Diffusion and thermodynamics of phosphorus, carbon, chromium, and nickel in welding joints of steels

The paper deals with P, C, Cr, and Ni redistribution in four types of weldm ents. The joints were created on carbon steels with differing concentration s of P (0.1 and 0.4 wt. %) and with carbon content of 0.41 wt. %, which wer e welded: a) with corrosion-resistant steel CSN 41 7242 (Cr18Ni8 steel) and b) with a carbon steel with low concentration of P (0.014 wt. %) and with carbon content of 0.42 wt. %. Contact welded joints (12 mm diameter and 8 m m height - 4 mm for each steel of the pair) were used in the experimental s tudy. The welding process was carried out by an electric shock in protectiv e Ar atmosphere. The diffusion pairs were isothermally annealed in the temp erature range from 500 to 1100 degreesC with 50 degreesC intervals. Then, t hey were cut perpendicularly to the weld interface and were metallographica lly polished on the cut planes. The concentrations of P, C, Cr, and Ni were measured by applying the X-ray wave dispersion analysis method (WDA) with use of the analytical equipments JEOL JXA 8600/KEVEX and PHILIPS MICROSPEC. From the concentration curves, the P, C, Cr, and Ni diffusion coefficients in welded steels and weldments, coefficient of thermodynamic activity of P , and the thermodynamic and diffusion interaction coefficients were calcula ted. Among other findings, "uphill" diffusion of phosphorus was observed on the weld interface of the corrosion-resistant austenitic steel and unalloy ed carbon steels with 0.1 and 0.4 wt. % of phosphorus concentrations.