The transfer behavior of nitrogen into the welding metal during gas tungsten arc welding process of 32Mn-7Cr-1Mo-0.3N steel was investigated. The effects of gas tungsten arc welding process variables, such as the volume fraction of nitrogen in shielding gas, arc holding time and arc current on the nitrogen content in the welding metal were also evaluated. The results show that the volume fraction of nitrogen in gas mixture plays a major role in controlling the nitrogen content in the welding metal. It seems that there exhibits a maximum nitrogen content (depending) on the arc current and arc holding time. The optimum volume fraction of nitrogen in shielding gas is 4% or so. The role of gas tungsten arc welding processing parameters in controlling the transfer of nitrogen is further (confirmed) by the experimental results of gas tungsten arc welding process with feeding metal.
SEM and Field emitting TEM-EDAX were used to investigate the fracture surface of series impact specimens and the grain boundary chemistries of VIM(vacuum-inductionmelted) Fe-38 Mn austenitic alloy before and after ESR(electroslag remelting,).The quantity and the size of inclusions were also examined.The results show that the VIM Fe-38 Mn austenitinic alloy water-quenched from 1 100 C undergoes an obvious ductile-to-brittle transition,and the impact work at ambient temperature is 242 J,the corresponding fracture surface exhibits a dimple character.However,the impact work at 77 K of VIM alloy is only 25 J and the fracture mode is IGF(intergranular fracture).After ESR,the impact work at ambient temperature is 320 J and the fracture surface exhibits a character of "volcano lava"(meaning excellent toughness);The impact work at 77 K is up to 300 J and the fracture mode is micro void coalescence mixed with quasi-cleavage.The segregation of Mn is not found in all specimens,but the segregation of S is observed,and the S segregation is decreased after ESR.The examined results of inclusions show that ESR reduces the quantity and improves the morphology of inclusions.From the above results it can be seen that the cryogenic IGF of VIM Fe-38 Mn austenitic alloy is related to the S segregation at grain boundary.After ESR the decrease in the quantity and size of inclusion results in the increase of the impact work at ambient temperature,while the restriction of IGF is related to the decrease in the total level,and hence in the grain boundary segregation of S.
