T15, when heat treated, is often used up around the 65 Rockwell "C" range. Grinding in that case is usually preferable. In addition, if using wrought T15 steel, know that it is a bit more prone to surface cracking when performing post-heat treatment operations such as grinding. The larger carbides that are good for wear unfortunately like to be ripped out of the steel by a grinding wheel. You might get better results using a P/M grade vs. a wrought grade.
Turning prior to heat treating? It's tough stuff that is wear resistant, so you'll wear out your inserts much faster than if turning something like A2 or 4140.
We were supplied 4 pcs of steel by one of our customers.
Two at 14" diameter and 2 at 22" diameter. They were received with over 3" of excess stock to remove prior to heat treating along with some milling work to be done. We were instructed by our heat treating company to leave .120 stock on all dimensions(O.D./I.D.and width). We used carbide inserts at a very slow speed with little success. Tried using ceramics, but not much better. Question is what type of insert might be best used for removing this large amount of stock. Secondly, after heat treat, what type of insert might be best suited. We believe ceramic might be our best bet, but haven't tried it yet.
One other problem is that our heat treter cracked one of the larger rolls so we are in a bit of a predicament with that also
Thank you for your input.
we are not equiped to grind anything except the overall width
Grades like T15 are always machined using EDM or grinding. I can't imagine trying to turn it. Definitely talk to your steel provider to see if they have any documentation on turning. Ceramics sound like a better option than carbide for inserts. Don't screw around with any of the commodity insert manufacturers-- go directly to Sandvik, etc.
I've turned smaller punches (Ø1.5"-Ø3") and will admit that you will go through inserts. I can't imagine turning a Ø22" bar. And 3" of stock is pure insanity.
If it's a thinner disk, under 5" thick, I'd tell you to send the thing out to a water jet house and have a good portion of the stock roughed off there. Depending on the geometry, they might be able to rough it completely for a reasonable cost. If you need exact sizes and smooth surfaces prior to heat treatment, you can run skim cuts on the part when it comes back in.
If your required hardness is less than 65 HRC, I'd recommend heat treating the piece in a vacuum furnace to minimize distortion. Thicker pieces will likely need an oil quench, which may be why your heat treater wants 1/8" stock all over.
Tight tolerances post-heat treat will likely need to be ground as was mentioned prior.
