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What are grain refiners?

Controlling grain size and microstructure for steel castings

Grain refiners are a class of cerium-containing inoculants for steel that reduce grain size and increase grain uniformity, with consequent improvements in mechanical properties and product quality. They are primarily used for steel castings, but increasing attention is now being given to their application to steel products.

The concept of grain refiners for steel dates back to 2001, when a team at Elkem, in collaboration with the Norwegian University of Science and Technology (NTNU), patented a method for manufacturing and using a grain-refining alloy to improve the microstructure of austenitic and ferritic steels.

Grain refiners are in essence a type of master alloy that work in a similar way to inoculants for cast iron, by causing the formation of a uniform dispersion of heterogeneous nuclei (‘active inclusions’) within the melt. The steel then solidifies upon these nuclei in a controlled fashion, giving two main benefits:

  • Better-quality castings, with reduced shrinkage porosity, hot cracking and segregation, and substantially reduced columnar regions near the edge. This results in reduced need for repair-welding of cracks or grinding-out of surface defects.
  • Finer grain structure throughout the casting provides increased strength and toughness for the final product, giving a significantly longer service lifetime (in a trial we performed in our own quartzite-crushing facility, the lifetime of our grain-refined manganese steel mantles was 50% higher than the average).

Elkem grain refiners for superior nucleation of steel

Elkem grain refiners (EGRs) are ferrosilicon-based alloys that use cerium as the active ingredient. On addition to the melt, this yields particles of cerium oxides, sulfides, oxysulfides and aluminates – all of which have a close lattice match with steels, and so provide excellent nucleation properties with minimal undercooling needed.

Compared to other cerium-containing alloys, Elkem grain refiners show excellent recovery when added to molten steel, due to their precisely controlled composition. A key feature is the absence of lanthanum or other rare-earth metals, which leads to a better grain-refining effect than other alloys containing a mix of rare-earths.

Grain refiners for stainless steel and manganese steel castings

Elkem offers two classes of grain refiner, both of which contain nominally 10 wt% Ce:

  • STAINSEED™ grain refiner is optimized for stainless steels, and contains nominally 30 wt% Cr
  • WEARSEED™ grain refiner is optimized for manganese steels, and has nominally 24 wt% Mn and 10 wt% Cr.

These products are available in a 0.2–2 mm grade for rapid dissolution in ladles up to 3 tonnes, and in a 2–20 mm grade for use in larger ladles. For optimum performance, the addition of EGR StainSeed™ and WearSeed™ must be tailored to the process at the foundry or steel mill in question. We can advise on when and how to add the grain refiner to the melt in order to achieve this.

Using grain refiners in steel foundries and steel mills

At first, the use of grain refiners was largely restricted to highly alloyed steels such as austenitic stainless steel and duplex stainless steel. But more recently use has increased amongst foundries producing carbon steel castings (amongst others), since refining the as-cast structure produces a larger influence on grain size than the conventionally-used heat treatment.

In addition, in recent years there has been growing interest in using grain refiners for products from steel mills, such as ingots, billets, blooms and slabs. This is a more challenging application because of the scale of the operations, but we’re working hard to find practical ways of using grain refiners to produce semi-finished steels. Please contact us for the latest developments in this field.

Buying grain refiners from Elkem

With you at every step

We’re more than just a manufacturer – buying grain refiners from us is a collaboration. We’ll listen carefully to your requirements, help you select the right product to deliver maximum product quality and cost-effectiveness for you, and offer expert guidance and insight at every stage of the production process.

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