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S-in motion® for chassis

New advanced steels lightweight critical chassis components

One of the most important structures in a vehicle is the chassis system. Forming the under-structure of a vehicle, the chassis includes of a series of fundamental components which manage vehicle dynamics, comfort, suspension, and steering. Chassis parts are also critically important to passenger safety, particularly when unexpected events occur while the car is in motion. An S-in motion® study from ArcelorMittal shows how OEMs can maintain the safety of the chassis while achieving significant weight savings with ArcelorMittal’s advanced high strength steels.

The scope of ArcelorMittal’s S-in motion® Chassis study covered both pickup trucks and passenger vehicles

Some of the parts studied included (from left to right): twist beam, suspensions, lower control arms, front subframe, pick-up truck frame and rear multi-link subframe

 

Specific requirements for chassis parts

Chassis parts must provide adequate stiffness for the vehicle while resisting cyclic, incidental, and accidental loads. They also need to resist the effects of aggressive corrosion environments as they are located close to the road. In order to meet these highly specific criteria, ArcelorMittal has developed AHSS for cold stamping with specific properties including excellent forming and fatigue properties.

During the development of these grades, the properties of the steels were optimised to facilitate the manufacturing of chassis components. The modifications enhanced cut edge formability and the hole expansion properties of the steels, allowing OEMs to design chassis parts with flanged edges and stretched holes.

Parts were assessed for their production feasibility and against different crash load cases

New cold stamping grades for chassis applications

One of the grades ArcelorMittal has developed for chassis applications is FB590HHE (HHE stands for High Hole Expansion). This exceptional hot rolled ferrite-bainite steel offers excellent hole expansion. The grade allows OEMs to optimise the formability and manufacturing of cold stamped parts with flanged holes and stretched edges such as lower control arms.

The most promising grade for significant weight reduction is CP800SF, a hot rolled steel suitable for stretch forming (SF). This grade was developed with an ultimate tensile strength (UTS) of 800 MPa. Hardening is achieved through a micro-alloyed complex phase microstructure.

CP800SF was used to form the lower control arms, achieving a weight reduction of 16 percent compared to the baseline

The ultimate AHSS for chassis applications is the cold rolled grade CP1000SF (Stretch Flangeable). The steel has a UTS of 1000 MPa while offering excellent stretch flangeability. In the S-in motion® Chassis study, the grade was used in combination with hot rolled CP800SF to achieve weight reductions of 15 percent on the engine cradle.

The use of CP800SF and CP1000SF enabled the weight of the engine cradle to be reduced by 15 percent

Hot stamping solutions also examined

The S-in motion® Chassis study also assessed hot stamping solutions. Hot stamped parts typically exhibit good geometry and better fatigue properties. The hot stamping process allows the design of more complex part geometries, fewer forming steps, and higher mass savings. For example, a study of a lower control arm showed that hot stamped Usibor® 1500 could be used to achieve a 26 percent reduction in mass compared to a cold rolled solution.

In addition to these new grades, ArcelorMittal has also extended our coating offer to meet the corrosion resistance performance targets required for chassis components. For some applications, the steel can be provided with a thicker zinc coating than normal. Parts can also be finished with ArcelorMittal’s exceptional new Zagnelis® Protect coating which offers a very high level of corrosion resistance.

ArcelorMittal’s latest S-in motion® study for chassis components demonstrates again that significant weight savings are achievable at little to no additional cost using the latest AHSS. The steels are already available in most regions of the world and can be implemented in production vehicles today.

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