Effect of N2 content in shielding gas on formation quality and microstructure of high nitrogen austenitic stainless steel fabricated by wire and arc additive manufacturing

Abstract

The composition of shielding gas exerts a crucial influence on high nitrogen austenitic stainless steel (HNASS) deposited by gas metal arc additive manufacturing. The proportion of N 2 in shielding gas greatly affected the formation quality and microstructure of deposited parts. As N 2 proportion improved, the formation quality became worse gradually and the nitrogen concentration of deposition metal increased. The maximum nitrogen concentration of deposition metal was more than 1%. However, N 2 porosity in the deposition metal became serious when the N 2 content was over 10 %. The microstructure of the deposition metal changed from two phases of austenite and ferrite in shielding gas of 0∼10 %N 2 to complete austenite with 15 %∼25 %N 2 content in shielding gas. With optimal shielding gas of 5%N 2 +2%O 2 +10%He+83%Ar, the deposited parts of HNASS demonstrated good formation and excellent properties. The average ultimate tensile strength of 920 MPa was achieved and the elongation was 27.7%.