1965 Volume 34 Issue 2 Pages 128-136
Nitrogen is not always detrimental to weld metal. It may have an effect of increasing of hardness of wear resisting steel and strength of steel at elevated temperature. Moreover it may stabilize austenitic phase.
It was studied in this report to use nitrogen from welding atmosphere as alloying element of weld steels. three kinds of electrode wire were used : 1 Mn-0.5 Si, 2.5 Cr-1 Mo and 5 Cr-0.5 Mo. Bead-on-plate specimens were made by each of these electode wires with CO2-N2 or Ary-N2 shielded arc welding. Nitrogen content of supplied gas was varied from 0 to 10%. Weld steels were given various heat treatment : as welded, water quench and anneal at temperature from 100 to 600°C after water quench. Vickers hardness was measured about those specimens. And then mechanical properties of all weld metals by these electrode wires with CO2, CO2-A, CO2-N2 shielded arc welding were compared at room temperature and 400°C.
The experiment has revealed the following ;
1) There is a certain relation between a nitrogen content of weld steel and one of supplied gas, and it is variable according to a content of alloying element of weld metal. Chromium decreases a nitrogen content of weld metal and increases a critical nitrogen content of atmosphere in which a weld metal becomes porous.
2) Increasing the nitrogen content of weld metal, it becomes harder.
3) The more chromium content of weld metal increases, the harder nitrogen makes weld metal.
4) A weld metal which contains nitrogen and some alloying elements became harder in the case it was annealed at 100 to 300°C after water quench than in the case it was only water quenched.
5) A weld metal by 5 Cr-0.5 Mo electode wire with CO2-N2 shielding gas revealed a higher value of ultimate tensile strength than CO2, or CO2-A shielding.