Question

Nitrogen cannot be used for ferrous and nickel based alloys in hydrogen removal technique because_____

(a) it leads to form high dross in metal castings

(b) it gives rise to porosity in metal castings

(c) it affects the grain size

(d) it generates blow holes in metal castings

The question was asked during an interview.

This interesting question is from Gases in Metals topic in chapter Pouring – Gating Design, Melting Furnaces, Melting and Casting Quality of Casting-Forming-Welding I

Answer 1

Correct choice is (c) it affects the grain size

For explanation: For ferrous and nickel based alloys, nitrogen cannot be used because it is soluble in these and also it may form nitrides which affect the grain size; therefore, in ferrous alloys in particular, accurate control of the nitrogen is necessary. In such situations, carbon monoxide bubbles are used.