Effective Solutions to Challenges in SG Iron Treatment with High Sulphur Metal!

Spheroidal Graphite Iron (SG Iron), also known as ductile iron, is a preferred material in automotive, pipe, and heavy machinery industries due to its excellent strength, ductility, and castability. However, when the base metal contains high sulphur levels, producing quality SG Iron becomes a complex task.

S G Iron Treatment With High Sulphur Metal presents challenges such as increased magnesium demand, reduced nodularity, and higher slag content. To maintain consistent casting quality, foundries must adopt specialized treatment techniques.

Understanding the Sulphur Challenge

Sulphur is a harmful element in ductile iron production. It binds with magnesium, the key agent in transforming graphite flakes into spheroidal shapes. The presence of excess sulphur leads to:

• Higher magnesium consumption

• Irregular graphite formation

• Increased inclusion defects

• Lower mechanical properties

Without proper control, the metal may fail to meet ductility and strength standards, making it unfit for critical applications.

Key Challenges in SG Iron Treatment

1. Magnesium Loss Due to Sulphur

When sulphur content is high (e.g., >0.06%), a significant portion of magnesium reacts to form magnesium sulphide (MgS), which is non-useful in nodularization. This demands higher magnesium input and reduces process efficiency.

2. Poor Graphite Nodularity

Sulphur delays or suppresses the spheroidization of graphite, resulting in flake or vermicular graphite — both undesirable in SG Iron.

3. High Slag Volume

Slag is created when sulfur and additives combine, and it must be regularly removed. Fluidity can be decreased and inclusions trapped by too much slag.

4. Cost Implications

Increased alloy usage, slag removal, and quality rejections can drive up costs and reduce profitability.

Practical Solutions and Process Adjustments

1. Desulphurization of Base Metal

Pre-treatment desulphurization using agents like calcium carbide (CaC₂), magnesium lime, or soda ash (Na₂CO₃) is an effective way to reduce sulphur before the main nodularization step. This makes magnesium treatment more efficient.

2. Use of Optimized Nodularisers

Foundries should use high-quality ferro silicon magnesium alloys that release sufficient magnesium even in the presence of sulphur. Nodularisers like FeSiMg 8–10 are well-suited for treating base metal with moderate sulphur content while maintaining magnesium recovery and minimizing fade.

3. Accurate Alloy Addition

Graphite form and magnesium recovery are consistent when FeSiMg 8–10 is added carefully. Over-treatment should be avoided as excess magnesium can cause dross or shrinkage.

4. Temperature Control

Ideal treatment temperature ranges from 1400–1450°C. If temperature drops too low, magnesium recovery suffers; if too high, it may increase fade and fume losses.

5. Slag Skimming and Metal Cleanliness

Frequent and effective slag removal, clean ladles, and minimal turbulence during pouring ensure fewer inclusions and better metal flow, especially in high sulphur scenarios.

6. Inoculation and Late Magnesium Addition

Inoculation with ferrosilicon or special inoculants enhances graphite nucleation. Late magnesium addition, such as in-stream or sandwich methods, can reduce magnesium losses to sulphur.

Inoculation and Post-Treatment Practices

Even after nodularization, sulphur can affect graphite shape. Therefore, inoculation is necessary to promote uniform nucleation and reduce carbide formation. Use of:

• Inoculants containing FeSi + Ca + Ba

• Late-stream inoculation techniques

• In-ladle additions immediately before pouring

These steps help stabilize the graphite structure and reduce chilling tendencies in thin-walled castings.

Treatment Techniques: Sandwich vs. In-the-Stream

Choosing the right magnesium treatment method affects recovery and control:

• Sandwich method: Cover the magnesium alloy with cover material after inserting it into the ladle bottom. It offers better recovery and is safer.

• In-the-stream method: Suitable for automated lines; magnesium is added as metal is poured. Good for large batches but more volatile.

When working with high sulphur metal, the sandwich method is preferred for better recovery and process control.

Real-World Considerations

Foundries often have no choice but to use high sulphur scrap or pig iron due to cost or availability. In such cases, adapting treatment methods and using suitable alloys can help meet specifications without compromising quality.

When S G iron treatment with high sulphur metal is handled properly, it is entirely possible to achieve good nodularity, strength, and consistency in castings—even under challenging input conditions.

Conclusion

High sulphur in base metal creates real challenges in SG Iron treatment, but with the right techniques, these can be effectively managed. Pre-desulphurization, proper alloy selection, and tight process control are key to producing high-quality SG Iron from sulphur-rich materials. Foundries that adopt these practices not only maintain quality but also reduce waste and improve cost-efficiency.

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