CANADA'S LEADING INFORMATION SOURCE FOR THE METALWORKING INDUSTRY

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CANADA'S LEADING INFORMATION SOURCE FOR THE METALWORKING INDUSTRY

CANADA'S LEADING INFORMATION SOURCE FOR THE METALWORKING INDUSTRY

Welding the unweldable: friction stir weld of ODS steel

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The Welding Institute (TWI) in Cambridge, United Kingdom, has successfully joined oxide dispersion-strengthened (ODS) steel, a metarial considered unweldable using conventional fusiion methods.

Detail of the surface of friction stir welded MA956 showing a smooth high quality butt weldTWI is a research and technology organization with a focus on materials joining and engineering processes. In a recent press release, it notes that TWI was asked to friction stir weld samples of these steels as part of a PhD project by Huw Dawson of Manchester University in the UK.

These specialised alloys have been developed to deliver excellent strength and creep performance at elevated temperatures, making them suitable for applications in nuclear reactors and power generation equipment, where they are exposed to extreme heat.

These steels derive their properties from a distribution of fine particulates, usually ceramic-based, which impede deformation and so give the steel its strength and resistance to creep. Unfortunately, conventional fusion welding techniques destroy these strengthening particulates, preventing the steel from being effectively fabricated.

Being a solid-state process, friction stir welding does not melt the steel being joined and would therefore allow ODS steels to maintain their properties after fabrication.

A number of samples of MA956, embedded with thermocouples to monitor process temperatures, were successfully welded at TWI’s Yorkshire Technology Centre. These samples are now undergoing extensive testing at Manchester University, to assess their performance in hostile environments, including their susceptibility to irradiation damage. It is believed that the friction stir welding process, besides being able successfully to weld ODS steel, may also render it less prone to hydrogen cracking – a significant advantage for welds operating in a nuclear environment.

For more information on the research and the results of the recent friction welding project, contact TWI.

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