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Fe-Cr and Fe-Ni alloy sheets were welded by gas tungsten arc welding in an arc atmosphere-controlled chamber filled with argon-nitrogen gas mixtures in order to study effects of chromium and nickel on the nitrogen absorption of iron alloy weld metal. In Fe-Cr alloys, the nitrogen content of weld metal decreased with an increasing welding current. In Fe-Ni alloys, the nitrogen content of weld metal hardly depended on the welding current. In each alloy, the nitrogen content of weld metal increased with the nitrogen partial pressure of the atmosphere in low nitrogen partial pressure region, and was constant in nitrogen partial pressure more than 0.01 MPa. The nitrogen content of weld metal increased remarkably with the chromium content, but decreased slightly with an increasing nickel content. The nitrogen absorption of iron alloy weld metals was discussed thermodynamically by comparing with arc-melting and equilibrium data.