Nano-mechanical Behavior of H13 Tool Steel Fabricated by a Selective Laser Melting Method
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13 is one of the most widely used hot work tool steels applied to casting molds, extrusion tool, and forging dies, etc. due to its strong temper resistance and ability to maintain high hardness and strength at elevated temperatures.[1–7] Hot work tool steels fabricated by conventional methods require expensive dedicated tools and thus are not suitable for small-scale production and the production of complex shapes.[5–7] An additive manufacturing (AM) technique, which builds parts from 3D digital models typically by a layer additive process, has been an effective method to solve these problems.[5–14] Accordingly, a selective laser melting (SLM) method, a laser powder-bed AM process, should be suitable for processing of H13 because it
VAN LUONG NGUYEN, EUN-AH KIM, DONG-YEOL YANG, HAK-SUNG LEE, and JI-HUN YU are with the Powder & Ceramic Division, Korea Institute of Materials Science (KIMS), Changwon 51508, Korea and also with the Metal 3D Printing Convergence Research Team, Korea Institute of Machinery & Materials (KIMM), Daejeon 34103, Korea. Contact e-mail: [email protected] JAECHEOL YUN and JUNGHO CHOE are with the Powder & Ceramic Division, Korea Institute of Materials Science (KIMS). CHANG-WOO LEE is with the Metal 3D Printing Convergence Research Team, Korea Institute of Machinery & Materials (KIMM). Manuscript submitted January 22, 2018 Article published online November 30, 2018 METALLURGICAL AND MATERIALS TRANSACTIONS A
offers the ability to not only reduce the amount of machining and hence wastage of this expensive material but also to produce intricate molds with a nearly full density and a refined microstructure.[1–3,13] The mechanical behavior of the H13 prepared by the SLM process is one of the most important characteristics and has been reported recently.[7,8,15–17] Micro-hardness (Vickers, Rockwell, and Briness) tests and tensile tests have been conducted to evaluate the mechanical behavior of the SLM-ed H13 tool steel.[7,8,15–17] To conduct those tests, many samples with large volumes had to be prepared and the mechanical behavior (hardness or tensile strength) was measured at only low loading rates (static) and in particular the creep behavior could not be evaluated. Meanwhile, nanoindentation tests could provide the strain-rate sensitivity of materials, especially for small-sized materials that are not suitable for the above test methods.[18–23] Nanoindentation tests should be therefore applied to study mechanical characteristics of SLM-ed H13 material. However, many reports have noted that the correlation between the measured character from the indentation creep and those obtained from the conventional uniaxial tests are poor.[22,23] For example, Wang et al. reported that the creep rate under nanoindentation was typically excessive faster than that under uniaxial creep due to more complex and severe stress state under nanoindentation.[22] Shen et al. also claimed that the intrinsic discrepancy in the deformation mechanics caused the difference in the testing results by nanoindentation and uniaxial meth
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