CR780Y980T-CH-GI: High strength complex phase steel with improved formability

Rolled profiles find a widespread application in many current vehicles (e.g. Renault Clio). Due to the high initial yield strength and the good local ductility of a complex phase steel, it is ideally suited for use in the roll forming process.
CH steels represent a rigorous further development and evolution of the classic CP steels. They combine the unique advantages of complex phase steels with the usual high formability of dual-phase steels. Compared to a classic complex phase steel of the same strength class, the CR780Y980T-CH-GI can achieve a 1.6 to 2 times higher elongation at break (elongation at break of ≥ 10%). This goes hand in hand with improved overall formability as well as a higher residual formability after forming. Compared to corresponding dual-phase steels, the CR780Y980T-CH-GI can also achieve high strength in component areas with low deformation. By using these properties in the design optimization of components, a considerable potential for lightweight construction can be utilized.

The diverse portfolio of materials properties is attained by a tailored design of the materials structure at a microscopic level (Fig. 2). The fine-grained multiphase microstructure consists of carefully adjusted proportions of ferrite, bainite, martensite and retained austenite.

In addition to the exceptional forming properties, the CR780Y980T-CH-GI also provides excellent weldability. This material is particularly resistant to the harmful phenomenon of liquid metal embrittlement (LME), as exemplified by the crack-free resistance spot-welded joints in Figure 3.
These outstanding properties are a result of a combination of chemical composition and microstructure control.