Heat Treatment Design to Modify the Martensite Misorientation and Obtain Superior Strength-Toughness Combinations

A heat treatment methodology is described for obtaining ultra-high strength (> 1700 MPa) and increased - 40 degrees C toughness (> 45 J/cm(2)) in a steel. Thermodynamic approach to design heat treatments is demonstrated and utilized to produce refinement of the prior austenite grain size leading to superior properties. The cleavage energy was shown to correlate to both prior austenite grain size, according to an inverse root relationship, as well as the density of high-angle martensite lath boundaries.