Effects of Inoculation on Structure Characteristics of High Silicon Ductile Cast Irons in Thin Wall Castings

Abstract

Previous experiments pointed out that the deviation using a sphere as reference of graphite particles is noticeably increased by Si-alloying, with inoculation as a possible beneficial effect. The main objective of the present work is to evaluate the effects of commercial inoculants (Ca/Ca, Ba/Ca, RE-FeSi alloys) on 4.5%Si ductile iron, thin wall castings. FeSiMgRE treated iron (0.032–0.036%Mgres) is in-mold inoculated (a four-work-positions pattern). A complex chemical composition is obtained for each inoculation variant. Wedge casting W3 (ASTM A 367) is used to evaluate structure characteristics at different wall thickness (3–15 mm). Minimum and maximum size, area, nodule count, and representative graphite shape factors are evaluated. Roundness (including AG and Fmax) at 0.6–0.8 level illustrates the common formation of slightly irregular spheroidal graphite (Type V, ISO 945). Ca, RE-FeSi inoculation leads to the highest level of real perimeter and, consequently, to the lowest level of Sphericity. Ca, Ba-FeSi inoculation appears to be better than simple Ca-FeSi for improving graphite parameters, while Ca, RE-FeSi has the lowest beneficial effect, especially as it negatively affects the compactness degree of graphite particles. A two-step liquid treatment using RE-bearing FeSiCaMg master alloy and Ca, Ba-FeSi inoculant appears to be a solution to improve graphite parameters for high-Si ductile irons solidified in thin wall castings.