Stronger Steels by Design

Superman fans know that the man of steel has amazing strength because he was born on the planet Krypton. Greg Olson isn't superman, but he uses supercomputing, which in this case may be almost as good. With new theoretical insights about the microstructure of steel and powerful computing, Olson is figuring out how to use materials right here on Earth to make steel stronger, harder and tougher than ever before. In collaboration with solid-state physicist Art Freeman, Olson has combined quantum theory and supercomputing at the Pittsburgh Supercomputing Center to produce new insights about the effects of impurities on grain-boundary cracking in steel.

Olson directs the Steel Research Group (SRG), a large-scale multi-institutional research program centered at Northwestern University's Materials Research Center. Over 30 investigators participate, including researchers at Harvard, Brown, MIT and Illinois Institute of Technology, several Department of Defense laboratories and a number of steel companies. "It was conceived in 1985," says Olson, "as a six-year program to develop the fundamental models and database by which you could actually design alloys on the computer."

The work progressed on schedule, and in 1991 Olson's group at Northwestern designed a new steel for bearings in the main engine turbo pumps of the space shuttle. This prototype ultrahigh-strength bearing steel withstands pressure, corrosion and high temperature beyond any previous steel. With this success under its belt, SRG kept going, and it is now applying the same design methods to develop advanced steel for other weight-critical applications such as helicopters, high-performance race cars and naval aircraft landing gear. "Steel is heavy," notes Olson, "but sometimes it's the only thing that can do the job. If you can push the strength up so you use less of it, you can save a lot of weight."

Phosphorus and Grain Boundary Cracking
These contour plots from Greg Olson's quantum calculations at the Pittsburgh Supercomputing Center (with Art Freeman and Ruqian Wu) show how phosphorus at a grain boundary affects electron distribution in steel. In the top panels, color corresponds to electron density with yellow representing the highest density decreasing through green, blue and purple. The left panel shows iron atoms and a phosphorus atom at the grain boundary (the boundary runs horizontally through the center of the panel). The right panel shows the same steel fractured along the boundary with the top segment removed, so that phosphorus is at the "free surface" of the crack.

The lower panels are difference plots --showing how the electron distribution changes when phosphorus is in the steel compared to only iron. Electron gain is shown in pink (greatest), red, yellow and green, and electron loss is purple and blue (more negative). These plots show that phosphorus bonds much more strongly with the iron atom below it at the free surface (large pink area) than it does at the grain boundary. "Phosphorous at the free surface has lowered energy," explains Olson, "which means that phosphorus at the grain boundary reduces the work of fracture-promoting embrittlement of the steel."

Researcher: Gregory B. Olson, Northwestern University
Hardware: CRAY C90
Software: FLAPW (full-potential linearized augmented plane wave method)
Keywords: materials research, ultrahigh-strength bearing steel, iron, impurities, defects, stress, corrosion, martensitic transformation, crystal structure, engineering science, quantum theory, electron distribution, free surface, grain boundary, Steel Research Group (SRG).

Related Material on the Web:
Projects in Scientific Computing, PSC's annual research report.

References, Acknowledgements & Credits