View Full Version : Differential tempering

03-06-2003, 09:47 PM
Hi guys,
I have been reading up on differential heat treating done in the forge by conduction.
It seems that triple treatments (hardening and tempering) are in order but what about in between? By this I mean, say, after the first tempering (when you have all the colours just where you want them) would it be a good idea to quench the blade immediately after to halt the process. Or would quenching at this point undo what tempering had just been done and simply harden everything up again?



03-07-2003, 07:07 AM
Bearman,I recently read Great answer to this question by the King of Konduction,Tim Lively.

Short answer: naw, it wont take out the temper, or the hardness to quench at such a low temp.

Long answer: DON'T DO IT!

Why? cuz it gives Tim bad vibes. If doing such a thing gives someone with Tims experence "bad vibes" (even tho he says he don't know exactly why) it may be a good idea to follow his advice.
Wouldn't a better idea, if you want to temper three times, not to take your temper all the way where you want it on the first go?
Say for instance you want a bronze temper.

First temper: light straw
Second: dark straw
Third: bronze

The edge cools faster than the spine. When you see the the straw color getting close to the edge pull the blade and do a thousand thousand one thousand two. When the color stops remember your count and you will have a ball park of how long THAT blade takes to cool. Use that count to predict how long the other colors will take to stop running.

This is just my opinion.Opinions are like pie holes,and mine is usually full of pie. I have little experence and only a couple years of study here.
Click the link below for a more in depth (read coherent) explanation. You sound like a pounder, if so and you are into the old ways, you are in for a treat! 524.topic

03-07-2003, 06:50 PM
If I understand the question correctly,You want to know if after heating the blade to the proper temp,do you quench then,or let it sit or something then quench.Well it all depends on what steel your using,and the type of treatment your doing to the blade.The best answer is to educate yourself about the steel your using,from sources like the manufacturer,distributer,and anyone that has had exp. in using it.Different steels respond to different methods,there is no 1 way of treatment that works across the board for everysteel,as there is no 1 treatment method that crosses the board.It all depends.

03-10-2003, 04:33 PM
Hi guys,
Thanks for the info. about the tempering. Plenty to think about.


paul harm
03-11-2003, 04:48 PM
yes you can quench in water to stop the colors from running any further. i use my gas forge all the time by moving the blade back and forth [ in front of the door] with the spline closes to the heat. when the spline is blue and the edge a straw color, in the water it goes. buff the colors off- do it again and once more. just one of the many ways to do it. paul

03-13-2003, 05:38 AM
Cool idea Paul! thanks for the tip. Thats a good one for the tips and tricks thread.

paul harm
03-13-2003, 02:13 PM
another idea, from mr. lively [ not my idea] - bring the tip to a blue color. that would be close to a spring temper. you'd loose a bit on the hardness, but it won't break so easily. i started following this idea after playing around with one of my knives [ that i didn't like how it turned out- wasn't going to sell it]. was bending it to see how it would hold up- the tip broke. now granted it was a knife with a very thin blade- but it broke when stuck in wood and bent it - just the tip. so after regrinding/shaping i heated just the end to a blue color- did it again, no break. just another idea to play around with. paul

Ed Caffrey
03-16-2003, 08:56 AM
Don't mean to butt into the thread, but I have a strong opinion about quenching in water during tempering. Several folks who have failed to pass their JS test have treated their blades in such a manner. Their blades broke during the bending portion of the test. I did a great deal of experimenting early on with "soft back" drawing, and found that due to the blades spine NOT having the chance to soak, the interior of the spine was never softened, only a thin "skin" achieves the desired softer state. Often times there is a layer of crystalized steel just beneath this soft "skin", and beyond that the steel retains it's "as hardened" structure. If your seeking to pass the ABS JS tests, I would highly encourage folks to go about heat treating your blades from the edge quench method.....never getting the remainder of the blade hard. It seems that a lot of makers are using the soft back draw (the torch method) to save time, but I just don't think it's the way to go if your looking for "high performance". Just my two cents worth.

03-16-2003, 12:42 PM
I agree with Mr.Caffrey's statement.Edge quenching works because the edge is along the ground bevel of a knife,the steel is thinner and thus is able to respond to thermal treatments.If a knifes spine is full-thickness of the stock with no taper,it is futile to "torch" the spine.The soak time required for the stock,etc,plus if the spine is succesfully "hardned"(?) then just a tray of water with the edge in in will not prevent the ground portion of the knife from reacting,it will at a slower rate.Then the whole knife was hardned,that will not give the result of a soft spine/hard edge.Starting with an annealed piece,grinding the bevel,hardening the bevel,while leaving the rest of the blade is a safer way to go.

paul harm
03-16-2003, 08:14 PM
perhaps i should have given my whole procedure. i heat the blade until the edge is non magnitic- then edge quench in pre-heated oil. the spline is never hardened. i then heat the blade very slowly and carefully from the back until it turns blue. about that time the edge is turning a straw/bronze color. i put it in water to stop the edge from turning blue. i harden/ quench twice- then draw it three times. put an edge on it and test with a brass rod. the draw can be different depending if it's gonna be a skinner, camp knife, or maybe a throwing knife. james batson showed me the method of using water to control the colors when drawing [ at the abs school]. if someone thinks the method i just discribed has some faults, please say something. always interested in what others have to say- paul

03-17-2003, 07:18 PM
That is drawing the spine to reduce the hardness,The theory is if a knife of a given hardness is heated along the spine while the edge is in water,this can reduce the hardness along the spine without affecting the edge hardness.As far as water stopping the change of color,kinda common sense I think,your cooling??????. Are your blades ground full height??,And when you say "Back" to where does that apply?? I'm not knocking your method,just trying to understand,I just heat the edge to critical 3 times,quench ya know in between,but thats it,anything else without the aid of an oven(or forge) is not really doing anything.

paul harm
03-18-2003, 07:01 PM
i usually grind full height unless someone request otherwise. i'm not explaining too well. i don't leave the blade in the water while heating the back [spline]- but because i sometimes use my gas forge to h.t. /temper, after h.t. i hold the spline to the flame coming out the door, the edge away. this way about the time the spline is turning blue, the edge is getting straw. that is when i dip in water to stop the blue from running. i know of the other methods, just trying to explain why i thought it was ok to use water when drawing. on that thought, can anyone explain why using water in the draw process between heats would hurt anything. with carbon steels, we're only going to 375/450 degrees. paul

Ed Caffrey
03-19-2003, 08:35 AM
The reason that I believe water is not a good thing to use is due to the rapid cooling that takes place. This has a tendency to SHOCK the steel. When you heat at the door of the forge, then dip the blade in water to cool it, you create a crystalized "skin". This "skin" is the only portion (depth) of the blade that has achieved the temp that the color indicates. However, by cooling it rapidly in water, you negate the tempering effect because you have created a large, course grain in the very "layer" of steel you just tempered. In order to achieve a solid temper with the proper trasformation of the steel, it must be exposed to the heat in such a manner that allows it to soak. I would bet dollar to doughnuts that if you were to treat a blade in such a manner and then break it, you would see two to three different grain boundaries in the broken cross section. Chances are very good that the exterior layer will be somewhat "grainy" then a finer layer beneath that, and then the core will have the as hardened grain structure. (unchanged because there was not enough time for the heat to penetrate that deep) It's not a matter of the temp harming the's just like falling off a's not the fall that harms you, it's the sudden stop at the end! :D That's the same reason why water can be harmful to steel....that sudden stop of the time/temp curve.

paul harm
03-19-2003, 03:58 PM
well, now i'm going to have to find out. this next week i'll make a blade and break it . let you all know what happens. paul