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HiBC · May 18, 2017, 11:48 AM

If you look at the Rockwell "C" specs of many modern,commercial frames and slides you will see they are called out in the vicinity of 24 "C"

4140 etc are alloy steels that will heat treat and harden,but not to the degree tool steels will.

When I was still working in manufacturing,I occasionally filled in in the heat treat room.I was never given the job of cycling parts through the ovens,but they did use an ancient,WW2 vintage induction hardener.
There was basic fixturing to locate a part so the hardening would be where desired There was a timer so the hardening would be to the correct degree.
So the operator held the part in the right place and stepped on the pedal.A portion of the part turned red,and you drop it in a bucket of water.
This spot hardening is fast and effective.
As I have done the process,I "have eyes" for it. I have looked at GI 1911 slides,the locking lug areas,and said to myself "Ah,induction"
But without carburization,these steels just don't get Rockwell 50 "C" hard.
If you quench harden a carbon steel part like a slide made of,say O-1 tool steel...You had better count on warpage,and if its only .030 over the length,you are lucky.
With something like a 4140 slide,it can be hardened to a modest "hard and tough" degree,where it is still quite machinable.The stock or the blanks or the forgings would be heat treated(or not) before machining.
You don't heat treat after the slide rails are machined.

The Garand receiver was mentioned. Those were typically 8620. Excellent stuff! Sort of like a 4140,with some hardening capability,good strength and toughness,but it is also excellent for gas nitride surface hardening,and it has something in it to prevent brittleness.
8620 can be purchased from McMaster Carr,and it is a great steel for gunsmithing parts.

I have found it common for Mauser 98's to be spot hardened. They may seem soft where you check them,but try the locking surface or cocking cam area.
IMO,it means something when my Starrett auto center punch bounces off without leaving a mark on these surfaces,but the punch will mark other areas of the receiver.

May 18, 2017, 11:48 AM	#20
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,288	If you look at the Rockwell "C" specs of many modern,commercial frames and slides you will see they are called out in the vicinity of 24 "C" 4140 etc are alloy steels that will heat treat and harden,but not to the degree tool steels will. When I was still working in manufacturing,I occasionally filled in in the heat treat room.I was never given the job of cycling parts through the ovens,but they did use an ancient,WW2 vintage induction hardener. There was basic fixturing to locate a part so the hardening would be where desired There was a timer so the hardening would be to the correct degree. So the operator held the part in the right place and stepped on the pedal.A portion of the part turned red,and you drop it in a bucket of water. This spot hardening is fast and effective. As I have done the process,I "have eyes" for it. I have looked at GI 1911 slides,the locking lug areas,and said to myself "Ah,induction" But without carburization,these steels just don't get Rockwell 50 "C" hard. If you quench harden a carbon steel part like a slide made of,say O-1 tool steel...You had better count on warpage,and if its only .030 over the length,you are lucky. With something like a 4140 slide,it can be hardened to a modest "hard and tough" degree,where it is still quite machinable.The stock or the blanks or the forgings would be heat treated(or not) before machining. You don't heat treat after the slide rails are machined. The Garand receiver was mentioned. Those were typically 8620. Excellent stuff! Sort of like a 4140,with some hardening capability,good strength and toughness,but it is also excellent for gas nitride surface hardening,and it has something in it to prevent brittleness. 8620 can be purchased from McMaster Carr,and it is a great steel for gunsmithing parts. I have found it common for Mauser 98's to be spot hardened. They may seem soft where you check them,but try the locking surface or cocking cam area. IMO,it means something when my Starrett auto center punch bounces off without leaving a mark on these surfaces,but the punch will mark other areas of the receiver.