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Microstructures of Powders and Additively Manufactured Objects of an Alloy Tool Steel for Cold-Work Dies

냉간금형용 합금공구강 분말 및 적층조형체의 미세조직

  • Kang, Jun-Yun (Metal Materials Division, Korea Institute of Materials Science) ;
  • Yun, Jaecheol (Powder & Ceramics Division, Korea Institute of Materials Science) ;
  • Kim, Hoyoung (Materials Research Team, Central Corporation) ;
  • Kim, Byunghwan (Metal Materials Division, Korea Institute of Materials Science) ;
  • Choe, Jungho (Powder & Ceramics Division, Korea Institute of Materials Science) ;
  • Yang, Sangsun (Powder & Ceramics Division, Korea Institute of Materials Science) ;
  • Yu, Ji-Hun (Powder & Ceramics Division, Korea Institute of Materials Science) ;
  • Kim, Yong-Jin (Powder & Ceramics Division, Korea Institute of Materials Science)
  • 강전연 (한국기계연구원 부설 재료연구소, 금속재료연구본부) ;
  • 윤재철 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부) ;
  • 김호영 (주식회사 센트랄, 재료연구팀) ;
  • 김병환 (한국기계연구원 부설 재료연구소, 금속재료연구본부) ;
  • 최중호 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부) ;
  • 양상선 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부) ;
  • 유지훈 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부) ;
  • 김용진 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부)
  • Received : 2017.05.31
  • Accepted : 2017.06.10
  • Published : 2017.06.28

Abstract

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

Keywords

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