End Quench Test
The End Quench Test, formally the Jominy end-quench hardenability test, measures a steel's hardenability—its ability to form hardened microstructures at depth under a specified quench. A standard cylindrical specimen is heated, then water-quenched at one end only. Hardness is measured progressively along the bar, producing a hardness gradient from which depth of hardening is determined.
On the shop floor, the Jominy end-quench test is a practical tool for heat treaters, machinists, and quality engineers. When a job calls for a shaft, gear, or die that must stay hard below the surface, the Jominy curve shows whether a given heat of steel will respond reliably to the quench cycle. By comparing hardness at set distances from the water-quenched end, the shop predicts how fast a specific section size will cool and whether the core will reach the required hardness. This guides alloy selection and heat-treatment parameters before expensive machining begins, reducing scrap from soft cores, uneven through-hardening, and thermal distortion. The test also verifies material substitutions and flags incoming heats that might behave differently than expected. Mounting the specimen at the correct height and controlling the water jet remain critical, because any variation changes the cooling gradient and makes the data unusable for process decisions.
What does a 'longer hard' Jominy curve mean?
A longer hard Jominy curve indicates higher hardenability: the steel retains hardness farther from the quenched end and is more likely to harden through thicker sections.
Does a Jominy test measure surface hardness directly?
No. It measures the hardness gradient along the specimen, which serves as a proxy for response to quench severity and depth of hardening, rather than a single surface hardness value.
Why is Jominy testing important for alloy selection?
Jominy data helps select steels and heat-treatment schedules that achieve required core hardness in the final part while minimizing distortion in shafts, dies, gears, and other load-bearing components.