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Finishing a railroad spike knife6/24/2023 Apply pressure on the edge to try and flex it, if the edge folds, you know that you tempered too much, if the edge chips, you know that the blade needs to be tempered at a higher temp, if the edge flexes and returns to true, you know you have a good temper. Sharpen the blade, then take a brass rod, clamp it in a vice and place the edge on the rod. Something you can try is what is known as an edge flex test. You can always start lower and work your way up. I would say that about 300F would be about as high as you would want to go. For a through hardened spike knife like you have made, you will not have to temper very much due to the lower carbon content, since the blade will not be as hard to begin with, you will not have to reduce the hardness as much inorder to impart the necessary toughness. If you differentially heat treat a blade (harden only the edge) you may not have to temper at all. For example, a sword must be tempered to a higher temperature than a small knife, this is becuase the sword will see greater stress than the knife and must therefore be softer than the knife in order to absorb the additional stresses. Tempering temperatures vary depending on steel of course, blade length, blade uses, and hardening methods. 535 F is far too hot for a tempering temperature for such a low carbon steel and is really too hot for most blades and steels. Following the hardening quench that is when you temper the blade. It still won't be up there with a good high carbon steel, but every little bit counts. With the HC railroad spikes, in order to gain maximum hardness use the fastest quench you can, cold water will give you some hardness, but a brine quench will give you a little more. After the last normalization cycle, there is no need to anneal, just go for your final heat and then hardening quench. You will probably want to do at least 2, 3 for good measure, and anything after that probably won't make much of a difference. I usually do about 3 normalization cycles. After you finish with the rough grind, then normalize the blade. You want to anneal it to make it easier to work as you grind and file it. When making a blade, after you finish your rough forging, normalize the blade one or two times, then anneal it. You won't really be gaining anything from that except extra practice. 3% carbon.Īs far as you heat treat steps go, it is unnecessary to harden the blade, then re-anneal, then re-normailze, then re-harden.
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