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

Jaecheol Yun,Van Nguyen,Ji-Hun Yu,Jungho Choe,Hak-Sung Lee,Sangsun Yang,Dong-Yeol Yang

doi:10.3390/met8121032

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−1 and 0.1 s−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.

Highlights

SKD61 and H13 are types of hot work tool steels applied to casting molds, extrusion tools, forging dies, etc., and the hardness of SKD61 (229 BHN) is lower than that of H13 (235 BHN) [1]
Very few studies have dealt with the mechanical behavior of powder bed fusion (PBF) SKD61 using nanoindentation
A constant rate of loading (CRL) method, where a steady loading rate is used until the tip depth rate becomes nearly constant, was used to determine the strain rate (ε) because allows for simple calculation of strain rates, and is proven to be more suitable to correlate with the conventional constant strain rate tests [12,15,16]

Summary

Introduction

SKD61 and H13 are types of hot work tool steels applied to casting molds, extrusion tools, forging dies, etc., and the hardness of SKD61 (229 BHN) is lower than that of H13 (235 BHN) [1]. Both steels are fabricated by conventional methods requiring expensive dedicated tools, and are inappropriate for small-scale or complex-shape productions [2,3,4]. PBF processing at an 800 mm/s laser scan speed was applied successfully for SKD61 powders [4,11]. Results for PBF-processed H13 at the same laser scan speed sourced from the literature are used in the evaluation conducted here [2]

Experimental Procedure

Discussion

Conclusions