Ductile iron — sometimes also referred to as ductile cast iron, nodular (cast) iron, spheroidal graphite (cast) iron, or SG (cast) iron — has been an industry favorite since its invention in the 1940s and gradual refinement in the '50s, '60s, and beyond. The reason? The spheroidal graphite nodules dotting its infrastructure, lending structural integrity that regular cast iron (aka gray iron) does not have.
Unlike the graphite flakes in gray iron, spheroidal graphite holds ductile iron together without fracturing as it bends and acts as a built-in buffer against wear. This results in products with greater ductility, tensile and yield strength, heat dissipation, and vibration and sound dampening properties than their gray iron counterparts.
The higher the nodule count in a ductile iron casting, the better its strength and elongation properties. At Urick Foundry, we achieve consistently high nodule counts through vertical in-mold inoculation. In this method, molten metal is inoculated with magnesium as it's poured into each mold, ensuring uniform distribution both within the mold and between molds. Our proprietary vertical casting process minimizes gas bubbles and other structural deficiencies, while consistently producing nodularities of 85% or better — far exceeding industry standards.
Ductile iron offers flexibility both in its physical properties and from a design standpoint. Its castability, machinability, and ability to elongate and deform without fracture are far beyond gray iron.
Ductile iron comes in at a significantly lower price point than cast steel, and only slightly more than gray iron. However, its overall performance and wear resistance make it a cost-effective solution.
Ductile iron is an exceptionally resilient material in terms of both yield strength and tensile strength, meaning it can withstand immense physical stress without changing shape or breaking.
Urick produces ductile iron castings in accordance with the latest SAE J434 standards for hardness, strength, and elongation.
|Grade||Typical BHN||Tensile Strength (min)||Yield Strength (min)||% Elongation|
Austempering is a heat treatment process that enhances the hardness and toughness of ductile iron. Urick is capable of providing various grades of austempered ductile iron (ADI) castings through our trusted partner Applied Process, in accordance with the latest standards set forth by ASTM International.
What is ductile iron?
Ductile cast iron is iron that has been treated with magnesium and other elements to enhance its ductility, or ability to stretch when tensile force is applied. A ductile metal is better able to be pulled or bent in various directions while resisting snapping or breaking.
What is the difference between ductile iron and cast iron (aka gray iron)?
The difference between ductile iron and regular cast iron (aka gray iron) is the spheroidal graphite nodules in its microstructure. Unlike the graphite flakes in gray iron, these nodules do not fracture as the material is subjected to tensile strain.
How is ductile iron better than steel?
Ductile iron is better than steel in several ways. Ductile iron castings offer a better value than steel forgings or fabrications, as a single casting can produce multiple components with a better strength-to-weight ratio (10% lighter than steel). Its ductility and other physical properties yield products with better design economy that are closer to near-net shape.
What is ductile iron composed of?
Ductile iron is composed of up to 94% iron with smaller percentages of carbon, silicon, manganese, magnesium (the nodulizer), phosphorus, sulfur, and copper. By applying the principles of physical metallurgy in post-production, the composition can be further tweaked to suit your needs — for instance, adding tin or copper for a stronger casting or nickel or chromium for better corrosion resistance.
What is austempered ductile iron (ADI)?
Austempering is a sophisticated heat treatment to fortify ductile iron for improved mechanical performance. Urick supplies all six grades of austempered ductile iron (ADI).
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