DailyTech last month reported that Great Britain was working on super steels. These ultra-strong steels would be made possible by preventing irregularities in steel, which weaken its internal magnetics, making it more susceptible to heat.
Now it appears that the Americans have beaten the Brits to the punch, unveiling their own completed super steel. The new steel was developed at the Oak Ridge National Laboratory and the U.S. ITER Project Office, which is housed at ORNL. The ORNL was recently in the news for inventing a new titanium manufacturing technique.
With its new cast stainless steel, it continued its successes. The new steel is approximately 70 percent stronger than comparable steels and could be a boon to the fusion industry. Its material parameters are being evaluated carefully, as it is being considered for use in shielding ITER's fusion device.
ITER is a multibillion-dollar international research and development project which is accessing the viability of creating a commercial fusion reactor.
The new steel will need to be ultra strong at high temperatures. One key goal of the project is to develop self-burning plasmas. Hundreds of tons of shielding will be needed to block heat and radiation from this plasma. The shielding, primarily composed of super steel, will be close to the plasma, which will be heated to 100 million degrees. While the shielding itself won't be this hot, it will get more than a little toasty.
ITER is being built at Cadarache, France. The United States, China, the European Union, India, Japan, the Republic of Korea and the Russian Federation are all contributing components. The reactor will be of a tokamak design -- a torus of hot plasma contained by a magnetic field. The device is expected to produce around 500 MW of fusion power when functioning.
Jeremy Busby of the ORNL Materials Science and Technology Division says designing steel to withstand the extremes of the reactor is a difficult challenge. He states, "The United States must produce nearly 100 of these modules that are 3-4 tons each and include geometric shapes and openings."
The holes drilled in the steel will weaken it and will result in the loss of 30 percent of the material. While casting the shape would be more economical and efficient, cast steel traditionally is much weaker. However, thanks to recent breakthroughs the researchers are beginning to get the problem under control.
Explains Mr. Busby, "We're working to improve the materials' properties to reduce the amount of machining and welding and allow for better performance. The use of casting can have potential value engineering benefits resulting in cost savings on the order of 20 to 40 percent as compared to machining, so this could be a fairly significant economic issue, both for ITER and in other future uses."
Mike Hechler, USIPO manager of Blanket Shielding and Port Limiter systems, initially approached Mr. Bosby and his team with the request that they design super-steel shielding for the reactor. Mr. Bosby adds, "He talked with us because of ORNL's materials science expertise. He was familiar with our industry work and hopeful that we could help provide a solution."
Eighteen months later, the work is almost finished.
In order to strengthen the steel, scientists focused on fracture properties, tensile strength, microstructure properties, welds, impact properties, corrosion performance and radiation resistance. Through carefully controlled attempts using different casting techniques and varying the composition slightly, his team was able to almost double many key strength properties.
Now Mr. Bosby and his team have to await the final word from ITER on whether the material has passed its standards. He states, "We expect to hear fairly soon about how our cast stainless steel may be used in this groundbreaking project."
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