1095 hardening problems, rough day as a newbie

[Zeb Camper]

You know, I think it would work. I personally would want to be able to over correct as much as possible. Better to have and not need than need and not have. But, if you have a small blade that has that much bend in it after heat treat, chances are you have alot more to worry about. At that point you must question your geometry. I would make it out of maybe half inch square bent to 90° around the jaw. Just use the vise as a natural form for the hot bar. You can then grind the edges round where it will contact the blade. Then grind your slot for it to interlock with the top of the jaw. Look for custom handrail makers in your area. They have half inch square scrap up to their eyeballs (I work at such a place, so I know). I guess you could also over pay for something at a hardware store if you had to though.

[Brian Dougherty]

You typically have to over-bend to straighten because the steel springs back to some extent, so flat plates would be a bit limiting.

[Alan Longmire]

You need to be able to overbend it.

[Zeb Camper]

11 hours ago, Devin D said:

Would two flat plates the size of the knife work or do you need it setup so as to over correct ?

Yeah, sorry I mis-informed you. I thought you meant 3 plates made of flat bar similar to the one I showed you. 

[Gerhard Gerber]

Hi

I haven't tried this, but I've seen the advice of clamping a warped blade to something like a piece of angle iron (that won't bend) while tempering.

[Vern Wimmer]

1 hour ago, Gerhard said:

Hi

I haven't tried this, but I've seen the advice of clamping a warped blade to something like a piece of angle iron (that won't bend) while tempering.

That is done by some, I guess, but it introduces all kinds of variables/problems into the process like , "how are you going to get a blade cooled down and around the pearlite nose within 1/2 a second with this heat sink attatched?".

[Alex Middleton]

Vern. He's referring to tempering, not quenching.  I use the angle iron technique to straighten out my blades during tempering.  After the first cycle you simply clamp the blade to a piece of angle iron using two c-clamps and place a space at the point of the bend.  Use a big enough spacer to overcompensate for the bend, and then run another tempering cycle.  Sometimes you have to do it multiple times, gradually over bending it more and more.  It works pretty well.

[Brian Dougherty]

2 hours ago, Gerhard said:

Hi

I haven't tried this, but I've seen the advice of clamping a warped blade to something like a piece of angle iron (that won't bend) while tempering.

I do this all the time now.  I have been making a lot of kitchen knives lately, and the long thin profile usually leaves me with a very slight warp.  Maybe 0.5mm over the length of the blade.  Generally, I'll clamp the blade to a straight bar (after the first temper cycle) so that I over correct the warp by 100% and temper it again.  This usually straightens them right up.

[GEzell]

There's basically three ways to straighten a warp.

The first way I've already described, after the quench but before martensite forms.  Quench long enough to get past the pearlite nose, then straighten by hand (with thick gloves) before the blade cools past 400-500°.... This is also where the aluminum plates come in (they don't have to be aluminum, steel and even wood will work), they can be used to keep everything straight until the blade has fully cooled.

The second method is to straighten during the temper by clamping the blade to a hunk of steel, over-correcting a little past straight.  This can take a few tries to get right, but works most of the time.

 

The third method involves three points in a vise, a torch, and bad odds of breaking and/or over-heating the blade.... Avoid this method if at all possible.

[Vern Wimmer]

25 minutes ago, Alex Middleton said:

Vern. He's referring to tempering, not quenching.  I use the angle iron technique to straighten out my blades during tempering.  After the first cycle you simply clamp the blade to a piece of angle iron using two c-clamps and place a space at the point of the bend.  Use a big enough spacer to overcompensate for the bend, and then run another tempering cycle.  Sometimes you have to do it multiple times, gradually over bending it more and more.  It works pretty well.

Ah, OK, got it. I always had the impression that if there was a tendency for a blade to warp a normalization cycle should relieve the causal stresses. IE straighten it and, if your geometry and dimensions are good a normalize cycle should set you back up for another try. If a blade keeps warping in the same manner there is probably an underlying lesson to be learned. But getting a straight blade is the goal.

I generally work with sub 6" blades so I don't run into some problems others have. Mea Culpa.

Edited October 11, 2017 by Vern Wimmer

[Alex Middleton]

I have a lot of lessons to learn.  Even my 4-5 blades usually come out with some kind of warp! 

[Vern Wimmer]

You may well call me crazy but this is a little thing from my experience.

I was having trouble with warping from time to time with no cause I could figure out. Still working at a basic level. An old-timer (a fantastic story himself) who had a wealth of experience in a lot of areas saw me starting up to forge one day. 

" Just a second there. You aren't going to put that hot steel (it was an almost finished blade) on a cold anvil are you? No wonder your blades warp"

Believe it or not, when I started pre-heating the anvil my warping diminished severely.

 

Edited October 11, 2017 by Vern Wimmer

[Joël Mercier]

42 minutes ago, Vern Wimmer said:

You may well call me crazy but this is a little thing from my experience.

I was having trouble with warping from time to time with no cause I could figure out. Still working at a basic level. An old-timer (a fantastic story himself) who had a wealth of experience in a lot of areas saw me starting up to forge one day. 

" Just a second there. You aren't going to put that hot steel (it was an almost finished blade) on a cold anvil are you? No wonder your blades warp"

Believe it or not, when I started pre-heating the anvil my warping diminished severely.

 

I can't see how anything done before normalization could affect warpage. I just don't understand.

[Zeb Camper]

1 hour ago, Joël Mercier said:

I can't see how anything done before normalization could affect warpage. I just don't understand.

The theory is if you don't anneal the blade before normalization, then risidual stresses can cause a warp (like how some claim leaf springs will take back their old shape during the quench). I stopped annealing when I switched to propaine and I have seen no real difference in the end result. Most of my blades that are under 12" rarely warp at all and a lot of times I twist and bend warps out cold after forging. I just run three good normalization cycles and it turns out great 90% of the time. So, is there is truth to this? I don't know. I think alot of times the steel gets blamed for uneven grinding that ultimately caused the warping. Or, perhaps you didn't quench with the blade vertical, causing one side to cool first. 

[Vern Wimmer]

1 hour ago, Joël Mercier said:

I can't see how anything done before normalization could affect warpage. I just don't understand.

I am a big fan of heat treating cycles and normalizing, but, the evidence i.e. blades warping after normalizing, tells me that it doesn't "fix" everything or else we've done something else wrong.

The old-timer explained to me that when he was young an old-timer told him that when you put a hot piece of steel on a cold anvil you are (in terms today) accidentally diferentially tempering the piece across its thickness. The down side hits the cold anvil and contracts slightly while you are banging away on the hot side and stretching it. 

Now "everbody knows" normalizing should fix all that......but......? I know my rate of warpage dropped when I preheated with a torch or hot scrap. If there was an OWT about wearing a jockstrap on your head to forge a better blade and I tried it with success then I'd have a real funny looking driver's license photo.

 

[Brian Dougherty]

Somebody like Jerrod could explain this better, but the forces that can be caused by temperature differentials in a piece of steel are quite large.  Just a few degrees can generate enough force to bend hot steel.

Even a properly normalized blade is going to see forces that may warp it during the final quench sequence.

There is simply no way for something the general shape of a blade to be heated evenly to a point where the entire blade is at the exact same temperature, and then quenched so that every atom is then cooled at the same rate.  There is always going to be internal stress.  The longer, or thinner, or more asymmetrically ground it is, the more warping  is going to occur.

I think a lot of the quirkier practices to prevent warps have evolved as a way to explain the mysticism of the warping god.  There are so many variables at play that people are not aware of.  Once they find a method that works for them they are prone to attributing the success to controlling the wrong thing.

 

Edited October 12, 2017 by Brian Dougherty

[Jerrod Miller]

3 hours ago, Brian Dougherty said:

Somebody like Jerod could explain this better

I'd say you did just fine.  There is a thread from a while back where different quench mediums were discussed.  The main gist of it is that the temperature gradients are the thing to be watching out for.  Water isn't too fast for most things, it is that it is really fast where it is touching the metal, but it too readily creates a vapor barrier that is uneven (some places on a blade will be touching the vapor barrier, others getting the liquid water, and the vapor barrier moves).  That is the main point of many of the other quench mediums: get as fast as possible while maintaining even heat transfer.  

My first few blades were way too thin (I was a freshman in college, I had found Don's original website, but certainly didn't know enough about what I was doing).  My burners were not aligned properly, I put my blades right in the hot spots, didn't move them around enough, but I did quench in vegetable oil (but it was room temp).  May blades warped like crazy just during the heat up!  That was due to the uneven heating.  Cooling did it too, but I eventually got lucky with those early blades.  I eventually tested them to destruction (never even put handles on them).  

Anyway, temperature gradients, and especially heating/cooling gradients are the big things to watch out for.  If you have normalized properly, any/all stresses before normalizing will be gone.  If you find that is not the case, then you aren't normalizing properly.  If you normalize properly and still get warps, then it is not from prior stresses, but from stresses after normalizing, most often caused by those pesky thermal gradients.