Influence of Nitrogen on the Structure and Low Temperature Impact Properties of 304 Type Austenitic Stainless Steel Weld Metals by SMAW Process(Materials, Metallurgy & Weldability)

Abstract

Experimental covered electrodes(lime-titania type)were made by selective additions of Mn-nitride or Cr-nitride to the electrode covering. 304LN stainless steel base plates(t=12mm)whose edge preparation was machined to single sided V, 60°included angle were clamped in a jig and were welded together bymulti-pass shielded metal arc welding process.Nitrogen content of wcld metals was adjusted by changing the content of Mn-nltride or Cr-nitride in the electrode covering.Effect of nitrogenon the microstructure of weldmetal, δ-ferrite content, mean grain width, hardness and δ-ferrite secondary arm spacing were studied. Impact test for as welded specimen and solution treated specimen have been carried out at temperature range from 77K to room temperature.Influence of nitrogen on the impact value of wcld metals was mainly discusxsed.Results obtained are summarized as follows:(1)δ-ferrite content in the weld metals is influenced largely by the nitrogen content.(2)Impact value of weld metals increases with increasing of the nitrogen content of the weld metals up to about 1700 ppm after then the impact value falls as the nitrogen further increased.(3)The strengthening mechanism of weld metals due to addition of nitrogen is estimated that the effect of austenitic structure stabilized and inetrstitial solution hardening. Micro fissuring and precipitation of cluster(nitride)in excess of nitrogen containing weld metals decrease the impact value of weld metals.(4)Nitrogen content up to about 1700 ppm of weld metal which is introduced by SMAW process gives a good influence on the impact properties at low test temperature under condition of this study.