Solidification process and graphite morphology of vermicular graphite cast iron

High purity pig iron, scrap steel, ferrochromium, ferrovanadium, ferromolybdenum and other master alloys are selected. Copper and tin are added as pure metals and melted in a 20 t medium frequency induction furnace. Carburizing agent is used to adjust the carbon content of molten iron. After melting, raise the temperature to 1520 ℃ and leave the furnace after holding for 10 minutes. The chemical composition of raw molten iron w (%): 3.90 ~ 4.00 C, 1.00 ~ 1.20 Si, 0.70 ~ 0.80 Mn, ≤ 0.025 P, ≤ 0.012 s, 0.20 ~ 0.30 Ni, 0.15 ~ 0.25 Cr, 0.20 ~ 0.30 Mo, 1.60 ~ 1.80 Cu, 0.04 ~ 0.06 sb. The peristaltic treatment of vermicular graphite cast iron adopts Eken compactmg alloy and RESiFe alloy for composite treatment. The inoculant is 0.4% Siba or 0.4% 75sife. The peristaltic process of vermicular graphite cast iron is the punching method. 2500 kg of molten iron is treated each time. The amount of residual re and residual mg after the peristaltic treatment of vermicular graphite cast iron and the amount of inoculant added to the gate box.

Take the vermicular graphite cast iron and pour the molten iron into the thermal analysis sample cup after vermiculation and inoculation, and use the Agilent data collector (34970A, American Agilent) to record the temperature data during the cooling process of molten iron. The test sample cup is resin sand mold square cup and K-type thermocouple, and the data acquisition frequency is 70 times / min. measure 3 groups of data under each treatment condition to reduce the test error. The collected data are processed to obtain the T-T cooling curve of temperature changing with time in the process of liquid iron cooling, and the first-order differential and second-order differential of T-T cooling curve are carried out respectively to obtain the characteristic value of cooling curve.

The main dimensions of the cylinder liner casting are 326 mm inner diameter, 2350 mm high, 110 mm thick at the upper large end and 55 mm thick at the lower small end. The casting weighs 1600 kg.

Samples were taken from the thermocouple part of the thermal analysis sample cup and the big end of the cylinder liner, and the microstructure of vermicular graphite cast iron was observed after grinding and polishing.