Improved 2 1/4 Cr-1 Mo Pressure Vessel Steel Through Electroslag Remelting

Abstract

Results of a detailed investigation of the internal quality and mechanical properties of electroslag remelted 2 1/4 percent Cr-1 percent Mo steel are presented. Superiority over air melted-vacuum degassed electric furnace product in terms of homogeneity and cleanliness is evident. This quality enhancement is reflected by significant increases in ductility-dependent mechanical properties, and minimal anisotropy. Overall plate quality was established by straight-beam ultrasonic testing 100 percent of the volume to strict flat-bottom hole standards. Quality was further evaluated in critical locations by means of extensive chemical analysis, macro-etch tests, sulfur prints, and inclusion ratings. Comparison of results from various locations within the plate and gage demonstrated the advanced degree of uniformity and cleanliness. Mechanical property data exhibited improvements in toughness and tensile properties in all conditions—annealed, normalized and tempered, quenched and tempered. For example, exceptionally high CVN upper shelf energies are shown by quenched and tempered plate at three strength levels. Mechanical isotropy is greatly increased by electroslag remelting, particularly in the through-gage direction. Other improvements noted are superior fracture toughness as measured by KIc , resistance to slow crack growth (da/dN), and resistance to bending fatigue.