Cold-rolled complex-phase steels: AHSS material with remarkable properties

The reduction of the body-in-white weight, in combination with stiffness and crash safety improvements is of fundamental interest in the automotive industry. Therefore, several Advanced High Strength Steel (AHSS) grades have been developed in the last several years, whereby the main focus was laid on dual-phase (DP) and TRIP steels. Recently, a new high strength steel grade - complex-phase (CP) steels - is gaining more and more interest. In contrast to DP grades of similar strength level, CP grades have a significantly higher yield strength and thus a higher yield ratio. Although, CP grades reach lower elongation values in the tensile test, they show an excellent bendability and stretch-flangeability. Due to this remarkable balance between strength, bendability and stretch-flangeability, complex-phase steels are potential candidates for roll-formed parts and parts where sharp radii and/or a good formability of punched edges are required. Therefore, the microstructure, the processing, and the formability of CP grades are discussed in detail in this work. (orig.)