**Comparison of Nano-Mechanical Behavior between Selective Laser Melted SKD61 and H13 Tool Steels**

**Jaecheol Yun 1, Van Luong Nguyen 1, Jungho Choe 1, Dong-Yeol Yang 1, Hak-Sung Lee 2, Sangsun Yang 1 and Ji-Hun Yu 1,\***


Received: 8 November 2018; Accepted: 4 December 2018; Published: 6 December 2018

**Abstract:** Using nanoindentation under various strain rates, the mechanical properties of a laser powder bed fusion (PBF) SKD61 at the 800 mm/s scan speed were investigated and compared to PBF H13. No obvious pile-up due to the ratio of the residual depth (*hf*) and the maximum depth (*hmax*) being lower than 0.7 and no cracking were observed on any of the indenter surfaces. The nanoindentation strain-rate sensitivity (*m*) of PBF SKD61 was found to be 0.034, with hardness increasing from 8.65 GPa to 9.93 GPa as the strain rate increased between 0.002 s<sup>−</sup><sup>1</sup> and 0.1 s<sup>−</sup>1. At the same scan speed, the *m* value of PBF H13 (*m* = 0.028) was lower than that of PBF SKD61, indicating that the mechanical behavior of PBF SKD61 was more critically affected by the strain rate compared to PBF H13. PBF processing for SKD61 therefore shows higher potential for advanced tool design than for H13.

**Keywords:** Laser powder bed fusion; selective laser melting; SKD61 tool steel; nanoindentation; strain-rate sensitivity
