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 Ms temperature is lowered.
• B. Hardenability is decreased AND the Ms temperature is lowered.
• C. Hardenability is increased AND the Ms temperature is raised.
• D. Hardenability is decreased AND the Ms temperature is raised.

Hint:

Mn, Ni, Cr, and Mo generally increase hardenability. Austenite stabilizers (like Ni) reduce the Ms temperature, while ferrite stabilizers (like Cr, Mo) tend to raise transformation temperatures.

Answer 1

The Correct Option is A

Step 1: Effect of Ni on hardenability.
Nickel is a strong austenite stabilizer. By stabilizing austenite, it delays the transformation to pearlite/bainite, which allows martensite to form at lower cooling rates. This increases *hardenability*. Step 2: Effect of Ni on Ms temperature.
- Ms (martensite start) temperature is the point where martensite transformation begins.
- Alloying elements that stabilize austenite, like Ni, decrease the Ms temperature. This means martensite starts forming at a lower temperature. Step 3: Eliminate wrong options.
- (B) and (D): Hardenability cannot decrease with Ni → incorrect.
- (C): Although hardenability increases, Ni does not raise Ms temperature → incorrect.
- (A): Matches both effects correctly. \[ \boxed{\text{Correct Answer = (A)}} \]