Junk steel - how to identify?

Question

I recently I milled a piece of 3/8" steel bar that I pulled out of my junk pile. It wasn't cutting very well and on inspection I saw that the cutter was dull and put on another one. Very shortly it stopped cutting and was found to be dull. This stock had cut and drilled easily, so it wasn't hardened. I concluded that there must have been a bad spot in the stock, an inclusion of something hard. Does that happen?

If so, how do I avoid it? If I buy stock from a place like OnlineMetals can I have any confidence that it won't have this problem? I'd hate to throw out my carefully acquired junk but buying new stock would be cheaper than buying new cutters.

Thanks, Bob

Bob Engelhardt · Accepted Answer

Thanks for all the replies - a lot of good information (as one would expect from RCM).

As for identifying the type of steel, I'm a 2-type guy: hard and mild. If the steel fails the file test, I don't use it. The stuff that I make just doesn't need "hard" (well, occasionally I've used oil-hardening that I've hardened AFTER machining).

Thanks for confirming my suspicion about the non-homogeneous stock (that would be heterogeneous, right?). I.e., that mild stock can have hard inclusions in it. I guess the only way to avoid it is to buy "fresh" stock (not scrap yard stuff). As much as I hate to give up the nice collection of stock that I got at the dump, it just isn't worth it if I'm going to ruin cutters on it. Worse, if it means that I'll put significant time into a part only to be unable to finish it because of an inclusion.

I'm thinking that I should make a list of the stock I'm likely to use and just buy it to have around. And buy nice stuff (12L14 comes to mind). Then throw out my dump stock. Life's too short for that kind of aggravation and I don't use so much stock that it matters.

Thanks again, Bob

Junk steel - how to identify?

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