Tempering a chisel

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I had an apprentice make, harden and temper a chisel today. He did what I have always done, after he had forged it he dressed it up on the grinder and then heated the end red, plunged 1/2 of it in water and then cleaned it with emery quickly and waited till it turned straw and plunged it in the water.He had done a beautiful job of shaping it but when I looked at it there was a crack through, which subsequently broke off when I smacked it with a hammer.I had done several chisels earlier by this method without any problem. The only thing I can think of is that when he was forging he didn't have it hot enough and kept hammering when he should have had it back in the heat. Plus the chisel could still have been a bit red when he plunged it a second time Any suggestions?Clive
Reply:Suggestions?  Have him do it again.Maybe there was a material defect in the steel to begin with and the forging and hardening brought it out or made it worse.  Maybe he hammered the steel when it was too cold to flow and put the crack start in it.  Maybe, maybe, maybe.So, he does it again.
Reply:I have found water cools the steel too fast.  I had a situation of forklift ring gears going bad.  I worked for a dealer at the time.  I changed flywheels on a lot of machines.  Finally I had a freind with a Rockwell hardness tester.  I heated the ring gear to cherry red, and dropped it water, hydraulic oil and used motor oil.  The ones that went into the water were too hard.  The factory guy came around and asked me if we were having problems.  I said "Just look in the scrap bin".  It had a bunch of ring gears in it.  I heat treated quite a few in used motor oil.  If the guys replacing them heated them up too hot to install them, they didn't last anyhow.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:I figured if Clive is a blacksmith with an apprentice, he should know the difference between O1, W1, A2, or other steel alloys and whether to use air, oil, or water as the quenching medium.   But yes, too harsh of a quench or an inappropriate heat or quench can break the steel as well.At which point, you do it over and try again.
Reply:Originally Posted by MoonRiseI figured if Clive is a blacksmith with an apprentice, he should know the difference between O1, W1, A2, or other steel alloys and whether to use air, oil, or water as the quenching medium.   But yes, too harsh of a quench or an inappropriate heat or quench can break the steel as well.At which point, you do it over and try again.
Reply:usually water will cause it to crack unless its a water hardening steel, once you find out what kind of material it is you should be able to find out the specifics from the machinery handbook.  thats a bummer when you spend a lot of time and effort on anything only to junk it start over.  the only way to avoid ever having to do that is to never try anything.
Reply:I believe he should have quenched it in oil.  Thats always worked for me.  It could have been a defective piece of steel though.  I never used water, I was taught to use oil in metal shop.Hobart 140 Handler w/ gasHyperTherm Powermax 380 Plasmaoxy/acetylene
Reply:Use oil preheated to about 120F. Any kind SHOULD work.
Reply:Used motor oil.
Reply:I really should say any thick oil should work, thin oil isn't much fun.
Reply:Here is a great source of information on all things related to blacksmithing. http://www.anvilfire.com/iForge/If you click the drop-down menu on the upper right and click FAQ's, then scroll down just a little you will find a very nice write-up on heat treating.Miller EconotigCutmaster 38Yes ma'am, that IS a screwdriver in my pocket!
Reply:my father was a tool and diemaker by trade, he taught me to use oil for quenching.  I still hav some of his needle files, they still work better than anything I've been able to buy today.
Reply:OK, I went back to the stores and asked what steel they got, they said "we couldn't get what you asked for so we got something else" my fault for assuming they would let me know of any problems. So I went to the supplier and it is AISI S1 which anneals at 760oC, hardens  860-900oC in "oil or hot bath 180-220oC(quote) according to their chart it is tempered at 550oC for 2 hours.We have an electric oven which goes up to 1200oC so that is that problem solved I hope. I will try it in oil at 180oC next week.Thanks for your help guys it is appreciated.Clive
Reply:WTF???  You ordered a certain steel from the supplier and they gave you something else instead?  With no mention or discussion of the  material change?That should be a BIG apology from them.If you -know- what steel you have, you can usually work it (forge, quench, temper, etc) it properly.  If you have something different than what you thought or ordered and use processes suitable for some -other- alloy, then all bets are off as to whether the outcome will be OK or whether you will end up with failure.Quenching a water-hardenable steel in oil isn't going to give you the desired properties.  Neither will quenching an oil-hardenable steel in water.  And air-hardenable steel would not quench properly in oil or water.So you asked for W-1 and they gave you S-1 instead?  Grrrr.  That should have them bending over backward to apologize for THEIR error.
Reply:Originally Posted by MoonRiseWTF???  You ordered a certain steel from the supplier and they gave you something else instead?  With no mention or discussion of the  material change?That should be a BIG apology from them.If you -know- what steel you have, you can usually work it (forge, quench, temper, etc) it properly.  If you have something different than what you thought or ordered and use processes suitable for some -other- alloy, then all bets are off as to whether the outcome will be OK or whether you will end up with failure.Quenching a water-hardenable steel in oil isn't going to give you the desired properties.  Neither will quenching an oil-hardenable steel in water.  And air-hardenable steel would not quench properly in oil or water.So you asked for W-1 and they gave you S-1 instead?  Grrrr.  That should have them bending over backward to apologize for THEIR error.
Reply:Ahhh, you keep leaving out parts to the story Clive.Anyway, S-1 tool steel is decent stuff.  Not super high in carbon (nominal about .5%), but has some tungsten and touches of chromium, vanadium, manganese, molybdenum, and silicon.  Hold at 1650F-1750F for 15-45 minutes, and then use oil for the quench.  Quenched from 1750F (955C) and then tempered at 300F (150C) should give Rc=58.  Temper at 500F(250C) and Rc=54.  Temper time probably 2 hours -after- the part reaches the temper temperature.S-1 (and the other S-grade shock-resisting steels) are listed as recommended for chisel usage, among other uses. Note:  my references indicate to AVOID a tempering temperature of ~500C.  At that temperature range you can run into "temper embrittlement".  And just because S-1 uses oil for the recommended quench medium doesn't mean other steels would use it.  S-2 is recommended to use water or brine as the quenching medium.Last edited by MoonRise; 10-26-2007 at 12:18 PM.
Reply:Originally Posted by MoonRiseAhhh, you keep leaving out parts to the story Clive.Anyway, S-1 tool steel is decent stuff.  Not super high in carbon (nominal about .5%), but has some tungsten and touches of chromium, vanadium, manganese, molybdenum, and silicon.  Hold at 1650F-1750F for 15-45 minutes, and then use oil for the quench.  Quenched from 1750F (955C) and then tempered at 300F (150C) should give Rc=58.  Temper at 500F(250C) and Rc=54.  Temper time probably 2 hours -after- the part reaches the temper temperature.S-1 (and the other S-grade shock-resisting steels) are listed as recommended for chisel usage, among other uses. Note:  my references indicate to AVOID a tempering temperature of ~500C.  At that temperature range you can run into "temper embrittlement".  And just because S-1 uses oil for the recommended quench medium doesn't mean other steels would use it.  S-2 is recommended to use water or brine as the quenching medium.
Reply:Clive,The hardness of the finished chisel has more to do with how quickly you quench(reduce the temperature) and the time and temperature of the second heat treatment step.The 2 options listed by Moonrise should produce a chisel that is plenty hard.  The first option(300°F for ~2 hours) will produce a chisel almost as hard as most files(Rockwell Hardness~58).  In my experience, files range from 58 - 64 Rc hardness.  My gut says 58HRc may be too hard, and make the chisel very difficult to sharpen.  I'd opt for the second tempering condition(500°F for 2 hours).  This will produce a very hard chisel with a tougher edge.  The Rc~54 hardness will be easier to shape with a standard file, and faster and easier to sharpen and hone.  It should still be hard enough to retain a good edge when used on most materials.
Reply:Originally Posted by A_DAB_will_doClive,The hardness of the finished chisel has more to do with how quickly you quench(reduce the temperature) and the time and temperature of the second heat treatment step.The 2 options listed by Moonrise should produce a chisel that is plenty hard.  The first option(300°F for ~2 hours) will produce a chisel almost as hard as most files(Rockwell Hardness~58).  In my experience, files range from 58 - 64 Rc hardness.  My gut says 58HRc may be too hard, and make the chisel very difficult to sharpen.  I'd opt for the second tempering condition(500°F for 2 hours).  This will produce a very hard chisel with a tougher edge.  The Rc~54 hardness will be easier to shape with a standard file, and faster and easier to sharpen and hone.  It should still be hard enough to retain a good edge when used on most materials.
Reply:A chisel for what?For a wood chisel for fine work, I'd want it pretty darn hard and with a fine grain.  And a polished honed edge with microbevel.  Scary-sharp is just about right for a fine wood chisel.A brick chisel I'd want softer to lower the risk of cracking and chipping the chisel.You -could- temper at the 300F setting and then see how the chisel works for you at the Rc=58 hardness.  If too hard, you could go back and retemper at 500F to lower the hardness to Rc=54.And the 'proper' tempering temperature depends on the steel alloy, and the desired balance of hardness and toughness for the job.For 'fine' chisels and knives, I have gotten to the point where I prefer premium steel alloys and hard.  As in up by Rc=60.  Chisels and knives at Rc=52-54 seem pretty soft to me now.  But that's for knives and chisels cutting 'soft' things.  For a tougher blade or edge for rougher usage, I might go for that Rc=52-54 hardness, but still with a good steel (for the fine grain or other characteristics the steel might have).And each steel has an upper hardness limit and a different balance point between hardness and toughness.  M2 or D2 knife blades are nice at Rc=60-62, it would generally be silly to temper them down to Rc=52 for a knife or chisel.Last edited by MoonRise; 10-29-2007 at 02:12 PM.
Reply:Originally Posted by MoonRiseM2 or D2 knife blades are nice at Rc=60-62, it would generally be silly to temper them down to Rc=52 for a knife or chisel.
Reply:minor hijack by JimJim, they are alloy steels.  Just like clive's batch of steel that he ended up with was S1 steel.  When what he used to have or thought he was getting was something like W1 (or W-1).
Reply:Sorry 'bout the hijack, just that I have a WWII army knife and it is labeled M2 Imperial.Jim