4145M is a low alloy steel that is commonly used in downhole tools, tool joints, and drill collars. It is a heat treatable alloy steel that contains nominally .45% Carbon, with Chromium and Molybdenum as the primary hardening elements.
As compared to 4140, the 4145 mod grade has higher levels of Chromium and Molybdenum, which will provide much deeper hardening into the steel after austentizing, quenching and tempering.
This alloy should not be confused with AISI 4145, as the chemical limits for the modified version are much higher.
110,000 psi minimum yield - 285-341 Brinell surface hardness
120,000 psi minimum yield - 285-341 Brinell surface hardness
Annealed or As-rolled - no mechanical properties; suitable for further heat treatment