Dual-Phase Steels

A relatively recent development, dual-phase steels are produced by rapidly cooling a medium-carbon steel, containing vanadium or molybdenum, from the twophase ferrite plus austenite region. The austenite transforms into islands of martensite (stabilized at room temperature by the V and Mo additions) in a ferrite matrix. Depending upon the alloy content, the martensite islands can also contain austenite that is retained below the transformation temperature (called retained austenite). Thus, dual-phase steel may contain both martensite and austenite as a second phase (called MA constituent). The unique characteristic of dual-phase steels is the continuous yielding behavior during deformation; i.e., there is a lack of a yield point during deformation. This provides increased uniform elongation and work hardening so that those components or parts produced from dual-phase steel actually gain strength during the forming operation. Dual-phase steels are being applied in applications such as automobile wheel rims and wheel disks. Because of their energyabsorbing characteristics, dual-phase steels are being used in critical locations of the automobile for safety to protect the occupants in the event of a crash.

Bruce L. Bramfitt

International Steel Group, Inc.

Research Laboratories

Bethlehem, Pennsylvania

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