medieval Posted March 30, 2009 Share Posted March 30, 2009 I teach blacksmithing at the local community college. I brought some automotive coil springs to class to make punches/chisels. Forged to shape, brought up to non-magnetic and quenched in water. We got cracks lengthwise, so I tried an oil quench. Some cracked, some didn't. I tried air hardening, some worked, some didn't. Testing with a file produced a strange result......:confused:......Outside layer of piece was not hardened, center was hard. I am pretty knowlegable, but this one has me stumped? Any opinions will be welcomed. Thanks Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted March 30, 2009 Share Posted March 30, 2009 Have you tried getting them up to temp (non magnetic) and then leaving them in the forge when you shut it down for the day and plugging the door? This slow cool may do the Trick. If you finish your tools before you are ready to shut the forge down, set them on top in a nice worm place to keep them worm until you do shut down. Hope that works! Quote Link to comment Share on other sites More sharing options...
Glenn Posted March 30, 2009 Share Posted March 30, 2009 You may want to place the punches/chisels across a couple of welding rods with about 2 inches free air below the rod and let them air cool. Quote Link to comment Share on other sites More sharing options...
Quang0 Posted March 30, 2009 Share Posted March 30, 2009 While spring isn't a particularly complex alloy, it shouldn't be quenched in water, especially cold water. Also it should, as with every other tool/job you forge be normalized before heat treatment. It can save you a lot of grief down the track. I make a lot of chisels and punches from spring this way and to date have never had such a thing happen. It's by no means impossible to get a bad batch of spring, but you need to treat it right in the first place, and that includes your forging technique and temperatures- not too hot, not too cold, and you need to get a through heat for your harden and temper processes. Cheers, PaulI teach blacksmithing at the local community college. I brought some automotive coil springs to class to make punches/chisels. Forged to shape, brought up to non-magnetic and quenched in water. We got cracks lengthwise, so I tried an oil quench. Some cracked, some didn't. I tried air hardening, some worked, some didn't. Testing with a file produced a strange result......:confused:......Outside layer of piece was not hardened, center was hard. I am pretty knowlegable, but this one has me stumped? Any opinions will be welcomed. Thanks Quote Link to comment Share on other sites More sharing options...
kbaknife Posted March 30, 2009 Share Posted March 30, 2009 (edited) I'm thinking a couple things here. And putting them together indicate something to me. If you are blacksmithing you are more than likely forging in coal? Not all that important, but possibly. Are you using coal? If you are getting cracks from quenching in both water AND oil, then the cracks may already exist BEFORE the quench. You may have got extreme grain growth from forging at too high a heat. Which is common with untrained students. With chromium steel that is more than likely in the springs you are using, you need to do a couple of post-forging steps to normalize your forging stresses, or cracks will be common. As well, if these are 5160 which is a deep hardening steel, and you have forged at too high a heat, the reason you have a layer of material on top that did NOT get hard, and it seems harder underneath, then you may have created a layer of steel that has decarburized from the etreme heat. The exterior won't get hard now no matter what, but the deep hardening qualities of the steel you are using will harden underneath it. Problems in quenching are one thing, but many times, these problems are a result of the forging and post-forging steps improperly done. Edited March 30, 2009 by kbaknife Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted March 30, 2009 Share Posted March 30, 2009 Decarburization will even happen at normal forging temps if you are slow working the steel---very common with new students at the forge. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted March 30, 2009 Share Posted March 30, 2009 (edited) Have you tried getting them up to temp (non magnetic) and then leaving them in the forge when you shut it down for the day and plugging the door? This slow cool may do the Trick. If you finish your tools before you are ready to shut the forge down, set them on top in a nice worm place to keep them worm until you do shut down. Hope that works! And how is this suppose to harden steel ? You are confusing annealing with hardening. As to the point in question, I agree that decarb of the outer layers is why is is not hardening the outside, and if you read the stickys on heat treating you would know that with unknown steels, we first try air, then try oil if air doesn't get it hard, then we try water if the others didn't work. I will admit that there IS a small possibility of too small a grain from excess thermal cycling in the outer layers resisting hardening, even with a chrome steel. Either way salvaged materials of unknown alloy always pose this risk. Edited March 31, 2009 by steve sells typos Quote Link to comment Share on other sites More sharing options...
kbaknife Posted March 31, 2009 Share Posted March 31, 2009 We didn't even touch the subject of what KIND of oil?!? Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted March 31, 2009 Share Posted March 31, 2009 And how is this suppose to harden steel ? You are confusing annealing with hardening. Steve- Thats what I thought when I heard it! It is a technique explaned to a friend of mine by Joseph Habbermin. I have used it on several tools (Hot cutters and chisels) with great result. I don't profess to know a great deal about steel types and hardening techniques but for what I have used these tools for they have been exceptional and hard. Quote Link to comment Share on other sites More sharing options...
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