Development of a high strength high toughness ausferritic steel

A new ausferritic steel with high strength and exceptionally high fracture toughness has been developed. This steel has been synthesized integrating concepts from Austempered Ductile Cast Iron (ADI) technology. The influence of the austempering temperature on the microstructure and mechanical properties of this steel at room temperature and ambient atmosphere has been examined. The effect of microstructure on the plane strain fracture toughness and on the magnetic, electrical, and thermal properties was also investigated. Compact tension and cylindrical tensile specimens prepared from the low alloy medium carbon steel with high silicon content were initially austenitized at 927 deg. C for 2 h and then subsequently austempered at several temperatures between 260 deg. C (500 F) and 400 deg. C (750 F) to produce different microstructures. The microstructures were characterized by X-ray diffraction, scanning electron microscopy and optical metallography. A combination of exceptionally high yield strength (1336 MPa) and a high fracture of toughness of 116 MPa√m (a value comparable to maraging steel) was obtained in this steel after austempering at 316 deg. C (600 F) for 2 h. Potential applications of this steel include the inexpensive fabrication of armored plates and components requiring high reliability and durability.