The complex-phase steel family has a new member: the CR780Y980T-CP-GI

Complex-phase steels are a universally applicable material solution offering enormous advantages for lightweight automotive construction. With its hot-dip galvanized CR780Y980T-CP-GI, Salzgitter Flachstahl offers an innovative material in this product class.
Classic complex phase steels (CP steels) are already characterized by a number of material-related achievements. These include low susceptibility to cracking in the edge area, high bending capacity, and increased crash performance. This makes complex phase steels particularly suitable for cold-formed complex components in the automotive sector. This applies in particular to roll-formed components.

The diverse portfolio of properties is made possible by the targeted design of the material structure at the microscopic level (Figure 2). The fine-grained multiphase structure consists of carefully adjusted microstructural components with bainite as the main phase and targeted ferrite and martensite contents in various tempering stages, which forms the basis for achieving high strength and good forming properties.

To classify the property portfolio, the mechanical/technological standard requirements according to VDA-239-100 and advantageous forming operations are compared in the following table. For comparison, two additional grades from strength class 780 MPa are listed: the dual-phase steel CR700Y980T-DP-GI and the complex-phase steel CR570Y780T-CP-GI.

A direct comparison of the two gigapascal steels CR700Y980T-DP and CR780Y980T-CP with their typical properties is shown in Figure 3. The complex-phase steel CR780Y980T-CP is particularly characterized by high hole expansion, which is reflected in high local ductility and allows good formability of shear-cut edges. The Rp0.2 yield strength and the yield strength ratio are significantly increased compared to classic DP steel.

In order to quantitatively evaluate the potential of CR780Y980T-CP-GI compared to CR700Y980T-DP-GI, a component made of CR700Y980T-DP-GI is considered, which is exclusively subjected to tensile stress. If the component is designed in such a way that it does not undergo plastic deformation during operation or in cases of misuse, then sheet thickness and yield strength are the decisive parameters. If the yield strength is 80 MPa higher when using CR780Y980T-CP-GI, the sheet thickness can be reduced by 7 percent accordingly. The resulting reduction in material usage would reduce costs by approximately 6 percent. If less material is required for the same component performance, less CO2 is also generated during component manufacturing. This reduces the CO2 equivalent by 0.7 kg per kilogram of the component's initial weight (excluding processing at the supplier).