African Fusion August 2016

effects on high temperature ductwork”; Energytech, p.5, 2014. [3] Samuals LE: “Light Microscopy”; pp. 165-183, 1999. [4] Okada M: “Graphitization of weld heat-affected zone in carbon steel”; Transaction of the Japan Institute of Met- als, pp. 353-359, 1982. [5] Dennis, W: “Heterogeneous Nucleation of Graphite in Hypo-EutectoidSteel”; Iron andSteel Institute, pp. 59-64, 1952. [6] Harry E: “Subcritical decomposition of carbide phase in some low-carbon silicon steels”; The Journal of the Iron and Steel Institute, pp. 109- 112, 1954. [7] Brown F: “Nucleation of Graphite in Steel”; Welding Journal, pp. 257-261, 1954. [8] He K: “An electron microscopic study of spheroidal graphite nodules formed in a medium-carbon steel by annealing”; Acta Materialia, pp. 2919-2927, 2007. [9] Foulds JRandShingledecker JP: “Anupdatedassessment of graphitization of steels in elevated temperature ser- vice”; Journal of Materials Engineering andPerformance, vol. 24 no. 2, pp. 586-597, Dec. 2014. [10] Moss C: “Graphitization in type A201 carbon steel in petro- chemical plate after long term service”; Aus- tralian Nuclear Science and Technology Organisation, pp. 351‑359, 1994. [11] ASME Boiler and Pressure Vessel Code: vol. IX, Welding, Brazing and Fusing Qualifications, 2013. [12] Toft L and Marsden R: “The Structure and Properties of 1%Cr- 0.5%Mo Steel”; The Iron and Steel Institute, 276‑294, 1963.

Figure 10: Complex structure of graphite inclusion, visible on an over-etched surface (high resolution SEM image, original magnification 26 790×). coupon failed through the graphitised HAZ. • Prolonged heat treatment at 635°C, at times for up to 1 200 hours, resulted in spheroidisation, but not in noticeable graphitisation. • Repair welding on graphitised material can be performed successfully. References [1] Foulds JR and Viswanathan R: “Graphitization of steels in elevated-temperature service”; Journal of Materials Engineering and Performance, vol. 10, pp. 483-492, Aug. 2000. [2] Meier A, Hammerschmidt DandSkibbe E: “Graphitization

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