At what temperature is temper and HT adversely affected??

Hey Guys,
I was doing a couple of rehandlings and one of the knives got pretty hot up into the blade even though i went through many precautions to prevent this. I was wondering, at what temperature does HT and temper start to be adversely affected? Of course I didn't have an accurate temp, suffice to say, the spine of the blade above the heel and about 1" forward was hot to the touch but not so hot as to burn one's skin. the edge was a touch cooler but still hot.
Maybe Cris, Will C, Mert, Ian, Randy, really any of the pro craftsmen here could answer this?
Thanks!
Matteo

 

Ping them! Ping them all
@CrisAnderson27 @William Catcheside @chefcomesback @Haburn @HHH Knives

My bet is that no damage should be done to HT if it's not even causing skin burns

 

It will depend on the steel. You can google tempering charts for steel. I think you're fine. Most carbon steels are tempered at around 200 deg C.

If it's hot but not burning I'd guess you didn't get above even 60 deg.

 

Does depend on the steel, but most stainless and carbon I use will be temper above 150degrees C, and you need to hold it at that temperature for an extended period to properly temper it. Unless you have got it hot enough to start to see heat colours in the steel or held it higher than 150 degrees for an extended period I doubt temper will be effected. You can check after thinning on the stones see if there is distortion or any difference in distortion where you got it hot by pushing the edge with your nail. No need to worry about the spine anyway, I often relieve temper on very hard knives on the spine and tang with a gas torch , (Edge clamped to soak heat away from the edge).

 

Hahahah...
Anton is right, you're probably fine. Temper soaks are typically done at 350 F - 400 F depending on steel and desired attributes. Those temps are held for 2-4 hours so a quick flash at 400 F shouldn't adversely affect the steel.

 

Thanks Dudes!
Always helpful around here, appreciate it.
Cheers
Matteo

 

@thedispossessed Did you notice any coloring of the steel? Or did it just feel really hot? If yes to color, then as long as it didn't go past the yellow to dark yellow range than your good. If it got to a red-brown or purple color then there might be issues. Otherwise if it just hot to the touch but no color you "cool". I've been grinding blades for a lot time and once the blade gets to around 200-250F it's too damn hot and its time for me to dunk to blade. Both because it's burning my dang hand and to protect the HT of the steel. Hope this is helpful.

 

Looks like these guys covered it. Color is the first indicator that you've exceeded temper...with a light gold being the first color you'll see (375°F-400°F). That's the range I temper my knives in. From there the gold will darken, turn to bronze, purple, blue, and grey. Most of those would be bad for a knife in the 60HRC or higher range...but as Will said, it's really only an issue with the edge area, as the top 2/3 of the knife can be tempered dead soft if you were able to do it. Clay hardened blades like mine take this to an extreme.

 

Lol, Mareko barely beat me to the punch .

 

@thedispossessed Another side note, are you wearing leather gloves when you're doing this work? Whenever I'm doing any kind of finish grinding work, I wear 5 mil nitrile gloves. While you do have to be a bit more careful that you don't grind you hands off, it gives me the ability to really feel whats happening temperature wise in the blades as well as being able to dunk my hand too when it does get up to that 20oF range, without getting retched prune fingers. They're cheep through harbor freight and have textured finger tips that help me keep a hold of my material. I'm also freehand grinding so this might not even apply to you. Cheers!

@CrisAnderson27 Great minds think alike!

 

Thanks Mareko and Cris!
I was just heating the very end of the tang over a stovetop gas burner for a rehandling job. I indeed did not see any color so 'we cool'.
I was working on 2 knives of similar size, what i found interesting was how cool one stayed (heiji semi-stainless) and how hot the other (kato) got.
I basically just laid the knife down on a magazine, placed a bag of frozen peas over the blade down to the heel, and put just the last 1/4" of the tang into the flame of a gas burner. It was cray the heiji got real cold and the kato got real hot in the same area near the heel.
Not that this thread warrants pics, but what the hell.
So I swapped these handles yesterday as I thought their size would be ideal on the other knife. The handle that came with my new Kato 180 was an oversized octagonal and the d-handle that came w the heiji was a good fit, but works much better on the petty.
The only issue was the heiji took the new handle at a slight angle (the tip of the knife sweeps up) which is actually great functionally but I'm OCD so it's bothering me a little. Also my photos are awful, i know, sorry guys...

Cheers
Matteo

 

Also just FYI for curious folks the dark hagane discoloring is the patina that the Heiji SS will take, it's pretty pronounced.

 

One of my favorite things about stainless san mai is the contrast between jigane and hagane .


Nice work!

 

cris, whatever little i've done to get a compliment from you, i'll take it!
It took about 6 attempts to get the heiji handle installed (huge tang). fortunately, my super chill 8 month old son was pretty patient while i did this.

 

For sure my friend, lol . I know all about working and keeping little ones occupied!