Question

Which of the following gases can be beneficial in imparting certain desirable qualities to the castings?

(a) Oxygen

(b) Nitrogen

(c) Hydrogen

(d) Carbon monoxide

I had been asked this question during an online exam.

This intriguing question originated from Gases in Metals in section Pouring – Gating Design, Melting Furnaces, Melting and Casting Quality of Casting-Forming-Welding I

Answer 1

Right option is (b) Nitrogen

The best I can explain: Nitrogen can be added in castings to impart desirable qualities. For example, when this gas is added to steels, it improves strength, fatigue life, corrosion resistance and many other properties. Nitrogen would affect these properties only if it remains very fine nitrides in solid solutions.