STRONG BAINITIC STEELS BY CONTINUOUS COOLING TRANSFORMATION

G. Gomez, T. Perez and H. K. D. H. Bhadeshia

Abstract

Using metallurgical models, three steels were designed to obtain carbide-free bainitic structures in the as-rolled condition. Experimental castings were hot-rolled in a pilot mill and their austenite decomposition kinetics were measured using dilatometry. Tensile and Charpy impact proper ties were measured and the microstructures were characterised using X-ray diffractometry, optical and scanning electron microscopy. Promising results were obtained when the microstructure was composed of a fine mixture of bainitic ferrite and retained austenite. In this case, 140 ksi (965 MPa) of yield strength was achieved in combination with good toughness. Conversely, when the structure was coarse with blocks of retained austenite between bainitic sheaves or when large mar tensitic regions were present, the impact proper ties were strongly impaired.

New Developments on Metallurgy and Applications of High Strength Steels, Buenos Aires 2008, Argentina (2008).

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