4140 = Chrome/Nickle, 4340 = Chrome/Nickle/Moly, often referred to as just Chrome/Moly. Both are normally through-hardened, not case hardened & the usual quench is oil. Drop the carbon content to 30 points as 4130/4330 & they become Water hardening.

I have no info on the French XTC at all, but I cut a pile of those others in my career & while I didn't personally do the heat treating of them I know how it was done.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra