Comparative study on dynamic mechanical properties of additive manufacturing high strength steel and wrought high strength steel under high strain rate

Abstract

Additive manufacturing high-strength steel has a unique manufacturing process and has broad application prospects in military equipment, aerospace, and other fields, but it is often threatened by dynamic loads such as explosion and high-speed impact during use, which has attracted wide attention. In this paper, the dynamic impact of additive manufacturing high-strength steel LMD-BK and wrought high-strength steel BK was carried out at strain rates of 1000 s−1–5000 s−1 by the Split-Hopkinson pressure bar (SHPB) test, respectively, and the differences in the dynamic mechanical properties of the two were investigated under the impact of different strain rates. Using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) micro-observation techniques, the microstructure morphologies of LMD-BK and BK before and after dynamic impact were characterized, and the microstructure evolution mechanism of the two was investigated. The results show that both LMD-BK and BK are strain rate sensitive, and the dynamic compressive strength increases and then decreases with the increase of strain rate, with a maximum at 2000 s−1 and a minimum at 1000 s−1. The maximum and minimum values of dynamic compressive strength for LMD-BK are 1978 MPa and 1757 MPa, respectively; for BK, the maximum and minimum values of dynamic compressive strength are 1389 MPa and 1329 MPa, respectively. The final strain of the material increases as the strain rate increases. At the same strain rate, the final strain of BK is always larger than that of LMD-BK. With the increase in strain rate, the impact work absorbed by the material increases, and at the same strain rate, LMD-BK can absorb more impact work than BK. Microscopic observations show that after dynamic impact, LMD-BK undergoes fragmentation of the columnar structure and compression of the cellular structure to form a deformation localization zone. These results are of great significance for the study of dynamic mechanical properties and microstructure evolution mechanism of high-strength steel made by additive manufacturing under extreme environments such as explosion and high-speed impact.

Keywords

• Additive manufacturing high-strength steel
• SHPB
• Dynamic mechanical properties
• Microstructure evolution