پژوهشنامه ریخته گری
سال پنجم شماره 3 (پیاپی 18، پاییز و زمستان 1400)

The fine-graining process by applying heat treatment methods. cannot be effectively applied to austenitic single-phase steels, including Hadfield steels, Other grain refining methods, such as thermomechanical methods, need more energy, cost, and more environmental consequences. In this paper, REM-based inoculations (Rare Earth Metals) and specifically CeO2 and Hf with values of 0, 0.05, and 0.1 wt% of CeO2, as well as 0 and 0.05 wt% of Hf, were added into an austenitic high Mn Hadfield cast steel. The results showed the effect of inoculation amount on austenite grain size, segregation, reduction of shrinkage microporosity, pearlite layer spacing, and increase in hardness of these steels despite small changes in mechanical properties. Changes in the amount of hardness in inoculated steels compared to base steels led to an increase of 80.95% in the as-cast condition, which is a particularly important feature due to the need for high anti-wear properties in these steels.

This research investigated the cooling curves and tensile test results of three casting methods conventional CO2 sand casting (CSC), ablation casting with a water-soluble binder (ABL), and Ablation casting with Na2SiO3 binder (DWS). With the as-cast CSC samples, the σUTS and εf were 125 MPa and 3%, respectively which were promoted by the DWS process to 193 MPa and 11.5 %, respectively. The ABL process could increase the σUTS and εf to 210 MPa and 19 %, respectively. According to metallography examinations, the SDAS of α-Al dendrites decreased from 80µm in CSC to 40µm in DWS and 20µm in ABL. Ablation with a water-soluble binder had the most effect on tensile mechanical properties as it provided the highest cooling rate (1.2 °C/s) comparing to the two other processes. The differences between these two Ablation procedures were 50% in SDAS and 65% in εf, while 13% with respect to σUTS. Prior researches attributed these enhancements to the α-Al dendrites SDAS affected by the high cooling rate experienced. The DWS results, however, reveal a research gap indicating the participation of other factors besides merely the α-Al dendrites in improvement of the mechanical properties in Al-Si alloys.

The effect of chemical composition and amount of inoculant on microstructure specially ferrite phase and graphite nodule count and mechanical properties containing ultimate tensile strength (UTS) and hardness of ferritic ductile iron were considered. In this project, three conditions were evaluated. They were without inoculant, barium and silicon base inoculants were used. Inoculant percentages were 0.1, 0.15 and 0.2 percent. The results show that inoculation encourages the ferrite formation from 75 percent to 90 percent in matrix, increasing the nodule count from 125 to 175, decreasing the hardness from around 200 HB to close 160 HB and decreasing the UTS from more than 500 MPa to close the 400 MPa. In comparison between barium and silicon base inoculants, it was seen that effect of inoculants on the microstructure was same but on the mechanical properties was different and barium base inoculant had more appropriate effect in comparison with silicon base inoculant.