Inoculation and Higher Potency Alloys

The growth and diversity of iron casting in the Asian markets has led many foundries to re-examine their inoculation processes. New iron grades demand new process solutions, growth in production stretches the availability of good quality melting stock, and end users require higher specifications.

Traditionally, the Asian market has used calcium/barium based inoculants and these are widely available, albeit of hugely variable quality. However, their low potency leaves them unsuited to many applications in this changing market.

Challenges such as shrinkage control in both gray and ductile iron, producing higher strengths in thinner section lighter weight castings, and matrix structure all offer the opportunity for an examination of the inoculants available today.

In gray irons, strontium containing inoculants, such as Superseed, are globally used at low addition rates to prevent shrink, while giving excellent type A graphite structures. Variants on Superseed inoculant are marketed for foundries operating at low sulphur levels.

In ductile iron where the properties are controlled by the matrix, good nodule number, shape and ferrite promotion are pre-requisites to obtaining the right mechanical results. A number of medium and high potency inoculants, such as Alinoc and Ultraseed Ce inoculants have been designed to meet these needs, the former being a powerful ferrite promoting inoculant and the latter designed for more difficult-to-inoculate low base nucleation irons.

With the incidence of chunky graphite becoming more of a concern, a new rare-earth free high potency inoculant is now being launched. Known as Ultraseed Zr, this alloy has been formulated to add back the key constituents necessary for inoculation, sulphur and oxygen during the formation of the nuclei whilst being RE free, and having the ability to generate new nuclei during solidification, the tendency towards chunky is reduced.