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Farrier Rasp Steel Type ?


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I recently forged some wrap & weld hawks from farrier's rasps. Would someone know a proper quenching and tempering method for that type of steel? One I quenched in motor oil that didn't harden enough to skip a file, but I don't necessarily need that hard an edge for a throwing hawk, do I? I've been tempering with a propane torch to a bronze type color. Thanks, John

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i no longer even think I know how to harden a farriers rasp until I take off a piece from the rasp I want to use and test it. Here is why: years bacek I needed a small pice so I heated a rasp up and quenched in water. Then I smacked it flat on the anvil with the piece I needed hangin off the far side. It bent over like mild steel, Likely as said above it was case hardened and not high carbon steel...

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Rich, That's interesting. I didn't try water quenching because I thought it would cause the steel to be become very brittle. The hawks I did took a good edge. I was suprised the files didn't become very hard prior to tempering. Thanks, John

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You mentioned quenching in motor oil but didn't say if you warmed the oil first. Nor did you mention the weight of the oil or how you determined the temperature of the steel when quenched or if you soaked the steel.
Room temp oil is a slower quench than warm (about 120-140 F) oil. Light weight oils are faster than heavier oils.
Quality rasps that I've played with have been very similar to 1095, although one required a soak to harden. And some are case hardened which may not harden in water.
You may have had only partial conversion to martensite if they held some kind of edge which may indicate
1 that steel needs a soak
2 that steel needs a faster quench
3 that steel doesn't have enough carbon to get harder
4 you didn't hold your tongue correctly when quenching
5 you didn't get the steel to the quench fast enough (1095 needs to be quenched in something under 1 second)
6 or something I'm not thinking of off the top of my head.

ron

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Bellota rasps (Spanish) are the hardest I've seen. The problem with a hard rasp rather than case hardened is the likelyhood of breaking if you drop it on the ground and it gets stepped on. I've also seen farriers break a Bellota hitting a horse with it, but they deserved to learn a lesson by breaking a $25 rasp. Most of us prefer the case hardened ones.

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Ron, Thanks. I'm useing new 30 weight motor oil. Its probably fairly cool as it's outdoors. I quenched when the steel became non-magnetic. I was in no particular hurry to quench, but I didn't take more than a few seconds. I don't even know what a soak is. Farrier rasps aren't exactly falling out of trees like crab apples around here, so I have to use what I can get. I'm going to try again today if it doesn't rain too hard. Thanks for the assist. John

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the rasps i get given which i turn into draw knives and steel strikers all harden well in water at non magnetic, the draw knives i then put a near edge and polish, heat a 2"x2" bar to white heat place the back edge of the blade on the block and watch the colors run up to the edge removing when it gets peacock blue air cool and sharpen. this seems to soften the back to allow flex but it takes and keeps a very good edge. good enough to work seasoned welsh oak and elm. hope this helps . the rasps are (save edge usa)and(mercury)

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I've never used motor oil. I use old cooking oil myself. I warm it to around 120 (warm to the touch). Today's motor oil has a lot of additives. Don't breath the smoke it you use it.
Non-magnetic is a good starting point if you don't know to look for the decalesence (not sure on that spelling, the steel darkens for a moment as it undergoes the phase change) but you have to catch the non-magnetic point as it heats not as it cools.
If you rasp is something like 1095 you need to get the temperature down from non-magnetic to below 800-900 F in under 1 second to get as much martensite as possible. In other words, don't dawdle.
A soak is merely holding the steel at temperature (non-magnetic) for a while. Hard to do well in a forge, easy in a heat-treat oven.

ron

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Mr. Grufty, I just checked my rasps. They are save edge USA. Guess I lucked out on that. I like your tempering method. Very interesting. I don't think I need nearly so hard an edge on my hawks as on a draw knife. If I tempered to a violet color with a propane torch, do you think that would achieve an appropriate hardness for a hawk? Would a slower oil quench give me a less brittle result? Ron, I'm glad you told me about needing to hit non-magnetic on temp rise. I haven't been doing that. Perhaps that's part of my problem. Its also difficult for me to get a uniform temperature on the entire blade. The tips of the edge of the blade heat and cool more quickly than the rest of the blade. I know this is a lot of questions. I really appreciate the help. John

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A slower quench will result in less austenite converting to martensite. This likely will be less brittle, but as martensite is what makes it possible to hold the edge it won't be as sharp or stay as sharp as an edge with more martensite. Untempered martensite is very brittle, tempering it makes it less so. A better edge will be had by tempering to a higher temp to reduce the brittleness.

Non-magnetic on cooling is a bit cooler than on heating, you may not have been quenching while the steel is still fully austenic.

How are you heating? Torch, forge (solid fuel or propane), something else?
If you are using a forge a muffle pipe can help getting an even heat. The tang end can me preheated to 800 or 1000 F before heating the rest so it come to heat at the same time as the tip or the tip can be cooled before it gets too hot to slow the heating of the tip.

Have you read the stickies on heat treating under knies?   link removed do to relocation, see the knife reference section

That may help with your questions.

ron

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Ron, I'm useing a propane forge . I've been tempering with a propane flame, either a torch or if needed the hotter flame on my kitchen stove. Neither will reach tempering temps with my larger heads. I'm considering trying to temper with either map gas or acetelyne, if needed. Is this a good idea? I tried tempering in an small electric oven, for 2 hrs , 3 times. It didn't seem to do much. By a muffle pipe do you mean a 3 or 4 inch diameter steel pipe to place my hawk in to kep it from the direct heat of the forge? I will read those stickies . Thanks Again, John

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Yes a muffle pipe is a pipe placed in the forge to even the heat on the blade. I don't find it as necessary in a propane forge as in a solid fuel (coal or charcoal) forge. You may be able to adjust the temperature of your forge by adjusting the propane / air mix. If you can reduce the propane to a point that the forge holds stable at the correct temperature for quenching (around 1500 F) you won't have to worry about overheating.

For tempering you only need to reach between 300 and maybe 600 F for simple steels depending on the desired result. You should be able to reach that with any propane torch. For tempering you don't need to have the whole piece reach temperature at the same time. I've tempered springs to 550 F in my kitchen oven before and a lot of people use toaster ovens for tempering.

ron

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  • 7 months later...

Why are many rasps case hardened? For a number of reasons, Farriers often just drop a rasp on the ground as they reach for another tool. If a horse steps on one that is hard clear through, it's apt to break and $25 or so is quickly history. Bellota is or at least has been hardened clear through. Haven't used one in a long time. Maybe a manufacturer would give you info on the steel. Wouldn't hurt to call and ask.

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