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The TRansformation Induced Plasticity (TRIP) phenomenon in low alloy multiphase steels has been investigated as a mechanism to improve strength and ductility. Most characterization studies performed to date on TRIP steels consider only quasi-static tensile loading, although stress-state and strain-rate are known to affect the martensitic transformation. In this paper, quasi-static and dynamic tests are performed in tension and compression to evaluate the mechanical response as well as to determine the role of strain-rate on the amount of retained austenite. The results indicate a differential response between compression and tension and show considerable rate dependency for the low alloy TRIP steel.

The ULSAB-Advanced Vehicle Concepts (AVC) project presents a holistic approach to the development of a new advanced steel automotive vehicle architecture based on a 2000 lbs curb-weight vehicle. These advanced concepts will help automakers use the new steels more efficiently and provide a structural platform for achieving the following benefits: Safety Affordability Fuel Efficiency Environmentally friendly. The scope of the project encompasses the body-in-white structure, closures, suspensions, engine cradle, and all structural and safety relevant components. Porsche Engineering Services, Inc. (PES) conducted a comprehensive benchmarking of existing vehicle concepts and an investigation of trends in vehicle development. PES and the ULSAB-AVC Consortium established targets with reference to the U.S. PNGV (Partnership for a New Generation of Vehicles), EUCAR (The European CO2 reduction program) projects, and anticipated future IIHS and NHTSA safety requirements.

The high strain rate deformation behavior of commercially available dual phase steel was studied by means of split Hopkinson bar apparatus in shear punch mode with an emphasis on the influence of microstructure. The cold rolled sheet material was subjected to a variety of heat treatment conditions to produce several different microstructures. Dual phase microstructures with different fractions of martensite were obtained by changing intercritical annealing temperature and time. Various microstructures of ferrite plus pearlite, or acicular ferrite/bainite, or bainite and martensite/carbide were obtained by changing the cooling rate after annealing. The effects of low temperature tempering and bake hardening treatment were also investigated for some selected specimens.

Tempered martensite assisted steels are of recent research interest for good strength and ductility combination. This paper discusses the effect of tempered martensite volume fraction on the final properties of cold rolled and subcritically annealed Al containing TRIP steel. The samples were TRIP annealed and the retained austenite volume fraction was measured using X-ray diffraction technique. The steel samples were subsequently cold rolled to obtain strain induced martensite, deformed ferrite and bainite in the microstructure. The final tempered martensite volume fraction corresponds to the initial retained austenite volume fraction of the steel. The cold rolled TRIP steel samples were subsequently subcritically annealed at 500°C for 1 hour to obtain tempered martensite, fine ferrite and bainite. Shear Punch testing was used to evaluate the mechanical properties. The properties are analyzed and the results are discussed.

Resistance to dents and dings, caused by plant handling and in-service use, is generally recognized as an important performance requirement for automotive outer body panels. This paper examines the dent resistance improvements that can be achieved by maximizing surface stretch, through adjustments to the press settings, and substitution of a higher strength steel grade. Initially, the stamping process was optimized using the steel supplied for production: a Ti/Nb-stabilized, ultra low carbon (ULC) grade. The stamping process was subsequently optimized with a Nb-stabilized, rephosphorized ULC steel, at various thicknesses. The formed panels were evaluated for percent surface stretch, percent thinning, in-panel yield strength after forming, and dent performance. The results showed that dent resistance can be significantly improved, even at a reduced steel thickness, thus demonstrating a potential for weight savings.

Bumper engineers at the OEMs and Tier One suppliers are faced with the challenge of designing economical and lightweight bumper systems that are compatible with current styling trends. This paper is aimed at helping North American bumper engineers meet the challenge. There is a wide range of high-strength and ultra high strength bumper steels available. Many of these steels were not in the marketplace as recently as five years ago. These steels are reviewed as well as appropriate manufacturing methods for converting them into bumper facebars and reinforcing beams. Leading edge bumper beam examples are given. Steel, aluminum and composite reinforcing beams are compared from the weight (mass) point of view. Bumper systems incorporating beams made from these materials are also compared from the manufacturing cost and repair cost points of view.