440C Ulu Heat Treat problem

[Joel K]

Heat treated in an evenheat oven wrapped in SS foil at 1850 for 20min. Air cooled to about 150 then tempered 220 for 2h then 200 for 2h.  

The darkness on the left isn't buffing out... and edge feels a bit soft to the HRC test files.  Is it a prob with the steel or prob with my heat treat?

Thanks

Joel

[velegski]

What hardness were you shooting for and what are files giving you for reading. 

Which temp scale you using. F or C.  200? 200F isn't a common temp on tempering charts.

[Joel K]

Shooting for 55-60 HRC file test.  It's passing the hardness test, except maybe the one little blade edge spot in the middle of the dark spot on left.  The 440C heat treat guidance I used was from Evenheat to 1850f 20 minutes, air quench to no less than 125f then temper at 220f 2 hours, air cool then final temper at 200f 2 hours.

Still wondering if I did something wrong or is this a metal flaw in the piece of 440C.

Thanks

Joel

[velegski]

I'd try a coupon and see if you get similar results. 

Then try using the heat treat numbers from other sites and see if there's a change. 

Using 220f for a tempering cycle should have resulted in 60+ hrc numbers.  

As to blotch, Steel quality is might come into play. But then test coupons will confirm.

[Steve Sells]

Suggested heat treat for what thickness, most of those charts are for 1 inch or more thickness, which is why we have a separate area for blade HT,  btw I relocated your post here because of that. Also be aware that some discount steel places, don't always ship out what your ordered, they substitute often for "close enough"

[Joel K]

Thanks for relocating my post here Steve.  The Temps I used are from Evenheat website for knife heat treat.  I'm still curious about cause of black blotch....maybe a bad spot in steel??

[velegski]

Bad steel or one commercial heat treat site mentioned that improperly cleaned steel can sometime bake any organic materials into the steel. 

Another might be oxygen. The foil packet wasn't sealed good and allowed oxygen in, allowing  that area to develope scale.

[Frosty]

It's unlikely the steel has a bad "spot" in it even if it's not what you actually ordered, you would've spotted the indications cutting and grinding if that were the case. In all probability it's operator error, as mentioned the foil may have needed another layer or better fold/crimp. Or maybe a fingerprint, were you wearing clean fabric gloves when you handled it?

Won't it polish out?

Frosty The Lucky.

 

[Joel K]

Thanks for the feedback everyone!

I did clean it thoroughly with acetone before bagging it and used paper towel to put it in the foil pouch.

I believe it was a leak in the foil pouch...so scale from oxygen during heat treat.  It did not polish off with a scotchbrite wheel hence my concern and post here.

Took it back to the grinder which eventually cleaned it up.  

Will have to perfect my pouch sealing technique.   Double folded edge and sqeezed edge tight in a vise...  

Have heard of a scale preventing liquid, Espon,  that works up to 1280c but can't find a source to buy. 

Flux burns away at too low a temp.

Thanks!

J

[Steve Sells]

try adding a few small pieces of charcoal inside the foil to use up O2

[Joel K]

Yes, thanks I actually put a piece of brown paper bag in this one... but had the leaky pouch in spite of it.

[Frosty]

The paper  may have caused or added to the stain, use charcoal it's clean, especially if you make it yourself. You're only going to need maybe 1/2 tsp worth.

Frosty The Lucky.