Simple explination: 4130 before heat treating, it's almost shatter-proof.
Most 4130 when bought new is in a condition called "Normalized." In this condition the yield strength is 75,000 psi and the ultimate is 95,000 psi. It is sold this way so the user can work it (machine it for example) more freely. To develop its highest strength it is then heat treated. This will take it to a yield to over 100,000psi and the ultimate to over 125,000 psi. If you are possibly going to buy some 4130 make sure you know if it's "Normalized" or "Heat Treated." All the surplus 4130 I've seen has been was normalized.
