0-1 failure to fully harden?

Question

Months ago, we made some small machine parts from 1" x 1/2" x 2" ground stock from McMaster. The instructions to my heat-treater were to make them "as hard as possible" 58-63R. They are a big outfit running 24/7 and do a lot of 0-1. But, when we got the parts back we tested to 49R. We had taken out tester there many months ago to make sure we and they got the same readings. When we called about the low numbers they said our parts were with a big batch that tested OK. they didn't test our parts specifically. They said it was probably the steel. We used the parts hoping 49R was good enough...it wasn't. The parts have a carbide pinch roller in a slotted pocket and the carbide coined into the roof of the pocket in a few months and now won't function properly. The bitch of it is that the parts have 12 really, really persnickety, time consuming machining operations with pockets at angles and tiny slots and holes.

So, I have to make new parts and I still have a couple feet of the same bar and need the parts right now! I had my "Midnight Machinist" get started tonight to make at least 2 parts (they work in pairs) that had to be finished ASAP and I'll heat treat them in-house even if they only hit 49R.

So, did the steel fail or the heat treater? I don't think I've ever had 0-1 fail to harden before, is it common? Tomorrow, I'll cut a whack of the bar, torch it and test it. If I torch the old part, will it harden like new if I torch it?

I do have a new mechanism design that will make these parts obsolete if it works but the prototype is weeks away so I don't want to put a whole lot of time or money into this but they have to work in two machines until then.

Ed Huntress · Accepted Answer

You can't tell from this information. When hardness is critical, send the heat-treater a couple of coupons cut from the stock you're using before you send him the finished parts. If you have time, await the hardening results on the coupons before machining the parts.

O1 is a very reliable steel but, unless the source of your steel is certified, God knows where it came from or who made it.

I don't think I've ever had 0-1

It's not common in O1.

Probably not. Soak time will be a variable if the steel starts in a hardened state. O1 is relatively insensitive to it, but a torch isn't going to be reliable enough for the test you want to do. And if the part failed its hardness test in the first place it could have been due to burning or excessive soaking, which will keep the part from re-hardening properly but won't tell you a thing about the rest of your steel stock, or about how your heat treater will perform with the *next* batch.

If your heat treater is running O1 parts all the time and if it won't cause unacceptable delay, send the coupons first.

whit3rd · Answer

The prescription for O1 hardening is to quickly oil-quench; if your part is complex (thick and thin parts) it might not quench perfectly uniformly. Can you ask your heat-treater about air-hardening steel options?

Wes · Answer

Were your small pieces next to a much larger piece? Might have changed how quickly it was quenched.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

0-1 failure to fully harden?

Join the Discussion

Didn't find your answer?