Brittle fracture caused when martensite forms unevenly and the expansion of transformation fights the contraction of cooling. Cracks start at sharp corners, keyways, holes, abrupt section changes and deep stamp marks, and usually run intergranular. Causes include an over-severe quench, excess carbon, overheating and delay before temper. Magnetic particle inspection finds them at the surface.
Quench crack running right out of the keyway corner, tell design that sharp inside corner gets us every time.
Temper scale or bluing on the crack faces means the crack was there before tempering, which points to the quench rather than to service loads.
Also heard as
- hardening crack
- quench cracking
Related terms
Snap temper
A quick, low-temperature temper given right after quenching to keep crack-prone parts from splitting.
Distortion
Unwanted change in shape or size of a part during heat treatment, such as bowing, warping or ovality.
Cooked
Shop slang for parts that were overheated or held too long, ending up with coarse grain or burned structure.
Quench severity
How fast a quenchant pulls heat out of steel, usually rated by the Grossmann H value.