castlegardener Posted July 24, 2011 Share Posted July 24, 2011 Hello all, This is my first real post, and it starts with a problem. Today I snapped a knife blade in half. A friend asked for a filet knife so I forged one as thin as I could get it. I am using a propane/firebrick forge. The steel was car leaf spring steel. I forged the blade. Normalized it twice. Heated it to bright orange, quenched it in motor oil once. Out of the motor oil the blade warped a small amount. I then polished the blade up some, and put it in a toaster oven at 400F for an hour. Once it was finished, I put it back into the oven for 425F for another hour. I began polishing again and sharpening the blade but still tried to figure out what to do with the warped blade. I took a small micro butane torch and heated the blade near the warp to a dark brown/ blue thinking it would add flexibility. I squeezed the blade in a vise but the warp remained. So, I grabbed the blade with two hands and attempted to bend it a little bit and the whole blade snapped in two. I will attempt to upload a photo, but this is my first attempt at photo uploading. I have crafted 10 or 11 blades before this but none this thin. Any help on troubleshooting my work procedures would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 24, 2011 Author Share Posted July 24, 2011 I guess this should probably have been in the knife section on heat treating...I missed that folder....sorry guys Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted July 25, 2011 Share Posted July 25, 2011 You tried to bend a hardened steel blade cold. That will usually do exactly what yours did. A lot of us had similiar troubles early in our learning. If it is not straight when it comes out of the quench it needs to be heated again and quenched again. Most of the time i do this on simple steels like you have without any fuss. Back in the forge straighten and reheat and back in the quench. You may find there is a reason for the bend to occur. Make sure you normalize before quench and make sure metal is heated evenly. Make sure you go straight down into quench. And you may find that after a hundred or so knives things start to get easier. Patches like you little torch dont work...lol Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 25, 2011 Author Share Posted July 25, 2011 thank you Rich...I will reforge the next blade and try again. Quote Link to comment Share on other sites More sharing options...
christian Posted July 25, 2011 Share Posted July 25, 2011 first off welcome to ifi, this is a great website you can learn ALOT here I have heard thats warps in blades could be caused by the smith hammering on one side more than the other. Quote Link to comment Share on other sites More sharing options...
MattBower Posted July 25, 2011 Share Posted July 25, 2011 Can we see a pic of the end "grain" of one of the broken pieces? And how thick was it? If I find a warp after the quench, I generally straighten it hot and start the whole heat treating process over. However, believe it or not, it is possible to remove the blade from the quench bath while it's still relatively hot (500+ degrees F) and remove warps with your gloved hand. Although the eventual formation of martensite is determined by the speed of the early portion of the quench, martensite doesn't actually begin to form in your blade until much lower temperatures (between 400 and 500 F is a good guess for simpler steels, or you can look it up on a TTT diagram; it'll be marked Ms). There's a period after the quench, when the blade is still cooling, where it's still austenite, and thus very soft and ductile. So it's very easy to fix warps by hand while the blade is in that temperature range. If you don't believe me, watch this. http://straightrazorplace.com/forge/51453-interupted-quench-2.html Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 25, 2011 Author Share Posted July 25, 2011 here is a photo of me holding both pieces between my fingers. Quote Link to comment Share on other sites More sharing options...
MattBower Posted July 25, 2011 Share Posted July 25, 2011 Your grain looks fairly coarse, which leads to brittleness. You likely overheated prior to the quench. How are you determining temperature? "Bright orange" is very subjective, and a whole lot depends on ambient light. Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 25, 2011 Author Share Posted July 25, 2011 my forge is indeed in bright light, and this metal was super thin...it is a good chance I overheated it.... Quote Link to comment Share on other sites More sharing options...
Stormcrow Posted July 26, 2011 Share Posted July 26, 2011 A trick I was told recently, that I have made good use of since learning, is to lay an old file along the warp, then C-clamp the blade to the file, pulling the warp out. Then cycle it through your tempering cycle again. If it didn't take it all the way out the first time, put a couple of spacers between the file and the blade, like pennies or washers, and cycle it through again. And yes, you do have a small amount of time after you quench to straighten warps before the steel fully sets up. Try using a magnet to check for critical temperature. You might be surprised at how cool the blade will harden satisfactorily. Quote Link to comment Share on other sites More sharing options...
Steve Shimanek Posted July 26, 2011 Share Posted July 26, 2011 It is fairly typical to overheat as a beginning bladesmith; your grain coarseness is a good indication it was overheated as said in the other replies. Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 26, 2011 Author Share Posted July 26, 2011 thanks everyone....will try again.. Quote Link to comment Share on other sites More sharing options...
MattBower Posted July 26, 2011 Share Posted July 26, 2011 Bright orange in bright light is indeed way too hot. To my eye, in dim light 1500 looks about the color of an orange. Just a shade above nonmagnetic is a reasonable approximation. Tempilaq is a better solution, although it tends to scrape off in solid fuel forges unless you use a muffle. An even better solution would be to learn to recognize decalescence, which is the point at which the phase change to austenite happens. It is literally visible in the steel if you know what to look for. See here: http://paleoplanet69529.yuku.com/topic/26894/Decalescance But you have to catch it as the temperature is rising; recalescence (the reverse process on the way down) happens at a much cooler temperature, and by the time you see it you've missed the window for quenching. Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 26, 2011 Author Share Posted July 26, 2011 thanks for the link...those are great photos...thanks Matt Quote Link to comment Share on other sites More sharing options...
MattBower Posted July 26, 2011 Share Posted July 26, 2011 Just remember, what he caught there was recalescence, when the blade was cooling. You want to catch the shift on the way up, which can be very tricky. You need dim ambient light, and it helps a lot to have a forge that isn't much hotter than the temp you're aiming to achieve. A very gentle blast in a good bed of real, glowing charcoal is pretty good. Quote Link to comment Share on other sites More sharing options...
Frank Turley Posted July 28, 2011 Share Posted July 28, 2011 Everyone sees heat colors differently. 5160 is hardened at a recommended 1525ºF, which is a full red, just above a bright cherry red. An orange heat is close to 1800ºF, too hot for hardening. Quenching in oil is the route to go, to help prevent warping. 425ºF is a pretty hard temper for a knife. 500 to 600 might be better. It is a matter of experimentation. The normalizing temperature is 1600- 1700ºF, a bright red color. Quote Link to comment Share on other sites More sharing options...
Woody Posted July 28, 2011 Share Posted July 28, 2011 Take a close look at he broken ends and the cause of the warp becomes quite obvious, the blade is unevenly ground. One side is ground flat and the other side is ground convex. When quenched the flat side cools more quickly than the convex side and the blade warps in the direction of the flat side. Straightening the blade and re-heat treating won't solve the problem the blade will just warp again. Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 28, 2011 Author Share Posted July 28, 2011 thanks everyone for the replies...I will change a few things before the next blade Quote Link to comment Share on other sites More sharing options...
JPH Posted July 28, 2011 Share Posted July 28, 2011 Hello: Way too hot at quench...5160 is a low Cr alloy and should not be any hotter than 1550F or so at quench... Also, on the temper::Way too low a temper for a filet knife...you want a full "blue" temper for more of a "spring" to allow for the extreme flex.. I have probably used close to 15 tons of 5160 over the years and it is a great steel..I can bend a sword blade 90 degrees have it come back straight and still be able to cut through a iron bar with it with no damage to the blade...all in the HT.... You pretty much toasted this one...as I have said before experience is what you get when you don't get what you wanted... JPH Quote Link to comment Share on other sites More sharing options...
castlegardener Posted July 28, 2011 Author Share Posted July 28, 2011 so...if I am to temper a blade at 500-600 what am I supposed to use to do this? My little toaster oven will only go to 450. Am I supposed to do the tempering in my forge? And if so, how am I going to get it that low of a temperature in the forge and be able to keep it running for an hour? I still have an old brake drum charcoal forge not being used anymore since I now use the propane/firebrick forge. Is the charcoal brake drum forge a better option for the heat tempering? Quote Link to comment Share on other sites More sharing options...
JPH Posted July 28, 2011 Share Posted July 28, 2011 CG: I realy am loathe to do this but there is a book in print out there that explains what you are asking (and a whole lot more BTW)...there are at least a half dozen ways I know of to do this.... for the record..I do NOT advocate using a toaster oven for any sort of tempering as they have "high" and "low" temperature points that "average out" to what the "setting" is on the thermocouple. Even a regular "kitchen" oven has the same drawbacks but they are usually a bit more closer between the extremes...and it is the high end of the extremes that can cause problems...if ou get above the top end of the tempering range you messed up..even if it was for "only for a minute or two"..once it gets above what you are going for..you messed up... Everyone works differently and has their own point of view on hings.I know what works and what doesn't work for me...It may or may not be the same for you..(OK I admit I am colourblind but still that doesn't stop me...) It would be better if you were to go out with some 1010/1018/A36 mild steel and start "practicing" in drawing a temper and seeing how the colours run into each other and the time it takes fpor the colours to "run" into each other.... Experience is paramount in doing this sort of work and I still to this day do it "by eye"..yeah I mess up from time to time..I am only human but I am pretty much dead on the vast majority of the time....but I have been doing this for well over 40 years..Oh heck..just forget I said anything and do what you want. I am too old and set in my ways to suggest to anyone that they do anything at all.. I need to learn to keep my mouth shut...that will be the easiest thing to do for all concerned... JPH Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted July 28, 2011 Share Posted July 28, 2011 when the wife is away use the home oven, clean the oil off first. Making blades isnt always easy on a low budget for equipment but it can be done. Some of us have spent a lot of money on equipment, and not just because it was fun to spend the money. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted July 28, 2011 Share Posted July 28, 2011 Tempil sticks melt at specified temperatures. They are about $20 each, so not too expensive for repeatable control, having just below, the specified temperature, and just above is a good idea though for process control. Most steel goes non-magnetic at 1450F or so. You can hang a magnet on a copper wire and let it swing as a pendulum. If the magnet attracts you are below 1450F, and if the magnet swings naturally you have gone above 1450F. The temperature is lower on the way back down though (around 800F). Phil Quote Link to comment Share on other sites More sharing options...
son_of_bluegrass Posted July 28, 2011 Share Posted July 28, 2011 You can minimize the thermal swing in ovens by adding thermal mass. I bought a used dutch oven at a pawn shop for a couple of dollars and filled that with sand. If you bury the blade in the sand it will heat up slower if the oven cycles hot and it will hold the heat when the oven cycles cool. But there are lots of ways to skin this cat. ron Quote Link to comment Share on other sites More sharing options...
MattBower Posted July 28, 2011 Share Posted July 28, 2011 Kitchen oven. Disposable aluminum roaster tray full of sand to even out the temperature swings. (Preheat it before you add the blade.) Oven thermometer to verify temp. (Candy thermometer stuck in the sand, if you can find one that goes to the temp you want.) You should be able to get to 550ish that way. Quote Link to comment Share on other sites More sharing options...
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