EPMA analysis of carbon content in austenite of nodular cast iron during austenitizing

(1) With the increase of casting modulus MS, on the one hand, the amount of graphite precipitation in nodular iron matrix increases, the diameter of graphite ball increases, while the spheroidization rate of graphite decreases, and the number of graphite balls decreases; on the other hand, the amount of pearlite in as cast structure decreases, while the amount of ferrite increases.

(2) In the as cast microstructure of nodular iron, the average carbon content in bovine eye ferrite is as high as 0.54%, and the carbon content in ferrite between two adjacent graphite spheroids presents a “U” distribution. When the casting modulus is small (MS = 0.50cm) and large (MS = 1.25cm), the carbon content in ferrite is higher, with the average value of 0.33% and 0.39%, respectively.

(3) Austenitizing temperature (t γ) is a significant factor affecting the carbon content in austenite during austenitizing. At low T γ (880 ℃), the amount of pearlite in the matrix has a great influence on the carbon content in austenite. The more pearlite is, the higher the carbon content in austenite is; at higher t γ (920 ℃ and 960 ℃), the higher the amount of ferrite, the higher the carbon content in austenite.

(4) The carbon content in austenite is in the range of 0.57% ~ 0.71% in the conventional austenitizing process. The recommended austenitizing process parameter is 920 ℃ / 2.0h.

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