The effect of the laser beam diameter on the microstructure and hardness of 17-4 PH stainless steel manufactured via the directed energy deposition process is investigated. The pore size and area fraction are much lower using a laser beam diameter of 1.0 mm compared with those observed using a laser beam diameter of 1.8 mm. Additionally, using a relatively larger beam diameter results in pores in the form of incomplete melting. Martensite and retained austenite are observed under both conditions. A smaller width of the weld track and overlapping area are observed in the sample fabricated with a 1.0 mm beam diameter. This difference appears to be mainly caused by the energy density based on the variation in the beam diameter. The sample prepared with a beam diameter of 1.0 mm had a higher hardness near the substrate than that prepared with a 1.8 mm beam diameter, which may be influenced by the degree of melt mixing between the 17-4 PH metal powder and carbon steel substrate.

Abstract
1. 서 론
2. 실험 방법
3. 실험 결과 및 고찰
4. 결 론

• 김우혁(한밭대학교 신소재공학과) | Woo Hyeok Kim (Department of Materials Science & Engineering, Hanbat National University)
• 고의준(한밭대학교 신소재공학과) | UiJun Go (Department of Materials Science & Engineering, Hanbat National University)
• 김정한(한밭대학교 신소재공학과) | Jeoung Han Kim (Department of Materials Science & Engineering, Hanbat National University) Corresponding author