Home built Heat Treating Oven

[DIYSwede]

Thanks for your confidence, hope I won't botch it!
Short answer: Trust the thermocouple - be wary of the IR thermo until you've figured out and applied this:

// EDIT: You wrote "the wrong thermocouple" -
did it max out at 600 C and the oven trampled on upwards, or what's the couple's upper limit?
I guess tool steel shouldn't be bright red at 600... Better recheck that before anything else of the text below...
Different types of thermocouples has different output voltages:



So having a wrong type could fool your controller into thinking it's 600 when really at cherry red 800-ish C...
For instance - plugging a "K" type into a controller set for a "J" type would perhaps be consistant with your result?
(Just follow the 33 mV line from the yellow "J" line (600C) to the green "K" line and read its temp below)
Sorry - I'm just about to hit the sack, so I wasn't really bright and fast enough...//

AFAIK: IR thermometers work by emission, and different materials have different emissivity values, kinda logical when you think of it.
Remember the black body/ polished body relative heat experiment way back in the physics classroom?
Emissivity is only radiated heat/ time unit - no more, no less.
There's one reason (besides sexiness) for black-anodizing cooling fins...

Then - a single, given material ALSO shows different emissivity att different temperatures as well - making it harder to measure correctly.
Also logical - starting at black at room temp, then heating it to fiery red - different rate of heat radiation/ time unit from the same piece.

For instance - I tried (in vain, of course) to use my IR thermo (1300C tops) for reading down into -80 deg C (CO2 extinguisher) a few weeks ago.

I quick-searched. and found some hopefully decent info regarding these matters (I'm not plugging their brand - and physics dont care for shareholders):
https://ennologic.com/ultimate-emissivity-table/
https://ennologic.com/emissivity-inf...eter-readings/

So for a proper readout - you need to know the emissivity of your chosen material, at the ball-park temp.

Personally, when it comes for my own Al alloy melts - the dross kicks my 30 quid fancy-pants IR's readings all over the place -
so I instead got a 5 quid cheapo thermocouple dipper/meter kit from China for consistent readings before the pour...

Hope this helps - guess someone more insightful reader here will correct me - and that's how I learn too!

Cheers
Johan