Tradgang folks are a good bunch of folks, all trying to preserve a traditional way of life. It seems that knife making is a natural extension of that effort. Our forum has attracted a lot of attention and I’m excited about that. Several are trying their hand at making their very first knife as we speak to round out their list of traditional equipment. I do believe there is some confusion on the matter of heat treating a blade and I would like to help clarify some things on this subject, if I may. The confusion, understandably, might come from entering a conversation midstream or ones jumping into knife making with both feet and in the excitement, being unclear as to just how to get the most for one’s time and effort. I enjoy seeing this excitement and that makes me want to speak up. We often see makers that use files in various stages of hardness for their knife blade. This information will apply to them as well. Most old US made files are 1095 steel, but since we can’t be sure; I refer to any steel that is not known as “mystery steel”. If after all of your efforts, you fail to make a good blade while following these basics, it’s likely that the mystery steel you used is not suitable to make a knife. Good knife steel will respond to sound methods of heat treatment.
My efforts here are to help and not push. So, please take this as a general opinion and not the absolute final say in the matter. Your situation may call for a differing view, but what I point out is basic steps and maybe a comment or two about the steps. I may even point out some pros and cons to doing it this way, but bear in mind, I base this on my experience and what I have been taught.
Some of us have made enough knives and heat treated enough blades to find this elementary, but I have learned that the foundation of a house needs checking every so often and basic heat treating is the foundation of good knife making and the principles and methods should be checked too.
I would like to separate the steps to a degree, but bear in mind that one step is in preparation for the next and contributes to the “whole”. I would separate the steps in this way:
#1-Forging (if it applies)
The chosen steel is shaped by means of a hammer and anvil. It is at this stage that the steel is beginning to be prepared internally on a molecular level for the upcoming steps either by normalizing, annealing, or spheroidizing. There is always some discussion on this point, but proper attention to grain reduction and distribution is important to the quality of the end product. I can’t over emphasize how important this aspect of blade steel preparation is. Remember, it’s all a matter of being in control of the heat. You control the heat and the steel will do the rest. It will respond.
* edited to clarify: Now (between #1 and #2) is when you normalize, anneal, or spheroidize. These are different technical operations with somewhat overlapping affects. Opinions will vary as to just which one/ones a maker should favor, but the fact is at least one or more absolutely should be done for a tough, durable blade.
#2-Rough Grinding
The profiling and general refining of the blade’s shape is done with either a grinder or by filing. If done by filing, it’s important to remove or soften the scale so as not to ruin the file. The scale is a very high Rockwell. It is also the stage when a maker stamps his mark into the ricasso. The annealing that has been done in the previous step enables the stamp to make its impression.
#3-Hardening and Testing
This step is began (at least by me) by thermal cycling the steel. I do this in three heats. The first is substantially (100 degrees?) above critical temperature (critical=steel becomes non-magnetic). The second heat is slightly above (25 degrees?) above critical temperature. Each of these heats is allowed to cool back to where the blade shows no red. The final heat is brought to critical and held a few seconds at that color/temp, then quenched. Test by attempting to file the edge. If the file skates, it got hard.
#4-Tempering (draw back)
Now according to the steel type, the blade should be drawn back or tempered as soon as possible after determining that it reached full hardness. A toaster oven or kitchen oven will achieve drawback temperatures for most simple steels. How do you determine the drawback temperature? This is where a maker either has to know his steel type and use a chart or start low and “climb the chart”. With 5160 steel I would draw it back 2 hours at 350 degrees twice. I would use this starting point for tempering any unknown or mystery steel. For 1084 steel, I use 400 degrees, again 2 hours twice. If I tried to draw back 5160 at 400 degrees, it would be too soft to hold a good edge. If I used 350 degrees for 1084 it would be too hard and the edge would be brittle. Each steel type may have a different draw back temperature to achieve “knife hardness”, some as high as 500 degrees or higher. 100 degrees off of the proper drawback temperature for that steel, one way or the other will make several Rockwell points difference in the final hardness of the blade. For this reason I like to know what steel I have. However, it is good for a maker to know how to climb the chart while using a mystery steel in the event he has to fly by the seat of his pants. Remember, start low on the chart and test. In general, after a successful tempering, a sharp file will barely cut the edge of the blade and it will take some force behind it to get it to cut.
#5-Finish Grind, Testing, and Hand Sanding
This amounts to a cleaning and smoothing of the blade shape and establishing the cutting edge. This can be done to some degree by machine, but I have to hand sand on most blades to be happy with the finish. Also, and this is important, the blade must not get above the drawback temperature from here on out. If using a machine, keep a bucket of water handy and dip the blade often. The edge is thin at this stage, so be careful. Any color change in the steel while grinding indicates that it’s getting too hot and by then some damage has been done to the hard earned heat treat. This takes discipline to prevent over heating the edge. From there, I square the ricasso shoulders in preparation to receive the guard or, if it’s a full tang, I flatten the tang sides. Before I do anything else, I test the blade. Yes, once more it’s tested. The cutting edge is established and it is sharp and I am happy with the edge’s geometry (a whole new can o worms). I now do a series of chopping or whittling or both to make sure that it will not chip, because if it does, that means it’s too hard and will have to go back into the oven at a slightly higher temperature ( I raise it 25 degrees)for two hours. If I am happy with the way it performs, I proceed with final clean up and it’s ready for the guard and handle. If it still tests too hard, I climb the chart by raising the temp in the oven 25 more degrees and so on. One thing, be patient and be certain of the blade’s performance before installing the guard or handle. It’s tempting, I know.
The way that I outlined is very basic and some steels will have to have different methods. But, this will work for some of the simple spring steels as well as some scrapyard steels. This step by step outline can be followed with complete confidence that you are heat treating your blade by traditional means. I expect and welcome discussion on any or all of the steps I have listed. I’m hoping Doug, Karl, and others can help me with some of the questions that may arise.
Lin
Topic: Thoughts on Heat Treating a blade (Read 1390 times)
