Mechanical Engineering - Engineering Materials - Discussion

The correct answer is Phosphorus.

Phosphorus is an impurity in cast iron that can make it hard and brittle. Phosphorus combines with iron to form iron phosphide (Fe3P), which is a hard and brittle compound that can lead to:

- Increased hardness
- Reduced ductility
- Increased brittleness

High phosphorus content can also lead to the formation of a brittle phase called "phosphide eutectic", which can further reduce the toughness of the cast iron.

The other options are not correct because:

- Silicon (Si) improves the cast iron's strength, toughness, and corrosion resistance.
- Sulphur (S) can lead to the formation of manganese sulphide (MnS) inclusions, which can improve machinability but do not significantly affect hardness or brittleness.
- Manganese (Mn) is a beneficial alloying element in cast iron, as it improves strength, toughness, and hardenability.

So, the effects of phosphorus on cast iron can be mitigated by adding manganese, which can counteract the negative effects of phosphorus.

Thanks @Pradeep.

Thank you @Pradeep.

Nice explanation. Thanks.

Thank you @Pradeep.

Very useful, thanks @Pradeep.

Thank you @Pradeep.

1. Silicon: It may be present in cast iron upto 4%. It provides the formation of free graphite which makes the iron soft and easily Machinable. It also produces sound castings free from blow-holes, because of its high affinity for oxygen.

2. Sulphur: It makes the cast iron hard and brittle. Since too much sulphur gives unsound casting, therefore, it should be kept well below 0. 1% for most foundry purposes.

3. Manganese: It makes the cast iron white and hard. It is often kept below 0. 75%. It helps to exert a controlling influence over the Harmful effect of sulphur.

4. Phosphorus: It aids fusibility and fluidity in cast iron, but induces brittleness. It is rarely allowed to exceed 1%. Phosphoric irons.