I casehardened for years, And only used an acetylene torch to heat whenever I was case hardening. I was taught to heat the item cherry red, coat it with the case hardening material, and heat it up again Until it is real red. for a deeper hardening effect, repeat this again. Scrape off the left over case hardener and dip the item into Water, shaking it so that it Cools evenly. It's always worked for me, I've done chisels and my frizzens for some time now that I've never had one break from doing this.
Squint