적층 제조된 공구강에 대한 표면 개질 및 AISI M4 열처리에 따른 특성 변화에 관한 연구

This study focuses on the changes in the surface characteristics and mechanical properties of high-speed toolsteel powder M4 deposited using directed energy deposition (DED) technology, followed by vacuum heatquenching-tempering treatment (VHQT) and ultrasonic nanocrystal surface modification (UNSM). To observethe effects of the post-DED processes (UNSM and VHQT) on the performance of the fabricated components,the hardness and roughness of the prepared samples are compared and analyzed. Additionally, the changes inthe microstructure and defects are examined. Experimental results show that the surface roughness of theDED-treated sample improved after the UNSM treatment. Hardness tests indicate an increase in hardnessfollowing VHQT treatment, and further improvement is observed after the combined VHQT and UNSMtreatment. The specimens treated with both VHQT and UNSM exhibit significantly higher hardness than theDED-treated sample. Microstructural analysis shows a uniform distribution of martensite and carbides after theVHQT treatment, whereas UNSM resulted in grain refinement. These results demonstrate that the combinationof UNSM and VHQT is crucial in enhancing the mechanical performance of DED-treated M4.