Dependence of Cast Iron Chill from its Carbon Equivalent

The numerical relation of cast iron chill characteristics (distance of chilled layer H and volume quota of ledeburite in it Ql) with its carbon equivalent СE was investigated. This data helps forecast the evolution of the surface chilled layer forming at the casting production with different thickness from cast iron of various chemical compositions. The study focuses on the unalloyed induction-melted cast iron with eight chemical-composition variants with carbon equivalent from 3.30 up to 5.53%. From these cast irons, step-by-step castings were made with steps sizes of 10 × 60 mm and thickness of 5, 10, 20, and 40 mm. The chilled-layer distance (depth) was measured at the casting fractures and gaged on thickness of full chill zone. Ledeburite volume quota was detected by a metallographic method using the “Nexsys-Image expert pro 3” computer program. According to experimental data, when the casting thickness is 5 and 10 mm, the through (at all thickness) full chill is formed at a carbon equivalent ≤4.08% and ≤3.67%, consequently. At the castings with 20- and 40-mm thickness, the zone of full chill is absent. In this case, the chilled layer depth increases with a decrease of carbon equivalent and decreases with an increase of casting’s thickness X. The dependence of H from CE have the exponential character and can be described by the equation H = Aexp(–kCE), where A and k are empirical coefficients. Ledeburite volume quota near the contact casting surface with chiller is near 90%, but it decreases with different intensity depending on changes of carbon equivalent and casting’s thickness with an increase in the distance from the surface. By mathematical processing of the experimental data received for the 5-mm distance from the contact surface of the casting with chiller, a numerical relation Ql in casting chilled layer with value of CE can be described by the exponential dependence: Ql = 1000(7/(X + 10))exp(–CE).