Properties of Ultra-high Strength Bainitic Structures

Résumé du livre

The tensile properties and fracture toughness were measured in sheet material for isothermally transformed lower bainite and tempered martensite in a series of alloy steels. The major experimental variables were transformation temperature, tempering temperature, carbon content, and alloy additions. Carbon contents of 0.55 to 0.60% or higher are required to develop ultra-high strength levels in lower bainite. Lower bainite with yield strengths above 220,000 psi had slightly to moderately lower fracture toughness than tempered martensite in typical low alloy steels at comparable yield strengths. At yield strengths below 220,000 psi, lower bainite was equal to or slightly better than tempered martensite in typical low alloy steels, except the 1Cr-1Mo composition which is superior to the other alloy steels studied at yield strengths up to 240,000 psi. The fracture toughness of lower bainite is discussed in terms of transformation temperature, M sub s temperature, and steel composition. A 9Ni-4Co steel developed an atypical bainitic microstructure at transformation temperatures just above the M sub s temperature.