205) The machinability of steel is increased by

Answer is:

phosphorous, lead and sulphur

Engineering Materials MCQ with Answers

206) The following element can′t impart high strength at elevated temperature

Answer is:

magnesium

Explanation:

The strength, hardness, and modulus of elasticity of magnesium-base materials decrease with increasing temperature. Also, the elongation increases with rising temperature up to just below the melting point where it drops to nearly zero.

207) Which of the following element results in presence of free graphite in C.I.

Answer is:

silicon

208) White cast iron

contains 1.7 to 3.5% carbon in free state and is obtained by the slow cooling of molten cast iron

is also known as chilled cast iron and is obtained by cooling rapidly. It is almost unmachinable

is produced by annealing process. It is soft, tough and easily machined metal

is produced by small additions of magnesium (or creium) in the ladle. Graphite is in nodular or spheroidal form and is well dispersed throughout the material

Answer is:

is also known as chilled cast iron and is obtained by cooling rapidly. It is almost unmachinable

Explanation:

White cast iron Is also known as chilled cast iron and is obtained by cooling rapidly. It is almost un-machinable
White cast iron is a cast iron without any alloy addition and with low Carbon and Si content such that the structure is hard brittle iron carbide with no free graphite.
A fast cooling rate prevents the precipitation of Carbon as graphite.