P20 and tapping
I've noticed that a lot of the P20 I buy from Uddeholm seems to have become harder to cut in recent years.
The last mold base I built was amost un-millable and un-drillable...I went through boxes of inserts and many drill sharpenings compared to times gone by.
I've heard that the chemistry of steels is slowly drifting toward a different end of the range for minor constituents.
Apparently it used to be that you'd find most alloying elements to be at the low end of the permissible range because it was cheaper to do it that way when the primary feedstock was mostly virgin iron.
Now that more of the feedstock is recycled scrap, supposedly the low cost way is to tolerate alloying elements at the top of the range if they're already in the melt.
Has any one else heard this?
Can anyone else confirm that the P20 they're using has gotten more difficult to cut over the last 5 years?
It would certainly explain the OP's problems tapping the stuff.
Mind you, I don't much like spiral flute taps...I find them prone to snapping on direction reversal.
I'm told it's due to the pitch errors induced when they twist and untwist as the torque changes during tapping cycles.
Apparently the transient pitch errors make them bind; and this will be especially pronounced on direction reversal with a duller tap that's had to have more torque applied to it to force the tap through the steel to get it to depth.
Maybe a change to a spiral point tap will help, but of course at the cost of having more of a problem removing the chips.
Cheers
Marcus
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