Question about tempering

[MyNameIsBo]

Hello!! I'm working on my very first knife made from an old file, and I think I messed up. I put it in an oven at 450 °F to draw the temper down, and meant to leave it for an hour, but when I went to check on it, the oven seems to have shut off after only 30 minutes. Can I just put it back in and make sure it stays for a full hour, or does it need to be re-quenched now?

 

[DevinT]

Just put it back in for more tempering. It will be even better.

Hoss

 

[Contender Machine]

Just put it back in and start over, it'll be fine.

 

[MyNameIsBo]

Just put it back in for more tempering. It will be even better.

Hoss

That's a relief, thank you for the info!

 

[MyNameIsBo]

Just put it back in and start over, it'll be fine.

Will do!! Thank you

 

[MyNameIsBo]

Just put it back in for more tempering. It will be even better.

Hoss

If I don't have time to do the 2nd hour long cycle tonight, will it still be fine to do that tomorrow, or does it need to be done relatively soon after the first cycle? Thanks again

 

[DevinT]

If I don't have time to do the 2nd hour long cycle tonight, will it still be fine to do that tomorrow, or does it need to be done relatively soon after the first cycle? Thanks again

Yes, fine for tomorrow. Tempering is pretty forgiving.

Hoss

 

[MyNameIsBo]

Yes, fine for tomorrow. Tempering is pretty forgiving.

Hoss

Thanks a ton!!!

 

[Alex Topfer]

If I don't have time to do the 2nd hour long cycle tonight, will it still be fine to do that tomorrow, or does it need to be done relatively soon after the first cycle? Thanks again

It's only the first temper that needs to be done soon after quenching, as it relieves some stress from martensite transformation. That stress can apparently lead to blades cracking, although i don't think i've ever had that happen
The second one is there as the first temper can convert retained austentite to fresh un-tempered martensite
Sometimes people don't do the second one. You often see that with flame tempering

The time is also pretty flexible; temperature is more important while the time is more there to ensure the entire piece reaches temperature

 

[Stacy E. Apelt - Bladesmith]

You chaps are missing something:
In this case, tempering delays do not matter ... because the file is already tempered.

Bo used a hardened file. which was tempered when it was manufactured... just to a higher degree than he wanted. The issues of stress and retained martensite are long gone.



Bo-
Temper again at 450°F when you get a chance. Tonight, or next week, it won't matter.

When shaping the file into a knife, and working on the edge, avoid getting it hotter than is comfortable to hold.

 

[MyNameIsBo]

You chaps are missing something:
In this case, tempering delays do not matter ... because the file is already tempered.

Bo used a hardened file. which was tempered when it was manufactured... just to a higher degree than he wanted. The issues of stress and retained martensite are long gone.



Bo-
Temper again at 450°F when you get a chance. Tonight, or next week, it won't matter.

When shaping the file into a knife, and working on the edge, avoid getting it hotter than is comfortable to hold.

Thank you so much for the detailed reply Stacy! I'm so excited to get this project going. I've been wanting to make knives for years, but never realized I could've been doing it all along with a few basic tools.