Warping when Hardening and Tempering

Follow up to some previous inquiries I made recently and more
questions.
The tool is a 3/4 x 1/8 x 2" long piece of W-1 water hardening tool
steel. It's bevelled along one of the long sides like a short planer
knife and it must be razor sharp.
Heated with Prestolite acetylene torch, quenched in water, temepred to
light straw at 500º in a toaster oven. [Yes, you can achieve this
temperature in a toaster oven. I got an oven thermometer and checked.
Leaving it in for 20 min gives a light yellow temper. 40 min. gives a
dark straw temper.]
They warped a little after hardening and tempering. Is this just
something you have to live with or are there home shop tricks that
prevent this? It's not that the warp is bad, but it takes a LOT of
grinding / honing to get the blade flat after it's hardened and
tempered. I didn't measure the warp, but my guess is that it's less
than 0.010" longitudinally.
The 6" belt on my belt sander shined up the bottom nicely, but it
certainly doesn't remove metal very fast. The belt was the standard
one that came on this Grizzly sander. Are there belts specifically
intended for metal grinding that will do a faster job?
Is Water hardening tool steel is more prone to warping than oil
hardening?
Observation - It's a lot easier to put a bevel for sharpening on the
tool steel with a milling machine before it's hard than grinding the
bevel afterwards, even if it has been tempered.
Another observation - you can't "spring" a blade that's been tempered
at 500º back to flat. It breaks first. Boy was that interesting.
The shop isn't really dim, but when that broke, there was a small
flash of light at the break!
Semi-OT - story I heard at college.
When they installed the big (4 or 5 stories tall IIRC) Baldwin testing
machine in Fritz Laboratory at Lehigh Unversity some time in the 50s /
60s they put a piece of steel in it that was at the tolerance of the
machine and stretched it till it broke. One of my professors who
spoke as though he had been there when the test was done said that it
let out a flash of light when it broke and it felt like there was a
small earthquake in South Bethlehem. A few windows in nearby homes
broke according to the professor.
RWL
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RWL
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That's an excellent way to draw the part!
I think you're experiencing the release of stress in the material by removing stock unevenly, a function of the bevel of which you spoke. If you have many of these to do, you may find that quenching them on a very small angle as they enter the water could cool the front side (with the bevel, which I'm sure is the crowned side) every so slightly faster than the back side, adding the small amount of stress necessary to hold the part straight. I'm sure you can see that could be difficult. How you introduce the part to your quenching media is critical. If you drop them in flat side first, they will warp terribly, so a slight modification of the process could yield a lot of variables.
It's not that the warp is bad, but it takes a LOT of
Not really all that bad, considering, but it sure as hell is irritating, isn't it?
I've not used the new blue belts (their composition evades me at the moment, but I think they're boron carbide), but they are much better suited to metal removal than the older style belts. One thing of which to be certain is that your belt is not silicon carbide, which is not suited to grinding steel. An aluminum oxide belt will do a much better job and create a lot less heat. Silicon carbide dissolves into the steel, dulling the grain almost instantly, thus it doesn't cut, and creates lots of heat just rubbing.
To my knowledge, no. You could, however, try using an air hardening steel, which will circumvent the rapid cooling. These steels are well known for their stability. You would likely have to use a small furnace in place of the torch, though. The torch itself can be the source of the warping due to uneven heating.
That is true when working as you do, but you could grind the bevel with a surface grinder rather easily, although the stress that causes the piece to warp would still be a factor. If I had the job to do, I'd rough the parts, heat treat, then grind all over. You are almost guaranteed a part flat within less than .0002" if you're much of a grinder.
Yep, lots of energy released when you break something that has the high tensile strength of heat treated tool steels. Dangerous, too. Pieces have been known to take out eyes and any other soft tissue. Heat treated items do not lend themselves to bending unless they are drawn well down, and then it can be difficult.
Harold
Reply to
Harold & Susan Vordos
The angle of approach to the water quench can cause some warping. I would probably quench it bevel first into the water. Some knife makers even quench in such things as watermelons. Do not over heat the steel. Do you have access to a surface grinder? If so, the piece can easily be trued and sharpened after tempering. I have a blade clamping jig for resharpening my jointer/planer blades. It holds them at the correct angle and really allows for a good edge grind. This could make for a quick/easy solution to your problems. The final edge could then be honed by hand, if needed. Jim
Reply to
JAMES RISER
Hi Bob
You can buy spare blades for the Herdim peg sharpeners.
Flattening backs (something you do to a chisel only once in its life): I grind a bit on a stone to see where the high spots are, then grind a tiny bit off with the bench grinder or a Dremel tool, Repeat as needed. Flattenthe stone somehow (I have a diamond plate I use for that - never liked it for sharpening tools, but I use it to keep my stones flat.)
Dave Golber
Reply to
DGolber
Just didn't work for me. One of the ones without the pattern of holes in the top. But it's great for flattening my waterstones.
Dave
Dave
Reply to
DGolber
Yes, and yes. The presence of the bevel causes some warp. The quenching technique contributes as well.
You can take advantage of the latter to counter the former. In general, edge tools tend to warp so as to crown the bevel. That is, the surface opposite the bevel will be concave. OTOH, the first portion of the steel to hit the quench will "shrink" forming a concavity there. Consequently, you can start the quench at the bevel in order to counteract it's tendency to crown.
It takes some experimentation to determine the best angle at which the tool should enter the quenchant, as well as the best agitation motion for the tool while in the quench. Sometimes it's better to plunge with the tool pointing straight down and then move it in the direction of the bevel. Sometimes it's better to plunge the tool straight down, but held at an angle so the the bevel hits the quenchant first, and then move the tool straight up and down in the quenchant.
You can also reduce the amount of warping by clamping the tool between two thicker pieces of flat steel, and heat treating the whole unit.
That's really not too bad for a thin W-1 edge tool, but it can be done with less warping.
Surface grinding can restore the tool to flat after hardening, but with a 1/8" thick tool, you must shim it carefully while grinding the first side. Otherwise, the magnetic chuck will pull it flat(ter) and the tool will be ground parallel, but not flat. It will spring back curved after being released from the chuck.
If you surface grind the part flat after quenching, you will need to surface grind the bevel also. Still, it is better to rough out the bevel before hardening, so as to minimize the amount of grinding needed on the bevel after hardening. Unless you have flood coolant, it is very easy to overheat the tool's working edge while grinding the bevel. Mist coolant is inadequate unless the metal is removed at a snail's pace.
Aluminum zirconia belts (sometimes called blue belts) are the ticket for fast(er) stock removal. However, the belt grinder will leave you with convex rather than flat surfaces.
Yes. But the quenching technique can have a greater effect on the degree of warping than the difference between W-1 and O-1.
Cheers,
Jim
Reply to
Jim Wilson
For thin pieces being heat treated they made flat tongs that sandwiched the metal and held it flat so it didn't curl or skelter. You could probaly bolt it between a couple pieces of scrap and heat treat the entire assembly. Faster stock removal with the blue norzon belts and you can help carry some of the heat off with bar soap or spray lube like WD 40
Drawing temper in molten solder might be a usefull trick for you to try. 50/50 is liquid at 417°F and radio solder at 361° F
What is the tool intended to do?
Reply to
Beecrofter
That's often the best answer, but the blade won't harden quite as much because the extra pieces slow the quench.
Gary
Reply to
Gary Coffman
That will also depend upon the quenchant. He can speed the cooling with brine or lye. Or leave the very edge proud of the fixture which is advantageous.
Reply to
Beecrofter
I hadn't mentioned it in one of my posts, but before I bought an oven thermometer, I tried doing this with my lead melting pot. The wheelweight alloy was difficult to keep liquid at much below 500º, but in the end I got nice dark straw temper color on the steel.
They're blades for peg shavers to put the correct taper on ebony pegs for string instruments (violin & viola). They look like big pencil sharpeners.
RWL
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RWL

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