Abstract
This study investigated the effect of post-weld processes including annealing and drawing on the microstructure and mechanical properties of high-Mn steel pipes welded by gas tungsten arc welding. The weld metal showed a solidified microstructure having coarse and elongated grains due to coalescence of columnar dendrite into welding heat direction. After post-annealing, the solidified microstructure changed into equiaxed grains due to recrystallization and grain growth. Mn segregation occurred during welding solidification and caused lower stacking fault energy (SFE) in the Mn-depleted region. Although ε-martensite formation in the as-welded state and during deformation was expected due to decreased SFE of the Mn-depleted zone, all regions showed a fully austenitic phase. The annealing process decreased strength due to grain coarsening but increased ductility. The drawing process increased strength of weld metal through work hardening. All pipes showed decreasing strain rate sensitivity (SRS) with deformation and negative SRS after certain strain levels. It was confirmed that negative SRS is related to less formation of mechanical twinning at a higher strain rate. This work provides fundamental insights into manufacturing a high-Mn steel pipe and manipulating its properties with annealing and drawing processes.
Highlights
High-manganese steels have excellent tensile strength, ductility, formability, and low temperature toughness [1,2,3]
This study mainly focused on the effect of those processes such as welding, drawing, and heat treatments on the microstructure and mechanical properties of the pipe
Thegrowth three samples of pipes R, 10D, 10DH had distinct microstructures base dendrite metal and grain in the heat-affected zone to aand maximum of 66.8 μm
Summary
High-manganese (high-Mn) steels have excellent tensile strength, ductility, formability, and low temperature toughness [1,2,3]. This combination of high strength and ductility is caused by twinning-induced plasticity (TWIP), which occurs during plastic deformation. Multiple slip and twinning systems operate and further increase the work-hardening rate [1,4,5]. This high work-hardening rate of high-Mn steel is related to the deformation mechanism, which depends on stacking fault energy (SFE). The TWIP effect activates at 20 ≤ SFE ≤ 50 mJ/m2 , Metals 2020, 10, 1366; doi:10.3390/met10101366 www.mdpi.com/journal/metals
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