*Article* **The Microstructure, Mechanical Properties,and Corrosion Resistance of UNS S32707 Hyper-Duplex Stainless Steel Processed by Selective Laser Melting**

#### **Feng Shang 1,2, Xiaoqiu Chen 2, Zhiyong Wang 2, Zuchun Ji 3, Fei Ming 1, Shubin Ren 1,\* and Xuanhui Qu 1,\***


Received: 15 August 2019; Accepted: 12 September 2019; Published: 17 September 2019

**Abstract:** UNS S32707 hyper-duplex stainless steel (HDSS) parts with complex shapes for ocean engineering were prepared by selective laser melting (SLM) process. In the process of SLM, the balance between austenite and ferrite was undermined due to the high melting temperature and rapid cooling rate, resulting in poor ductility and toughness. The solution annealing was carried out with various temperatures (1050–1200 ◦C) for one hour at a time. The evolution of microstructures, mechanical properties, and corrosion resistance of UNS S32707 samples prepared by SLM was comprehensively investigated. The results indicate that a decrease in nitrogen content during the SLM process reduced the content of austenite, and a nearly balanced microstructure was obtained after appropriate solution annealing. The ratio between ferrite and austenite was approximately 59.5:40.5. The samples with solution treated at 1150 ◦C and 1100 ◦C exhibited better comprehensive mechanical properties and pitting resistance, respectively.

**Keywords:** selective laser melting; hyper-duplex stainless steel; microstructure; mechanical property; corrosion resistance
