Question

Hardenability of steel is measured using which test?

• A. Rockwell test
• B. Brinell test
• C. Jominy test
• D. Izod test

Hint:

Understand the difference:
- Hardness is a surface property (measured by Rockwell, Brinell, Vickers).
- Hardenability is a depth/structural capability (measured by the Jominy End-Quench test).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question asks to identify the standard metallurgical test used to measure the hardenability of steel.
It is important to clearly distinguish between "hardness" (resistance to plastic indentation) and "hardenability" (the ease with which a steel forms martensite at depth during quenching).

Step 2: Key Formula or Approach:
The standard test for hardenability is the Jominy End-Quench Test (defined by ASTM A255).
This test measures the variation in hardness along the length of a standardized steel specimen that has been subjected to a highly controlled cooling gradient.

Step 3: Detailed Explanation:

• Jominy Test Setup:
- A cylindrical steel specimen (typically 1 inch in diameter and 4 inches long) is heated to its austenitizing temperature.
- It is transferred to a fixture where a water jet quenches only the bottom circular face of the specimen under standard flow conditions.
- This configuration creates a highly rapid cooling rate at the quenched end, which decreases continuously with distance from that end.

• Hardenability Curve:
- After cooling, flats are ground along the length of the specimen, and Rockwell C hardness measurements are taken at regular intervals from the quenched end.
- High-hardenability steels retain high hardness values deep into the specimen (slow decline on the plot), indicating they can easily transform to martensite even at slow cooling rates.
- Low-hardenability steels show a rapid drop in hardness close to the quenched end.

• Other Options:
- Rockwell and Brinell tests measure surface hardness directly, not hardenability.
- The Izod test measures impact toughness (energy absorbed during fracture).


Step 4: Final Answer:
The Jominy End-Quench test is the standard method used to determine the hardenability of steel.
Therefore, option (C) is the correct choice.