensite. Lots of carbon in solution will result in a highly tetragonal plate martensite. Tempering can relax this until the individual crystals looks more or less cubic, but the fundamental overall plate vs lath structure doesn't really change much.

Lath is tougher, more ductile. Plate tends to propagate fractures worse and has less elongation at yield so can fail more catastrophically but it does better with a crisp edge and can even seem more durable in use. Up until it fails. All of this is outside of the hardness.
Click to expand...

This plus carbide volume are the two biggest impacts on toughness (assuming controlling for hardness. Harder equals less tough.)
 
I have often pondered on this as well. What got me thinking about it was my test results from AEBL. Does higher temps offer anything to you if your just going to temper back to a level that’s easily obtainable with a lower temp.

Photo%20Jun%2016%2C%201%2012%2013%20AM.jpg
 
JTknives said:
I have often pondered on this as well. What got me thinking about it was my test results from AEBL. Does higher temps offer anything to you if your just going to temper back to a level that’s easily obtainable with a lower temp.

Photo%20Jun%2016%2C%201%2012%2013%20AM.jpg
Click to expand...

You need sophisticated testing and micro graphs to really see what is going on. My experience with z-wear tells me that austenitizing temp controls potential hardness, but different structures give us different performance outcomes. Get the right structures for your intended application, and temper for optimum performance for that structure.
 
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