hardening/tempering time line

G

GRapp

Joined
Nov 14, 2022
Messages
197
If I'm cooling the blade via quench, does it matter when the temper happens? By that I mean do I need to temper right away or could it wait hours or days? In my mind the grain structure will wait for me but I just hardened my first blade so obviously, I have no experience. This is 1084 quenched in Parks 50. Thank you for taking the time.
Gary
 
The steel is under maximum stress immmediately after quench. If conditions are correct, those stresses can cause a blade to sit there and simply break without coercion. Small micro-cracks may propagate that may cause later failure. Tempering reduces those stresses to reduce that possibility and place the steel in a form we can use with some reliability (if done properly). The entire process is best kept as continuous a flow as possible.
 
If you have to wait, you can do a snap temper to relieve some of the stress in your blade. I’d at least temper for 30 minutes at 350 degrees after quenching.
 
fitzo said:
The steel is under maximum stress immmediately after quench. If conditions are correct, those stresses can cause a blade to sit there and simply break without coercion. Small micro-cracks may propagate that may cause later failure. Tempering reduces those stresses to reduce that possibility and place the steel in a form we can use with some reliability (if done properly). The entire process is best kept as continuous a flow as possible.
Click to expand...
I’ve heard this but I’ve never actually seen it happen after heat treating about 100 blades and even having water quenched 1095 sit until the next morning before tempering.

For me tempering has to wait until the next morning so the kiln can cool.
 
There are several metallurgical reasons to temper as soon as possible. A snap temper at 200-300°F for 30-45 minutes will get you to tomorrow.
A cheap toaster oven set at 250°F will work just fine. The next day do the proper temper schedule.
 
They are not closely regulated but won't swing more than +/-25°. That is why I said to set it at 250°F. This is not to replace a regulated tempering oven, just to do a 30-minute snap temper ... which can be anywhere between 200°F and 300°F.

The newer toaster ovens use digital controls and have much tighter temps. Some keep +/- 10 degrees.
A pretty good affordable tempering oven is a countertop convection oven.
 
Stacy E. Apelt - Bladesmith said:
They are not closely regulated but won't swing more than +/-25°. That is why I said to set it at 250°F. This is not to replace a regulated tempering oven, just to do a 30-minute snap temper ... which can be anywhere between 200°F and 300°F.

The newer toaster ovens use digital controls and have much tighter temps. Some keep +/- 10 degrees.
A pretty good affordable tempering oven is a countertop convection oven.
Click to expand...
I have one when set to 450 it’s actually only 350 I have others that are more accurate.
 
Thescrawnylumberjack said:
Yeah I could do a low temp over night I see a probably a 25 degree variance there but if it set it to 225-250 before doing the real temper that should be fine
Click to expand...

I find my kitchen oven is more accurate for low temper temperatures than the knife oven. Obviously if you are doing high temperature tempers kitchen oven will not work.
 
Thescrawnylumberjack said:
The issue with this is temperature control in toaster ovens are abysmal
Click to expand...
It's simple to add mass:

5cy8oGO.jpeg


Note the temp probe just above the axe head; it's connected to a DT33C multimeter. Very slow to change - if anything - it's too slow. Very stable but not all that accurate from the dial. hence, I use the temp gauge to adjust temps. I tempered this axe head for 390 degrees for 1 and 1 1/2 hours. Temps never moved more than 1-2 degrees +/-.
 
Last edited:
I’ll also chime in and say in my experience a good kitchen oven is just as accurate or more so at low temperatures in the 300-400 range. Often if it’s off it has to do with calibration which can usually be done easily if you have a secondary probe or thermometer to check the temp. My current oven that I use for tempering was off until I calibrated it for the readout and now it’s very accurate and consistent. Best part is not having to wait until the next day to temper.
 
I'm with Josh. Most kitchen ovens are very precise once they have pre-heated and been allowed to soak a little while. I still do 90% of my tempering in the kitchen oven. I have checked it with a reliable pyrometer and found it within 5°+/-.

Once the smithy is rebuilt this summer/fall I will install a convection oven there.
 
I'll third Josh, and second Stacy. Our kitchen oven holds a very accurate and precise temperature for tempering, especially with one of those very large, thick, and heavy stone baking sheets or whatever they are. Every so often I'll throw in 3 different thermometers just to verify, and they are always within 5° of each other, and the oven thermostat.
 
You must log in or register to reply here.
Back
Top