Trad Gang
Main Boards => Hunting Knives and Crafters => Topic started by: Lin Rhea on January 13, 2011, 10:06:00 AM
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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
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You're a good man, Lin.
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Nice and very easy to understand. Thanks for the help.
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Very nice Lin,
Is there a chart that I/we can print out with all the different steels as far as heat treating and tempering, not that i use all types of steel but maybe later in my adventure.
Thanks for every thing you do.
Dana
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Thanks for the great info-much appreciated.
Jeremy
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Lin,
Very nice & easy to understand without confusing words for someone just starting...but in depth enough for someone a bit more experience to review their procedure. Thanks...Jeff
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Thank you Lin
I have a ? on #2 you say "remove or soften the scale" why do I have scale? and how do I soften or remove it without the file?
I am a stock removal fng
Kurt
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Thanks.
Kurt, If you did not forge you wont have scale unless it is from the mill. You can grind it with a disc grinder to remove it or you can soak it in Muratic acid for a few hours. Then the file will cut into the bar.
Dana, With a known knife steel there are charts or specs sheets that tell you the draw back temperatures to achieve different hardnesses with that steel. For knives, we will want in the range of 59 RC or so. You can find this information on the internet or by asking another maker or the steel manufacturer. With a mystery steel you work up the chart by climbing the thermometer. Start low, somewhere around 350 degrees and draw it back and test. If it's too hard, raise the temperature of the oven 25 degrees and do it agin and test and so on.
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Thanks Lin, I haven't made a knife, yet. But when I do your instructions will really help me.
Gilbert
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well said lin, as a begining knife maker i always have questions and your always right there trying to help me and everybody else you can. not many people out there in the world today with that kinda outlook on things and id like to thank you for being so kind a patient to me and all the others trying to become a great knife builder such as yourself.
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Lin, I appreciate the information you provided. As a rookie, its nice to be able to get encouragement and good advice from the people I look up to. I would like to see if either yourself or someone else could expand on a couple of your steps. What is the benefit of thermal cycling before quenching? How important is it to rush from quench to temper? I have been taking time to clean the residue from the blade. Last, what is the benefit of two temper cycles?
Thanks for any additional information.
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Thanks again Lin
As a rookie then scales are both material for handles and something that is on your blank after forging.
Could you explain the difference between annealing and tempering and when you do them?
I guess if I am going to look stupid, I can do it in one dose
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Thanks Lin, very good Information!
You wrote in #1
"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."
How does "spheroidizing" differ from Normalizing and annealing? And is the goal of spheroidizing to pool the carbon into tiny spheres within the steel structure? And to what end is that done?
Also I have an atmospheric forge and no thermocouple. Is there another way to determine the temp in the forge without one?
Thanks
Steve
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Potomac Forge
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Thanks for taking the time to do this. I was confused when I first started about thermal cycling, but read some of the posts you and Karl wrote on the subject. That has made a huge difference (although I still don't get all the terms right!) Also, thanks to you and others for stressing the importance of knowing what steel you are working with. I've experimented with some "mystery steels," but am nowhere near experienced to be successful that way. When I started researching what the makeup of the reclaimed steel I was using actually was, it REALLY helped.
Again, thanks for being patient with guys like me and sharing your knowledge! :) I'm trying to soak it all up!
Regards
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Great post. Lin is definately the voice of experience on the subject.
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Been gone all day so just seeing this, you done good Lin!! I'm certainly no Metalurgist or opperating at Lin or Karl's level yet but I'll try a couple of Mulie's questions fore I hit the sack.
1. "What is the benefit of thermal cycling before quenching?"
Can't come up with the technical words off the top of my head but when your forging/grinding a blade you put all kinds of internal stress into the steel. No matter how careful we are there is probably going to be some grain distortion, maybe there were a few more hammer blows on one side than the other, grinding might relieve a little more stress from one side than the other... Thermal cycling is going to help relieve those stresses and "relax" the blade prior to hardening to eliminate the chance of warping or cracking...
2. How important is it to rush from quench to temper? When we quench the steel is again put under tremendous stresses when we hopefully "froze" it at it's hardest state. It can feasably crack from these internal stresses. Getting it back up to tempering temps releaves this stress and softens the steel back to where we want it.
"what is the benefit of two temper cycles?" Not trying to be a SA but the short answer is whatever the first cycle don't get the second hopefully will, insurance.
Night guys... :wavey:
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Thanks a bunch guys that answered a lot of questions for me.
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Doug,
Thanks for the explanation. I want to learn the whys as well as the hows of this craft.
Judd
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Doug,
I could not have said it better. I figure Karl can explain spheroidizing better than me, but here is a link that helped me. Notice that steels with higher carbon content, I believe .75%, ie 3/4 of 1 percent or higher, are more easily machinable after spheroidizng.
web page (http://info.lu.farmingdale.edu/depts/met/met205/ANNEALING.html)
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Yep Lin, Karl is the big word guy, wish I had his intelligence. I've read and studied most all of it but it's kinda like recalling Algebra back in high school trying to put it into words...
Steve asked about telling temps in his forge... Lots of guys have lots of ways of working without a pyrometer and most do very well by them so this is certainly no slam on anyone's methods. I originally installed mine when we moved from MO to MT because I was having trouble welding damascus at this higher, drier elevation. Now I've come to rely on it for things other than knowing my welding temps. Controlling heat treat temps, I use my forge, is probably the biggest benefit. Bottom line is I can't see any way to "accurately" control temps without a pyrometer. To me it's no different than knowing what kind of steel I'm working with, it all goes toward making the end product better...
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In spherodizing, you are basically pulling all the carbon into small "spheres", which allows for cutting instruments like drill bits and mills and taps to cut through the steel.
I spherodize my 5160 - 0.60%C, as well as the hyper eutechtoid steels.
My last step in thermal cycling at the end of forging is to bring the blade up to temp and quench for martensite, which also reduces grain size.
Sort of like jumping into a cold pool!
But now the blade is hard, or if it was 5160, without even quenching, it will air harden and smoke a good drill bit.
Most people take that blade up to some sort of real hot and then try to slow cool it in some media.
But why take it up hot after we've spent a whole bunch of time reducing grain size?
I don't want to risk endangering the grain size, but I still want to drill and mill with ease, so the blade gets soaked at around 1300 for an hour and slow cooled in the oven. It's this sloooooooooooow cool from a high sub-critical that spherodizes the carbides, making for easy machining, yet leaving ultra fine grain.
If a maker has a heat treating oven, it should really be put to use in this manner.
This also leaves the carbon in the right spot to just JUMP! into the making of martensite.
When steel is annealed from above critical, you not only risk grain growth, but it's also more necessary to soak the steel for extended periods of time to pull all the alloy into solution so as to get completely dissolved when it comes time to quench.
When spherodized, about all you gotta do is get 'er hot! Everything is sort of set up already.
I have not burnt a drill bit, or had a tap hang up, etc., in spherodized steel, in , well, a really long time. Years.
And have kept grain size and carbon location right where it needs to be at all times.
I paid a thousand dollars for that oven I'm gonna use it!
This is just the basic concept, without going into everything else that, quite honestly I don't understand, but it's a basic guideline.
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That's great Karl. Even I understand it the way you told it.
Something doug said reminded me of a point. Usually, a given color equals a temperature. If you can read the color, you can get pretty dang close. A pyrometer is best, but for some of us here on TG, we need to learn color.
One reason an oven is a such a good tool is that you can achieve EVEN heating throughout the thick and the thin areas of the blade. If all you have is a forge, you should do all you can to learn to control your heating so the whole blade is the right temperature/color for the intended operation.
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I am one of those "color" guys. With a wife in college and two kids to fund, I am still saving up to buy a knife oven.
With practice using the steel color works great. A hunting buddy was just raving last night about how a knife I made him has cleaned, skinned, and boned multiple animals now and is still razor sharp.
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You know what, maybe what I've been doing is not even the best way to do it.
It's just how my knife making has evolved.
Lot's of good knives were made before heat treating ovens became so popular.
As a result of some recent "awakenings" and a few discussions I've had, I may even employ some more simplistic methods and see what happens.
Having a good heat source helps, and experience at failure is crucial!
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There are a lot of ways to make a great knife. Each smith learns what works best for them. The learning process is a big part of what I enjoy about creating knives and tomahawks.
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Karl,
I'd put my money on your way as far above average. Your understanding of heat treat and steel behavior is well known and respected so I dont recommend changing it. I have learned as much from our discussions as anywhere.
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No doubt about that Lin, wish I could retain half what Karl says/shows. Just goes to show you what you can achieve when you live and breath steel.
I've learned more in the last four or five years than in the previous 15 after getting involved with guys like you, Karl, Jon, Ed and several others in the ABS. While experience, good and bad can teach you banging around in the shop mostly on your own isn't conducive to higher learning.
Thank you to all of you :notworthy:
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Karl don't forget to tell about the extra piece of steel in the oven.To let it even cool down slower.
After I did the steel in the bottom of the oven it takes a lot longer to cool down ,which I supose makes it even softer.??
By the way great job guys,I even understand what you guys are talking about nowadays.LOL Boy it took a Long time.LOL
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No, Kevin, it won't make it any softer, but what that does is keep the cycling range of the oven to only a few degrees and more steady/accurate.
But it will ensure that the slow cool takes as long as possible and everything is as evenly distributed as can be.
But you are right, it'll slow down that cooling off period forever!
Guys, I have a 1" thick floor of wrought iron in my heat treat oven. I bring it up to heat as well and let the oven soak at temp for about an hour before I ever put a blade in.
This really ensures that I have equal heat throughout the oven and helps to distribute the heat evenly.
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Hey Karl, when your oven is running what range in temp is there? I assume probably just a few degrees with that being a pretty much closed environment and everything being automatic. Running my forge manually bout the best I can do is stay within a 15-20 degree range... If I get sidetracked for just a minute that goes out the window. ;)
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great thread! damn I am confused now! LOL
time for a re-read~
L.R. :D
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join the club lol i think being confused at first is some wierd form of anitiation lol but really addicting, the more i learn the more i wanna apply my new knowledge to a new project, there is simply not enough time in the day.
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Great stuff guys, Thanks for starting this one Lin.
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Many thanks to Lin, Karl, Doug and all the other skilled craftsmen on this forum for helping the rest of us improve.
I am just a hobbyist and make no claims of "expertise". However, I thought I'd share a few things I've learned from others on this forum that have helped me immensely with regard to heat treating.
1. As Karl has said repeatedly in the past, get some good quench oil. Until I did this, I was really struggling.
2. For me, the normalizing step is the most critical for achieving a quality blade.
3. I can only properly heat treat one blade at at a time. Takes all of my attention to get it right!
3. As Lin says, test the blade before putting on the handle. Much easier to repeat the heat treatment this way (Don't ask me how I know that!)
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Bump for some of the new guys.
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Thanks Lin, I have not started any make knives yet but this thread and Karl's video series have been very enlightening on all the details it thanks to get it right.