Papers by Keyword: H13 Hot Die Steel

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Authors: Kuk Tae Youn, Young Mok Rhyim, Jong Hoon Lee, Chan Gyu Lee, Yun Chul Jung
Abstract: It is well known that the main failure mechanisms in die-casting mould are heat checking due to thermal fatigue and melt-out caused by chemical reaction between die and molten alloys. Thermal fatigue tests were carried out using the thermal cycle simulator to establish the proper method to estimate the thermal fatigue resistance of hot die steel. In this study, the thermal shock tester consisted of induction heating and water spray cooling unit was constructed to evaluate thermal crack propagation resistance and the sum of crack length per unit specimen length, Lm is proposed as the index representing the susceptibility to crack initiation and propagation. Also, new concept of measurement for the melt-out behavior was suggested. AISI H13 hot work tool steel was solution treated and tempered at various temperatures, to control the hardness and toughness that have effect on the behavior of thermal crack propagation. The result of thermal fatigue test showed that there is optimum value of hardness and impact energy to maximize the thermal crack propagation resistance. The influence of nitriding on melt-out resistance was also investigated. The dissolution rate due to melt-out phenomenon tended to be smaller for thicker compound layer. Furthermore, the resistance to melt-out was affected by the compound layer thickness rather than that of diffusion layer. The results of the both tests properly reflect the effect of materials properties on failure modes of die-casting mould and it means those test methods are suitable to evaluate the durability of hot work tool steel for die-casting.
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Authors: Kuk Tae Youn, Young Mok Rhyim, Jong Hoon Lee, Young Sang Na, Wee Do Yoo, Chan Gyu Lee
Abstract: For hot die steel, failure is mostly caused by heat checking and melt-out on its surfaces which are in contact with molten metals. In the present research, resistances to melt-out and heat checking of surface modified H13 hot die steels, such as gas nitriding(GN) and micro-blasting(MB), were investigated. The evaluation of melt-out behavior was carried out by measuring the mean depth from the original surface after immersion. To examine the thermal fatigue resistance, a cyclic thermal shock system consisting of induction heating and water spray quenching was constructed. The value of Lm is proposed as the index representing the susceptibility to crack initiation and propagation. The melt-out depth was the lowest for the GN treated surface. MB-GN and MB-GN-MB treated specimens also showed good resistance to melt-out. In the case of GN treatment, while the white layer was completely melted out, the diffusion layer still existed even after immersion for 43 hours. This implies that nitriding significantly reduced the rate of melt-out. From the total crack number, it is seen that crack initiation was reduced to the extent of half after surface treatment. This result means that the residual compressive stress and nitrided layer were beneficial to crack initiation resistance.
443
Authors: Kuk Tae Youn, Young Sang Na, Jong Hoon Lee, Young Mok Rhyim, Wee Do Yoo, Chan Gyu Lee
Abstract: In order to understand the melt-out mechanism of H13 die casting mould material, microstructural investigation was conducted for the immersion-tested surface in Al-alloy melt. The surface condition of H13 tool steel was modified by varying nitriding conditions and by surface blasting. In particular, long-term behavior of melt-out phenomena during immersion testing of up to 43 hours was focused in this article. It was observed that an ion-nitrided H13 surface showed higher resistance towards melt-out than a gas-nitrided or blasted surface. This was related to the surface layers that are normally formed by nitriding.
509
Authors: Kuk Tae Youn, Young Mok Rhyim, Won Jon Yang, Jong Hoon Lee, Chan Gyu Lee
Abstract: The influence of surface treatment such as nitriding, TNHT(Ti Nano Heat-treatment, PHILOS TECHNOLOGIES, INC.) and PVD coating on the thermal crack propagation behavior of hot work die steel was investigated. To examine the thermal fatigue resistance, the cyclic thermal shock system consisted of induction heating and water spray quenching unit was constructed and Lm is proposed as the index representing the susceptibility to crack initiation and propagation. Thermal stress depending on test temperature was also simulated by FEM. The TNHT specimen showed lower Lm value than as-heat treated specimen but, in the case of maximum and average crack length, the TNHT specimen exhibited higher value than those of as-heat treated specimen. This means that the small number of large cracks were initiated and propagated selectively in the TNHT specimen. This result can be caused by two contrary effects of diffusion layer, those are introduction of the residual compressive stress good for mitigation of thermal tensile stress and very high surface hardness harmful for crack initiation. However, Lm value of salt-bath nitriding specimen was very high due to the white layer in spite of the existence of diffusion layer.
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