Effect of cryogenic treatment on the microstructure and mechanical properties of selected laser melted H13 steel

Abstract

The H13 steel was formed by selective laser melting process, and the as-deposited samples were cryogenically treated at -196 °C and tempered at a low temperature of 200 °C, respectively. The microstructure and properties of the samples under cryogenic treatment and low temperature tempering were analyzed. The results show that the grain structure of the as-deposited H13 steel parts is very fine and accompanied by 19.1% retained austenite at the grain boundaries, which is due to the very fast laser melting and cooling rate. The purpose of cryogenic treatment and low temperature tempering is to retain the desired misconstruction characteristics and to eliminate retained austenite and stresses accumulated during rapid solidification and cryogenic treatment thermal history. After the post-treatment, it was found that many fine carbides were precipitated in the gaps of the martensitic laths, and the retained austenite content was reduced to 5%. Through the tensile test, it was found that the tensile strength of the cryogenically treated and low temperature tempering samples reached 1917.3 MPa, and the elongation after fracture reached 19.3%, which was 4% higher than the deposited tensile strength, and the elongation after fracture increased 64%. It can be seen that the cryogenic treated and low temperature tempered samples obtained excellent mechanical properties.