On friction stir welding of a medium manganese austenitic steel

ABSTRACT

The plates of an Fe–12%Mn–0.5%C–1.5%Al austenitic steel with an original grain size of 80 µm were subjected to friction stir welding using a spherical welding pin. The fine grained microstructures with a grain size being dependent on the welding feed speed were evolved in the stir zones. The microstructure evolution in the stir zone resulted from a kind of post-dynamic recrystallisation. An increase in the welding pin motion along the seam favoured remaining the fine grained microstructure in the stir zone behind the pin. Therefore, an increase in the welding feed rate resulted in a decrease in the mean grain size and an increase in the dislocation density in the stir zone. A unique power law relationship with a grain size exponent of about −0.5 between the grain size and the dislocation density was observed. Almost linear correlation between the grain size and dislocation strengthening enables one using a Hall–Petch-type equation to predict the yield strength, which exceeded 500 MPa in the stir zone.

KEYWORDS:

• Medium manganese steel
• friction stir welding
• microstructure
• mechanical properties

Acknowledgements

The authors are grateful to the personnel of the Joint Research Centre, Belgorod State University, for their assistance with instrumental analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).