Difference between SG iron, cast iron, and high chrome cast iron – grades, properties, microstructure, and applications IntroductionWhen engineers search for cast iron grades, SG iron properties, or the difference between SG iron and cast iron, they are usually looking for one thing — the right material for their application.As a foundry manufacturing SG iron and cast iron castings, Shanthala Spherocast Private Limited frequently receives queries such as:Which is better, SG iron or cast iron?What is the difference between FG 260 and SG 500/7?Can SG iron replace cast steel?What heat treatment is required for SG iron? What is cast iron? Cast iron is an iron–carbon alloy containing 2.5% to 4.0% carbon, where carbon is present mainly in the form of graphite flakes. These graphite flakes provide:Excellent castabilityGood machinabilityHigh vibration dampingLower tensile strength compared to SG iron Cast iron is widely used where compressive strength, rigidity, and cost efficiency are more important than ductility. What is SG iron (ductile iron)? SG iron, also known as ductile iron or nodular iron, is a modified form of cast iron in which graphite is present as spheroidal graphite instead of flakes. This spheroidal graphite structure is achieved by adding magnesium or cerium during molten metal treatment. As a result, SG iron offers:High tensile strengthExcellent ductilityBetter fatigue resistanceHigher impact strengthProperties approaching cast steel Key difference between cast iron and SG iron quill.clipboard.dangerouslyPasteHTML(`<table border="1" style="width:100%; border-collapse:collapse;"><tr><th>Property</th><th>Grey Cast Iron (FG)</th><th>SG Iron (Ductile Iron)</th></tr><tr><td>Graphite shape</td><td>Flake graphite</td><td>Spheroidal graphite</td></tr><tr><td>Tensile strength</td><td>Low to moderate</td><td>High</td></tr><tr><td>Elongation</td><td>Almost zero</td><td>Up to 18%</td></tr><tr><td>Impact strength</td><td>Low</td><td>High</td></tr><tr><td>Machinability</td><td>Excellent</td><td>Very good</td></tr><tr><td>Weldability</td><td>Poor</td><td>Better than grey iron</td></tr></table>`);Grey cast iron grades and properties (IS 210) FG 200 – 200 MPaFG 220 – 220 MPaFG 260 – 260 MPaFG 300 – 300 MPa Typical applications include engine blocks, flywheels, gearbox housings, machine tool beds, and brake components. SG iron grades and properties (IS 1865 / ASTM A536) SG 400/15 – 400 MPa, 15% elongationSG 450/10 – 450 MPa, 10% elongationSG 500/7 – 500 MPa, 7% elongationSG 600/3 – 600 MPa, 3% elongationSG 700/2 – 700 MPa, 2% elongation Microstructure comparison – why it matters Cast iron microstructure:Flake graphite acts as stress concentratorsCrack propagation is easierLower fatigue and impact resistance SG iron microstructure:Spheroidal graphite arrests crack propagationUniform load distributionHigher strength and ductility Heat treatment requirements Cast iron heat treatment:Stress relievingAnnealing for machinabilityNormalizing for strength improvement SG iron heat treatment:Annealing for improved ductilityNormalizing for increased strengthAustempering to produce ADIStress relieving for dimensional stability ADI grades can achieve tensile strengths up to 1400 MPa. Mechanical properties comparison FG 260 vs SG 500/7:Tensile strength: ~260 MPa vs ~500 MPaElongation: <1% vs 7%Impact strength: Low vs medium to highFatigue resistance: Low vs highPressure tightness: Poor vs excellent Typical applications – where to use what Use cast iron when:Vibration damping is criticalLoads are staticCost sensitivity is highComplex shapes are required Use SG iron when:Strength and ductility are requiredComponents are dynamically loadedPressure containment is neededWeight reduction is important Can SG iron replace cast steel? Yes. In many applications SG iron provides comparable strength, better castability, lower cost, and superior machinability. High chrome cast iron – wear resistant alloy cast irons In addition to grey and SG iron, Shanthala Spherocast Private Limited manufactures high chrome cast iron castings for severe abrasion environments. High chrome grades offered:28% chromium30% chromium35% chromium These alloys provide:Exceptional abrasion resistanceHigh hardness (550–700 BHN)Martensitic matrix with chromium carbides Typical applications include crushers, mill liners, chutes, hoppers, and pump impellers. Why customers choose Shanthala Spherocast Private Limited Controlled chemical compositionVerified microstructure and nodularityMechanical property validationGreen sand and no-bake molding capabilitySupport in grade selection and casting development Final thoughts Choosing between cast iron, SG iron, and high chrome cast iron is not about which material is better, but which material is right for the application. Understanding grades, microstructure, and mechanical behavior ensures longer component life, reduced failures, and optimized cost. For technical support, grade selection, or casting development, contact Shanthala Spherocast Private Limited.
