Comparison of microstructure characteristics of different smelting process in 028 alloy for oil pipes. (July 2014) - Meng, F. G.
Abstract : Using optical microscopy, scanning electron microscopy, X-ray energy spectrum analysis and thermodynamic calculation software Thermo-Calc, inclusions, grain size and precipitates from different positions in the forging ingots of two different smelting process are compared and analysed, along with the formation mechanism of the precipitates. The results show that the sizes of inclusions in forging ingots from two different smelting process do not change, but reduce in number after the electroslag remelting process, and neither do the species change: mainly aluminium oxide and silicate inclusions. The average grain size after electroslag remelting is smaller than before, and the main equilibrium precipitates of 028 alloy include γ, M23 C6, σ and α-Cr phases. The precipitates after electroslag remelting are fewer in number, with uneven distributions. Regarding chemical composition, the precipitates are mainly in the σ phase, containing Fe, Ni, Cr and Mo elements. This severely reduces the corrosion resistance of 028 alloy, and can be eliminated by solid solution treatment for 2 h at 1160°C.