COMPOSITION REFINEMENT STUDY, 5NI-CR-MO-V STEEL.

Studies to date have shown that a 0.10 C, 0.75 Mn, 5.0 Ni, 0.55 Cr, 0.55 Mo, 0.07 V steel is very promising as an HY-130/150 steel. However, the minimum yield-strength range (130 to 150 ksi) and the plate-thickness range of interest (1/2 through 6 inches) are quite broad and may demand composition modifications to meet the full range of HY-130/150 requirements. Therefore, the yieldstrength and thickness requirements were broken down into four classes: (1) 130 to 145 ksi through 3 inches, (2) 140 to 155 ksi through 3 inches, (3) 130 to 145 ksi in 3 through 6 inches, and (4) 140 to 155 ksi in 3 through 6 inches; and a statistically designed program was initiated to determine the changes in the manganese, nickel, chromium, and molybdenum contents of the 5Ni-Cr-Mo-V steel that would be needed to meet the various requirements. The results showed that no modifications in the standard composition of the 5Ni-Cr-Mo-V steel are needed to meet requirements (2) and (3), and that requirement (1) could be met by lowering the molybdenum to about 0.40 percent. Requirement (4) could not be met by simply increasing the hardenability because the Charpy V-notch energy absorption fell below 60 ft-lb at 0 F. Further examination of the results of the present study on Laboratory steels indicates that the best combination of strength and toughness is achieved when the manganese is decreased and the nickel is increased. (Author)