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Clayton M.

Dumb Question about tempering

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I've spent quite a bit of time looking on the heat treating forum and on other forums on this sight. I can't figure out a general tempering time for a knife. 

I know a guy who used to make knives for TOPS Knives and he said that the knife i made would probably take anywhere from two to three hours to temper. I'll post a picture of the knife when i can find a picture of it. I also don't know what kind of steel the knife's made of. The steel came from an old style pitchfork and that's all i know about it.

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Sounds like it's most likely a simple high carbon steel, probably 1070 to 1095, posibly W1.  Or it could be anything really.

 

It's a good idea when heat treating knives to do at least 2 temper cycles.  Long complicated story, but basically after the blade cools down from the first temper you wind up with more martensite forming and since it formed post temper it's untempered and potentially brittle.  A good rule of thumb is 3 two hour temper cycles.  Also longer time at temp means you can temper slightly lower temp and still have the same flexibility with slightly better edge holding.

 

Being mystery steel you'll have to sneak up on the proper temper.  Best way is the brass rod test, sharpen and flex the edge, if it chips raise your temper 25 deg.F. and temper again until it stops chipping.  If it stays flexed or bent, you went to soft and will have to re harden.

 

I have played with a lot of mystery steel and have learned a lot from it, but have had a lot of failures while learning also.  This is one reason I highly recommend new makers to use known steel, cuts down on frustration.

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If you had continued to scroll further down the main page, you would have notived that we have an entire section here about knives, since the thin sections require different treatments than most other smithing shapes do.  Perhaps you could have a look through it and find your answer.  I will relocate this post to that location to make it easier for you to find it.

 

Welcome to I Forge Iron

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I did my first 2 hour temper the other day, a friend gave me an old toaster oven. Hammered out a blade from tool steel, cranked the beast up to 450 and left it in there for 2 hours. Came out a beautiful straw color and took a wicked edge! I just always assumed 2 hours was a good rule of thumb, depending on the steel type. 

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My problem is that i don't think my piece will fit in a toaster oven, the knife measures 12 1/2 inches long from handle to blade. I could use a kitchen oven but i'd like to avoid doing so just because i fell that it would be a waste just to do one piece. Anyways here are the pictures of my knife, i know it may look a little weird bit there wasn't much steel to work with, and it is my first piece.

post-55159-0-35605200-1408631168_thumb.j

post-55159-0-45231800-1408631220_thumb.j

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Go ahead and put in your regular oven...pretend you're baking a cake.

 

I use my wife's oven all the time...no problems.  Maybe next time I'll get her to stick a cake in it along with the steel; might as well conserve some energy  :)

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My problem with using a kitchen oven is this, i quenched the blade in motor oil and when i ground the carbon off the blade to get it ready to temper i could taste and smell the motor oil. It's not a pleasant taste and i don't want to have to smell the rest of the residue that i wasn't able to get off the of the blade. Otherwise using the kitchen oven would be a wonderful idea and i would do it except for the motor oil. I would do it if i didn't live with my parents and had my own place but i don't.

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I wouldn't want the burning oil in my own home; let alone my parents'. Hot soapy water will remove the oil. Its okay, dry it off with a paper towel so it won't rust. The hot soapy water gets the black of your hands at the same time ;)

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I have a shift sale toaster oven in the shop and in fact smoked it up good yesterday tempering a new 4140 bottom die for the Little Giant. I gave it some 4 1/2 hrs. at 400f and the whole shop smelled like OLD fryer oil, still does.

 

I'm going to put the toaster oven outdoors under a cover next time. I've said that the last few times I've stunk up the shop. <sigh>

 

Frosty The Lucky.

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Thanks for the link Dave, got it bookmarked.

 

Frosty The Lucky.

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I have a shift sale toaster oven in the shop and in fact smoked it up good yesterday tempering a new 4140 bottom die for the Little Giant. I gave it some 4 1/2 hrs. at 400f and the whole shop smelled like OLD fryer oil, still does.

I'm going to put the toaster oven outdoors under a cover next time. I've said that the last few times I've stunk up the shop. <sigh>

Frosty The Lucky.


At least it was a benign oil. When I was first started to seriously smith (I was about 13 at the time) I was quenching in used motor oil. When I finally got something decent out of the forge, i went inside and used my mother's oven to temper it. Needless too say, she want happy with the results.

In hindsight, I don't know how she put up with me...

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After rethinking my earlier post it raises a question in my mind. To be fair I have only done 3 blades and a few tools, and I do all my HT either in my open garage or outside. I have never actually washed my materials and was suggesting it only to avoid the smoke and fumes while tempering indoors. I know you want to temper immediately after hardening so would washing even in hot water hinder the HT process? My apologies if anyone tried this with poor results. I sometimes speak faster than my gray cells work, but I try not to type in the same manner :o As a side note, the blades I did at home in my garage toaster oven didn't seem to give off any great amount of smoke or fumes that I recall but I did wipe off as much oil (I've been using new ATF) as possible...

 

Scott

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I've got another question for you guys. It's recommended to temper in three cycles of two hours each. If I temper a knife to light straw and then tempered it again would the oxidation colors change and spread across the blade?

 

I am assuming that the color would not change so long as you protect the knife from the full power of the heating elements. I assume that because it's also recommended to do at least two tempers before finishing off the knife.

 

Another thing to ask that's been bothering me. Can I "retemper" my blade after it's all finished to get back the oxidation colors of the blade?

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the oxide colors will not last, they wipe off easy.  To check colors of second and third cycles, just clean the blade off betwen cycles :)

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................... I know you want to temper immediately after hardening so would washing even in hot water hinder the HT process? My apologies if anyone tried this with poor results.........................

Scott

 

Sooooooo, would it??

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washing is advisable...  so sayeth my wife, who claims the kitchens gas oven I use, as hers.she hates the smell of oils baking too

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It is incredibly hard to temper without having a reference point from maximum hardness after ht to where you want to be on the rc scale without the aid of a rockwell tester. Anything less is just guesstimation. My suggestion for anyone serious about their blades is to find someone who has one, work out some temper times/temps and keep using the same materials until you are happy with the results. The key is consistency of the process imho.

John

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I went to temper another knife last night, and i was looking for a straw color on the blade and just twenty minutes in i pulled the blade out and the entire blade was purple. To protect the blade from the full power of the heating elements would two firebricks suffice?

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Brick are not necessary. Just a cookie sheet or even tin foil on the bottom rack to block the elements  However, I should first ask, how close to the elements was the blade and are you sure your oven temps are accurate? I use an independent thermometer as well as the oven's setting. My garage sale toaster is off by about 40º. A household oven can vary from one rack to the next. Middle is about average but you want to put thermometer on that rack to get a more accurate temp. Make sure oven is not on broil setting so top elements stay off

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I've got two elements one at the top and one on the bottom. I put the rack in the middle of the oven. I'm going to get a thermometer for it because I don't thinks it's accurate within 50 degrees. On bake the bottom element is and the top off and on broil it's the other way around. The problem with that is that I don't know at what temp bake is or broil is.

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Yes its standard in household ovens; Top element for broiling, bottom for baking. IMO best practice is to follow the laws of physics; heat rises. YMMV but using the 'Bake" setting should give more even heat. As the "Broil' setting is generally used with the food or what ever being broiled as close as possible without catching fire i.e. steaks and such, you aren't as concerned with overall oven temps as you are when you bake a cake (or temper a piece of steel ;) ) The temperature of an oven on broil (I'm guessing;never tested) could vary 100º from top to bottom due to that physics law thingy. I doubt the variance would be so great on bake. Hope this helps.

 

Scott

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