Question

Which of the following statements is/are CORRECT when Ni is added as an alloying element to a low alloy steel?

• A. Hardenability is increased AND the \( M_s \) temperature is lowered.
• B. Hardenability is decreased AND the \( M_s \) temperature is lowered.
• C. Hardenability is increased AND the \( M_s \) temperature is raised.
• D. Hardenability is decreased AND the \( M_s \) temperature is raised.

Hint:

Nickel is an important alloying element that improves the hardenability of steel by lowering the \( M_s \) temperature. This allows the steel to be hardened more deeply when quenched.

Answer 1

The Correct Option is A

Nickel (Ni) is commonly used as an alloying element in steel to improve hardenability. Hardenability refers to the ability of steel to form martensite when quenched. Nickel increases hardenability by slowing down the transformation from austenite to pearlite or bainite, allowing for a deeper hardening depth. Additionally, Ni lowers the \( M_s \) temperature, which is the temperature at which martensite starts to form. This results in a more favorable condition for forming martensite at lower temperatures. Thus, the correct statement is that Hardenability is increased and the \( M_s \) temperature is lowered. Therefore, Option A is correct.
Step 1: Analyzing each option - Option (A): Hardenability is increased AND the \( M_s \) temperature is lowered. - Correct: Ni increases hardenability and lowers the \( M_s \) temperature, making this statement accurate.
- Option (B): Hardenability is decreased AND the \( M_s \) temperature is lowered. - Incorrect: Ni increases hardenability, not decreases it. Hence, this option is incorrect.
- Option (C): Hardenability is increased AND the \( M_s \) temperature is raised. - Incorrect: Although Ni increases hardenability, it actually lowers the \( M_s \) temperature, not raises it.
- Option (D): Hardenability is decreased AND the \( M_s \) temperature is raised. - Incorrect: Ni does not decrease hardenability, and it does not raise the \( M_s \) temperature.
Step 2: Conclusion The correct answer is Option A.