high purity materials because this prototype did not include ti the grain pinning dispersion of tic particles could not form as a result the average grain diameter was 83 u03bc and toughness was very low the cvn impact energy of the core material from this prototype was 5 ft lb at an ultimate tensile strength uts of 238 ksi a second 300 lb vacuum induction melt of fe 17 0co 7 0ni 3 5cr 1 5mo 0 2w 0 12c 0 03ti wt was prepared from high purity materials this composition did include ti and the average grain diameter was 35 u03bc toughness improved substantially the cvn impact energy of the core material from this prototype was 23 ft u00b7 lb at a uts of 238 ksi the corresponding processing condition was to carburize and concurrently solutionize the steel at 927 u00b0 c for 8 hours quench with oil immerse in liquid nitrogen for 1 hour temper at 496 u00b0 c for 8 hours and cool in air the fracture toughness in this condition was 100 ksi u221a in the dbtt in this condition was around room temperature a 10 000 lb vacuum induction melt of fe 16 3co 7 5ni 3 5cr 1 75mo 0 2w 0 11c 0 03ti 0 02v wt was prepared from high purity materials half of the melt was converted to a 6 5 inch diameter barstock while the other half was converted to a 4 5 inch diameter barstock the optimum processing condition was to carburize the steel at 927 u00b0 c for 3 hours cool in air solutionize at 1000 u00b0 c for 40 minutes quench with.