Jominy end quench test

The ASTM standard for the Jominy End-Quench Test is:

🔹 ASTM A255 – Standard Test Methods for Determining Hardenability of Steel

Key Features of ASTM A255:

Defines the Jominy End-Quench Test procedure.
Specifies sample preparation, heating, quenching, and hardness measurement methods.
Outlines how to plot the hardenability curve from hardness test data.
Provides guidance on interpreting results to compare hardenability of different steels.

Jominy End-Quench Test

The Jominy End-Quench Test is a standardized test used to determine the hardenability of steel. It measures how deeply a material can be hardened when subjected to quenching.

Test Procedure

Sample Preparation
- A cylindrical steel specimen (usually 25 mm diameter × 100 mm length) is heated to the austenitizing temperature (around 800–900°C, depending on the steel composition).
- The sample is held at this temperature to ensure a uniform structure.
Quenching Process
- The heated specimen is placed vertically in a test stand.
- A controlled jet of water is sprayed onto one end of the sample, cooling it rapidly.
- The cooling effect gradually decreases along the length of the sample, creating a varying hardness profile.
Hardness Measurement
- After cooling, the sample is cut along its length.
- Hardness measurements (Rockwell or Vickers) are taken at regular intervals (e.g., every 1.5 mm) from the quenched end toward the opposite end.
- A hardness curve is plotted, showing how hardness decreases as the distance from the quenched end increases.

Factors Affecting Hardenability

Carbon Content – Higher carbon increases hardness but reduces toughness.
Alloying Elements – Elements like Cr, Mo, Mn, Ni improve hardenability.
Grain Size – Larger grains increase hardenability.
Cooling Rate – Faster cooling increases hardness but may cause brittleness.

Applications of the Jominy Test

✅ Selecting steels for heat treatment processes.
✅ Comparing different steel grades for hardening performance.
✅ Quality control in industries like automotive, aerospace, and tool manufacturing.

Step-by-Step Procedure of Jominy End-Quench Test

The Jominy End-Quench Test is used to determine the hardenability of steel by observing how its hardness varies along its length after a controlled quenching process.

Step 1: Preparation of the Specimen

A cylindrical steel sample is prepared with standard dimensions:
- Diameter: 25 mm
- Length: 100 mm
The surface is machined and polished for uniformity.

Step 2: Heating the Specimen

The specimen is heated in a furnace to the austenitizing temperature (typically 800–900°C) depending on the steel composition.
It is soaked at this temperature for a specified time to ensure a uniform microstructure.

Step 3: Rapid Transfer to the Quenching Stand

The heated sample is quickly transferred to the Jominy quenching setup to minimize heat loss.
It is placed vertically in a special fixture.

Step 4: End-Quenching the Specimen

A controlled jet of water is sprayed only on the bottom end of the sample.
The top part cools more slowly than the quenched end, creating a gradual hardness variation along the length.

Step 5: Cooling & Sample Preparation

The specimen is allowed to cool completely after quenching.
It is then ground or polished along its length to ensure accurate hardness measurements.

Step 6: Hardness Testing

Hardness is measured using Rockwell (HRC) or Vickers (HV) hardness tests.
Measurements are taken at 1.5 mm intervals from the quenched end toward the opposite end.

Step 7: Plotting the Hardenability Curve

The hardness values are plotted against the distance from the quenched end.
A hardenability curve is created, showing how hardness decreases with distance.

Step 8: Interpretation of Results

Steels with high hardenability (e.g., alloy steels) maintain hardness over a longer distance.
Steels with low hardenability (e.g., plain carbon steels) lose hardness quickly as distance increases.

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