Effect of heat treatment on anisotropic microstructure of additive manufacturing 316L stainless steel

doi:10.13251/j.issn.0254-6051.2021.10.008

Abstract

Abstract: 316L stainless steel prepared by selective laser melting (SLM) was taken as the researching object. First, the porosity and microstructure of the printed parts were characterized, then the influence of heat treatment on anisotropy of the microstructure and hardness was explored. The results show that both the volume fraction and the area fraction of porosity of the printed parts are low (below 1%), and no obvious difference between the two. For the XY plane perpendicular to the printing direction, it is mainly composed of strip micro-melt pools passing across each other at angle of 67°. Each micro-melt pool consists of both columnar and cellular microconstituents. The former is mainly located at the boundary of the molten pool, with a length of about tens of microns and a width of about 400 nm. The latter is mainly located at the center of the molten pool with a size of about 400 nm. For the YZ plane parallel to the printing direction, it is mainly composed of fan-shaped microstucture containing columnar and cellular microconstituents. However, the distributions of these columnar and cellular microconstituents are more complex. The columnar microconstituent running through the multilayer molten pool, XY plane and YZ plane have obvious microstructure anisotropy. The appropriate heat treatment process can effectively decrease the anisotropy of the microstructure in the different planes. The XY plane can basically be homogenized after annealing at 800 ℃ for 2 h, while the YZ plane can be homogenized at 900 ℃ for 2 h. Additive manufacturing parts with micro-nano size structure have higher hardness than that of the traditional parts. In generally, the heat treatment can decrease the hardness in different directions, but the descender is greater in the vertical printing direction.

Key words: additive manufacturing, 316L stainless steel, microstructure anisotropy, heat treatment

CLC Number:

TG156

Dong Zhihao, Zheng Zhijun, Peng Le. Effect of heat treatment on anisotropic microstructure of additive manufacturing 316L stainless steel[J]. Heat Treatment of Metals, 2021, 46(10): 45-52.

References

[1]卢秉恒, 李涤尘. 增材制造(3D打印)技术发展[J]. 机械制造与自动化, 2013, 42(4): 1-4.
Lu Bingheng, Li Dichen. Development of the additive manufacturing(3D printing) technology[J]. Machine Building and Automation, 2013, 42(4): 1-4.
[2]李小丽, 马剑雄, 李萍, 等. 3D打印技术及应用趋势[J]. 自动化仪表, 2014, 35(1): 1-5.
Li Xiaoli, Ma Jianxiong, Li Ping, et al. 3D printing technology and its application trend[J]. Process Automation Instrumentation, 2014, 35(1): 1-5.
[3]易明. 激光增材制造316L不锈钢的显微组织与力学性能研究[D]. 长沙: 湖南大学, 2019.
Yi Ming. Study on microstructure and mechanical properties of 316L stainless steel by laser additive manufacturing[D]. Changsha: Hunan University, 2019.
[4]尹衍军. 选区激光熔化成形316L不锈钢流动规律及组织、性能研究[D]. 北京: 北京科技大学, 2019.
Yin Yanjun. Study of flow law, microstructure and mechanical properties of 316L stainless steel by selective laser melting[D]. Beijing: University of Science and Technology Beijing, 2019.
[5]王迪. 选区激光熔化成型不锈钢零件特性与工艺研究[D]. 广州: 华南理工大学, 2006.
Wang Di. Study on the fabrication properties and process of stainless steel parts by selective laser melting[D]. Guangzhou: South China University of Technology, 2006.
[6]陈莹莹. 316L不锈钢微细球形粉末的制备及其SLM成形试验研究[D]. 广州: 华南理工大学, 2018.
Chen Yingying. Preparation of 316L stainless steel microsphere powders and research on its SLM forming test[D]. Guangzhou: South China University of Technology, 2018.
[7]Herzog D, Seyda V, Wycisk E, et al. Additive manufacturing of metals[J]. Acta Materialia, 2016, 117(1): 371-392.
[8]Wang Chengcheng, Tan Xipeng, Liu Erjia, et al. Process parameter optimization and mechanical properties for additively manufactured stainless steel 316L parts by selective electron beam melting[J]. Materials and Design, 2018, 147(1): 157-166.
[9]Li Zan, Voisin Thomas, McKeoun J T, et al. Tensile properties, strain rate sensitivity, and activation volume of additively manufactured 316L stainless steels[J]. International Journal of Plasticity, 2019, 120(1): 395-410.
[10]Qiu C, Kindi M A, Aladawi A S, et al. A comprehensive study on microstructure and tensile behaviour of a selectively laser melted stainless steel[J]. Scientific Reports, 2018, 8(1): 1-16.
[11]Nguyen Q B, Zhu Z, Ng F L, et al. High mechanical strengths and ductility of stainless steel 304L fabricated using selective laser melting[J]. Journal of Materials Science and Technology, 2019, 35(2): 388-394.
[12]Wang D, Song C, Yang Y, et al. Investigation of crystal growth mechanism during selective laser melting and mechanical property characterization of 316L stainless steel parts[J]. Materials and Design, 2016, 100(1): 291-299.
[13]Michał Ziętala, Durejko T, Marek Polański, et al. The microstructure, mechanical properties and corrosion resistance of 316 L stainless steel fabricated using laser engineered net shaping[J]. Materials Science and Engineering A, 2016, 677(1): 1-10.
[14]Yang Y, Zhu Y, Khonsari M M, et al. Wear anisotropy of selective laser melted 316L stainless steel[J]. Wear, 2019, 428-429(1): 376-386.
[15]Shifeng W, Shuai L, Qingsong W, et al. Effect of molten pool boundaries on the mechanical properties of selective laser melting parts[J]. Journal of Materials Processing Technology, 2014, 214(11): 2660-2667.