Question

Nickel and manganese elements in steel 0.4pt the critical temperature.

• A. Raises
• B. Lowers
• C. Do not change
• D. Raises and lowers

Hint:

To easily remember the effect of alloying elements, categorize them: Austenite formers (e.g., Ni, Mn, C, N) lower critical temperatures, while Ferrite formers (e.g., Cr, Si, Mo, V) raise them.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The "critical temperature" in steel refers to the temperatures at which phase transformations occur, such as the eutectoid temperature (A1), and the temperatures at which ferrite (A3) or cementite (Acm) fully transform to austenite upon heating. Alloying elements in steel can be classified as austenite stabilizers or ferrite stabilizers, which affects these transformation temperatures.

Step 3: Detailed Explanation:
Alloying elements have a significant influence on the iron-carbon phase diagram.

• Austenite Stabilizers (or Austenite Formers): These elements expand the austenite (\(\gamma\)-iron) phase field. By making austenite stable over a wider range of temperatures, they lower the critical temperatures (A1 and A3). Nickel (Ni) and Manganese (Mn) are strong austenite stabilizers.

• Ferrite Stabilizers (or Ferrite Formers): These elements expand the ferrite (\(\alpha\)-iron) phase field. They raise the critical temperatures and restrict the austenite region. Examples include Chromium (Cr), Silicon (Si), and Molybdenum (Mo).
Since the question specifically asks about Nickel and Manganese, which are both potent austenite stabilizers, their addition to steel will make the austenite phase stable at lower temperatures. Consequently, they lower the eutectoid temperature (A1) and the upper critical temperature (A3).

Step 4: Final Answer:
Nickel and Manganese are austenite stabilizers, and their presence in steel lowers the critical transformation temperatures.