Standard hardenability test (ASTM A255, SAE J406) in which a 1-inch diameter bar, 4 inches long, is austenitized, set in a fixture and quenched on one end only by a water jet. Flats are then ground along the length and hardness is read every 1/16 inch from the quenched end. The curve shows how far hardness persists, and steels can be bought to a guaranteed Jominy band as H-steels such as 4140H.
Ask the mill for the Jominy test on this heat, if J8 is under 45 I'm not trusting it on the big shafts.
Mills quote Jominy readings as J plus the distance in sixteenths of an inch, so J8 means half an inch from the quenched end.
Also heard as
- end-quench test
- Jominy
- Jominy end-quench test
Related terms
Hardenability
A steel's ability to form martensite to a given depth, set by its chemistry and grain size, not its hardness.
DI
Ideal critical diameter: the largest bar that would reach 50 percent martensite at its center in a perfect quench.
Quench severity
How fast a quenchant pulls heat out of steel, usually rated by the Grossmann H value.