In this study, the effects of austempering on the microstructure, mechanical properties (micro hardness, impact energy and tensile strength) and corrosion behaviours of AISI 1018 low carbon steel were evaluated. The steel specimens were subjected to heat treatment by austenitizing at 830°C, maintained in this condition for 90 min before rapid cooling in a NaNO3 salt bath sustained at 300°C for isothermal transformation for additional 50 min and finally allowed to air cool to room temperature. The as-received and the austempered samples were tested for corrosion in both 0.5M aqueous acidic (HCl) and 0. 5M alkaline (NaOH) media. Microstructural investigation using scanning electron microscope (SEM) reveals transformation from ferrite/pearlite phases to bainite over the austempering process. Interestingly, significant improvements of 15.7% to 95.7% in the various mechanical properties (micro hardness, impact energy and tensile strength) and corrosion resistance in both media were observed.
The influence of variable stirring speeds on cast aluminium-copper alloys and the resulting enhancements in mechanical properties have been described in this study. Aluminium-copper (Al-Cu) alloys with 0-15 wt% Cu compositions were prepared via electro-mechanical stir casting process using various stirring speeds (0 rev/min, 10 rev/min, 50 rev/min and 90 rev/min) and the alloy materials produced were tested for microhardness and tensile strength. Increase in both wt% Cu compositions and stirring speeds were observed to have led to improvements in microhardness and tensile strength. The microstructural and mechanical characterisations also revealed that improvements in material properties recorded could be attributed to three mechanisms which are: solid solution hardening, precipitation hardening and the stirring effect.
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