Builder of Nations: Steel Continues to Shape the Future

11-Aug-2009 9:00 AM EDT

ASM International

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Newswise — The material that builds nations continues to shape the world's future industrial growth, particularly as it relates to energy-related applications.

"Whatever the challenge, the answer is steel -- especially for the next generation of materials for energy applications, from oil and gas challenges to new materials for lighter weight vehicles," said Riad Asfahani of U.S. Steel Research & Technology, a Fellow and Trustee of ASM International, the materials information society.

Asfahani is the chairman of the ASM-organized symposium on Steel Product Metallurgy and Applications, a highlight of the Iron and Steel-related programming at the 2009 Materials Science & Technology (MS&T) Conference & Exposition, Oct. 25-29 in Pittsburgh.

" Oil and gas application challenges are being met with newly developed tubulars that withstand the harsh hydrogen sulfide environment in deep sour wells," Asfahani said. "At the same time, new CAFÉ standards will be very challenging to the automotive and steel industry."

From advanced high-strength steel to twinning induced plasticity " TWip steel " presenters will show that steel remains highly competitive with other materials for performance-related applications of the future.

"Special programming will honor Professor David Edmonds of the University of Leeds for his achievements in the study of steels," Asfahani said. "Speakers from across the continents will be gathering during two full technical sessions to honor his accomplishments."

Materials Science & Technology, the leading forum addressing structure, properties, processing and performance across the materials community, will be held at the David L. Lawrence Convention Center. In addition to programming on Iron and Steel, MS&T covers ceramic and glass materials, electronic and magnetic materials, environmental and energy issues, fundamentals and characterization, materials and systems, nanotechnology, processing and product manufacturing.

This partnership of four leading materials societies brings together scientists, engineers, students, suppliers and others to discuss current research and applications, and shape the future of materials science and technology. MS&T is organized by ASM International (the materials information society), American Ceramic Society (ACerS), Association for Iron and Steel Technology (AIST), and The Minerals, Metals and Materials Society (TMS). For more information about MS&T 2009, visit www.matscitech.org.

The following presentations provide a look at the breadth of steel coverage at MS&T 2009:

"Effect of Ti on Charpy fracture energy and other mechanical properties of ASTM A 710 Grade B Cu-precipitation-strengthened steel" (S. Vaynman, Y-W. Chung, M. Fine, Northwestern University; R. Asfahani, United States Steel Corporation)

Addition of titanium to ASTM A710 Grade B Copper-precipitation-strengthened steel significantly increases the impact-absorbed fracture energy and reduces the ductile-to-brittle transition temperature. The effect of titanium correlates with the reduction of the amount of pearlite in the ferritic microstructure. A thorough study of the mechanical properties of Ti-modified A710-B steel is presented. The ductile to brittle transformation in steels depends on interplay of the fracture stress and the flow stress. In steels the flow stress depends on temperature and strain rate because the motion of screw dislocations is function of temperature and strain rate. In this work the fracture stress has been assumed essentially independent of temperature and strain rate. At high temperatures and low strain rates thermal energy is sufficient to give plastic flow at stresses below the fracture stress, but this is not so at low temperatures and strain rates; thus there is ductile to brittle transformation temperature.

"Aspects of formability of AHS Steels determined by instrumented hole expansion testing" (A. Karelova, C. Krempaszky, E. Werner, Technical University of Munich, Germany; Christian Doppler Laboratory of Material Mechanics of High Performance Alloys; T. Hebesberger, A. Pichler , Voest-Alpine, Austria)

The main challenges in implementing new materials such as advanced high-strength (AHS) steels for automotive applications are defined by forming, because an increase in strength is generally coupled with a decrease in material formability. One of the methods characterizing formability of sheet materials in multi-axial loading states is the hole expansion test. A parameter is proposed by a simple analytical approach in order to analyze the kinematical stabilizing effect present in hole expansion testing. Since the stabilizing effect is strongly dependent on the punch cone angle, punch cones with different angles were utilized to study experimentally the stabilizing effect on the hole expansion ratio. Specimens from industrially produced complex-phase and dual-phase steel grades were tested and analyzed. The experimental results are compared and discussed with respect to the stabilizing effect on the formability, considering also the influence of the microstructure and mechanical properties.

"The effect of carbon content on the microstructure and mechanical properties of high-Mn steels" (E. Yang, H. Zurob, J. McDermid, McMaster University, Hamilton, Ontario, Canada)

Light-weight vehicles with improved fuel efficiency and vehicle safety are the new demand for the automotive industry. Materials with high strength and ductility need to be developed to handle the reduced material consumption. Transformable Face-Centered Cubic (FCC) austenitic steels are ideal candidates for these applications due to their high work hardening capability, making them useful for energy absorption parts or structural components. Transformation Induced Plasticity (TRIP) and TWinning Induced Plasticity (TWIP) high-Mn steels are particularly interesting due to transformation products during deformation that effectively decrease the mean free path for dislocation motion. In the present case, TRIP steels transform austenite into ε-martensite upon deformation, while TWIP steels transform by forming twin boundaries. The ε-martensite phase is a Hexagonal Close Packed (HCP) phase, while the twin boundaries maintain the face centered cubic (FCC) phase. The difference between the TRIP and TWIP transformation is based on the Stacking Fault Energy (SFE) of the alloy, where it is thought that the SFE plays a critical role in determining the nucleation of twins or ε-martensite. In Fe-22wt% Mn steels, the SFE strongly influences the transformation products and the mode by which the steel deforms. Low SFE alloys favor forming ε-martensite, while higher SFE alloys tend to form twins, both of which act as barriers for dislocation motion. By varying the carbon content within the steel, the SFE was altered to include formation of ε-martensite, twinning, or both.

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