High Toughness Secondary Hardening Steels With Nickel as a Primary Strength and Toughening Agent

A steel alloy, comprising:

• a medium carbon secondary hardening steel composition containing:
• 0.3-0.45 wt. % carbon;
• 4-6 wt. % chromium;
• 0-2.5 wt. % molybdenum;
• 0-3 wt. % tungsten;
• 0-1.0 wt. % vanadium;
• less than 0.75 wt. % silicon;
• less than 3 wt. % cobalt;
• and
• less than 1 wt. % manganese;
• and
• an addition of nickel to the medium carbon secondary hardening steel composition in a wt. % that:
• increases a yield strength of the medium carbon secondary hardening steel composition to at least 1500 MPa;
• increases an ultimate tensile strength of the medium carbon secondary hardening steel composition to at least 1800 MPa;
• and
• increases a KIc fracture toughness to at least about 86 MPa√m.