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One temp fits all anneal.... and heat treating for helper tool

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Ok, new to blacksmithing and definately new to heat treating. I have a couple of projects where I need to heat treat. Fist off I want to make some simple tools such as a hand held butcher from old files and like. I want to anneal first. I beleive I sould heat up to critical temp using a magnet to test. Then cool slowly. I do have an electric kiln with computer controlled ramp / soak controller (used for glass work mainly) that I could use. Because I will not know the grade of steel can I just heat up to the higher end of temps for annealing and cool slowly in a kiln instead? It looks like the higher the carbon content the lower the temp. Can I anneal say somewhere in the range of say 1450 to 1500 without the the magnetic test and get satisfactory results? I.e. if it was W1 steel that lists anneal temp as 1375 to 1400, what is the implication of holding at 1500 for 30 mins and cooling off slowly from there? I would still be going through the annealing temp at a slow rate regardless of the carbon rate. 


I ask this because putting multiple pieces of steel in the kiln sounds easier than cooling slowly in a bucket of lime or similar. By the way, I don't really want to open the kiln and do a nagmetic test when hot as this does not do the kiln bricks a lot of good.


Hardenning is another issue as I don't know what to quench in. I am guessing that air hardenning seel is unlikely from the scrap I am likely to be using but I could try air hardenning and taking at it with a file just to be sure. I was thinking of just trying oil. Pressumably if the steel was supposed to be water hardenned then I would just end up with a tool that was not properly hardened, is that correct, as I am not making mission critical components then this would be OK? Obviously I don't want a hand tool to shatter when in use so water quenching an air hardenning steel sounds like a bad idea.


Tempering will be done on a steel plate over a coke forge  by colour.


Right, now that one is out of the way, I plan to make a blacksmith's helper tool. I have some annealed O1 25mm x 50mm x whatever stock for the dies.


I plan to:


1) Size and shape the dies.

2) Harden by quenching in oil. Question - should I harden the whole die (yes I think on the bottom as its only about 1.5" loing - on the top it will be abount 100mm long so I could only quench the bottom inch or two - this sounds right to me?) 

3) Then stick weld on a striking button of mild steel

4)  Then temper - again I hope to do this in the kiln and for the dies I will know the steel grade so I can set a precise temp in the kiln


Anything wrong with the above sequence? Any other tips?


Sorry for all the dumb questions - new at all this.



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Oh, another question if I may. For both the butcher tool and helper dies what sort of hardness am I after. Will light straw be appropriate which I beleive is about 445F? Reading up the soak time should be 1 hour for 1 inch + 1 hour from what I can make out. Just to be sure I will leave it a bit longer.


Cheers, BM.

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temper depends on the alloy and the use and the preferences of the user.  Straw for O-1 seems awfully hard for a tool working hot steel as being buried in hot steel will draw it further in use.


Note that that cross sectional area makes a difference in quenching; some steels that are oil quench in 25 mm sq will be air quench at knife blade edge thicknesses; however in general you are safe going one quenchant gentler, (water => oil, etc).


Overheating steel is pretty much a bad thing; some steels tolerate it better than others; some can be "repaired" by subsequent heat treat.  In knife making especially we try to catch the right temperature on a rising heat and not overshooting and catching it on a falling heat.

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Hi Steve,


I have done some reading, my baseline would have been even lower otherwise :(


There is a lot of contradictory info out there so I wanted to get some idea if I was on the right track. I take it from your comment that I am completely lost and wasting everyone's time so apologies to all. The trouble with trying to learn from internet is there is sometimes too much information and I don't know anybody locally who can actually show me.


Hi Thomas, OK, sounds like the one temp fits all anneal was a duff idea. Happy to use the magnet if that will get good results. As for the tempering hardness I will do a bit more research.



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Hi BM, Where to start?


Simple tools from old files and the like, OK, probably a carbon steel, so general rules apply.


W1 and O1 are tool steels, (highly alloyed steels), each with its own special properties and are all heat treatable in different ways, refer to makers recommendations.


Does your kiln cover the range 720*C to 950*C which is the upper critical range for the carbon steels, ?


Here are some guidelines from our toolmaking course with regard to general heat treament,


First off , understand the Terminology used in heat treating steel.


NORMALISE; ( or Stress relieving) Reduce the stresses introduced into the metal when forging or for other reasons, at the same time the grain structure is refined.


ANNEAL; To return the material to its softest state, similar to normalising, but a slower process.


HARDEN; To make the metal as hard by use of heat or working to enable steel to cut or resist wear


TEMPER; To bring the metal to a usable state.


NORMALISING is a heat treatment , carried out to relieve stresses in the metal caused by forging or cold working, at the same time, the grain structure is refined.

The material is heated to a temperature 30 to 50 degrees C above the upper critical point and allowed to cool in still air. Draughts should be avoided as they cause the steel to cool too quickly.


ANNEALING This is a heat treatment similar to normalising except the cooling is delayed.


This is done similar to Normalising. The material is heated to a temperature 30 –50 degrees C above the upper critical point and held at that temperature long enough to ensure a fully austenitic structure throughout.



The blacksmith does this by heating to a full red heat, allowing time for the heat to soak through and penetrate throughout the item.

The air is then turned off the metal completely covered with the hot coke and allowed to cool inside the fire overnight, alternatively the fully heated metal is buried in a heat retaining substance, such as vermiculite, dry ashes or dry sand, or lime


HARDENING To harden steel, the metal must be brought from hot to cold quickly , and this rapid rate of cooling is done by quenching


The more rapid the rate of cooling, the harder the steel will become, but care must be taken in choosing the appropriate quenching medium, because certain steels will crack if quenched too quickly, or if the item being quenched is of an intricate shape


The quenching medium is chosen according to the rate at which it is desired to cool the steel


For most steels we use oil or water, Water should be clean and fresh from a tap, warm water will give a much slower rate of cooling but will be somewhat more rapid than oil,


Warm oil is more rapid than cold oil, Mineral oils are more rapid than Animal oils, and Animal oils are quicker than Vegetable oils.




It must be heated to between 30 to 50 degrees C above the upper critical point and then quenched in the medium that will be produce the desired rate of cooling.


The medium used will depend on the composition of the steel and the ultimate properties required.


All components should be agitated in the medium during quenching.


A fully hardened tool steel is very brittle, and the stresses set up by quenching make its use in this condition inadvisable except in extreme cases. To relieve this brittleness a heat treatment called TEMPERING is carried out


This is done by reheating the steel after hardening to a temperature dependant on the work the steel has to do, such temperature always being below that of its lower critical point.


Tempering can be achieved by observing the colour of the oxide film on polished surfaces, but this colour temperature relationship is only applicable to plain carbon steels.


The colours are obtained by polishing a hardened component with emery stone or paper, then, with the application of heat, the oxide film on the surface takes on a light straw colour , which gradually develops or darkens and increases with the rising temperature until it is a full blue


The oxide films colours, indicating temperatures between 230 and 300 degrees C are only a reliable guide when the item has been progressively raised in temperature, and accuracy depends on the skill and experience of the operator.


Tempering can be done in the forge directly from the fire, or indirectly by using heated steel blocks/heavy jawed tongs to transmit heat from and into the workpiece.


Now we can move on to the more difficult bit, the O1, this is not a task to be taken lightly especially with little experience, this material is better suited to your kiln, refer to  manufacturers instructions


1) Size and shape the dies       OK


I would drill and tap before HT to allow a striking button to be screwed on (M12?) rather than (3)weld on a button, welding and heat treated O1 gets complicated.


2) Harden by quenching in oil.         OK


Question - should I harden the whole die (yes I think on the bottom as its only about 1.5" loing - on the top it will be abount 100mm long so I could only quench the bottom inch or two - this sounds right to me?)    Not sure what you mean by this?


If you are doing it in a kiln, as it is O1, harden it all, then as soon as possible temper it all to the required state, 


Just my take on it, and apologies for the length of reply.


For most applications the O1 as is will work fine, so long as your working piece is hot, 

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Thanks for taking the time for such a detailed reply John. Tapping the dies for M12 bolts for the strikers sounds a really good idea and takes a whole load of variables out of consideration. The kiln should certainly get hot enough, It is a ceramics kiln and I think it probably tops out at about 1150C. I like the idea of using the kiln because I can get nice long soaks at a known stable temperature. Temperatures for glass work are very critical and the thermocouple and controller have been calibrated. I may just wheel the kiln outside and use it to heat the dies for the hardening as well as the tempering. Mrs BM will get grumpy if I do the hardening in our conservatory, I will stink the house out and probably crack the slate floor dropping hot lumps of hot steel on it. 


I am feeling a bit more confident now :)  I will try with one die to start with to see if I can get the process down properly. I have only purchased a 500mm length of O1 so if I totally screw it up it's not a complete disaster. If I can get it to work then more dies can come later.


The steel won't arrive until after the bank holiday which will give me some more time to prep and read up. Oh, and mull it over with a few pints :) In the interim I will can crack on with making the frame.


Cheers, BM. 

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Just checked, kiln is good for 1300C so plenty of headroom.


O1 anneal is 740 to 760 although I should not need to anneal again. 

Normalizing is 670 to 700. I think with this I can soak for 30 mins and then just turn the kiln off.

Hardening is 780 to 820 with a soak at about 400 and then a soak at full temp for 30+ mins per 25mm - (I will soak for longer to ensure an even heat) . Not sure what a suitable ramp up rate is so need to check.

Tempering is from 100 to 350 - Just need to work out a suitable hardness for the dies. For tempering I have read I should soak for at least 2 hours. I think I should then be able to turn the kiln off and let cool under its own steam - it will cool very slowly at this sort of temp but just in case I will set a ramp down for 40 degrees F (sorry mixed units there).


I will set up some schedules with pre-heats soaks and hopefully it will all work out.



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the reason I did not type more is that I already answered your questions here   http://www.iforgeiron.com/forum/151-knife-class-reference-material/

top of the page pinned for easy location.  I dont mind people asking, but when the answers are posted, it makes me wonder.


Also your comment of just getting started, then you show you did read a little knowing the general range of the curie temperature, but then you stated you do not want to bother with a magnet, tells me you have not read too much because many places state the magnet is the easiest way to know the correct temp.


We all begin at square one, that is fine.  We all have a problem with the net having good info mixed with clueless wannabe's posting trash. dont give up,  I do not intend to sound harsh, I know I do come off that way too often.  It is hard to show intent in cold text on a computer screen and for that I am sorry.

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Hi Steve,


I hope I have not caused offense and I have not taken any either. I had read many posts including your sticky but clearly I was confused about a few things and I feel more confident now. On the notion of using / not using a magnet, this came from experience I have with glass where you can anneal unknown glass by overheating and ramping slowly down - I wanted to know if the same concept could be applied to steel. Apparently not. Good job it works with glass though as magnets are of little use there :)


Best wishes, Chris.

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At risk of asking another really dumb question...


I have annealed some scrap from the car boot sale. Some in the forge using a magnet and some in the kiln. A crowbar I bought for £1 had the decency to have the steel grade stamped on the side. All appeared to work OK as far as I can tell - they all ended up in a soft state to machine (I know this isn't the full definition of success).


I also now have the O1 for the dies. I have shaped my first die pair but still waiting for the M12 taps for the button. 


I did however come up with a potential snag in my kiln HT plan. If I use the kiln to get up to a precise temp to harden then said kiln will be way too hot to temper immediately after the quench. Shock cooling the kiln is very bad idea as it will destroy the bricks very quickly and the kiln is too good to screw up like that. So I am looking at alternatives:


1) Would it be OK to temper (at a lower temp than I ultimately need for my desired hardness) in the kitchen oven. My oven probably will not get hot enough for the final hardness I am after and it is definitely not very accurate. Then a day later temper again in the kiln at the required temperature? I have seen posts on double and triple tempering (which appears to be a good practice by most - well double anyway). However from what I can tell double tempering is usually at the same temp. Will there be any adverse side effects of tempering at a lower temp in my oven first and then tempering at the desired temp in my kiln a day later.


2) I do actually have a second kiln (homemade one this time - post box annealer design). This kiln was designed for glass annealing so will struggle to get to critical temp for steel but will definitely get to annealing temps. Sadly I have used its controller for the other kiln. I could make up a simple PID controller for this (but want to avoid the cost of a ramp / soak PID unit). I could still ramp down albeit by manually changing the temp setting every 10 mins.


3) Last option is to use a thermocouple in a multimeter and man a switch :(  That sounds like a real PITA and not something I want to do.


4) Leave the kiln to cool down for say 10 hours'ish and then temper - leaving the steel in its quenched and hardened state all this time. Everything I have read says not to do this. Is it a big risk on a 1 x 2 x 4 inch block of O1?


If option 1 will work then great, no more outlay of cash. If option 1 is a bad idea I think I will go for option 2. Option 3 just sounds too much hassle, too much time and too much potential to cock it up.


So in short, will option 1 work adequately?


Regards, BM. 

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Tempering ASAP after hardening is often a requirement for knife steels.  I have a friend who once hardened a blade late at night and decided to temper it next morning.  When he got back to it the next morning it had broken into 3 pieces just sitting on the workbench.


For knife work the kitchen oven *WITH* an added thermometer often is in the correct range, (all puns intended).  If you want to go higher an immediate temper in the oven will help "hold" the blade until you can draw it at a higher temp later.


Note using vegetable oil(s) as a quenchent can often help the "abuse of kitchen appliances" argument with an SO.

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Cheers Thomas, 


Sounds like option 1 is a goer then - I like this having just forked out for a very expensive car service :(


I was planning on using veg oil as i don't fancy the outlay of purpose quench oil or the toxic chemicals of engine oil. Had already tested the oven idea out on SWMBO and got raised eyebrows but no outright objection :)



For O1 I found:


Tempering Temperature F Rockwell C 300 65 350 63 400 62.5 450 61 500 60 600 57


Still trying to find the correct answer but it looks like tempering towards the top of the top of that range is probably appropriate and beyond my oven's temp. I was planning to temper at about 530F that I think will be about 59 Rockwell. It seems that is what hammer heads are typically hardened to. As my dies will have striking buttons I am not going to be thumping the die directly with the hammer. 


Cheers, BM. 

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If the post-box (glass) annealer can get to a set temp (i.e. cheap controller), it'd be just fine for temper. No need to ramp up or down there.


Multiple tempers is valuable.


One light temper (too low a temp) will be good enough to give you time. (My little toaster oven actually will hit 550°F as indicated by the oven thermometer I stuck in there...)

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 Leave the kiln to cool down for say 10 hours'ish and then temper - leaving the steel in its quenched and hardened state all this time. Everything I have read says not to do this. Is it a big risk on a 1 x 2 x 4 inch block of O1?



Hi Chris, to quote Thomas,


"Tempering ASAP after hardening is often a requirement for knife steels.  I have a friend who once hardened a blade late at night and decided to temper it next morning.  When he got back to it the next morning it had broken into 3 pieces just sitting on the workbench."


The key thing here is Knife, and I think everything you have read is probably blade shape oriented.


On a piece of O1 the size you are using, you are talking engineering die sizes, and I would not expect that to crack as you will have machined rather than forged it to the required shapes.


I would be more concerned about getting an even cooling throughout its section, as although it does retain its shape well, if you don't have the coolant freely circulating, then you may get different results to the hardness (this is when we as blacksmiths can use this property to our advantage in the hearth as opposed to the regulated kiln/oven )


For your application, you don't need the extreme high end of the hardness range as you will/should be using it on hot metal, it could also cause problems around the screwed on striking button threads.


Have fun

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  • 2 weeks later...



Thanks for all the help. The HT is now done and as far as I can tell all was OK. Used ceramic kiln for hardening heat. Quenched in auto gearbox oil. Tempered in mail box kiln (swapped the controller over from the main kiln). Used gas forge and off-cuts of steel to pre-heat the quench oil.


All in all a dirty, messy job but not difficult. Only slight drama was nearly losing one of the dies down the side of one of the kiln shelves in the top loading kiln. That would have been annoying as there would have been no way to retrieve until the kiln had cooled.


All that is left is to forge and weld on a stake so I can place the helper in my anvils hardy hole. I will do a separate write up of the tool, might help another newbie like me.


EDIT: Other post will have to wait - don't appear to be able to create a new thread or even send a PM to the admininstrators. Permission error :( I don't think I have done anything so terrible to get barred :(




You have done nothing wrong that I know of. We are working on the software posting perrmissions code.

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