I built two laser cut receivers made of 4130 steel and heat treated both of them. The first one I did the entire receiver and oil quenched. The specs for 4130 steel are as follows:
AISI 4130 Steel, water quenched 855°C (1570°F), 480°C (900°F) temper
As quenched hardness: 51 HRC surface, 50 HRC
After 900 deg. F temper :Hardness, Rockwell C 36
Link-http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=M4130F
I did the entire receiver and I did not attain the hardness listed. I checked the receiver on a rockwell hardness tester and it was still soft or annealed. I then used my torch oxy/acy. and spot treated all the features I wanted and WATER quenched. The material hardened this time.
I did all of the fire control group holes,front trunnion rivet holes and receiver rails. I did the rails 1/2 at a time. After flame hardening and water quench I put it in the draw onev at 900 F.
When I checked some features this time they were in the Rc 35 range.
The oil quench was the problem. I think the metal cooled to slowly. If anything I normalized my welds from the first trip in the furnace. I did not get any warpage from the oil quench. I did get a little warpage from the water quench and torch treatment. Nothing on the rails but a small amount by the front trunnion rivets. This warpage is minimal and will not be seen after riveting the trunnion in place. Any future builds I will always use my torch and a bucket of clean water.