Abstract
The relationship between the morphology and the mechanical properties in the isothermally transformed low-carbon low-alloy bainite has been investigated in comparison with those of tempered martensite.
The strength of bainite increased with lowering the transformation temperature because of the reduction of the thickness of the ferrite laths. As the decrease in the transformation temperature also reduced the unit crack path for cleavage fracture, the toughness in the impact test was improved. In the martensitebainite duplex structure formed by isothermally below Ms, higher tensile strength was achieved without losing toughness and this structure exhibited better impact properties than the martensite tempered at lower temperatures to produce the equivalent strength. The toughness of this duplex structure, however, was not so good as that of the bainite-martensite duplex stru
