Böhler K460 / O1 tempering problems

P

Pemihan

Joined
Jul 31, 2020
Messages
6
Hi guys,

My first post here :-)

I have an issue with heat treating Böhler K460 which should be equivalent to O1. When I temper according to the manufactures specs it comes out softer than I'm aiming for.

I soak at 800c / 1470f for 25-30 minutes and quench in oil which gives me about 63 HRC before tempering. I then temper at 230c / 446f for 2 hours x 2 and end up with around 55 HRC. According to specs I should be around 60 HRC.

I can't see what I'm doing wrong here. Both my hardening and tempering ovens are precise and I temper the blades straight after hardening.

Any ideas?

Also is it possible to reharden a knife? Anneal it and start over?

Thanks
Peter
 
Are you using a digital controlled oven for tempering? How was the hardness determined? The numbers aren't coming out right.

At that austenitization, you should have been at Rc65 as-quenched.
At that tempering temperature the hardness should be Rc60.

Yes, you can reharden the knife. No need to anneal it.
 
It’s best to run some coupons to see where the peak hardness is, with and without cryo if possible.

Your furnace might be running a little low or high so you probably need to adapt to the equipment.

There is no need to soak that long which may be leading to a little more retained austenite. I recommend cutting the soak time to ~15 minutes.

It doesn’t hurt to start low for tempering and increase the temperature by 25’f until you get the desired hardness.

Hoss
 
Stacy E. Apelt - Bladesmith said:
Are you using a digital controlled oven for tempering? How was the hardness determined? The numbers aren't coming out right.

At that austenitization, you should have been at Rc65 as-quenched.
At that tempering temperature the hardness should be Rc60.

Yes, you can reharden the knife. No need to anneal it.
Click to expand...

Hi Stacy,

My tempering oven is our fairly new kitchen oven. I have controlled both that and my heating kiln (A Paragon Kiln) with a secondary thermometer and both are running at the correct temperature. So that side of things should be ok.
The hardness was determined with this: https://www.newegg.com/p/2Z3-001U-00001 Not mine unfortunately, but another maker nearby is so kind to do the tests for me.

When heat treating I preheat the oven to 800c, then in with the knives and when it get back up to 800c I start the hold time, if that makes sense.

I agree that the numbers aren't right, but can't get my head around it. The numbers should in the ballpark of what you mention.
I will call the dealer where I buy the steel tomorrow to get their take on it.

And I will try to reharden the knife and temper at a lower temperature.

Thanks
Peter
 
DevinT said:
It’s best to run some coupons to see where the peak hardness is, with and without cryo if possible.

Your furnace might be running a little low or high so you probably need to adapt to the equipment.

There is no need to soak that long which may be leading to a little more retained austenite. I recommend cutting the soak time to ~15 minutes.

It doesn’t hurt to start low for tempering and increase the temperature by 25’f until you get the desired hardness.

Hoss
Click to expand...

Hi Devin,

I have controlled my furnace at 250c and it is correct at that temp, haven't tried 800c though, difficult to find anything to measure that temp with :-) I would assume that a Paragon Kiln would be correct though, but of course you never know.

The manufacturer of the steel recommends a soak time of 15-30 minutes, I have tried around 12 minutes which gave me the same results.

So let me get this right, you mean that I can temper one piece at lets say 200c and if that's to hard after two hours give it another go at 225 and so forth? Or one piece at 200, one piece at 225 and so forth?

Thanks
Peter
 
Pemihan said:
So let me get this right, you mean that I can temper one piece at lets say 200c and if that's to hard after two hours give it another go at 225 and so forth? Or one piece at 200, one piece at 225 and so forth?

Thanks
Peter
Click to expand...

I'm not Hoss, but yes. You can start with a low temper, and increase temp till you get the hardness you want.
 
You must log in or register to reply here.
Back
Top