[georgeld]

Nice work Al:

A bit more on case hardening and tempering from the metalurgy
classes I took in college.

IF you heat a metal part and quickly dunk it to quench, then take it
right back out without letting it cool down much, that hardens the
outside: Re: Case harden. The longer you cool it, the deeper the
hard layer gets.

IF you dunk the hot item in until plumb cold, that tempers it all the
way thru.

"Color case hardening" is a misused term. That's using a bone meal bedding to slowly cool the metal, the bone meal chemicals absorb into the steel at varying rates making the color variations. It's actually annealing the metal, NOT hardening it. Try it sometime and see if a file will cut it. IF it will, that means the surface is soft. I can temper good tool steel that will eat the teeth off a file, that's damned hard!"

Actually, if you highly polish metal, then play a torch around on it with or without acids you can get about the same color effects
without the bone meal adding its various chemicals and carbon absorption.

I spent 5 summers on a ranch as a teen with an older rancher that did a LOT of blacksmithing. Including making our own rock drills to drill holes for blasting. And making four 1/2"x4" steel "tires" for a wagon out of flat bar.

Over the years I've made a great many chisels and rock drills. Some of the best tool steel to be found is oil well sucker rod. I've always wanted to get a length of 3/4" or 1" and never have. I did get a few hundred feet of 1/2". Mostly to use as a top rail on my back fence.

Some of the extra I've kept for making tools with it. I made some that have drilled a hole thru two feet of concrete that never dulled enough to need resharpening. The temper has to be just about right. IF it's too hot and quenched cold too fast. It can be brittle and will chip. When making one I also temper the head so it won't mushroom over but, not as hard as the cutting edge. The trick is knowing and watching the heat color fade to just the right shade of pink. Barely pink for the head will never mushroom over and each hit with the hammer will dent the hammer face.

A fairly medium bright pink quenched cold will make a long lasting cutting edge. IF it's too bright, not quite yellow, it's going to be brittle and you may get hit with a chip like i was once.

Actually to "PROPERLY" heat treat any metal needs to be done over many hours soaking in various acids at certain temps. I never got into that, where I was a machinist we had a heat treating dept and I saw it being done. Instead of working I was wandering around the big plant seeing what other depts were doing.

When it comes to brass cases. Torch it just to where the case mouth down to the bottom of the neck 'just starts' to turn color. Then drop it into a can and let it air cool. When one right, the color/heat will travel just past the shoulders. The anneal will be perfect. IF you quench it, that rehardens it and it will crack. Someone many years ago claimed to quench it to soften. That mis-information is still repeated today and most likely will get some of you to argue with me again now.

All I can say is try some both ways and test them. I split 47 necks of $1 per case brass. After heating and let air cool, I never split another out of 500. for a test I air cooled 20 and quenched 20. 7 of the first 10 quenched split and not a single one of the air cooled did. Those were 7mmg and 300 RUM cases I was necking out to 35 cal and had paid a buck each for used brass. Those 47 that split I sent to BillK.

Again: try it both ways and see what happens when you open the necks.