Question

Manganese steel is used for making railways because.
A) It is hard with a high percentage of \[{\text{Mn}}\].
B) It is soft with high percentage of \[{\text{Mn}}\]
C) It is hard with small concentration of manganese with the impurities
D) It is soft with small concentration of manganese with impurities

Answer 1

Hint: Railway lines are called permanent paths. They need high tensile strength and reliability otherwise they will form cracks along the line. Steel is used in the construction of railway lines and is mixed with carbon and manganese

Complete step by step answer:
Railway lines also known as permanent paths are made of steel which has crack resistant properties. Modern tracks typically use hot-rolled steel. We know that iron and steel is used in many industries of the present-day world. But the steel used for railway lines cannot be like that. It must be made of very high-quality steel alloy. The alloy selected for railway line construction is selected as such that it would have hard-wearing capacity and must be resistant to cracking.
For this the composition of steel to be used is carefully selected and the process of cooling the hot rail is carried out in a controlled manner.
Mixing of manganese metal with iron produces steel of desired quality. It converts iron into st6ell. As it decreases the brittleness of steel, the mixing of manganese gives strength to the metal. Along with that heat treatments have been developed to control the cooling rate and the microstructure of steel which in turn adds up to the hardness and strength of the steel. Also accelerated cooling increases the hardness of the material.
Therefore, manganese mixed steel produces hard wear-resistant steel which is the best for railway lines.

So, the correct answer is Option A .

Additional Information:
The hardness of steel is measured in Brindle Hardness Number (HB). The typical hardness of a high carbon rail steel is about \[{\text{280 HB}}\]. Steel used to make rails must also be free from internal cracks which is caused by hydrogen trapped in the molten steel.

Note: Railway steels must be free from cracking and wearing. Iron used for other industry purposes may not be suitable for this purpose. So, we mix some other metals or compounds with iron to make it suitable for our needs. The commonly mixed compounds are carbon and manganese.