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Knife Edge Chipped


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I recently made and sold a knife to a guy at work. He wanted a knife to skin deer with so I made a skinner with a flat grind. He was skinning the deer and the blade stayed sharp throughout the skinning process. However, he brought the knife to work so I could see how sharp it is still and I noticed a chip in the edge! The blade is still sharp but the chip really bothers me. Does this mean that I didn't temper the blade enough? All of my heat treating is backyard style. Home made forge with no temperature control. Using Canola oil to quench heated to roughly 100 degrees before quench. I use a small oven to temper the blade at around 400F. Blade material is 1095 which should be pretty forgiving in the heat treat dept. I'm assuming the blade is still too brittle. Is this correct? He must have been cutting bone or something for it to chip though. Surely skinning a hide wouldn't do that.

 

Sorry for the ramble. It's just a bit frustrating that I produced a poor quality blade. But I guess that's why there's a warranty! I'll have to make him another sometime and temper it better.

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I hope someone chimes in here with more credibility than me, but since I have been playing primarily with 1095 steel, I thought I might was well tell you what I think I know. Keep in mind that most of this I have culled from the all mighty interweb which, when it comes to knife making, is full of bad information.

 

1095 is not as forgiving as the other 10xx steels. I'll paraphrase what a true metallurgist would tell you and simply say that 1095 has more carbon in it than can be captured in the particular crystal structure that we are trying to achieve in a knife blade. It is a lot like when you are dissolving salt in water. At some point, you just can't get any more to dissolve, and the excess just sits at the bottom of the glass. With 1095 you have to be careful with your temperature so that that extra carbon goes someplace harmless rather than forming other crystal structures that cause problems.

 

Tempering at 400F might have been a bit cool for a field knife. I tend to see people talk about tempering kitchen knifes at temperatures between 350 and 400F. Field knives I seem to see more in the 400 to 450F window. Again, the information is suspect, but if you average it all out, that would make me think you might have been a touch on the cool side.

 

Now I am going to gladly step aside, and let someone correct anything I have wrong. (And teach me in the process :) )

Edited by Brian Dougherty
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I thought 1095 and 5160 were a couple of the easier steels to heat treat. They are more suited for backyard heat treating versus D2 or 01 steel. I could be completely wrong but I thought that's what I had read somewhere. When you say be careful with the heat treat what do you mean? Over heating it before the quench? I normalize 3 times letting it cool back down to no color between each cycle then Heat up to nonmagnetic and quench in canola. This is the correct way of heat treating right?

 

I agree. I believe I was too cool and it didn't relax the edge enough. I need to start numbering all knives I make and document every step I take so I can troubleshoot issues such as this. I remember most steps I took in the making of this knife (I've only made a few so far) but documentation would really be helpful!

 

Thank you very much for your reply. I've been at work since I wrote this and have been checking often as I can hoping for answers or advice! :)

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1084 steel is a better choice for simpler back-yard heat treat methods because it doesn't have much extra carbon. I usually hear 1095 being referred to as a bit more challenging, but still doable.

 

Someone else needs to step in here an answer your question properly, but with 1095 you need to give it a few minutes of soak time around 1500F before quenching, but getting up over 1550F will cause issues. I have been using a thermocouple to measure the temp while heat treating, and trying to stay in that window, but only because that is advice I have received.

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1095 and 5160 are easier than D2 and O1, but not the easiest. Nothing is more ideal than 1080, and I'd say 1060-1084 is the safest/easiest batch to use for not having temperature controls. That being said, 1095 and 5160 are certainly doable without temperature controls. As is O1 if you have the experience, but I highly recommend avoiding D2 without a controlled heat source.

 

That said, how hard the knife should be is entirely up the intended use and user. If your customer is happy with it, job well done; even if you aren't happy. Just do the next one so you are happy too. Did you double temper or just single? If only single, I recommend adding a second cycle as a good first step on the next one. Then attach a temporary handle and test it (realistic abusive service). If it chips add 25 or 50 degrees and try again. Don't go over 550.

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Brian - Thank you for the reply. I'll have to get some 1084 and try that next go round until I get a temperature control setup. Its funny you mention that because I was just talking to a couple coworkers about setting up an arduino for my temp controls. Anyhow...Thank you for your help!

 

Jerrod - Thank you very much for the advice! I just did a single temper cycle and the reason I did that is because I was assuming this was going to be strictly a skinning knife. I didn't think about the knife hitting bone or a broadhead that may be stuck in the hide. I was going for edge retention. That's my own fault. I will be doing 2 cycles next time and testing like you mentioned. Thank you for the reply!

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There are a few other things to consider, including edge geometry. A really thin edge will chip at the same temper a more obtuse edge will hold for days. Also, have you put a good oven thermometer in your tempering oven? Most toaster oven type things (and most kitchen ovens) are wildly innacurate. My kitchen oven averages 15 degrees hotter than the dial setting, but cycles over a range of 100 degrees. In other words, if you set it at 400 it can be anywhere between 350 and 450 at any given moment, but averages 415. My toaster oven in the shop is accurate, but cycles between 50 degrees colder and 25 degrees hotter than wanted.

 

Test your oven and take that range into account.

 

However, I bet Jerrod is right, all you really needed was a second tempering cycle. ;)

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"Easy" is a very relative term. Yes, 1095 is easy compared to O1 and D2. 5160, however, is much easier and more forgiving than 1095. The thing to remember about 1095 is that it is hypereutectic, i.e. it has more carbon in the alloy than the iron can hold in solution. The extra carbon forms carbides, which are very hard, and add to the wear resistance of a steel. However, the carbon in steel is in solution and previous thermal treatments (like annealing) can move the carbon out of solution and precipitate it within the grain boundaries as carbides. When heating the steel up prior to quenching (austenitizing) the carbides take more time, at austenitizing temperatures to dissolve and allow the carbon back into solution.. That is where the recommendation to "soak" 1095 at temperature, prior to quenching, comes from. If not enough carbon is in solution when 1095 is quenched it can fail to harden or not harden to the full extent it is capable of. Raising the austenitizing temperature will allow the carbides to dissolve faster but, at the expense of grain growth, something that is not desirable in a tool because, it makes the steel more brittle than an object with a finer grain - at the same RC hardness!

 

Assuming that your heat treatment is spot on, tempering at 400 degrees Fahrenheit would yield a RC hardness of around 62-63. Quite a bit harder than the usual recommendation of RC 58! However, heat treating, by eye, in a forge, using a magnet to test for austenitic - my instinct is that the steel got a bit hot at some point and you have a larger grain than is optimal. This would make the 1095 easier to harden and make for a blade that is, slightly, more brittle, at the same RC hardness, than a blade with finer grain. In your shoes, I would harden a piece of scrap in the same fashion then break it and try to determine if the grain was acceptable or not. My other recommendation would be to temper hotter. Here is a link to a chart (down the page a bit) of tempering temperatures and approximate hardness of 1095. Link.

 

~Bruce~

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Alan - Thank you for your reply. Just out of curiosity, would you put a convex edge on a skinner or a hollow grind? On this particular knife I did put a flat grind that went all the way down. No secondary bevel that can be seen. It was sharpened using a lansky sharpener but it doesn't have a high secondary bevel. I will try to post a pic soon as I get a chance so you see what I mean. I'd like to show the chip anyway. I haven't checked my oven temperature with a probe yet. I'll have to do that tonight. I'm going to print all of this out so I have it for future reference so keep the advice coming! :)

 

Bruce - Wow...Thank you very much for the wealth of information! I'll have to google the "in solution" that you are talking about. I'm not entirely sure what that means.

 

I've been doing a lot of reading and research but I think its about time I actually get to testing some scrap steel and learn this. Thank yall very much for all your help and advice. It is very much appreciated. I'll try to get that picture up sometime today

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Here is the knife I made my boss at work. As you can see there is a small chip in it. He did mention that there was a broadhead in the deer and that he did cut the tail and hit a bone with the blade. But that blade should still be able to handle all that without chipping if heat treated properly. I reckon I'll be making him a new knife soon...in 1084 steel! :)

 

http://i1378.photobucket.com/albums/ah93/BradGalles/IMAG4889_zpsff8482e1.jpg

 

http://i1378.photobucket.com/albums/ah93/BradGalles/IMAG4890_zps9712c67c.jpg?t=1415734245

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Brad-

1) I like the overall shape of that knife. As others tend to point out, the last little bit of blade near the handle will be hard to sharpen, but who uses that part anyway? (I jest people, the whole edge can be used.)

2) Edge geometry for a knife like that is pretty user-preference oriented. Each style has their own pros and cons. For a hunting I would say convex or flat are better than hollow just to keep it a bit stronger. I personally like flat for everything.

3) I get the feeling you may really enjoy reading the "Metallurgy and Other Enigmas" sub-forum here. If you can't find the answers to metallurgy and heat treat there, you don't need to know the answer. Again, I'm joking. If you can't find it there, ask there. Someone will likely know the answer or be curious enough to find it for you.

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Thank you Jerrod....The metallurgy forum is my next stop. At least that way I'll get a better understanding of what is going on with the steel, even if I don't have the temperature control yet. I mean...They were making some pretty amazing blades back in the day when PID controllers and Thermocouples weren't around :) That means there is hope for me yet!

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Brad I am going to take a guess that small chip is not from a bone. That strikes me as the knife hit something with a hard edge. Like the edge of a sharpening stone, or something metal. Could be wrong, have been before. Most of the time chopping a bone will either chip larger than that if the blade is on the too brittle side and if on the too soft side it will deform or roll. I like the design and overall look of it.

 

Work within our parameters, meaning if you don't have the proper oil, HTing equipment or the ability to monitor it all, use the KISS method, KEEP IT SIMPLE STUPID, and no I didn't just call you stupid the KISS method was introduced to me a long time ago!

 

1075 - 1085 is a range of metals that you can do relative to the back yard method without too much trouble if you tighten your control down as much as possible and them means hitting the right times and temps for the given steel. It also means using outside controls when monitoring temps.

 

Here is the other thing testing of your techniques. It nearly kills me to take a near knife. Definition of a near knife is as follows: one that has not necessarily a beauty but the shape is right, the angle of the blade is right and the metallurgy is right and then see what it stands up too! Will it chip, will it hold and edge, how is it at resharpening the edge, and then the deflection test to see when and if it will break. If it breaks you get and insight into either where your design failed or the metallurgy side of the knife failed!

Edited by C Craft
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I was wondering when you would see this post Mr. Craft. Thank you for the reply. I brought the knife home with me so I can sharpen it and do some testing on it to replicate the chip somehow. If it is too brittle it will chip again through testing. If it doesn't chip, that tells me that it's more likely what you mentioned... Operator error. Which I hope is the case! I will also be ordering some 1084 when I get some extra cash. May have to wait till after Christmas though. Again... Thank you for the reply! And I refer to the KISS method often at work :)

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It's possible that with the single tempering cycle that there was some retained austinite that converted to untempered martensite that was left untempered. As mentioned above there is also the final edge geometry. Yes, 1095 can be austinized and soaked by eye but I really doubt that it can be done so with consistency. Can't really know about that without breaking all of your blades. Any steel with above 0.85% carbon will tend to give a problem with retained austinite without a regulated heat source like a high temperature oven or a molten salt pot to heat treat with.

 

Doug

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Thank you for the response Doug. I actually just finished reading some of your comments in the knifedogs forum under the knifemakersarea/heat treating. I learned a lot! I'm not sure where I originally got my information about 1095 but I was way off. I've learned everything I know on knifemaking from google and youtube until I recently started spending more time on these forums. Anyway, thank you for your reply and I will get some 1084 to practice with until I get a better heat treating setup. In the meantime I think I might have found a local place to heat treat the 1095 knives that I have ground already.

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So just an update. I took the knife home and ran several tests on it before sharpening it. First test was chopping a 2x4. I don't believe this is a very good test for a skinning knife but i wanted to see how the edge would react. I chopped half way through the 2x4 and notice that I could see little ripples in the edge where it was rolling slightly. I then proceeded to the brass rod test.The first time I performed the test I was dragging the edge along the brass rod as if I was stropping with quite a bit of pressure. This cause the edge to chip like crazy. I could here it cracking.

I currently have the lansky sharpening system so I used it to see at what angle I had put the edge on it. It was at 17 degrees. I remember putting that edge on because it was strictly going to be a skinning knife and I assumed the thinner edge the better. I think that was a bad idea.

All of these tests were performed after I had just got off my 12 hour day shift. I stayed up till just past midnight performing tests and wondering where things went wrong. I decided to get to bed and see how things went in the morning.

Next morning I had an excellent idea! I would put a new edge on at 25 degrees and perform the same tests over again. So that's what I did. The first test with the 2x4 went great! No rippled edge or chips. I was pretty excited so I decided to look up how to properly perform the brass rod test. I found an excerpt from Wayne Goddards book that said exactly how to do it. So I performed the brass rod test and watched the edge flex and return back to original form! That was very cool by the way. I checked it all the way along the edge with no issues. I double checked the area where the chip was and everything seemed perfect. So my very last test was to chop 2x4 again, then cut a bunch of scrap leather, then try to cut paper without any issues and shave hair. The knife performed flawlessly! I didn't even have to strop it before shaving hair after all the previous tests. I am very impressed with the knife. I have no idea how the owner got that chip in it unless there is something he is not telling me. He did mention hitting his broadhead with it while it was stuck in the deer but I'm not sure if that would chip it or not.

I'm sorry this is such a long post. I'm just so very relieved that I didn't sell a bad product. It was my first knife sale so I was already nervous about its long term performance since I'm so new to this. I really appreciate all the help and advice everyone posted. I am still going to drop down to 1084 since I don't have the proper heat treating equipment for 1095. I am also going to keep poking around in the metallurgy section on this site and soak up as much information as I can. Again...Thank you all very much for the help!

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Well done! So it was the edge angle after all. I'm glad you tested it out. Oh, and a second tempering and you probably wouldn't have gotten the chipping during the rod-stropping you did. ;)

 

Don't be afraid of 1095, you've shown you can do it.

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I skimmed this, so someone may have said it already - but 1095 has more carbon that can be put into solution at temperature, so you need to soak it a bit before quenching to dissolve the carbides. My personal procedure for this steel is to bring it up to temp, hold it for 5 minutes or so, and then do my normalizing cycles, then up to temp once more, hold for a couple minutes, then quench. I temper 1095 around 450-475 (same toaster oven problem, but I have I fire brick in there to act as a giant balancing heat sink) and haven't had problems with it. Make your grain fine, and temper it back a little more, it'll survive even with a thin edge.

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Brad good for you, know you know the rest of the story, as they say!

 

Yes a blade with a thinner degree of sharpening angle, (17 degrees can and will chip when it hits a broad head). The edge is thin and the broad head is hardened steel. If he is making a sweeping stroke while skinning and hits the knife edge against the broad head it chipped it! That explains exactly why the chip was so small! That one is operator error but if you feel responsible make him another but with the 25 degree edge. The average knife is 20* or better, when it comes to skinning, or hunting knives!!

 

I would be willing to bet he may have never even known he chipped until he finished and was cleaning up! A tiny chip like that would more than likely not hurt performance!

 

 

Refine your process to nail the parameters you are shooting for and you should be good to go!!!

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Christopher Price - Thank you for your response. Quick question with the fire brick in the toaster oven. Do you lay the knife on the brick? Cut a groove in the brick for even tempering? Thank you.

 

C Craft - I def have a lot more refining to do in the heat treat dept. I knew that the average hunting knife is 20 degrees or more. I just thought that a skinner may perform better at a steeper angle. That was my own fault for trying something different than what has been tested and proven. I know better for next time though :)

You know what...he never even knew the knife had a chip in it until I showed it to him! So i'm not sure at what point the chip happened but he said the knife performed very well and he was pleased with it. I did end up regrinding the edge to a 25 degree angle. I'm very happy with the knife I was able to make. It performed well for me and the tests I put it though

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  • 2 weeks later...

I just lay the knife on the brick, and add an hour to the cycle - it will take a while for the brick to heat up, but it will hold and radiate a much more even heat in a toaster oven than just a blade lying in the middle of empty space with the oven cycling over a wider range of temps... works for me. I'm using a 1 inch thick hard brick, too.

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