Quenching with water and tempering
That is, after quenching, it is heated to about 250-300 degrees Celsius.
The hardness can reach HRC40-45.
How can we know the tempering temperature without an electric furnace?
It can be burned with acetylene gas.
When did the oil drip on the wrench and catch fire?
Stop heating.
Then quickly cover the wrench with white ash (especially fine furnace ash)
You can take it out in three or four hours.
There are simpler ones.
It is best to send it to the heat treatment workshop.