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Effect of post-heat treatment cooling on microstructure and mechanical properties of selective laser melting manufactured austenitic 316L stainless steel

Saad Waqar (Key laboratory of High efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan, China and Research Centre for Aeronautical Component Manufacturing Technology and Equipment, Jinan, China)
Jiangwei Liu (Key laboratory of High efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan, China and Research Centre for Aeronautical Component Manufacturing Technology and Equipment, Jinan, China)
Qidong Sun (Key laboratory of High efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan, China and Research Centre for Aeronautical Component Manufacturing Technology and Equipment, Jinan, China)
Kai Guo (Key laboratory of High efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan, China and Research Centre for Aeronautical Component Manufacturing Technology and Equipment, Jinan, China)
Jie Sun (Key laboratory of High efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan, China and Research Centre for Aeronautical Component Manufacturing Technology and Equipment, Jinan, China)

Rapid Prototyping Journal

ISSN: 1355-2546

Article publication date: 24 September 2020

Issue publication date: 28 November 2020

709

Abstract

Purpose

This paper aims to investigate the influence of different post-annealing cooling conditions, i.e. furnace cooling (heat treatment (HT) 1 – slow cooling) and air cooling (HT 2 – fast cooling), on the microstructure and mechanical properties of selective laser melting (SLM) built austenitic 316L stainless steel (SS).

Design/methodology/approach

Three sets of 316L SS samples were fabricated using a machine standard scanning strategy. Each set consists of three tensile samples and a cubic sample for microstructural investigations. Two sets were subsequently subjected to annealing HT with different cooling conditions, i.e. HT 1 and HT 2, whereas one set was used in the as-built (AB) condition. The standard metallographic techniques of X-ray diffraction, scanning electron microscopy and electron back-scattered diffraction were used to investigate the microstructural variations induced by different cooling conditions. The resultant changes in mechanical properties were also investigated.

Findings

The phase change of SLM fabricated 316L was observed to be independent of the investigated cooling conditions and all samples consist of austenite phase only. Both HT 1 and HT 2 lead to dissolved characteristic melt pools of SLM. Noticeable increase in grain size of HT 1 and HT 2 samples was also observed. Compared with AB samples, the grain size of HT 1 and HT 2 was increased by 12.5% and 50%, respectively. A decreased hardness and strength, along with an increased ductility was also observed for HT 2 samples compared with HT 1 and AB samples.

Originality/value

From previous studies, it has been noticed that most investigations on HT of SLM fabricated 316L were mainly focused on the HT temperature or holding time. However, the post-HT cooling rate is also an equally important factor in deciding the microstructure and mechanical properties of heat-treated components. Therefore, this paper investigates the influence of different post-annealing cooling conditions on microstructure and mechanical properties of SLM fabricated 316L components. This study provides a foundation for considering the post-HT cooling rate as an influential parameter that controls the properties of heat-treated SLM components.

Keywords

Acknowledgements

Conflict of Interest: All authors affirm that there is no conflict under any sense during the experimentation, manuscript writing and publication phase of this article.

The authors acknowledge the financial support from the National Natural Science Foundation of China (NSFC, Grant No.: 51905306), the Major Scientific and Technological Project of Shandong Province (Grant No.: 2019GGX104006), the Taishan Scholar Project of Shandong Province of China (No.ts20190975), the Special Support for Post-doc Creative Funding of Shandong Province (201902005).

Citation

Waqar, S., Liu, J., Sun, Q., Guo, K. and Sun, J. (2020), "Effect of post-heat treatment cooling on microstructure and mechanical properties of selective laser melting manufactured austenitic 316L stainless steel", Rapid Prototyping Journal, Vol. 26 No. 10, pp. 1739-1749. https://doi.org/10.1108/RPJ-12-2019-0320

Publisher

:

Emerald Publishing Limited

Copyright © 2020, Emerald Publishing Limited

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