Jominy Or End Quenching Test

The Simplest and most reliable of these methods is the Jominy or end quench test. The standard Jominy specimen consists of a cylindrical rod 100 mm long and 25 mm in diameter. In making a test, the specimen is first heated to a suitable austenitic temperature and held there long enough to uniform austenitic structure. It is then placed in a jig and a stream of water is allowed to strike one end of the specimen. The experimental arrangement is shown in the image.

The advantage of the Jominy test is that in a single specimen one is able to obtain a range of cooling rates varying from a very rapid water quench at one end to slow air quench at the other end. Following the complete transformation of the austenite in the bar, two shallow flat surfaces are ground on opposite sides of the bar and Rockwell hardness values are taken at 1.5 mm Intervals along the bar. The results of the test are expressed by the hardenability number lc, in which l is the distance from the quenched end to the point with a semi-martensite structure, and c is the hardness value. The measured hardness values may also be plotted against the distance to obtain a hardenability curve. A typical example is shown in the image where it can be seen that the hardness is greatest where the cooling is most rapid - near the quench end.

After plotting such a curve, a horizontal line may be drawn at the corresponding hardness of the semi - martensite zone for the given steel. The intersection this line with the curve will indicate the length of the hardened zone ( distance from the quenched end ).

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