TWI

An investigation is presented into tool material development of large polycrystalline cubic BN blanks to facilitate friction stir welding of thick section steel specimens (thickness 9.5 or 20 mm). Tool materials were produced from 90% polycrystalline cubic BN with a ceramic second phase and from 60%BN with W-Re. Blanks were sintered using a high pressure-high temperature process, and the cell design and pressure capability were employed to enable tool pin lengths of 9.5 and 20 mm. Tools were tested in the 2G flat butt welding position and the 5G pipe welding position. The grades studied were 1018 low carbon steel for plate welding (thickness 20 mm) and X52 steel for girth welding (thickness 9.5 mm). Girth welds were made on an expandable internal mandrel. Tool temperature was monitored during pipe welding, including the carbide shank, to assess effects of temperature on tool life and weld quality. Experiments were conducted to optimise process parameters (tool rotational speed and welding speed). Welded joints were characterised by microstructure observations and tensile tests. Welding tools were examined for wear and cracks.

9th International Symposium, 15-17 May 2012, Session 10A: FSW Steel, Paper 02