The hardness and microstructure analysis of Co-30Cr-5Mo-0.3C on variation of hot roll pre-heat holding time as an option of cardiovascular stent material

Coronary heart disease is one of the main causes of death. The risk of death in coronary heart disease can be reduced by the percutaneous coronary intervention (PCI) technique or coronary angioplasty in the form of stent placement. Therefore, it is necessary to develop stent materials. Co-Cr alloy is one of the materials that can be applied. In this study, Co-Cr alloy material was developed with the addition of 5% Mo and 0.3% C (wt.%). The Co-Cr-Mo-C material was alloyed in vacuum casting, then homogenized for 12 hours at 1200°C and followed with furnace cooling in argon atmospheric. The ingots were then hot-rolled by varying the holding time for 15, 30, 45, and 60 minutes at 1200°C and followed by water quenching. The characterization carried out was a hardness test and microstructure observation with optical metallography and SEM. The hardness number after the hot-roll process with various pre-heat holding times is decreased from 54.8 to 47.8 HRc due to the intermetallic compound of σ phase transform to M23X6 precipitate. The microstructure forms a precipitate that transforms from lamellar to blocky dense after the hot rolling process. The precipitate type is σ phase in condition 15-minute holding time then transform to M23X6 precipitate after the holding time is more than 45 minutes.