Evaluation of concentration dependant diffusion coefficients of carbon in a dissimilar joint of ferritic steels

Abstract

When dissimilar weldments between 9Cr-1Mo and 2¼Cr-1Mo ferritic steels are exposed to high temperature, microstructural and microchemical modifications are observed near the weld interface. Diffusion of carbon driven by the activity gradient from low Cr to high Cr steel leads to the formation of carbon enriched 'hard' zone and carbon depleted 'soft' zone near the fusion joint. The present paper deals with the measurement of carbon diffusion profiles and the evaluation of concentration dependent diffusion coefficients of carbon across the interface at a temperature of 1023 K. Accurate carbon concentration profiles are generated using carbon calibration graph. The profiles are smoothened to reduce the experimental scatter and the concentration dependant diffusion coefficients are determined using Den Broeder's method. In the base materials, where the concentration gradient is extremely small, D(c) values are determined using Hall's method. Variation in D(c) across the weld interface is understood based on the microstructural and microchemical changes that take place during heat treatment.

Carburization behavior of AISI 316LN austenitic stainless steel – Experimental studies and modeling

“…A specialized computer package called as 'QUAN-TA' was used for quantitative analysis which takes care of the corrections to be incorporated while calculating the concentrations of various elements. The carbon concentration profiles were corrected using a calibration graph [15] to avoid overestimation due to contamination.…”

“…8 shows the carbon concentration profile obtained using the electron microprobe. To avoid overestimation of carbon due to contamination a calibration graph was constructed between true and observed carbon contents using standards, details of which are given elsewhere [15]. All data points in the 'as recorded' profile were re-evaluated using the calibration graph to obtain true carbon concentration values as given in Fig.…”

Metallurgical Characterization and Diffusion Studies of Successively Buttered Deposit of Ni–Fe Alloy and Inconel on SA508 Ferritic Steel

“…Owing to Fe and Cr in Ni-Fe alloy and Inconel 82 respectively, the carbide precipitation could increase the diffusivity than pure Ni. Sudha et al 37) reported on the diffusion coefficient of carbon (D) for 9Cr-1Mo hard zone as 2.95 × 10 -13 m 2 /s and 2.25Cr-1Mo steel soft zone as 2.85 × 10 -9 m 2 /s. The diffusivities in Ni-Fe alloy are observed to be very less than the soft zone diffusivity of 2.25Cr-1Mo steel interface.…”

Microstructure variation effects influence on characteristics and mechanical properties of Monel 400 and low alloy steel (ASTM 387-Gr.11) GTAW dissimilar joint

“…Carbon depleted zone CDZ usually has soft mechanical properties because of the carbon depleting and called soft zone. According to this, carbon enriched zone with hard mechanical properties called hard zone formed just adjacent to welding fusion line in welding zone [13,14]. Optical micrographic of A387-Gr.11 portrays distinctive CDZ because of Widmanstatten ferrite structures and ferrite grains with white appearance presence.…”

“…This high percentage will cause carbon diffusion or migration phenomena to take place from the high percentage A387-Gr.11 HAZ towards the low carbon weld metal zone. And at the same time, diffusion or migration phenomena will happen from high percentage chromium zone in weld metals to low chromium percentage in A387-Gr.11 HAZ [13,14]. Microstructure in low alloy steel side in Fig.…”