Design of Strong, Ductile, HSLA and Dual Phase Steels

摘要

This paper summarizes our alloy design programs at Berkeley which utilize the concept of two-phase steels as a means of optimizing these mutually exclusive properties. The underlying principle here is to design composite microstructures whereby the advantages of the second phase are optimized while the less desirable features of this phase are simultaneously mitigated by the presence of the other constituent phase. The size, distribution, shape and volume fraction of the second phase critically control the mechanical properties, especially fracture and fatigue of the dual phase systems. As a consequence, these structures offer a degree of metallurgical flexibility that is absent in single phase structures or in many precipitation strengthened systems, for attaining optimum sets of mechanical properties. Examples are presented here of martensite/austenite (approx.2 to 5%) mixtures designed for optimum combinations of high strength, toughness, and wear properties in medium carbon steels, e.g., for mining and agricultural applications, and martensite/ferrite (approx.80%) structure for high strength, cold formability and improved low temperature ductility in low carbon steels. Applications to sheet, line pipe rods and wires will be demonstrated for the latter class of steels. (ERA citation 11:036270)