Leaf springs for a knife

T

ta2edfreak

Member
Now that I have your attention, please hear me out. I don't use leaf springs or lawnmower blades or anything like that to make knives. I have made a small one out of a coil spring but just as play with my new forge. My question is why can't someone use leaf springs or coil springs to make a knife? Im not talking about annealing them, bending straight and using stock reduction to make it. I know about micro fractures and cracks, memory retention and such. However, if I normalize the steel a couple of times, then bring it up to welding heat and lightly tap all over as if I was making damascus or layered steel, would this close all those micro cracks?

There have been a couple of threads that talk about steel having memory until you get past critical temp. Considering that forge welding temp is well above critical, would this not effectively erase that memory? I have no intention of using found steel for knives but i would appreciate it if someone could discuss whether this method has value or not. Do the cracks close up? Does the memory erase? Whether the steel is actually good for a knife or not is irrelevant, you can tell people all day that it isn't good for them but they will do it anyway, and they have just enough info to be dangerous. However if you can explain to them metalurgically, it might get through.
 
Talking about memory in steel can open a real can of worms. Some hold that it is an absolute fact. Some hold that it's an old wives' tale and that once the steel is heated to above critical temperature the temper of the blade is erased and the crystals reform and so does the grain. I'm in the latter camp.

If you want to use mystery metal for making knives, old springs are probably the safest bet for getting something that has enough carbon in it to make a serviceable blade from. Just remember that bronze can also be used to make springs from but if you can't figure which is which, you've got problems. It sounds like you've done your research and know what you're up against. If you want to take the time to break the springs down, forge blades from them, and figure out the heat treatment then go for it. I would start out with the assumption that the steel is hypoeutectic and austinize to about 1500° then quench in warm oil and temper at 375° and test for proper hardness as a starting point. If that is too soft then you may want to repeat the hardening, this time trying to hold the blade between 1450° and 1500° and soak at temperature for about 5 minutes then re-quench and temper at 375° again and test the edge. If it comes out too hard in either case you can then just grind out any chipping that occurs and temper at 25° higher. Just accept that you may end up having to play with the heat treatment for a while to find the right mix.

Doug
 
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I have a knife made out leaf springs out of an old military truck, I was in the Marines in 1984- stationed in Camp Swab, Okinawa, Japan. I took the broken leaf spring to a Japanese Black smith, and he made a Bolo type knife, 17 inches long - it's double edged, one side is for cutting, the other side for chopping. Wood handles- Ugly Knife but it works. heat treated - very HARD, a File will not scratch it, very hard to resharpen. I wish I had pictures. love that knife.
 
Making a knife from them is irrelevant, my question remains, does the work at welding heat close the micro fractures and normalization erase the spring memory?
 
The work at welding heat usually will not close the fractures as the fracture has oxidized and won't weld,as for memory I'm in the camp that believes good nomalizing will eliminate any memory.Just my .02
Stan
 
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