"Non-Beginner Steels" to Heat Treat

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duurza

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Jul 4, 2015
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I've been lurking the forums for a while now reading up on anything heat treat related and the one topic that always comes up is the difficulty of heat treating steels other than 1080 or 1084. Only these two are recommended for beginners or for anyone without electronically controlled precision based equipment.

Why are certain steels not worth heat treating in something like a backyard campfire? From a scientific stand point, I understand that by not getting all the variables correct, the product won't be in the absolute best state that it has the potential to be.

Suppose someone heat treated 1095 without equipment and it is not in the best possible state. How would this compare to tools made before metallurgy? If bladesmiths are aiming to get the absolute best state, then what about something like 100% bainite? I know many of you don't like discussing bainite but it fascinates me simply because not many makers seem to even attempt it.
 
"before metallurgy " ??? when was that ?
Why do you assume that bainite is 'easy' ? It still needs careful temperature control .1095 done improperly can give you a brittle dangerous blade ! Stick to 1084 , a fine blade without problems .
 
Let's say before people understood why certain properties are achieved when they followed a set of steps.

I am not assuming bainite is easy. I'm just curious as to why not a lot of smiths try it out once in a while.

To me, it's important to understand why certain steps lead to better quality but at the same time, I also like knowing how quality degrades if you stray from these steps and how far you can push that before it becomes utter crap.
 
In simplest terms, overheating steel that is hypereuctoid results in very undesirable structures that can be brittle, have sift/hard spots, retained austentite etc. In the "olden days" smiths used folding to compensate for impurities and spread them out, and differential hardening to compensate for potential brittleness. There was a lot of broken blades in those days, and I've read that 1/3 of kitchen knives made by traditional Japanese smiths don't pass testing. I'm not an expert on that though. These traditional methods were passed through the generations, rather than each smith starting from scratch in their back yard, without an experienced smith teaching them. Good blades weren't made by people guessing.
 
Thanks. That's understandable to me.

Not sure if you would be able to answer this but since you brought up Japanese smiths, were the knives heat treated like katanas? Were they quenched in water/oil/whatever and then tempered?

I've seen a lot of videos of katanas being quenched (Man at Arms 12 minute mark https://www.youtube.com/watch?v=Q598DP27tGA) but none of them ever mention tempering. Any time a sword is made in any of the Man At Arms episodes, they usually discuss and show the tempering process as well but for the Katana builds, it's absent.
 
duurza said:
Thanks. That's understandable to me.

Not sure if you would be able to answer this but since you brought up Japanese smiths, were the knives heat treated like katanas? Were they quenched in water/oil/whatever and then tempered?

I've seen a lot of videos of katanas being quenched (Man at Arms 12 minute mark https://www.youtube.com/watch?v=Q598DP27tGA) but none of them ever mention tempering. Any time a sword is made in any of the Man At Arms episodes, they usually discuss and show the tempering process as well but for the Katana builds, it's absent.
Click to expand...

Tempering is needed, but if only quenched to 400f, there is auto tempering too. Sometimes it is just skipped to save time in the show like forged in fire.

The chef's knives are typically high carbon bits forge welded to softer steel, and water quenched, or if monosteel differentially hardened. San Mai, and go Mai saved the amount of high carbon steel needed too. The process from my limited knowledge is ritualized and romanticized. Modern metallurgy separates the science from the mythology, and we can have 95+% repeatability in our process or better, even with hobbyist level kilns, and 5 gallons of the proper engineered quench oil. Our eyes can only tell temp with about 200f variance from actual temp. Look at the threads on W2, and we have a 20f variance before consistency falls off. With a 200f variance, plotted over a bell curve, you will get a handful of great blades, a bunch of good blades, and about 30% that don't perform.

I use primarily hypereuctoids, and it's only a handful that don't turn out with my repeatable process. It still happens as my equipment is OK, but not anything like the professionals use.
 
An experienced smith can watch for decalescence, which looks like a shadow passing through the steel. This is the steel changing structure to austentite. A little hotter is good, but too much hotter results in grain growth and alloys moving places you don't want them too.

[video=youtube;Fv7GQVg-XPI]http://www.youtube.com/watch?v=Fv7GQVg-XPI[/video]
 
Unless you leave it a a "custom proprietary" hardness of 56Rc. ;)
mete said:
"before metallurgy " ??? when was that ?
Why do you assume that bainite is 'easy' ? It still needs careful temperature control .1095 done improperly can give you a brittle dangerous blade ! Stick to 1084 , a fine blade without problems .
Click to expand...
 
Willie71 said:
Tempering is needed, but if only quenched to 400f, there is auto tempering too. Sometimes it is just skipped to save time in the show like forged in fire.
Click to expand...

That's the thing that always throws me off. Tempering is an important step and most of the Man At Arms episodes explicitly show the tempering process or at least mention the word but when it comes to Katanas, it's left out. It seems really odd that this step is also left out on other videos. I'll try to find links to them.
 
duurza said:
That's the thing that always throws me off. Tempering is an important step and most of the Man At Arms episodes explicitly show the tempering process or at least mention the word but when it comes to Katanas, it's left out. It seems really odd that this step is also left out on other videos. I'll try to find links to them.
Click to expand...

I might be wrong, but I can't imagine a katana functioning without tempering. I'm no expert on katanas though.
 
Warren, if you watch some of Murray Carter's videos, you will see him tempering his hardened blades the old fashioned way which consists of heating them by moving them in and out of the forge until they reach a temperature where drops of water "dance" on the blade in a specific manner. It looks kind like a more precise version of checking if your skillet is hot enough.
 
jdm61 said:
Warren, if you watch some of Murray Carter's videos, you will see him tempering his hardened blades the old fashioned way which consists of heating them by moving them in and out of the forge until they reach a temperature where drops of water "dance" on the blade in a specific manner. It looks kind like a more precise version of checking if your skillet is hot enough.
Click to expand...

I don't get this romanticized way of doing things. Just temper properly. :grumpy:
 
The problem is that tempering is time and temperature sensitive. Getting to temp is one thing, but holding it for an hour times 2 isn't possible with that method.
 
Willie71 said:
Tempering is needed, but if only quenched to 400f, there is auto tempering too. Sometimes it is just skipped to save time in the show like forged in fire.
Click to expand...

Willie71, I can't tell if you mean that they completely skip tempering of the blades, or that they just don't show it on Forged in Fire. In case you meant the former, I asked one of the winning contestants, and he told me that they do indeed temper the blades, they just don't show (or even mention) the process on TV.
 
I think they skip showing the process of tempering, not skipping tempering all together,
 
The old katana makers also had failures . There reputations would suffer if they had too many failures in the real world --battles !
Temperature by eye ? I experimented once , checked by instruments and found I couldn't do better than +- 25 F !! Steels were simple in the old days and there was room for error ! Martensite is very stressed and tempering must be done to relieve the stress otherwise things would happen !!
 
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