Trade press, 2014-05-27, 12:07 PM
Multi-layer composite for weight reduction: TriBond
TriBond is a new high-strength steel that can absorb more crash energy than other steels of the same strength. Parts using TriBond are up to ten percent lighter than current hot-formed solutions and roughly six percent cheaper than a cold-formed reference product. In addition, this multi-layer composite opens up whole new possibilities for hot forming: While to date the use of hot-forming has been limited to structural elements, with TriBond it can also be used for parts subject to axial crash loads.
Steels have to unite various properties: On the one hand they need to be strong, for example to protect car occupants in a crash, while on the other hand they need to absorb impact energy by deforming. Combining these conflicting properties is difficult. That’s why to date auto manufacturers have made B-pillars from ultrahigh-strength hot forming steels like MBW 1500: These primarily deflect the crash energy of a side-on impact to other, softer components.
High-strength yet formable
With TriBond, ThyssenKrupp Steel Europe AG has developed a steel that combines high strength with enhanced energy absorption. TriBond is a composite with a core layer of manganese-boron steel MBW 1500 sandwiched between outer layers of MBW 500. With a strength of 1500 MPa, MBW 1500 is an ultrahigh-strength grade that protects occupants effectively in the event of a side-on impact; MBW 500 has a significantly lower strength of 500 MPa but is able to absorb some of the crash energy.
“Multi-layer composites make it possible to combine different and in part conflicting properties in one product – properties that cannot be produced in a single material,” says Dr. Julia Mura from the Hot Forming Product Launch department at ThyssenKrupp Steel Europe. “Material properties are controlled based on the application, not via a single material but by combining functional layers.” In a nutshell: The properties of the steels can be individually tailored.
In addition, TriBond opens up completely new possibilities for the use of hot forming. To date, hot-formed parts have mainly been used for high-strength structural elements where energy absorption plays a secondary role. For energy absorption they need to be combined with a softer material, e.g. by means of tailored blanks in which different materials are welded together, or by tailored tempering, which uses temperature control during hot forming to create a strength gradient in the part. The new multi-layer composite combines both properties – high strength and high energy absorption – in the material itself. No additional measures are needed. TriBond is also suitable for areas of the body subject to axial crash loads such as longitudinal members and crash boxes.
Lighter, cheaper, and suitable for processing on standard equipment
TriBond also offers further benefits: Parts are up to ten percent lighter than the current solution of MBW 1500 produced by tailored tempering, and costs are attractive. It is produced in similar fashion to conventional cold-rolled strip, but with an additional package-building operation in which the three steel layers are laid on top of each other and joined. Both manufacturing and fabrication at customers can be carried out on standard production equipment. The material will be production-ready in mid-2015.