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Korean Journal of Metals and Materials > Volume 58(1); 2020 > Article
Korean Journal of Metals and Materials 2020;58(1): 32-40. doi: https://doi.org/10.3365/KJMM.2020.58.1.32
레이저 가공 기반 사출 금형강의 선택적 표면 개질 연구: 레이저 나이트라이딩에 따른 AlN 형성 및 경화 거동
천은준1, 박창규2, 박원아3
1경남대학교나노신소재공학과
2한국기계연구원광응용기계연구실
3경성대학교기계자동차공학전공
Study on the Selective Surface Modification of Injection Mold Steels by Laser Materials Processing: Relationship Between AlN Formation and Surface Hardening During Laser Nitriding
Eun-Joon Chun1, Changkyoo Park2, Wonah Park3
1Department of Nano Materials Science and Engineering, Kyungnam University, Changwon 51767, Republic of Korea
2Laser and Electron Beam Application Department, Korea Institute of Machinery and Materials, Daejeon 34103, Republic of Korea
3Department of Mechanical and Automotive Engineering, Kyungsung University, Busan 48434, Republic of Korea
Correspondence  Wonah Park ,Tel: +82-51-663-483, Email: wpark@ks.ac.kr
Received: 16 July 2019;  Accepted: 16 October 2019.  Published online: 12 December 2019.
ABSTRACT
Laser surface heat treatment and laser nitriding processes were applied using selective surface modification techniques to investigate phase transformation, microstructural evolution, and surface hardening behaviors for two types of plastic injection mold steels, AISI 1045 and P21. During laser surface heat treatment, a 245% hardness increase compared to that of the base metal (290 HV) was achieved due to martensite transformation of the AISI 1045 steel. However, for the AISI P21 steel, hardness within the heat-treated zone was largely unchanged from that of the base metal (410 HV) despite being accompanied by martensite transformation. Compared to that of the base metal, this static hardness behavior of the heat treated P21 steel was due to coarsening of Cu particles induced by the laser irradiation. To overcome the static hardness behavior of P21 steel, laser nitriding was used. The laser-nitrided specimen (at 4500 J/mm heat input) was approximately 40% (577 HV) harder than the base metal (410 HV) and was highly correlated with nitride formation. Nitrogen successfully penetrated the surface of the specimen during laser irradiation and formed a nitrided layer mainly composed of an AlN phase. Thus, the surface hardening behavior of AISI P21 steel after laser nitriding could be largely attributed to the AlN phase development.
Keywords: plastic injection mold steels, surface modification, laser surface heat treatment, laser nitriding, nitride
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