Thread: What kind of plate?

Hi I'm new here but have been working metal for many years. Got some 1/4" plate at a good price [ almost free ] came from our old county jail built in the early 1920's. The only way to drill a hole in it is to use solid carbide drill and alot of oil and low RPM. The best hespeed drill that Fastenall could get me won't touch it. Anybody got an idea what kind of steel it might be. Thanks

Probably has a real high manganese content. Manganese is the cheapest way to strengthen steel and increase its abrasion resistance. Both good qualities for things used in jails, but not so much for things that need to be machined. The ultimate example of high manganese steels is the stuff used to make the working surface parts of rock crushers. For the most part, that stuff is rated non-machinable by common methods.

If it was a fastenal brand drill, it was probably junk.

Hand drill or drill press?

Used a drill press @ 25 RPM. It also makes the blade on a hot saw disapear, but it shur welds nice.

I think metl hit it on the head. There is a commercial name for the modern abrasion resistant stuff but cant remember it.

Thanks guys. I think he's right too. The only place it rusts is where it was cut with a torch and it has been outside for years.

Originally Posted by Mebfab

I think metl hit it on the head. There is a commercial name for the modern abrasion resistant stuff but cant remember it.

probably manganel(spelling?) Don't know if thats a trade name or generic.

Ar500 is one of the common wear plates used now... interesting stuff, I have welded some Ar500 once and it welds very nice.

Originally Posted by kustomizingkid

Ar500 is one of the common wear plates used now... interesting stuff, I have welded some Ar500 once and it welds very nice.

That and Ar550 is the choice material for steel riffle targets. An .556 round will go right through a .5" mild plate but bounces off the Ar5xx

Is it magnetic? I work at a company that makes rock crushers, and as such, we cast some special alloys for the wear materials in these machines. The manganese steel wear materials that we cast are non-magnetic (don't know if this holds true for other manganese alloys or not), whereas high-chrome and AR steels are magnetic. If you have a small enough piece that you can move easily, the best answer is to take it to one of the larger scrap yards in your area and have them 'shoot-it' with their spectrometer to determine the material content.

Also, if it is manganese, you have to take an agressive cut, as light cuts will cause the material to 'work harden' in front of your tool and makes it very difficult to machine.