<![CDATA[Low-carbon ST37 steel is widely used due to its good manufacturability, while surface performance is often improved through pack carburizing. This study investigates the trade-off between carbon uptake and impact toughness of ST37 steel after pack carburizing using coconut-shell charcoal and mangrove-wood charcoal (with an untreated control and a 50:50 blend as comparators). The process was conducted at 750 °C with a 180 min heating period and a 60 min holding time, followed by water quenching (≈28 °C). The main outputs were carbon content from chemical composition testing and Charpy absorbed energy (three replicates per condition). The results indicate that carbon content increased from 0.12% (control) to 0.63% with coconut-shell charcoal, 0.22% with mangrove charcoal, and 0.30% with the 50:50 blend. However, the mean Charpy energy dropped sharply for coconut-shell charcoal to 2.24 J compared with 35.92 J for the control, whereas mangrove charcoal and the 50:50 blend maintained high Charpy energy at 35.12 J. Fracture surface observations were consistent with these trends, showing brittle fracture for coconut-shell charcoal and ductile fracture for the control, mangrove charcoal, and the blend. These findings confirm a clear trade-off: the highest carbon uptake does not necessarily ensure adequate impact toughness. Therefore, media selection should be based on a dual-metric consideration of carbon increase and Charpy toughness, depending on the intended application requirements.]]>
