strantor Posted February 8, 2009 Share Posted February 8, 2009 Hey everybody, I am here today to report a most grievous failure on my part. I have been working on leaf spring kukri knife for the past couple of days. I quenched it today and then annealed the back, after which the blade split. I have posted a video on youtube so that you can see exactly what I did. here is the link: YouTube - Making the Leaf Spring Kukri Knife, Part2 (FAIL) please help! Quote Link to comment Share on other sites More sharing options...
J Anderson R Posted February 8, 2009 Share Posted February 8, 2009 (edited) First thing, when your drawing out the temper in the spine, you dont bring it up to red color. bring the spine to a blue color with a fine tip on your torch, then let it cool down in the air and repeat two more times. Next, if your blade split during the tempering it was caused by a fracture that developed during the hardening quench, most likely from a scratch or pit missed during the grinding, plus it looked like you overheated the blade befor you dipped it in the oil which would make for a weak, coarse grain structure and could have contributed to the break as well. If your unsure about hardening temp I would recomend getting yourself a magnet. When the steel loses its magnatism let it raise another 50 degrees or so and quench. I could only watch half the video and without sound cuz my speakers broke so if I missed something Im sorry. Keep trying, your design looks great Edited February 8, 2009 by J Anderson R Quote Link to comment Share on other sites More sharing options...
element Posted February 8, 2009 Share Posted February 8, 2009 Maybe you forged it too cold and the stress cracks that were probably already in the spring came out after. Starting with new stock is an insurance against hidden cracks. Also it looked a bit too hot when u quench it? Knife makers should be able to narrow down the problem for you. Quote Link to comment Share on other sites More sharing options...
strantor Posted February 8, 2009 Author Share Posted February 8, 2009 First thing, when your drawing out the temper in the spine, you dont bring it up to red color. bring the spine to a blue color with a fine tip on your torch, then let it cool down in the air and repeat two more times. OK, I didn't know that. I guess that's problem #1 Next, if your blade split during the tempering it was caused by a fracture that developed during the hardening quench, most likely from a scratch or pit missed during the grinding Do you reccomend polishing the blade before quenching to make sure all the scratches & pits are gone? It was full of 60 grit scratches because that is what I used to shape it and I never went higher than 60 grit. plus it looked like you may have overheated the blade befor you dipped it in the oil which would make for a weak, coarse grain structure and could have contributed to the break as well. If your unsure about hardening temp I would recomend getting yourself a magnet. When the steel loses its magnatism let it raise another 50 degrees or so and quench. What color should the metal be when it is 50 degrees past non magnetic? I thought about doing it while it was red but then waited till it was orange-yellow to quench it. . Keep trying, your design looks great Thanks! Quote Link to comment Share on other sites More sharing options...
J Anderson R Posted February 8, 2009 Share Posted February 8, 2009 (edited) I always seem to have different lighting conditions so I dont go by color, I always use a magnet to judge hardening temp. I would highly reccomend taking the whole blade to a 220 grit grind befor you harden it, Im sure those 60 grit scratches were a factor in the break.. and yes, all deep scratches and pits should be goneor they become stress risers and prime places for cracks to develope Edited February 8, 2009 by J Anderson R Quote Link to comment Share on other sites More sharing options...
TCooper Posted February 8, 2009 Share Posted February 8, 2009 I always seem to have different lighting conditions so I dont go by color, I always use a magnet to judge hardening temp. I would highly reccomend taking the whole blade to a 220 grit grind befor you harden it, Im sure those 60 grit scratches were a factor in the break.. and yes, all deep scratches and pits should be goneor they become stress risers and prime places for cracks to develope Not to mention it's WAY easier to get all those scratches out while it's still good and soft.:) Quote Link to comment Share on other sites More sharing options...
strantor Posted February 8, 2009 Author Share Posted February 8, 2009 Wow! I had no idea that 60 grit scratches would effect it. good to to know. I'll use a magnet next time. Thanks for the help! Quote Link to comment Share on other sites More sharing options...
jimmy seale Posted February 8, 2009 Share Posted February 8, 2009 well all you did was harden it- not temper in atf. what you are asking is about differental heat treat-i don't do it but iffin i recal it is normalize and heat edge and quench then temper-i agree with good steel and sanding, buti dissagree with how ya lit the forge(accelerent) and your atire- be more wise and careful-be a good example.maybe try clay on the spine? please don't take this as a condemnation- isn't ment to be.but you need to do a lot more reading - lots of info in the b/p's hate to see you put work in on something that will fail- but it will happen. hang the blade up so ya see's it and remember, best of luck, jimmy Quote Link to comment Share on other sites More sharing options...
strantor Posted February 8, 2009 Author Share Posted February 8, 2009 well all you did was harden it- not temper in atf. Yeah I get my terms mixed up sometimes, sorry about that.i dissagree with how ya lit the forge(accelerent) and your atire- be more wise and careful-be a good example. Yeah you're right, it doesn't seem very safe to me either, but how else do you light coal? I'm not being a smart *ss, I really would like to know a safer way to get that stuff lit because copious amounts of gasoline has been the only successful thing for me so far. Thanks! Quote Link to comment Share on other sites More sharing options...
Graham Fredeen Posted February 8, 2009 Share Posted February 8, 2009 It looks like what happend was you firstly quenched way too hot, resulting in a very corse grain structure within the blade and excessive stress build up, which is just asking for a fracture. Second mistake was skipping tempering all together (I assume you didn't temper since you did not mention it) and went straight into trying to aneal the spine blade. This left all the built up stress from the quench still in the blade. You can't really aneal the spine of a blade after quenching, if you heat the spine red hot you are bringing the spine up to critical temp, where this red hot spine meets the surface of the water, the water will try to rapidly cool this section of the blade, and water is much too agressive to quench 5160 in without fractures. As a result you will be hardening this area of the blade. You can draw a heavy temper on the spine using your method, but you only heat to around 600 F max (the deep blue color) not red hot. Since you heated the spine red hot it probably reached critical temp and you had the blade in the water which was attempting to act as a quenchant, you lowered the blade into the water slightly which quenched an area of the blade that you had heated, and the resulting stress caused the center of the blade at water level to expand which stressed the edge even more, it found a stress point in a gouge along the bevel from grinding at corse grit and pulled the bevel apart and split the blade at the water level. I do not think this happend from an existing fracture from the initial hardening. So basically you had everything working against you, huge grain and additional stress build up from quenching too hot, lack of tempering along the edge to reduce stress from quenching, heating the spine to critical and having it in water (the act the pushed the blade too far), and leaving course gouges from grinding to act as stress risers. For succesful HT temperatures are key. As mentioned, get a magnet to check the blade temperature for quenching. Unless you have consistant lighting conditions all the time you will not be able to judge temperature based solely off color. You don't want to overheat the blade before the quench because once you exceed critical temp, grain growth begins, the hotter you get the larger the grain. Forging the blade will result in large grain structure, as a result, this grain must be refined before hardening. To do this you must normalize the blade. To normalize the blade, heat the blade to critical temp, make sure the blade is evenly heated, and allow it to air cool. Do this a few times (I usually do 3 normailization cycles, reducing the temp gradually each cycle). Once the blade is normailzed it will have a good refined grain structure that is uniform throughout the entire blade. After normailzation you can go for the hardening quench, just make sure not to overheat the blade and to quench from critical not drastically above. Following the quench there is a huge amount of stress built up in the blade from the expansion caused from the formation of martensite, this stress must be relieved to make the blade usable without cracking (in some cases with some steels if you let a blade sit for a couple hours after quenching without tempering the resulting stress can crack the blade). To temper throw the blade in the oven for a few hours at around 375 - 400F (for a through hardened piece of 5160). This tempering will relieve stress built up in the steel from the quench and slightly reduce hardness to create a tough blade. Then, after tempering the entire blade at this lower temperature, if you want to further soften the spine you can submerge the edge in water and heat the spine to roughly a blue color (you will have to sand off the oxidization from the quench to see the temper colors run). If you want to differentially harden the blade (as in not hardening the spine at all) you have 2 options, edge quench or clay the spine. All the normalization and tempering still applies. Quote Link to comment Share on other sites More sharing options...
strantor Posted February 8, 2009 Author Share Posted February 8, 2009 Ok, now I realize that I didn't just have my terms confused, I actually didn't know what tempering really meant. Thanks TarAlderion! I get it now, and I went out and had a second look at the crack and you are absolutely right, the grains are huge! I guess I doomed that knife from the start. I never normalized & never tempered it & quenched way too hot. I guess I'll be changing up the way I do things now. Thanks everybody, this was really helpful! Quote Link to comment Share on other sites More sharing options...
kasaino Posted February 8, 2009 Share Posted February 8, 2009 I have used a similar forge to the one you used, and to light my coal I use a good ole' news paper, with a few coals on top, and a match or two. a little patience as far as magnets go, I bought an arts and crafts set, something like 50 magnets for about three dollars from wal-mart. I usually put two or three on the blade, one on the each end and one in the middle. I wait for the magnets to fall off, wait a few seconds longer, pull and quench. I put three magnets so i can better make sure everything is heating evenly. I have messed up and had bad "hot spots" where only one of the three magnets fall off... everyone makes mistakes no biggie another way that I have read how to anneal is to light a regular fire, and set the knife in the middle of it. old school but hey. I have read the same for tempering, then just let the knife air cool. Everyone gave you good advice, and your knife looked nice, so I wont be to shocked when your next blade is a total success! keep us posted, success stories are always good, keep it up! Quote Link to comment Share on other sites More sharing options...
MetalMuncher Posted February 8, 2009 Share Posted February 8, 2009 Strantor, listen closely to TarAlderian, he's helped me before. Nice video you got there though. Alright, from my experience, 5160(leaf spring steel)is very forgiveable, I have abused it severely and it held out pretty well. When I first started, I was also over heating my blades prior to the quench. I thought that the higher the temp, the harder it would become. But I wound up only cracking my blades (like you). Heres my heat treating cycle: I forge the blade, profile it, and grind out any pits or defects caused by my poor forging technique(hahaha).I dont usually anneal, I think it sucks out some carbon, but thats just me. I then bring it down to a 100 grit paper before HT. Now, I run 3 cycle called normalizing, which is used to reduce grain size. After that its ready or the quench. I pre-heat my oil, usually to 120 F, and quench my piece at critical. I then temper in the oven for an hour at 170 C (200 F?) That will result in an indestructable heat treat, which, if properly sharpened, will shave hair cleanly. I have run many destruction test and I cannot break my knives!! 5160 is very good steel. Many thanks to TarAlderian(he helped a bunch!!) Good luck dude! Quote Link to comment Share on other sites More sharing options...
MetalMuncher Posted February 8, 2009 Share Posted February 8, 2009 P.S- You might be interested in something called edge quenching. Where you heat the knife to critical, and only quench the edge. I quench about an inch up the blade. When the color has gone from the spine, submerge the entire piece. After tempering, this will result in a ultra hard edge and a softer spine(what you were trying to do) God bless! Hope that helps! Quote Link to comment Share on other sites More sharing options...
Graham Fredeen Posted February 8, 2009 Share Posted February 8, 2009 I tried to keep the original post fairly short so I gave the condensed version. If you run into any more snags or need any additional information please feel free to let me know. I work a lot with 5160 and have the HT down pretty well and would be happy to give you some more details. MetalMuncher, glad I could help. 2 suggestions though, firstly you might want to raise your tempering temp up a minimum of 6 C (that would be about 176 C, or 350 F) but I would recomend a higher temp of 375F - 400 F (190 C ~ 205 C). You can probabaly get by with the lower tempering temp on shorter blades that wont see some of the stresses of larger knives, but on a bigger knife that you chop with and really put through some punishment, they might be slightly too hard and brittle at the lower temp (unless you run a differential HT or differential temper). Also, depending on the type of oil you are quenching in, you might want to preheat it a little hotter (130 F -160 F, lower for a thinner oil, hotter for a more viscosious) And a note on edge quenching, while edge quenching works well for many blades, it cant be done very well on all blades, due to shape differences. Oil and water surfaces sit level, if you have a blade with large projections, dips, or negative curvatures, you will not be able to harden portions of the blade with the standard edge quench method. This kukri style is one example where edge quenching won't work that well. You could harden the belly just fine, but to get that back portion of the edge you'd practically have to harden the majority of the blade anyway (well this one is not quite as bad as a standard kukri, so you might be able to, you'd just have to look and see where the oil level would have to sit in order to successfully harden everything). If you wanted a differential hardening for something like a traditional kukri, your best bet would be to clay the spine. Again, if you need any more details, don' hesistate Graham Quote Link to comment Share on other sites More sharing options...
MetalMuncher Posted February 8, 2009 Share Posted February 8, 2009 I knew youd correct me Graham, thanks again for all the great information. I'm sure stantors problems will be solved in no time. Cheers! Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted February 9, 2009 Share Posted February 9, 2009 I don't want to be a kill joy, but gasoline to start the fire? burning up the blade with sparks all over? Just like I told Sabre, go back to basic's, read some of the posts, read the stickly's for knife making here, they say everything you need to get started, learn some basic smithing basic's and safety, before you try another knife. You are going to get hurt, and not only yourself. If you spent half as much time reading here at IFI as you have making U tube videos you could be a good smith. Forget showing off for a while, Knives are not toys. Quote Link to comment Share on other sites More sharing options...
J Anderson R Posted February 9, 2009 Share Posted February 9, 2009 Theres alot of great info in bladesmithing books by Wayne Godderd, Ed Fowler, and many other true masters of the craft. They are usualy fairly priced on Amazon.com and its well worth it to educate yourself on the basics. I think I read both of Waynes books befor I even fired the forge the fist time and it saved me alot of time and steel Quote Link to comment Share on other sites More sharing options...
strantor Posted February 9, 2009 Author Share Posted February 9, 2009 (edited) I don't want to be a kill joy, but gasoline to start the fire? burning up the blade with sparks all over? Just like I told Sabre, go back to basic's, read some of the posts, read the stickly's for knife making here, they say everything you need to get started, learn some basic smithing basic's and safety, before you try another knife. You are going to get hurt, and not only yourself. If you spent half as much time reading here at IFI as you have making U tube videos you could be a good smith. Forget showing off for a while, Knives are not toys. Thanks for your concern. I just learned of Iforgeiron.com the day before yesterday and since coming to the site I have learned tenfold what I knew before and since being previously scolded for using gasoline I have been told a new trick for lighting my forge. My intent for the youtube videos is not to show off. When you put yourself on video on the internet, you open yourself to the criticism of others (like yours) which can only help you. Some people go out of their way to call you an idiot, other post helpful information and everyone has a different perspective. It helps me out alot since I don't know anybody who does any type of metalwork so there is nobody there to look over my shoulder and tell me how & why i'm screwing up. I have the youtube crowd to do that for me. Like in the case of this kukri knife; if I hadn't been recording it, it would have snapped and I would never have known why. I could have described the problem in this forum, but a picture is worth a thousand words and a video is worth a thousand pictures. Thanks for the input! P.S. I thought about it some and you have a good point. I kinda know what i'm doing now, so I should forget the camera for a while and just get some experience under my belt. Edited February 9, 2009 by strantor post post reflection Quote Link to comment Share on other sites More sharing options...
strantor Posted February 9, 2009 Author Share Posted February 9, 2009 Thanks TarAlderion and MetalMuncher! I think you two have taught me about as much as I have the capacity to learn right now lol. Seriously, if I have learned anything from coming to this site (other than the things you guys have taught me), it is that I don't know jack about what i'm doing. My processes were seriously flawed and you guys set me straight. I will take what you have said and apply it and inform you of my results. I know that you can't learn everything about anything and I'm far from knowing alot about knifesmithing so I'm sure I will screw something up again and have more questions. I am greatly appreciative of your help. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted February 9, 2009 Share Posted February 9, 2009 Thanks for your concern. I just learned of Iforgeiron.com the day before yesterday I assumed you have been here a bit as your membership is shown as beginning in Oct 2008. Quote Link to comment Share on other sites More sharing options...
strantor Posted February 9, 2009 Author Share Posted February 9, 2009 I assumed you have been here a bit as your membership is shown as beginning in Oct 2008. Yeah that is a little decieving, but I explained the anomaly my previous posthttp://www.iforgeiron.com/forum/f14/my-first-finished-leaf-spring-knife-9713/ Quote Link to comment Share on other sites More sharing options...
MetalMuncher Posted February 9, 2009 Share Posted February 9, 2009 Any time strantor. Graham is great dude, always there to help. Might I ask how you cut your leaf springs up? Might I suggest hot cutting? That was a big issue for me when I started up, was just how do you cut something so xxxxxxx tough? God bless! And make some more vids when you get the kinks worked out! Quote Link to comment Share on other sites More sharing options...
strantor Posted February 9, 2009 Author Share Posted February 9, 2009 MetalMuncher said: Any time strantor. Graham is great dude, always there to help. Might I ask how you cut your leaf springs up? Might I suggest hot cutting? That was a big issue for me when I started up, was just how do you cut something so xxxxxxx tough? God bless! And make some more vids when you get the kinks worked out! I've never tried hot cutting, because I've only ever seen it done on an anvil with a hardie tool. I have a railroad track for an anvil so no hardie tools. I guess if I got somebody to hold the hot spring with the tongs I could hold my hatchet on there and hit the hatchet with a hammer. It's worth a try and would save me alot of acetylene because I currently use a torch to cut em up. Quote Link to comment Share on other sites More sharing options...
Graham Fredeen Posted February 9, 2009 Share Posted February 9, 2009 (edited) If you weld your blade billet to a handle or use a long piece of stock you can stick it between your legs and use your inner theighs to hold the stock while you cut it with the hand held hot cut (hatchet). Just make sure that the stock/handle is long enough to not heat up, since as you can imagine a hot piece of steel between your legs could get uncomfortable really fast. You might be able to do it with tongs as well, but thats even trickier and I probably wouldn't want to try it myself. It takes some practice but it works when you don't have an extra pair of hands available. That or get a vice and clamp the hatchet head (or forge up a designated hot cut) in the vice and use it that way (probably the best bet). You could also make an anvil hold down tool, but you'd need a hardie hole for that. Also, an angle grinder with cut off wheels is great for cutting up stock. It can go faster than hot cutting (depending on what exactly you are doing), doesnt distort the stock, and is much cleaner than trying to torch cut things. If you don't already have one and need a cheap angle grinder check if there is a harbor freight store near you. They can often be had for about $20 (some times cheaper if you catch them on sale). I have had mine for about 3 years now and have put it through some serious work and it still keeps kicking (original set of brushes too). Graham Edited February 9, 2009 by TarAlderion Quote Link to comment Share on other sites More sharing options...
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