Suddenly failing at heat treating 1095, 1080, and unknown steels after years of success.

[Tracey Cheuvront]

I’ve been making woodworking tools at a small scale for over ten years and have mostly been successful achieving good to excellent edge retention on axes, adzes, chisels, spokeshaves, and drawknives.  I always use the same basic heat treat: heat to just past non-magnetic with a charcoal forge or propane torch, quench in canola oil, temper at 400F for two hours.  I use mostly unknown steels, so any time a tool wouldn’t take a good temper, I chalked it up to that.  No biggie, most turn out great.  

 

Suddenly, none of my drawknives will harden properly, even using known 1080 and 1095.  I’m a professional woodworker, have restored and used scores of antique drawknives, and can fairly say that some of the ones I’ve made hold an edge as well as or better than even the best vintage ones.  Before becoming a woodworker and toolmaker, I was a technician in a biology research lab where even the tiniest deviation from protocol could ruin an experiment, so I’m meticulous and detail oriented in my process, simple though it is, and try to be as consistent as possible.  I’ve changed out my quench oil, tried quenching edge-first vs. spine-first, with the oil at 50F vs 135F, even tried quenching some in water instead of oil and they still won’t harden.  I mean, 1/8” to 3/16” 1080 and 1095 should not cut easily with a file straight out of a water quench, right?  I also tried grinding off an extra several thousandths from the back and the bevel in case of surface decarb.  But here’s the most bizarre thing.  If I make a chisel from the exact same piece of bar stock and do the exact same heat treat, the steel hardens properly and holds an edge.  And, one of the best drawknives I ever made came from a piece of bar stock that is now not hardening.  Could it possibly have something to do with the fact that I arc-weld the blade steel to the mild steel frame?  Because it seems it’s just the blades that get welded that don’t harden.  This doesn’t seem right to me since it has worked fine many times in the past, the edge is an inch or more away from the weld, and I do the weld before heat treat when the blade steel is factory annealed.  This has happened on a dozen drawknives in a row now, most of which I have attempted to heat treat more than once, all to no avail.

 

I’ve spent two solid weeks of shop time trying to figure this problem out and it just keeps getting more mystifying and discouraging.  Any insights or suggestions would be dearly appreciated!  And if anyone out there has professional equipment and could normalize and heat treat a small batch of drawknives for me, please let me know what you would charge for that service.  

 

Thanks!

[Jerrod Miller]

Have you tried heat treating in low light and watching for recalescence and decalescence?  

[Joël Mercier]

Also, did you try etching the steel post HT? It may reveal some clues...

[Alan Longmire]

It sounds like some variable has changed, somehow.  New brand of charcoal? Relined the forge?  New light source in the shop?

Don't laugh, when I replaced the standard fluorescent tubes in my shop with full-spectrum tubes I couldn't forge weld for over a month until I got used to the visual difference. List every single thing that has changed in your shop, no matter how apparently insignificant. Something on that list will be the culprit. 

[jake cleland]

Basically either 1. you're not getting it hot enough (non magnetic is around 1412f, you need around 1460f to get those steels to harden in oil), 2. you're not cooling it fast enough (with 1095 you have around a second to get it out of the fire, into the quench, and cooled to around 900f) or 3. you've mixed up your steel with something unhardenable I'd start by heating a piece a couple of hundred degrees hotter than usual and quenching in water - if that doesn't get it hard, nothing will. Then dial back the heat from there...

Edited February 12, 2022 by jake cleland

[Joshua States]

One thing you don't talk about is your normalization process. 

[Brian Dougherty]

I'm not a fan of using a magnet, but it seems to have worked for you for a long time.  As the others have said, some variable has changed on you.  Any chance you got your magnet hot recently?  They loose their magnetism with heat, and a weaker magnet might be triggering your "Non-magnetic" point a few degrees earlier than it used to.  A lot of debris on the end of your magnet would do the same thing if it has gotten dirty. 

 

 

[Tracey Cheuvront]

Thank you everyone for all your suggestions -- I think the problem has been identified.  Seems it is essentially a shop lighting issue.  I have moved my quench station just a few feet, but it used to be almost directly under a bright LED light and now it is at about the midpoint between light sources, so the metal appears brighter than it used to at the same temperature and (despite being slightly past non-magnetic) has not been getting hot enough for proper hardening at quench.  The big lesson for me, as some of you mentioned, is that no detail is too small to consider.  I've had four drawknives in a row temper such that I can aggressively rip through dry oak for fifteen minutes and an edge will still shave!  Thanks again all!

[Alex Middleton]

Glad you got it figured out.  That's one of the reasons why I heat treat in the dark.  It also helps tremendously when watching for decalescence.