Thermal Analysis of Rare Earth Grain Refined 4130

This paper discusses the thermal analysis of rare earth grain refined 4130. To accomplish this, heats of 4130 Baseline, 0.3wt% RE silicide, and 0.3wt% EGR were poured in a thermal analysis cup with a single S-type thermocouple at the bottom. A data acquisition system recorded the cooling curves whose values were compared to reference data. The samples were sectioned and macroetched. A scanning electron microscope analyzed the samples to determine inclusion composition. It was observed that the liquidus was similar for all the samples; however, the peritectic temperature for the 0.3wt% RE and 0.3wt% EGR was higher than the Baseline. This increase was thought to be due to RE oxysulfides acting as heterogeneous nuclei for austenite. A number of additional peaks appeared in the grain refined steels that seem to be related to the formation of RE oxysulfides during solidification. Macroetching found a larger equiaxed region in the TA cups from the treated steels and a finer structure. The improvement in microstructure seems related to the RE inclusions and peritectic temperature increase.