Low Temperature Mechanical Properties of High-Nitrogen Type 304 Austenitic Stainless Steel Weld Metals

Abstract

High-nitrogen bearing austenitic stainless steel weld metals were obtained by using type 304 electrode wire (1.6 mm) and N₂-Ar mixture shielding gas.
Tensile and impact tests on deposited weld metals were carried out at test temperatures from 0°C to -196°C.
The results can be summarized as follows:
Nitrogen content of weld metals increased considerably with N₂-volume percent in shielding gas, and at 100% N₂ shielding gas, the nitrogen content of weld metal showed about 0.2wt%.
A cast structure which contained δ-ferrite was observed in the weld metal in as-welded condition, but the content of δ-ferrite decreased with increasing nitrogen content of weld metals. There is no δ ferrite in the weld metals which contained about 0.18wt% nitrogen. The 0.2% proof stress increased with nitrogen content of weld metals. This tendency was clearly observed as the test temperature decreased and this behavior was discussed in relation to the strain-induced martensitic transformation in the weld metal at low temperature.
The tensile strength of weld metals increased as the test temperature decreases but was not changed by nitrogen content of specimens.
At impact test, the absorbed energy of weld metals slightly increased with increasing of nitrogen content of weld metals.
The effect of nitrogen on the absorbed energy of high-nitrogen bearing weld meatl can be changed by welding methods and source of nitrogen to weld metals.
High-nitrogen bearing type 304 austenitic stainless steel weld metals can secure a high proof stress without decreasing of the toughness at low temperature.