Abstract
The hot ductility of low-carbon austenite has been studied in order to reveal the hot-cracking mechanism related to sulphur segregation and sulphide precipitation during solution treatment and deformation. Ductility was greatly reduced during high-strain-rate tensile deformation in the temperature range 1073-1373 K. Fracture occurred via a typical intergranular mode, characterized by both shallow dimples caused by microvoid coalescence and rather smooth facets caused by intergranular decohesion. The former morphology is a result of the dense precipitation of sulphides, identified as Fe-rich (Fe, Mn) S, on the austenite grain boundaries. Finely dispersed sulphide particles within the grains and the existence of precipitate-free zones along grain boundaries enhanced strain localization in the vicinity of the boundaries during deformation. The intergranular decohesion arises from the decrease in grain-boundary strength produced by sulphur segregation. Hot ductility is improved on decreasing the solution-treatment temperature, on decreasing the cooling rate from high solution temperatures, and on isothermal holding at the deformation temperature before starting the tensile test. These effects can be explained in terms of MnS precipitation and particle coarsening during these processes.
MST/60
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