Evaluation of post-treatments of novel hot-work tool steel manufactured by laser powder bed fusion for aluminum die casting applications

A.M Vilardell,S.B Hosseini,M Åsberg,A Dahl-Jendelin,P Krakhmalev,C Oikonomou,S Hatami

doi:10.1016/j.msea.2020.140305

A.M Vilardell, S.B Hosseini + Show 5 more

Open Access

https://doi.org/10.1016/j.msea.2020.140305

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Abstract

Additive manufacturing is a good alternative to conventional methods for the production of near net shape geometries with high geometric complexity shorter lead times, being a good option for the manufacturing of dies for die casting process. In this research, a novel hot-work tool steel for aluminum die casting applications manufactured by laser powder bed fusion was investigated. As-built and stress-relieved (AS-B + SR) state was established and used as the reference condition, and subsequent post-treatments were added and compared to the reference condition. Test parts were evaluated using tensile, impact, hardness and thermal fatigue testing. Compared to the reference condition, heat treatment (HT), significantly increased the hardness, yield and ultimate tensile strengths of the material, due to the obtained tempered martensite microstructure. Hot isostatic pressing (HIP) prior to HT significantly increased the impact toughness and ductility, and slightly increased the yield and ultimate tensile strength values compared to the HT condition. The addition of nitriding treatment after HT, without intermedium HIP step, resulted in the highest surface hardness and lowest impact toughness. Thermal fatigue was mostly affected by the hardness and the softening of the material during the thermal fatigue testing. Results showed that a high surface hardness resulted in a higher thermal fatigue crack nucleation, meanwhile conditions with a high softening during thermal fatigue performance resulted in a higher crack propagation.

Highlights

Additive manufacturing (AM) is the process in which a digital 3D CAD-design is used to build-up parts by adding material layer-by-layer
Higher elevated temperature tensile strengths at 600 ◦C have been reported for samples printed with pre heating platform to 200 ◦C, which is better compared to wrought H13, the ductility is lower [5]
The outer surfaces were subjected to grinding after stress relieving (SR) treatment, before they were subjected to the other post-treatments

Summary

Introduction

Additive manufacturing (AM) is the process in which a digital 3D CAD-design is used to build-up parts by adding material layer-by-layer. Retained austenite and carbides along the colony boundaries are typical features of as-built microstructure reported in literature [4,5,6,7]. This microstructure pos sesses high yield (YS) and ultimate tensile strengths (UTS) and hardness of about 1236 ± 178 MPa, 1712 ± 103 and HV0.5 894, respectively [4]. It has been reported that due to the fine microstructure and high amounts of retained austenite, as-built L-PBF H13 has better thermal fatigue resistance that forged H13 [9]. A preheating of the building platform generally aids to increase the relative density of parts, minimize crack formation, and enhance microstructural homogeneity. Higher elevated temperature tensile strengths at 600 ◦C have been reported for samples printed with pre heating platform to 200 ◦C, which is better compared to wrought H13, the ductility is lower [5]

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