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Press hardenable ultra high strength steel (UHSS) is commonly used for automotive components to meet crash requirements with minimal mass addition to the vehicle. Press hardenable steel (PHS) is capable of forming complex geometries with deep sections since the forming takes place at elevated temperatures up to 900 degrees Celsius (in the Austenitic phase). This forming process is known as hot-stamping. The most commonly used PHS grade is often referred to as PHS1500. After hot-stamping, it is typically required to have a yield strength greater than 950 MPa and a tensile strength greater than 1300 MPa. Most automotive design and material engineers are familiar with PHS, the hot-stamping process, and their capabilities. What is less known is the capability of 3rd Generation advanced high strength steels (AHSS) which are cold stamped, also capable of forming complex geometry, and are now in the process of, or have recently completed, qualification at most automotive manufacturers.

The ThyssenKrupp InCar Project is a comprehensive R&D development that gives automotive manufacturers modular solution kits for body, chassis, and powertrain applications. The solution kits developed within this project offer weight reduction, cost savings, or improved functionality. This paper will focus on the front longitudinal members of the body structure. The front longitudinal member is a key safety component responsible for absorbing energy in a frontal crash event. It must also have high local strength, stiffness, and fatigue resistance at the suspension attachment points. Within the InCar project, several different solutions for the front longitudinal members were developed, including stamped AHSS concepts, stamped AHSS tailored blank concepts, and tailored tube concepts using an innovative forming technology for closed section designs, called InForm T3 (Thyssen Tailored Tubes).

A typical forming operation of chassis components (control arms, cross members, etc.) often involves edge stretching and/or hole expansion. As a result, the edge split is a common forming failure mode. To overcome this problem, Japanese and European automakers use stretch flange high strength (SFHS) steel due to its high strength and excellent edge stretch capability. Recently, SFHS steel has gained greater attention in North America and is currently being used for upper and lower control arm applications. This paper includes a discussion on general edge stretch issues in forming operations, including material data that demonstrate the higher stretch limit of SFHS steel as compared to other high strength steels. In a case study, SFHS steel is applied to a control arm and finite element analysis (FEA) is conducted to evaluate forming and structural performance.