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Wire- and powder-based laser metal deposition of H11 wire and niobium powder for hot forging application

Poster presented at 10th International Laser Symposium & International Symposium »Tailored Joining«, February 27 - 28, 2018, International Congress Center Dresden
 
: Teli, Mahesh

:
Poster urn:nbn:de:0011-n-4944238 (241 KByte PDF)
MD5 Fingerprint: 621e93c2ccfa199edcb6586e2a102e64
Erstellt am: 29.5.2018


2018, 1 Folie
International Laser Symposium <10, 2018, Dresden>
International Symposium "Tailored Joining" <2018, Dresden>
Englisch
Poster, Elektronische Publikation
Fraunhofer IPT ()
Lasermaterialbearbeitung; Werkzeugbau

Abstract
Introduction: H11 hot-work tool steel is largely used to produce highly stressed hot forging dies due to its high levels of hardness, temper resistance and toughness. This steel is exposed to high thermo-mechanical loads, which leads to the failure of dies by surface cracks [1]. To address such kind of failures, many researchers tried to improve the above properties of H11 via refining the microstructure by means of conventional casting and powder metallurgy [2,3]. Nevertheless, conventional casting is accompanied by the relatively slow cooling rates resulting in a coarse microstructure. On the other hand, powder metallurgy is expensive and consists of critical steps. In this context, a little efforts have been put towards developing wire- and powder-based laser metal deposition (WP -LMD) due to the limited process knowledge. Therefore, the aim of the present study was to understand better WP-LMD process and its potential to add effectively Nb powder into the molten pool of H11 wire. This study then clarified the influence of niobium on the grain refinement, carbides' size and shape and their distribution in microstructure. Results: The experiments were performed by varying the powder flow rate and keeping other laser parameters at a constant value. The set of experiments was repeated once in order to understand the stability and reproducibility of the process. The results showed that the process is stable to reproduce clads [3]. The samples were sectioned in the transverse plane and sent for metallography; e.g., SEM, BSD and EDX. In metallography, the niobium carbides were observed not just along the grain boundaries but also throughout the grains. These niobium carbides may then act as seed for the other carbides to evolve as well as an inhibitor for the further growth of grains, and in turn show a significant effect on reducing the grain size by 80 %, the carbide size by 84% and the thickness of grain boundary by 79 %. Summary: The present study was intended to improve the mechanical properties of H11 tool steel via the microstructure refinement. In order to refine the microstructure of H11, the novel WP-LMD process was developed and was later implemented to simultaneously deposit H11 wire and Nb powder on the H11 substrate. Conclusion: The WP-LMD process was found to be effective to produce a refined microstructure of H11 tool steel . This microstructure has the ability to resolve the hardness-toughness paradox faced by plain H11 tool steel, and would be applied to develop coatings on hot forging dies for their longer lifespan and improved production efficiency.

: http://publica.fraunhofer.de/dokumente/N-494423.html