Hard spot on tool steel

[MarioM]

I bought a piece of 1/2" round tool steel from a well know local supplier, it is sold as DF2 or AISI 01. Outside it has a black color but it is not rust. Cut a small piece to mount on the lathe with the hand saw and all went OK, sharpened a couple of HSS tools to get ready for a good job. In the first cut just cleaning the saw marks on the other side there was a very hard spot at the edge......:wall:.....it ruined both tools and had to be resharpened.

The only idea that comes to my mind is that the big cutting machine the supplier used generated a lot of heat on the steel and developed a hard spot........is it possible??. Anybody having a similar experience????

Mario

 

[tornitore45]

If the supplier cut it with an abrasive wheel and the steel is of the "air hardening" type is very possible that it reached critical temperature and then cooled fast enough to harden. If cut with the band saw I doubt it could heat enough to harden.

 

[Swifty]

Agree that it could have been cut with an abrasive wheel, or on a saw with a blunt blade that work hardened in a spot.

May just have to try parting off a slice from the end to get past the hard bit.

Paul.

 

[MarioM]

Thank you very much for answering. Tacking a closer look it actually seems has been cut with an abrasive wheel. I will cut a slide and get rid of the hard spot.

Mario

 

[tornitore45]

Just for reference, hardened steel may be annealed with a torch by bringing up to bright red and letting it cool very slowly.
Is difficult to keep Air hardening stell tool below the cooling rate that hardens it but other tool steel can be slowly cooled by
-mooving out the flame slowly (barely adequate)
-dunking in a can filled with Vermiculite (better) (garden stores have it)
-Leaving under the ashes in the fireplace (Best)

 

[MarioM]

Reading the information regarding the steel it tells it is oil hardening. I have annealed file steel heating it with the torch surrounded by insulating bricks, like a small furnace, and let it cool. It works OK, have made cutting tools for the lathe and other tooling.
I got a very nice book called Hardening, Tempering & Heat Treatment by Tubal Cain. Lots of information, but had never happened to me to find a hard spot like this one.
What is really new for me is the Vermiculite!!.....just learned something new.

Mario

 

[2manyhobbies]

Dry sand (could be sold as play sand), probably on the same order as vermiculite, also works to help cool the metal slowly.

 

[tornitore45]

Dry sand works but need to be hot, like you heated the part and the sand then let the whole thing cool.
Sand is basically a stone, as such has fairly good heat conductivity, yet it has mass and heat capacity. If you touch sand at room temperature it feels cool, not as cool as, say aluminum, but cool; inducating high conductivity.
A soft fire brick feels worm, so does vermiculite which has the advantage of being light.