Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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Knifemaker / Craftsman / Service Provider
- Joined
- Aug 20, 2004
- Messages
- 38,513
Recent threads have brought a flurry of emails to my box. Most want me to post on these threads about procedures the OP and others use. I have no real desire to get into a "My procedures vs His procedures" discussion on these threads. However, I will yield to the requests for some explanation as to why I feel some of these procedures are not sound, metallurgically.
Please do not make this about personalities, or become a war,..... and keep replies to the subject of how things can be proven or disproven, improved, damaged, or unchanged.
STATEMENT ONE:
Any knife that you make that will stand up to the use it was designed for is a good knife. The methods on how it got hardened can vary greatly, but the metallurgy of what happens in the steel's structures as it heats up and cools down are fixed in physics, and aren't able to be changed by any chicken fat quench or special forging and HT technique.
In the same way, a knife that will do things that the intended use is not expected to do is not a better knife. There is a good reason that a fillet knife is a lot different from an axe. One is intended to cut meat cleanly and for a long time between sharpening. The other is made to take huge chunks out of trees, and be re-sharpened often. A fillet knife isn't a bad knife because it won't fell trees anymore than an axe isn't a bad axe because it won't slice tomatoes.
STATEMENT TWO:
Doing something that does nothing will not affect a blades final outcome at all. It is not proof that the process is superior when the outcome is the same as if you didn't do it. That is why you can't say that the chicken fat quench hurt or improved the blade...it was just the quenchant. If the blade properly hardened, it is a good blade. If the fat was a fast enough quenchant for the steel, it was OK. If a commercial quenchant is equally fast, there may be little difference on a single quench. However, if you do 100 quenches over a year, the commercial quenchant will defeat the chicken fat easily ( unless you render down 100 new chickens ever day). Stating that the chicken fat made a good blade is just defending your procedure, but does not making it superior.
STATEMET THREE:
Lets just go straight to the biggest contention about HT processes - Putting the blade in the home freezer overnight.
I will make an analogy - John and Jim both take a trip to Washington DC to see the Capitol. The trip is 200 miles. John drives 50 miles, spend the night at a motel, turns around the next morning, and comes home. Jim drives for four hours through traffic and gets to DC, he spends a few hours there and comes home. Which one saw the Capitol? Right, Jim. No matter what John says about his trip, he never made it to DC. He can tell you how much fun he had in the pool, how good his meal was, etc....but he can't say he saw the capitol!
When you quench a blade the steel structure changes from austenite at around 1500F to martensite at around 400F. This continues until the steel finishes the transition. For carbon steels, the finish line is usually around 200F. By the time it reaches room temp, the race is over. In complex steels with higher alloy ingredients, like stainless steel, the finish isn't until around -100F. A home freezer reaches about 0F, this is the same as John's trip. Going partway is just as good as not going at all. It won't make the steel a little harder by getting it a little colder. Also, the transformation happens literally at the sped of light. Overnight won't do anything that ten minutes does ( which in this case, is nothing). Overnight ten times won't equal -100F, either.
The thing that gets missed in most of these discussions is that if the steel is a carbon steel .... the steel was already converted to martensite at room temp. 0F isn't going to convert it anymore than 70F. If the blade has already been tempered before the freezer, what possible changes can be attained, as the martensite will be well stabilized by then, and RA will already have been converted. The freezer would have no more effect than putting the blade in a closet overnight.
STATEMENT FOUR:
The transformations of steel structures are well understood and not "still being discovered". The changes that can be made are governed by metallurgical science, and they can be used to get a desired result in a blade. However, adding steps that do nothing will not make the blade better. If the grain has been properly refined in preparation for hardening, one quench hardens the blade. Two more, or a hundred more, won't make it harder or appreciably finer grained. If the results are good, it was because the LAST quench was good, and the blade was properly prepared for that quench. Every time you re-heat the blade, the slate gets wiped clean. It does not remember every thermal event that ever happened to it. It only remembers where it was when you started to heat it up from room temp. Next time it will only remember where it is now.
Think about it, If the steel was permanently damaged by having a large grain structure, and it could never forget that, how could you make the grain smaller? How could you forge it? Now, I will admit that there are some things that can be made much more permanent in steel structures and things like carbides, but these things aren't what we are changing in normal HT procedures of carbon steel blades. Thermal cycling followed by a dead on quench in the proper quenchant is the key to a properly hardened blade. What you change from there as far as making some parts softer is up to you, but you can't improve on the final outcome by repeating the quench over and over.
STATEMENT FIVE
Anyone can say anything and someone will believe him/her. That is what a following is. Some may call him/her a dreamer, others a free thinker, some a fool....but if the claims can't be proven, they are only that persons ideas/words. If someone has a metallurgical reason that a new procedure does something, they can explain how their process works. In basic knife making this is pretty simple to do. It is just as simple to disprove a statement as not being sound. I don't have to test someone's knife to say that 0F is not -100F. If he is claiming that something happens at 0F that metallurgical engineers have never seen, I ask him to show the evidence of that. If the only evidence is that the knife is a good knife, refer to Statement Two.
FINAL COMMENTS
All the above doesn't make one persons knife a blade a good blade and another's a bad blade. What makes a good blade is a good HT, proper steel selection for the task, proper blade geometry for the task, and good procedures for the shaping and HT. Some do this with the most rudimentary of tools, and others with high-tech equipment. Again, one or the other does automatically make a blade good or bad. Learn HT by learning what happens and why it does. Then you can develop your HT procedures to fit your situation. In the final result, a good knife is a good knife.
Please do not make this about personalities, or become a war,..... and keep replies to the subject of how things can be proven or disproven, improved, damaged, or unchanged.
STATEMENT ONE:
Any knife that you make that will stand up to the use it was designed for is a good knife. The methods on how it got hardened can vary greatly, but the metallurgy of what happens in the steel's structures as it heats up and cools down are fixed in physics, and aren't able to be changed by any chicken fat quench or special forging and HT technique.
In the same way, a knife that will do things that the intended use is not expected to do is not a better knife. There is a good reason that a fillet knife is a lot different from an axe. One is intended to cut meat cleanly and for a long time between sharpening. The other is made to take huge chunks out of trees, and be re-sharpened often. A fillet knife isn't a bad knife because it won't fell trees anymore than an axe isn't a bad axe because it won't slice tomatoes.
STATEMENT TWO:
Doing something that does nothing will not affect a blades final outcome at all. It is not proof that the process is superior when the outcome is the same as if you didn't do it. That is why you can't say that the chicken fat quench hurt or improved the blade...it was just the quenchant. If the blade properly hardened, it is a good blade. If the fat was a fast enough quenchant for the steel, it was OK. If a commercial quenchant is equally fast, there may be little difference on a single quench. However, if you do 100 quenches over a year, the commercial quenchant will defeat the chicken fat easily ( unless you render down 100 new chickens ever day). Stating that the chicken fat made a good blade is just defending your procedure, but does not making it superior.
STATEMET THREE:
Lets just go straight to the biggest contention about HT processes - Putting the blade in the home freezer overnight.
I will make an analogy - John and Jim both take a trip to Washington DC to see the Capitol. The trip is 200 miles. John drives 50 miles, spend the night at a motel, turns around the next morning, and comes home. Jim drives for four hours through traffic and gets to DC, he spends a few hours there and comes home. Which one saw the Capitol? Right, Jim. No matter what John says about his trip, he never made it to DC. He can tell you how much fun he had in the pool, how good his meal was, etc....but he can't say he saw the capitol!
When you quench a blade the steel structure changes from austenite at around 1500F to martensite at around 400F. This continues until the steel finishes the transition. For carbon steels, the finish line is usually around 200F. By the time it reaches room temp, the race is over. In complex steels with higher alloy ingredients, like stainless steel, the finish isn't until around -100F. A home freezer reaches about 0F, this is the same as John's trip. Going partway is just as good as not going at all. It won't make the steel a little harder by getting it a little colder. Also, the transformation happens literally at the sped of light. Overnight won't do anything that ten minutes does ( which in this case, is nothing). Overnight ten times won't equal -100F, either.
The thing that gets missed in most of these discussions is that if the steel is a carbon steel .... the steel was already converted to martensite at room temp. 0F isn't going to convert it anymore than 70F. If the blade has already been tempered before the freezer, what possible changes can be attained, as the martensite will be well stabilized by then, and RA will already have been converted. The freezer would have no more effect than putting the blade in a closet overnight.
STATEMENT FOUR:
The transformations of steel structures are well understood and not "still being discovered". The changes that can be made are governed by metallurgical science, and they can be used to get a desired result in a blade. However, adding steps that do nothing will not make the blade better. If the grain has been properly refined in preparation for hardening, one quench hardens the blade. Two more, or a hundred more, won't make it harder or appreciably finer grained. If the results are good, it was because the LAST quench was good, and the blade was properly prepared for that quench. Every time you re-heat the blade, the slate gets wiped clean. It does not remember every thermal event that ever happened to it. It only remembers where it was when you started to heat it up from room temp. Next time it will only remember where it is now.
Think about it, If the steel was permanently damaged by having a large grain structure, and it could never forget that, how could you make the grain smaller? How could you forge it? Now, I will admit that there are some things that can be made much more permanent in steel structures and things like carbides, but these things aren't what we are changing in normal HT procedures of carbon steel blades. Thermal cycling followed by a dead on quench in the proper quenchant is the key to a properly hardened blade. What you change from there as far as making some parts softer is up to you, but you can't improve on the final outcome by repeating the quench over and over.
STATEMENT FIVE
Anyone can say anything and someone will believe him/her. That is what a following is. Some may call him/her a dreamer, others a free thinker, some a fool....but if the claims can't be proven, they are only that persons ideas/words. If someone has a metallurgical reason that a new procedure does something, they can explain how their process works. In basic knife making this is pretty simple to do. It is just as simple to disprove a statement as not being sound. I don't have to test someone's knife to say that 0F is not -100F. If he is claiming that something happens at 0F that metallurgical engineers have never seen, I ask him to show the evidence of that. If the only evidence is that the knife is a good knife, refer to Statement Two.
FINAL COMMENTS
All the above doesn't make one persons knife a blade a good blade and another's a bad blade. What makes a good blade is a good HT, proper steel selection for the task, proper blade geometry for the task, and good procedures for the shaping and HT. Some do this with the most rudimentary of tools, and others with high-tech equipment. Again, one or the other does automatically make a blade good or bad. Learn HT by learning what happens and why it does. Then you can develop your HT procedures to fit your situation. In the final result, a good knife is a good knife.
