Strain rate dependence of mechanical property in a selective laser melted 17-4 PH stainless steel with different states

The strain rate dependence of mechanical property in a selective laser melted (SLM) 17-4 precipitation hardening (PH) stainless steel with different states was investigated systematically by microstructure characterization, texture measurement and tensile test in the present study. The results reveal that as-built and annealed specimens have different initial microstructure and show the strain rate dependence of mechanical property, and their microstructure and texture have great changes during tensile deformation. Before tensile deformation, both as-built and annealed specimens are comprised of mixed grain structure, texture along building direction and dual austenite and martensite phases, however, the latter contains a larger amount of martensite phase. No matter as-built specimen or annealed specimen, the yield strength, ultimate tensile strength and elongation increase with the increase of strain rate. In contrast to the as-built specimen, the annealed specimen exhibits the higher ultimate tensile strength, but lower elongation at the corresponding strain rate, and the higher strain rate sensitivity. After the tensile deformation, the completely different microstructure and texture were developed including finer grain structure, more high angle grain boundaries (HAGBs), new texture along tensile direction and more martensite phase. There is a significant austenite-to-martensite phase transformation during tensile deformation. No matter as-built specimen or annealed specimen subjected to tensile deformation, the grain size, HAGBs and texture almost have no change with the increase of strain rate, but the phase transformation degree changes a lot.