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

• Main Authors: Iulian Riposan, Eduard Stefan, Stelian Stan, Nicoleta Roxana Pana, Mihai Chisamera
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Metals
• Subjects: high Si ductile cast iron; thin wall casting; inoculation; in-mold; structure; graphite
• Online Access: https://www.mdpi.com/2075-4701/10/8/1091

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%Mg_res) 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 A_G and F_max) 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.