THE EFFECT OF NIOBIUM ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AUSTENITIC CrNi STEEL PRODUCED BY WIRE-FEED ELECTRON BEAM ADDITIVE MANUFACTURING

摘要

Two billets of Nb-free and Nb-alloyed CrNi steels have been fabricated by the wire-feed electron beam additive manufacturing (EBAM) method. Alloying with Nb does not influence a columnar grain growth and formation of a two-phase austenitic-ferritic microstructure during the EBAM processing of the billets using a wire from CrNi austenitic steel. Niobium-alloying contributes to a change in phase composition of EBAM-produced austenitic steel as compared to Nb-free steel,i.e., causes a decrease in the δ-ferrite content and leads to the formation of coarse Nb-enriched precipitates along the intergranular or interphase (austenite/ferrite) boundaries. A comparative analysis of the microstructure and mechanical properties of Nb-free and Nb-alloyed EBAM austenitic steels has been carried out. The variations in strength properties and plastic characteristics of the steel have been discussed considering the effect of niobium on the phase compositionand the microstructure of additively fabricated austenitic steel.