• Almoussawi, M.
• Cater, S.
• Faraji, Masoumeh
• Smith, Alan

Abstract

This work investigates the role of welding speed<br/>in elemental segregation of Mn, Si, Al, and oxygen during<br/>friction stir welding (FSW) in DH36 steel. The experimental<br/>work undertaken showed that when the speed of the<br/>FSW process exceeds 500 RPM with a traverse speed of<br/>400 mm/min, then elemental segregation of Mn, Si, Al,<br/>and O occurred. The mechanism of this segregation is not<br/>fully understood; additionally, the presence of oxygen<br/>within these segregated elements needs investigation. This<br/>work examines the elemental segregation within DH36<br/>steel by conducting heat treatment experiments on unwelded<br/>samples incrementally in the range of 1200–1500 C<br/>and at cooling rates similar to that in FSW process. The results of heat treatments were compared with samples<br/>welded under two extremes of weld tool speeds, namely<br/>W1 low tool speeds (200 RPM with traverse speed of<br/>100 mm/min) and W2 high tool speeds (550 RPM with<br/>traverse speed of 400 mm/min). The results from the heat<br/>treatment trials showed that segregation commences when<br/>the temperature exceeds 1400 C and Mn, Si, Al, and<br/>oxygen segregation progress occurs at 1450 C and at a<br/>cooling rate associated with acicular ferrite formation. It<br/>was also found that high rotational speeds exceeding<br/>500 RPM caused localized melting at the advancing-trailing<br/>side of the friction stir-welded samples. The study aims to estimate peak temperature limits at which elemental<br/>segregation does not occur and hence prevent their occurrence<br/>in practice by applying the findings to the tool’s<br/>rotational and traverse speed that correspond to the defined<br/>temperature.

Topics

• impedance spectroscopy
• experiment
• Oxygen
• steel