Dependence of cast iron chill from its carbon equivalent

Numerical relation of cast iron chill characteristics (distance of chilled layer H and volume quota of ledeburite in it Qл ) with its carbon equivalent СE was investigared. This data helps to prognosticate with high probability the evolution of the surface chilled layer forming at the production of castings with different thickness from cast iron of various chemical compositions. The object of study is the unalloyed induction melted cast iron with eight variants of chemical composition with carbon equivalent from 3.30 up to 5.53 %. From these cast irons we made the step-by-step castings with steps sizes of 10×60 mm and thickness of 5, 10, 20 and 40 mm. The distance (depth) of chilled layer was measured at the fractures of the castings and gaged on thickness of full chill zone. Ledeburite volume quota was detected by metallographic method using “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 carbon equivalent ≤ 4.08 % and ≤ 3.67 % consequently. At the castings with 20 and 40 mm thickness the zone of full chill is absent, and 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 СЕ have the exponential character and can be described by the equation H = A exp (–k СE ), where A and k are empirical coefficients. Ledeburite volume quota near the contact surface of casting with chiller is near 90 %, but with an increase in the distance from the surface it decreases with different intensity depending on changes of carbon equivalent and casting’s thickness. By mathematical processing of the experimental data received for the distance of 5 mm from the contact surface of the casting with chiller, we have detected that numerical re lation Qл in casting chilled layer with value of CE can be described by the exponential dependence