An SG iron casting supplier in India should control the process that makes the iron ductile: magnesium treatment, inoculation and microstructure. SG iron, also called ductile or nodular iron, gets its strength from graphite in spheres rather than flakes.
Many foundries can pour grey iron. Fewer can make consistent SG iron, so check the capability before the grade name.
What makes SG iron different?
Grey iron, SG iron and steel castings explains the differences. SG iron is stronger and more ductile than grey iron, which is why it is used for pipe fittings, gear housings, brackets and pressure parts. Grades such as 500/7 or EN-GJS-500-7 are explained in casting grades.
The properties depend on how well the magnesium treatment works, and that varies from pour to pour if it is not controlled.
What capability should you look for?
Ask the foundry to show these:
- A treatment method for magnesium that the foundry can describe, with the alloy used and the time between treatment and pouring.
- A spectrometer for chemistry checks on each heat.
- A metallurgical microscope and a person trained to rate nodularity and graphite form.
- Separately cast or attached test bars for tensile and impact tests, as the specification requires.
- Heat treatment control, such as annealing, if the grade requires it.
What records should you ask for?
Request a material certificate for each heat showing chemistry and mechanical results, plus a micrograph showing nodularity and the amount of pearlite and ferrite. How to write an SG iron casting specification lists the values to specify.
Where the casting carries pressure or is safety-critical, add radiographic or ultrasonic testing, as described in the casting testing guide.
What are the warning signs?
A foundry that cannot show microstructure, quotes the same lead time for every grade, or gives a certificate without test bars is not controlling the grade. Be careful also with castings sold as SG iron that are in fact grey iron.
A simple check is to have an independent lab cut a sample and examine it. Cost depends on grade, weight, tooling and testing, so a quote needs a drawing and a specification.
How do you test an SG iron supplier before ordering?
Order a trial lot and send cut samples to an independent lab for tensile, elongation, hardness and a microstructure report. Compare the results with the supplier's own certificate. If they match across several heats, the control is probably real.
Ask about section thickness too. Thick and thin sections cool at different rates, and nodularity can drop in heavy sections. A good foundry will show you how it manages that on parts like yours.
Casting chemistry and the spectrometer and hardness testing for castings and forgings explain two of the checks you will rely on.
Finally, agree the acceptance criteria before the first pour: minimum nodularity, maximum carbide or porosity, hardness range and the test bar location. Written criteria turn a dispute about opinion into a comparison of numbers.
Next step
We find and audit SG iron foundries, check samples and certificates, have lots tested, and supervise production and loading, for one fee agreed in advance. Book a free sourcing review with your drawing and grade.