Jominy Hardenability Test Bar
The hardenability Jominy bar is a cylindrical test specimen used to determine the end-quench hardenability of steels. It helps evaluate the through-hardening behavior and shows resistance to martensitic transformation.
Physicochemical Mechanism of Action
The hardenability Jominy bar consists of a cylindrical specimen that is drilled through the center and then suspended in a liquid melt. After cooling, hardness is measured along the bar. The face quenching (the outer part) cools faster than the interior, resulting in a gradient hardness distribution.
Metallurgical Relevance & Risks in Welding
The hardenability Jominy bar is used to analyze the through-hardening characteristics of steels. Too fast cooling can lead to high hardness and a martensitic structure, causing cracks and fractures. Too slow cooling coarsens the grain and reduces hardness.
Workshop Practice & Action Instructions
To correctly use the hardenability Jominy bar, the bar is suspended in a liquid melt and then cooled. Hardness is measured along the bar and compared with a Jominy diagram. A t8/5 value of 10 to 20 seconds is typical for a through-hardened condition, while a value below 5 seconds leads to excessive martensite and above 30 seconds to coarse grain formation.