Warped during Heat treat, yay...

[Malice9610]

So I took my first whack at heat treating this weekend, and while I was able to successfully harden the steel, I ended up with some warping. 

I forgot to take pictures, so I will add those later today once I get back home. 

However, there are a few odd things to this, I think I have it figured out as to the cause, however I would like some second opinions on my very newbish knowledge of the process. 

First off is the manner of the warp, I treated 5 pieces Sunday, 4 of which were " identical " blade profiles, of very similar thickness, The warping on these blades is also similar, each one warps to the right ( if looking down the edge with the point away from you ) slightly towards the tip.  The fifth one started off much thinner then the other 4, and the entire blade seemed to warp creating a convex side and concave side. This knife was also longer then the rest ( 6 inch blade vs 4 inch blade ) 

Now, I think the reason for these warps, is two fold. First being my " Heat treat bucket "  which is a standard metal bucket, However due to the volume of oil I had, the depth was not enough with it resting flat to fully submerge the pieces, So in my newbishness, I tilted the bucket during each quenching, which also caused me to create the second issue, as I was not able to put the blades straight into the quenchant, they went in bottom tip edge of the knife first. and due to the angle I suspect the warp came from one side being angled into the oil more then the other side and /or unintentional side to side movement while putting the piece in the oil.

The steel used was old leaf spring, So I assumed 5160, Quenched in heated veggie oil. Heated till non magnetic then put back into the fire for about 30 seconds ( to get back past non magnetic, it was kinda crappy weather yesterday, windy and colder then normal ) to get back up to a bit past non magnetic and then straight into the oil. The file test proves they did infact harden.

Am I correct on thinking that the very VERY small amount of time that one side cooled faster then the other, is a possible cause of the warps considering all 4 pieces went from the fire to the oil from the exact same spot using the exact same movement, the warp is on the " correct side " for how I was working. 

Next step for me, is to find a better container for my oil, so I can put the pieces in straight up and down point down instead of at an angle. I also think with a good normalization and some light hammering I can fix the warp without destroying the grinds and save the 4 similar pieces, But I suspect the 5th one is a lost cause. 

Also I read on another thread here that in some instances, its best to Heat Treat first, then grind the bevels, but I was not able to find the specific instances this would apply, I would think thickness of stock has a major determining factor on that based on how thin the edge would get on say a full flat ground blade with a 1/8th inch spine might qualify to minimalize warping, is that thinking correct, or are there other factors I have not though of ? 

 

Thanks everyone! 

[swedefiddle]

Good Morning,

Arnon uses a very light hammer he made from a rock drill, c/w the insert. After tempering, lightly work the blade to straighten it. Across the blade for a bend, in line with the blade for a twist. Go easy, it takes less time than making a new blade.

[ThomasPowers]

Tell us about your normalizations before the hardening?  Leaf spring may have some memory to it so the normalization and straightening during them can help.

[Malice9610]

Ok. 

First, I started off with a curved piece about 3 feet long, cut into pieces about 9 inches long, then each piece was heated and flattened out flat, and thinned a little bit ( started off about 1/4 inch thick ) with the goal being increase width from 2.5 inches to about 3 inches wide. Then each piece was heated and left to cool in the forge over night, then cut to a rough knife shaped object. these were then ground down to size, and then annealed to allow for drilling of lanyard / handle holes. then primary bevel ground. 

Once fully ground, they were sanded up to 400 grit and then heat treated, So I guess in addition to my other mentioned potential causes, I guess doing another normalization run before heat treating very well could have made all the difference.  My thoughts were essentially " well they didnt curve back up after flattening them out , how much strain could grinding only put on them " 

Which is now in hind sight, not exactly the best of plans, at least not in this instance. 

[ThomasPowers]

Heat treating does not mean hardening; heat treating includes such processes as: annealing, normalizing, hardening and drawing temper. So "doing another normalization run before heat treating" translates as doing another heat treating before heat treating.

Normalizing is often used to refine the grain size of forged blades and provides a nice set of places to straighten things and then re-normalize. (I generally repeat if the piece has curved appreciably after normalizing. A wooden hammer is handy in such cases too)

[Malice9610]

Thomas, 

I guess this is perhaps a failing of " online research learning " in a sense, as I use the term " Heat treating " specifically to describe the process of hardening and drawing temper of the piece.  I can see the logic in stating Normalizing and Annealing also fall into that category, even though in my mind ( even if wrong ) they are somewhat separate processes even if they entail the exact same conditions as they can and do create differing outcomes for the piece.  I would consider that a side effect of being an overly analytical geek who must compartmentalize and classify everything. 

here are the pics I promised, after looking at them again ( post frustration ) they are not that badly warped, and even a wooden hammer treatment might even save the larger one. 

 

The bottom two are of the larger knife, as you can see in the first pic, there is an obvious central curve to the knife, on the last one, the outward curve is VERY apparent. 

but, I am going to take a bash at them with a wooden hammer ( just gotta make one first which should be MUCH easier then making one of metal ) and see if I cant straighten these bad boys out some. 

[ThomasPowers]

Sorry but my definition of heat treat is based on what I learned in MatSci classes at Cornell University and is used world wide in Industry; get your geek on right as using heat treatment only for hardening is wrong!  Don't worry soon you will be able to sling the jargon perfecto!  (was discussing blacksmithing with my landlords Mexican handyman this morning at breakfast)  

Don't hammer hardened blades!  Some alloys have a, brief, period during hardening when you can tap a blade straight; but if you miss the window then it's tink time.

I still suggest normalizing and straightening and then re hardening and tempering.  Read up on grain refinement too.

[Malice9610]

Turns out the bigger thinner one was actually quite savable, without another heating, I had left enough steel on each side that I was able to very carefully re flatgrind the two sides without overheating the temper at all. Hopefully will have that knife complete tonight, along with another I have been putting off finishing due to not wanting to waste Epoxy for handles as I have a very limited supply at the moment. Going to redo the file test on that knife tonight just in case, I didnt get any oxide coloring while grinding it back out after tempering, But I want to be certain on this knife that it will stand up to some normal abuse well, its a gift for my friends father who is retiring and picking up and moving to Costa Rica the end of this week. 

Sorry if my previous comment might have indicated I was going to attempt to straighten the others without heating them first, I do plan to heat them back up, straighten them, then normalize them, then harden and temper them. I just needed to track down a good piece of wood first to make a wooden hammer out of, Lucked out and have a spare 2lb hammer handle to use and found a nice flat cut limb out in my wood pile that would make a serviceable hammer head for a try at straightening these. 

Thanks again Thomas for your guidance, I very much appreciate the help. 

[ThomasPowers]

I used to turn wooden hammer heads out of my firewood pile.  Now I use the "stinky hammer" a wrought iron mallet that does stink when it hits hot steel but does a good job.

I would put straightening as part of the multiple normalizing steps; but having at least on normalizing after straightening works.

Just remember sometimes the steel laughs *with* you and sometimes it laughs *at* you!

 

One reason the fellow I trained under did all his grinding bare handed was to make sure the blades didn't overheat; of course he was making swords generally.

[Malice9610]

Yeah, I prefer to do my grinding without gloves as well, but thats more due to the fact I would rather not mangle my hands because a piece of glove got caught in a rotating power tool of some kind. 

One of these days, probably a few years in the future after I have a good number of knives under my belt, I plan to take a whack at making a sword, actually have a machete in " MSO " form at the moment that i plan to play around with to see how things work as the blade gets longer.

[ThomasPowers]

Sorry not wrought iron but rawhide mallet---#$%^& auto correct!

[Malice9610]

Ok, so I have fixed the bigger one, cleaned it up, and triple tempered it. However, I think the oven got hotter then I should have let it get. 

To be honest, I was looking to go for a " more durable " blade for this one, as its bound for the jungles of Costa Rica on the belt of one of my best friends dad who retires to there this week. I did a file test on it after it had cooled and the edge ( not sharpened yet ) is still VERY hard to remove any stock from with a clean file, But this is what it looked like when I pulled it out of the oven after its final temper. 

I ran the oven at 400 deg. for 2 hours.  I dont have a Temp gauge for in the oven yet, that is something I plan to buy this weekend for when I fix my other knives that warped and start the temper process on my fully forged O1 knives I have been waiting to start on. 

Did I get this too hot, like I said, I was going for a more " chopper " level of temper so it could stand a bit more use and abuse before it eventually breaks. 

 

 

 

[turbo7]

Even a blunt knife is handier than a broken knife. Malice if you think the knife will eventually break, DO NOT send it out my friend.

[Malice9610]

well my thoughts are that it would break potentially because this is one of my first ones, I have a couple other blades that were " practice " ones out of the same section of steel this one came from, that I am going to harden and temper the exact same way today after work, and then do the bend test on them to see how durable it really is, I have till saturday morning to decide to send it with him or not. 

Its more a " I am not certain i know what I am doing " kind of concern more then anything else. 

[ThomasPowers]

Can you tell us how we should know how hard your customer likes their knives?  Machetes are traditionally a bit on the soft side to make them easy to sharpen in the field and less likely to chip and break in use.

 

Forget the colour it's the hardness you need to concentrate on.  Leaving it in the oven for a long time will shift the colour  more than it will shift the hardness.  Go by your testing of the edge with a file.

[Malice9610]

That is pretty much what I was hoping to hear, I kind of figured that would be the case with the colors getting a bit higher up on the scale due to time in the oven, but to have that confirmed by one more experienced then myself is better then " i hope so " 

With that being the case, the handle will be shaped and glued on tonight. 

Thanks again Thomas, I really appreciate all the help you have been, If you ever find yourself in Salt Lake City, dont hesitate to hit me up and I can treat you to a few cold ones.