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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 02-19-2010, 07:35 PM
Aaron Banger Aaron Banger is offline
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Temper after Heat Treat Question

Hi all, I am currently gathering supplies to build a small propane forge and will be heat treating my forged blades soon. I will have a two brick forge and possibly a tempering jig. One like the one Wayne Goddard describes in his book. Thus, after my edge quench, should I soft draw back or overall temper? Also, if I overall temper, what will the colors be at the edge? -Aaron
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Old 02-19-2010, 08:09 PM
Recurve Recurve is offline
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That will depend on the type of quench.the type of steel and the intended purpose. Are you using water/brine? Oil? What type oil? A medium straw color would be a good starting point, if it's too brittle take it a little darker till it fills your needs. -Jim-


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Old 02-20-2010, 05:27 AM
Ed Tipton Ed Tipton is offline
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Hi Aaron
Judging by your question, I am assuming you are a "newbie", although you did not say so. I still consider myself a "newbie", although I have made approx 50 fixed blade knives in my propane forge, all of which I have heat treated myself. All of my work to date has been with either 1080 steel or 5160 steel. I specifically settled on these steels since they can be easily heat treated by me in my shop using readily available equipment. You did not specify what type of steel you will be using, and without that critical info, this question is difficult to answer, but I will tell you how I do it using the steels I mentioned.
With both of my steels, I have used both water and oil for quenching. I have had better luck using the oil since the water is somewhat more aggressive, and if not properly prepared, you can crack the blade. By being properly prepared, I mean that all roughness and grind marks should be smoothed down to at least 120 grit. Using a finer grit will increase your chances of success. All edges shoule be broken (radiused), and the edge should be left relatively thick (.030-.050 inch). The final sharpening and grinding will be done after heat treatment.
Differential heat treatment of the blade is up to you. Differential heat treatment will help you in getting a nice hamon, but does not guarantee it. Differential heat treatment can be done using clay which is pretty easy to do), or by tight control of your heat/quenching/and tempering technique. Your other option is to just do a full hard/full quench/full temper cycle on. your blade. For your first few blades, I would suggest going the full hard route. Doing this will enable you to kind of "get the feel" of what you're doing, and will help you in finding out exactly how your steel reacts to the process.
For the tempering, I am using a standard toaster oven. I have found that using my oven, that setting the temp to the max temp and putting the steel in the oven for two hours works good for me. I initially started using a setting of about 350 de3grees, but found that for my oven, I needed the extra heat to get what I wanted. With both of the steels i use, the entire heat/quench/and temper cycle can be repeated if you feel that something isn't quite right. If you dont have a toaster oven, you can use your standard kitchen oven to do the same thing.
This should get you started. There is no substitute for experience. Try doing it, and as you do it, pay attention to the entire process. Think about what you are doing, and then adjust/modify as needed to get what you're looking for.
I STRONGLY suggest that you start with a KNOWN TYPE OF STEEL, AS OPPOSED TO MYSTERY METAL. Doing so removes all doubt as to what you're working with, and the type of steel will greatly influence the outcome. Take ownership of your process, and make it YOUR process. If you can find a mentor, that will greatly help you as you go along, and remove those "nagging doubts" we all have when venturing into the great unknown.
Good luck.
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Old 02-20-2010, 02:35 PM
Doug Lester Doug Lester is offline
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Dido on the recommendation against mystery metal. You have enough to learn without having to refigure the proper heat treatment for each piece of scrap that you use. If you are differentially hardening your blade (edge quenching) you do not have to differentially temper it (drawing back with a flame or tempering jig). I advise against tempering by color. One, color is dependent upon the ambient lighting another is that I worry about not exposing the steel evenly or for long enough time to convert the untempered martensite to tempered martensite or to convert the retained austinite to martinsite. I use the kitchen oven (no one to ask permission of) and toaster ovens are cheap. If you have any second-hand stores look there. Always use a thermometer reguardless of the type of oven used and keep it one the same rack as the blade. A tray of sand severs as a thermal mass to keep the heat to the blade from fluxuating as much as the heating elliments cut on and off.

Judge the correct temper by something like the brass rod test, I believe Wayne Goddard describes this method. If it chips out it is too hard and you will need to grind out the chip and retemper at a higher temperature. If the edge rolls over then you will have to requench the blade and then retemper at a lower temperature.

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Old 02-20-2010, 08:18 PM
Aaron Banger Aaron Banger is offline
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Thanks guys, I think I may be searching out a toaster oven now. I will most likely be using 5160 or 1084. The oven seems to be the easier route. -Aaron
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Old 02-20-2010, 10:38 PM
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NJStricker NJStricker is offline
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When you get your toaster oven, pick up an oven thermometer also. Don't trust the dial (mine is 75 degrees off--enough to screw up your temper). Use the oven thermometer and check whether it will maintain temperature without drastic fluctuations for at least 2 hours. If it won't do that, then you'll need to find another method (or another toaster oven) to temper. I got lucky with mine from a yard sale, but they don't all hold temp.
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