Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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Knifemaker / Craftsman / Service Provider
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In a recent discussion I referred to a properly heat treated and tempered blade. I was asked to elaborate on how to obtain such a blade. So, here is an excerpt of the reply:
..."When I say properly heat treated and tempered, I mean using the standard quenching methods that the type of steel would require, and then tempering to a desired hardness. Drawing the spine with a torch after tempering will make for a tougher blade with a harder edge. The combination of all the HT segments makes for a PROPERLY done blade.
If you are having trouble with edges dulling and rolling, the temper is probably too high, or the quench is not sufficiently fast to fully convert the austenite to martensite. Lets break it down into how to get a hard edge and a tough body:
Start with the steel. It has to be picked for the task. For the parameters we are looking for here ( a small sword in this discussion), a 10XX steel will be good. It will allow for a high degree of hardened edge, and can be differentially tempered. I would use 1084 ( or anything from 1070 to 1084) as a first choice, and 5160 as a second choice.
Next, look at the quench. Is it fast enough for 10XX steel? If it is a fast quenchant, like Parks/Heatbath #50, then it should easily convert the steel. If it is a slower quenchant, like ATF or some common oil, perhaps using a deeper hardening steel (like 5160 or O-1) would be a better choice.
The actual quench - Is it being done smoothly? Is the oil warmed to 130F? Is the steel being heated to the right temperature ( around 1450-1475F) and held at that temperature evenly for several minutes? Is the edge being overheated? ( this is the cause of most bad edges).
The temper - Is the oven accurate? Are you doing two ,two hour tempers? ( cooling to room temp between tempers). Is the temper being done at too high a temp?
For a differentially tempered blade, start with a slightly lower than desired temper, about 350F. Temper the blade completely. Test the edge on a brass rod - Grind a quick edge on the blade. Set the blade edge on the brass rod (1/4" rod works fine) at about a 30 degree angle, and press the blade down slightly - flexing the edge a little. If the edge chips, the temper needs to be done one more cycle at a temperature about 10 degrees higher. If the edge flexes and returns to straight, the temper is just right. If the edge bends and stays bent, the temper is too high, and you will need to re-do the quench and temper at a lower temperature. Sneak up to the right temper temperature by raising the temp 10 degrees at a time until you get a good edge. It may take two or three more temper cycles to get the right edge. Once you have done this, you will know the temperature that your equipment and procedures will require to get a well tempered edge. It will be different with other people and other equipment, so do this test regularly to keep on you best performance.
At this point the edge will be hard, but durable. It should not roll over, nor should it chip out unless hit on something too hard. However, the entire blade is the same hardness. While that is fine for a small blade or a fillet knife, it is undesirable in a sword or larger knife.
Differentially tempering - Take the tempered blade, which now has the perfect edge. Sand it to make the metal shiny (220-400 grit). Get a shallow pan that can hold 1/4" of water ( pizza pan or cookie pan). Put 1/4" of water in the pan. Set the blade in the pan with the edge sitting in the water. While drawing the spine temper, you will rock the blade toward the tip often, to keep the tip cool. Using a small torch, slowly run the flame along the spine to heat it up . Go from the tang toward the tip, stopping about 1" from the tip, and reversing direction.Watch the color as it starts to change and the color moves toward the waterline. The yellow/bronze color is the one you are watching. There may be much darker bluish colors forming at the spine, that is good. Don't overheat the spine and make it red, though. The trick is to gently heat the spine and blade body to about 500-550F. This will make it much tougher. Since the edge stays in the water, it never gets above 212F, and its temper is unchanged. The result is a harder and stiffer edge with a softer and springier back. Done right, this is a hard to beat combination.
Testing the blade - The brass rod test should have been done in the tempering stage, so now it is time to performance test the edge.
This starts with a properly sharpened edge. If the edge is for a sword ,it should be robust and at a higher angle (often convex). If it is a fillet knife, it should be flat ground ( or hollow ground) and at a very acute angle. Just because a knife is sharp doesn't mean it will do everything, so make the edge right for the job. Once the knife is sharpened, it is time to test it. While it is impressive to chop on paint cans, hack at trees, and such, it tells you little about the knife's abilities ( unless it is a crash axe or a brush chopper).
Test one - Get a length of 3/4" sisal rope, and lay it down on a piece of soft plywood. Make repeated cuts through the rope, continuing until you get bored or the knife slows down in cutting ability. Look at the edge with a magnifier. Is it worn to a rounded edge or still in fairly good shape?
Test two - Try cutting up cardboard. Make a couple dozen cuts through a cardboard sheet with a freshly sharpened edge. How does it do? what damage has the edge suffered?
Test three - If the blade is a chopper, chop up a pine 2X4 and look at the edge for rolling or chipping.
(Note: If the blade is a sword, doing cutting tests on rolled mats and many other things is a standard practise.....but you should not do sword tests without proper training and experience! Done wrong, the results can be misleading, and serious injury may result.)
The results of these tests will tell you if your HT is getting the results desired. If the edges are rolling, use a faster quench and/or a lower temper. If they are chipping, raise the temper, or look at the possibility of overheating when austenitizing...."
Hope this helps.
Stacy
..."When I say properly heat treated and tempered, I mean using the standard quenching methods that the type of steel would require, and then tempering to a desired hardness. Drawing the spine with a torch after tempering will make for a tougher blade with a harder edge. The combination of all the HT segments makes for a PROPERLY done blade.
If you are having trouble with edges dulling and rolling, the temper is probably too high, or the quench is not sufficiently fast to fully convert the austenite to martensite. Lets break it down into how to get a hard edge and a tough body:
Start with the steel. It has to be picked for the task. For the parameters we are looking for here ( a small sword in this discussion), a 10XX steel will be good. It will allow for a high degree of hardened edge, and can be differentially tempered. I would use 1084 ( or anything from 1070 to 1084) as a first choice, and 5160 as a second choice.
Next, look at the quench. Is it fast enough for 10XX steel? If it is a fast quenchant, like Parks/Heatbath #50, then it should easily convert the steel. If it is a slower quenchant, like ATF or some common oil, perhaps using a deeper hardening steel (like 5160 or O-1) would be a better choice.
The actual quench - Is it being done smoothly? Is the oil warmed to 130F? Is the steel being heated to the right temperature ( around 1450-1475F) and held at that temperature evenly for several minutes? Is the edge being overheated? ( this is the cause of most bad edges).
The temper - Is the oven accurate? Are you doing two ,two hour tempers? ( cooling to room temp between tempers). Is the temper being done at too high a temp?
For a differentially tempered blade, start with a slightly lower than desired temper, about 350F. Temper the blade completely. Test the edge on a brass rod - Grind a quick edge on the blade. Set the blade edge on the brass rod (1/4" rod works fine) at about a 30 degree angle, and press the blade down slightly - flexing the edge a little. If the edge chips, the temper needs to be done one more cycle at a temperature about 10 degrees higher. If the edge flexes and returns to straight, the temper is just right. If the edge bends and stays bent, the temper is too high, and you will need to re-do the quench and temper at a lower temperature. Sneak up to the right temper temperature by raising the temp 10 degrees at a time until you get a good edge. It may take two or three more temper cycles to get the right edge. Once you have done this, you will know the temperature that your equipment and procedures will require to get a well tempered edge. It will be different with other people and other equipment, so do this test regularly to keep on you best performance.
At this point the edge will be hard, but durable. It should not roll over, nor should it chip out unless hit on something too hard. However, the entire blade is the same hardness. While that is fine for a small blade or a fillet knife, it is undesirable in a sword or larger knife.
Differentially tempering - Take the tempered blade, which now has the perfect edge. Sand it to make the metal shiny (220-400 grit). Get a shallow pan that can hold 1/4" of water ( pizza pan or cookie pan). Put 1/4" of water in the pan. Set the blade in the pan with the edge sitting in the water. While drawing the spine temper, you will rock the blade toward the tip often, to keep the tip cool. Using a small torch, slowly run the flame along the spine to heat it up . Go from the tang toward the tip, stopping about 1" from the tip, and reversing direction.Watch the color as it starts to change and the color moves toward the waterline. The yellow/bronze color is the one you are watching. There may be much darker bluish colors forming at the spine, that is good. Don't overheat the spine and make it red, though. The trick is to gently heat the spine and blade body to about 500-550F. This will make it much tougher. Since the edge stays in the water, it never gets above 212F, and its temper is unchanged. The result is a harder and stiffer edge with a softer and springier back. Done right, this is a hard to beat combination.
Testing the blade - The brass rod test should have been done in the tempering stage, so now it is time to performance test the edge.
This starts with a properly sharpened edge. If the edge is for a sword ,it should be robust and at a higher angle (often convex). If it is a fillet knife, it should be flat ground ( or hollow ground) and at a very acute angle. Just because a knife is sharp doesn't mean it will do everything, so make the edge right for the job. Once the knife is sharpened, it is time to test it. While it is impressive to chop on paint cans, hack at trees, and such, it tells you little about the knife's abilities ( unless it is a crash axe or a brush chopper).
Test one - Get a length of 3/4" sisal rope, and lay it down on a piece of soft plywood. Make repeated cuts through the rope, continuing until you get bored or the knife slows down in cutting ability. Look at the edge with a magnifier. Is it worn to a rounded edge or still in fairly good shape?
Test two - Try cutting up cardboard. Make a couple dozen cuts through a cardboard sheet with a freshly sharpened edge. How does it do? what damage has the edge suffered?
Test three - If the blade is a chopper, chop up a pine 2X4 and look at the edge for rolling or chipping.
(Note: If the blade is a sword, doing cutting tests on rolled mats and many other things is a standard practise.....but you should not do sword tests without proper training and experience! Done wrong, the results can be misleading, and serious injury may result.)
The results of these tests will tell you if your HT is getting the results desired. If the edges are rolling, use a faster quench and/or a lower temper. If they are chipping, raise the temper, or look at the possibility of overheating when austenitizing...."
Hope this helps.
Stacy
