The ‘’Jominy test’’ is used to find
hardenability
The question asks about the purpose of the Jominy test. This test is a standard method used in materials science and engineering to assess a specific property of metallic materials, primarily steels.
Jominy Test Overview
The Jominy test, also known as the Jominy end-quench test, is a widely recognized method for determining the hardenability of steel. Hardenability refers to the ability of a steel alloy to form martensite (a hard, brittle microstructure) upon quenching. It is not the same as hardness, which is the resistance to plastic deformation, but rather the depth to which a material can be hardened under a given set of conditions.
- Purpose of the Jominy Test: The primary purpose of the Jominy test is to establish the hardenability curve of a steel. This curve shows how the hardness of the steel changes with distance from the quenched end of a standardized specimen.
- Test Procedure:
- A standard cylindrical specimen (typically 1 inch diameter, 4 inches long) is heated to a specific austenitizing temperature.
- The hot specimen is then quickly transferred to a fixture where a jet of water at a controlled temperature impinges on one end of the specimen. This creates a gradient of cooling rates along the length of the specimen, with the end receiving the water jet cooling very rapidly, and the other end cooling much slower.
- After cooling, flats are ground along the length of the specimen, and Rockwell hardness measurements are taken at specific intervals along these flats, starting from the quenched end.
- Results and Interpretation: The hardness values are plotted against the distance from the quenched end, resulting in a Jominy hardenability curve. Steels with higher hardenability will show high hardness values extending further along the specimen, indicating that they can harden more deeply even with slower cooling rates.
Hardenability Importance
Understanding hardenability is crucial in heat treatment processes, especially for steels. It helps engineers select the appropriate steel for a given application and design effective heat treatment cycles (like quenching and tempering) to achieve desired mechanical properties. For example, if a large component needs to be hardened throughout its cross-section, a steel with high hardenability would be required to ensure uniform properties.
Analysis of Options
Let's examine why the other options are incorrect:
| Option | Explanation |
|---|---|
| Young’s modulus | Young's modulus (or modulus of elasticity) is a measure of a material's stiffness. It is determined by tensile or compression tests, not the Jominy test. |
| Yield strength | Yield strength is the stress at which a material begins to deform plastically. It is typically determined by a tensile test, not the Jominy test. |
| Thermal conductivity | Thermal conductivity is a measure of a material's ability to conduct heat. It is measured using various thermal analysis techniques, not the Jominy test. |
Based on the function of the Jominy test, it is specifically designed to assess the hardenability of steel.
Important Questions from Hardening
The ductility of a material with work hardening
Hardenability of steel is a measure of
The true stress-strain relations of plastic deformation at which necking begins may be approximated. The value n for steel is \(\rm \sigma _ T= K \varepsilon _T^n\) The value n for low carbon steel is
Surface hardening is principally employed for
Which of the following hardness tester uses Diamond cone type indenter?
