Heat treating K390

[TigFur]

Hi everyone,
i have just finished my first hand filed batch of small K390 blades and i am ready to send them for HT.

Problem is i have to specify all the temperatures and the process.

What would you suggest i go for? What is your experience? Should i use cryo?




Ive seen people reaching up to 67 on this steel. My main focus is edge retention. Its just small neck knives. I think somewhere 64-66 should be perfect.

according to the manufactures sheath it can reach 64 when quenched at the highest temp 1180°C (2156F) and then tempered at 540°C (1004F) but that might be brittle?

I found some sources saying that with cryo one can move the temperature down and still get the same hardness but with a better toughness, or get a better hardness.



Thanks for your help.

 

[Larrin]

Does the heat treatment service offer cryo?

 

[john april]

just curious, who is doing the HT that needs instructions sent in as well ? if i was a shoe repairman, i would not expect you to give me directions on how to fix the shoes

 

[TigFur]

just curious, who is doing the HT that needs instructions sent in as well ? if i was a shoe repairman, i would not expect you to give me directions on how to fix the shoes

I asked about 6 places and most would HT it to 62 HRC by default, if you want something custom you have to provide instructions i guess. Or its a matter of insurance against problems when the blade breaks with an unusual HT...

Does the heat treatment service offer cryo?

yes - and you specify the temperature as well

 

[Larrin]

For your hardness target I would use 1950 and 400°F.

 

[TigFur]

1950F id understand however, 400F is far below the tempering range of K390, it starts somewhere around 930F according to specifications

 

[Larrin]

1950F id understand however, 400F is far below the tempering range of K390, it starts somewhere around 930F according to specifications

Yes ignore that and use 400°F instead.

 

[Willie71]

1950F id understand however, 400F is far below the tempering range of K390, it starts somewhere around 930F according to specifications

Cryo converts the retained austenite, so you don’t need the higher tempering.

 

[TigFur]

Thats really interesting, so both the quenching and tempering temperatures can go lower thanks to the cryo and still reach similar hardness but with better toughness?
Do you guys actually use these numbers with K390 or is it just an advanced estimate?

 

[DevinT]

Larrin did the testing for this steel, um, and lots of others.

Hoss

 

[TigFur]

Larrin did the testing for this steel, um, and lots of others.

Hoss

Ah the knife steel nerd page i see! Ive read a lot of very interesting and detailed information about metallurgy there.
Ill go for these expert temperatures then.

Just how cold and long should the cryo be?

it seems to have a wide range of temperatures... i guess around -150°C (-238F) ?
I might leave this up to the HT place.

Ill post the results and try a careful tip test.