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Tempering questions


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Do you mean before hardening? In between hardening and tempering the only thing I do on the blade is file test the edge & hand rub one side with 320 grit paper just enough to see bare steel for tempering colors. If I have any minor warping I grind out after tempering. Anything major & I anneal and start the heat treatment all over again.

 

How much I do before hardening the blade depends on the thickness of the blade. 1/8" or thicker I do all the profiling and grind the bevels leaving edge thickness of about a dime. Thinner than 1/8" I grind to shape but don't grind the bevels till after hardening & tempering.

 

As for the finish of the blade before heat treating, I go to 320 grit, but 220 grit is just fine.

 

Hope that helps

 

Dave Armour

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In general I get pretty close to the final shape before I harden and temper. I will have the final profile, minus any last minute adjustments after tempering, and grind the primary bevels down to about the thickness of a dime or a little less. Then harden and temper before doing the final grind to bring the bevels closer to finished product and remover minor warping as Dave said. If I have worse warping than that I shim and clamp the blade to a length of angle iron to counter bend the blade and repeat the tempering cycle. I've had to go up to three trials to get the bend out of a blade once but one time usually gets it.

 

If that doesn't work, normalize, straighten at a dull red, then repeat the heat treatment.

 

Doug

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I think we have a terminology issue.

 

Heat Treat: Hardening or often HT. This is heating the blade and quenching it to harden the blade.

 

Tempering: Re-heating post HT to relieve stress and trade off hardness for toughness.

 

Before HT I grind the edge blade so that the edge is a fairly even thickness and about .100, I cut the shoulders, drill the tang and finish to about 100 grit. I don't go farther because at that thickness there is still a bunch of grinding to do. For blades less than an 1/8 th I don't grind the bevels at all, I just profile and cut in any features that will be hard to do in hard steel.

 

Geoff

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I did mean tempering, but I guess the same question would apply to hardening. I am rough grinding my profiles and then hardening. Then I am finish grinding my blades almost to final proportions before tempering. Then I am finishing up my polish or finish. I guess I was mainly asking how think or unfinished a blade could be and still temper? Could i harden a rough ground blade and follow that with a temper and then finish the blade?

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yes, you should temper at least once immediately after hardening - untempered martensite is under a lot of stress, and can crack just sitting on a bench, or from the pressures from grinding, let alone if you drop it. plus it's a lot easier to grind and polish after tempering...

 

overheating during grinding doesn't care whether the blade has been tempered or not - it's the hardening that gets ruined, by over tempering.

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No one has mentioned it, so...

 

Oven dials are very inaccurate, of the 3 I've tested they were off by as much as 50 degrees. I strongly suggest getting a good oven thermometer and going by that, not the dial. Let the oven come up to heat before you put the blade in, and it is advisable to wrap/coat the blade in something to help even out the heat... A pan of sand, or even wrapping with foil helps.

 

I temper the blade at least twice, sometimes more (especially if I'm straightening a warped blade), and each tempering cycle lasts 2 hours. Between cycles I cool the blade under running water, then pop it back in the oven for the next cycle.

Edited by GEzell
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No one has mentioned it, so...

 

Oven dials are very inaccurate, of the 3 I've tested they were off by as much as 50 degrees. I strongly suggest getting a good oven thermometer and going by that, not the dial. Let the oven come up to heat before you put the blade in, and it is advisable to wrap/coat the blade in something to help even out the heat... A pan of sand, or even wrapping with foil helps.

 

I temper the blade at least twice, sometimes more (especially if I'm straightening a warped blade), and each tempering cycle lasts 2 hours. Between cycles I cool the blade under running water, then pop it back in the oven for the next cycle.

See, that is very good to know. I will have to try that.

 

Oh yeah! Some bricks in the oven help too. Wrap them in foil first, and don't ask me how I found out...

 

They keep the temperature more even.

I am assuming the wrapping of the bricks helps them if they break or shatter?

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That, and it keeps the oven clean so you will be allowed to use it again if the bricks are not sterile the first time... ;) Trust me, the womenfolk are NOT pleased if they come home to a house full of hot oil fumes and an oven that looks like you've been making mud pies. :lol:

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I have a thin fire brick for the toaster oven to act as a heat sink and even out the temperature, and a couple pizza stones in the big oven for larger work - one above, one below what's being tempered.

 

My wife complained about the oil smell once, then I showed her the check the knife brought, and she quit complaining... but I do try to get most of it off first. :)

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Hi guys,I need a little help,I don't have the option to temper after harding,I got the shape of my blades the way I wanted them, quenched them in oil ,then lightly grinded off any scale on them and then put them back in the forge touched them up and then quenched them in oil again (5160), then I grinded them down with a belt grinder to/with 120grit to the shape I want, before I do my final polishing on them,I want to temper them in the oven,I can't harden them and then temper them right away because the forge in way down back of my house (my dilemma ) when I was belt grinding them I was very careful that I did not over heat the steel at all.

So I have been looking for a straight forward answer on Google and everywhere ells it seam's,

So my question is how long do I temper 5160 steel,the blades are ranging from 14in to 20in long and 3/16th thick with a beveled edge???

 

I hope you guy's can help me? :)

P.S.

I did Google it,not straight forward enough for me and I was looking on are site also :)

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First of all, what kind of a forge do you have? Do you have a gas forge or are we talking about an electric kiln that you heat blades with? If it is a gas forge, you should not be operating inside your house. If you have a kiln, what kind of a temperature control does it have? All this will make it easier for us to be able to help you out.

 

Doug

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Cook - temper for an hour at a time, minimum, at least 2 times. but from your post, it seems like tempering may be the least of your problems - it sounds like you are forging to shape, then quenching in lieu of any normalising, then bringing it back up to forging temperature, eliminating any benefit from the first quench, then quenching again, then grinding to shape, then polishing then tempering?

 

a better process would be to forge to shape, then let it cool and check what else needs done. heat it up and tweak anything that needs tweaking, then normalise at least twice. grind to shape, and to quenching thickness. normalise once more, then heat to critical and quench. then take it home and temper 3x 1hr, and call it a day. you should be heat treating in low light anyway, so you can see the transformation to critical. do the final grinding/polishing etc the next day.

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@Jake,soory for the miss conception, I normalized one time with out doing anything to the steel,then the 2nd time I put a shape on it and let normalized,3rd time tweaked ,and then normalized. Then I heated to critical temp tweaked and quenched, did that 3x.

 

Then I started to grind on it and went up to 120grit sand paper

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Without a tempering cycle immediately after the heat treat, you risk cracks from internal stress, and if you were to drop the blade on a hard surface, like a benchtop or worse, the floor, it could shatter like glass. You really should temper it right after the quench.

 

If I read your post correctly you do a normalize before forging? Why, if I may ask? You don't get anything from it. I also don't think you get much effect from a triple quench in 5160. OTOH, I also thought (until a couple of years ago) that a triple quench in 1080 didn't have much effect, and I was wrong about that.

 

In real high stress blades in 1080/84, like competition blades, I do 3x normalize after forging, and 2x after rough grinding, just before HT, and these days I would do 3x quench as well, and then 3x 2hrs temper soak at about 400-425 F.

 

Geoff

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@Geoff,thanks, I'm in the middle of the process now, I have to blade's that they are just plane iron,I had them shot/scanned or what ever you want to call it (experimenting with them).

 

I have read so much in the past three day's my eye's went crossed :blink:. Its seam's everybody dos it just a little different,when it come to the soak time and how many times. As soon as there done I will post pic's of them in show an tell. If all goes well I will have them done in a month or so :)

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