Effect of metal borides on the hardness and wear of STD11 steel

This study aimed to manufacture a steel with high hardness and wear resistance by utilizing the precipitation of metal borides, which have much higher hardness than the high-hardness Cr carbide of the existing STD11 rolled steel. For this purpose, an alloy composition consisting of Mo 13–20%, Co 18–30%, V 3–6%, Cr 3–5%, C 1.5–3.5%, Si 0.5–1.2%, Mn 0.1–0.5%, B 2.5–4.5%, Nb 1–2%, W 1–3%, Al 0.1–0.2%, Ti 0.1–0.3%, and rare earth metals (RE) 0.1–0.2% as additives was designed. The mold for die casting was manufactured by installing a vent hole at the end of the product for gas escape, not installing a riser, installing a large sprue for quick molten metal injection, and making the sprue also serve as a riser. In particular, since the mold designed and manufactured in this study was based on a vertical split casting method, a well instead of a separate runner was installed to prevent eddies. After mold casting, quenching and tempering treatments were performed on the prototype, resulting in a high-hardness product with a hardness value of HRC66~68.