Why do I have to set my furnace to over 100 deg C more than recommended temp to harden it?

[Flynth]

Ericc, it definitely matches your description. I recorded a video of spark testing it:

And then W1, on the sand grinder with pressure as similar as possible etc:

I think it is the steel it should be. I'll try a different oil in future.

 

[ericc]

Hi. That looks about right. O1 has a strange, subdued spark. Without comparative coupons, it is hard.