The Jominy End Quench Test

H. K. D. H. Bhadeshia


A heat treatment that causes steel to harden is so much more than the meer plunging of hot metal into a fluid that is often a liquid. The initial red-hot state represents the austenitic condition and the subsequent cooling results in a variety of transformations that depend on the chemical composition of the steel. If the intention is to produce a martensitic structure, then the constituents of the steel must be such that the phase is obtained over the depth required.

The Jominy test provides a measure of the ability of a steel to harden by transforming into martensite under set conditions, i.e., a measure of the hardenability of the steel. A standardised bar, 25.4 mm diameter and 102 mm long, is heated to the austenitising temperature and then placed on a rig in which one end of the rod is quenched by a standard jet of water. This results in a progressive decrease in the rate of cooling along the bar from the quenched end. The depth from the quenched end, over which martensite is obtained, is then the measure of hardenability.

hardenability, Jominy, Jominy end quench, martensite, bainite

Jominy end quench unit for testing the hardenability of steels
hardenability, Jominy, Jominy end quench, martensite, bainite

Here a specimen is in place. A jet of water emerges from the cone at the bottom, to touch the lower end of the sample.
hardenability, Jominy, Jominy end quench, martensite, bainite

The sample.
hardenability, Jominy, Jominy end quench, martensite, bainite

The furnace used to heat the steel into the austenite phase field.
hardenability, Jominy, Jominy end quench, martensite, bainite

Safety equipment.
hardenability, Jominy, Jominy end quench, martensite, bainite

Two samples!



Chemical compositions, wt%
C Mn Mo Ni Cr
En8 0.4 0.6
En28 0.4 0.6 0.3 1.5 1.2
Calculated time-temperature-transformation diagrams for 1% transformation.
En8 TTT curve calculated En24 TTT curve calculated
hardenability, Jominy, Jominy end quench, martensite, bainite

A typical plot of hardness along the length of the 10 cm long steel rod. En 8 is a low hardenability steel when compared with En 24



Optical micrographs by David Saul, presented here in adapted form.

hardenability, Jominy, Jominy end quench, martensite, bainite

Structure of En 24 at 5 cm position along Jominy bar



hardenability, Jominy, Jominy end quench, martensite, bainite

Structure of En 24 at 10 cm position along Jominy bar, furthest from the quenched end



hardenability, Jominy, Jominy end quench, martensite, bainite

Structure of En 8 at the quenched end of Jominy bar



hardenability, Jominy, Jominy end quench, martensite, bainite

Structure of En 8, 1 cm from quenched end of Jominy bar



hardenability, Jominy, Jominy end quench, martensite, bainite

Structure of En 8 at 5 cm position along Jominy bar




4th edition
4th edition, 2017
3rd edition
3rd edition, 2015
1st edition
1st edition, 2017


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