karkaisukyky
Karkaisukyky, commonly translated as hardenability, is the capacity of a metallic alloy—most often steel—to form a hardened microstructure, such as martensite, at depth when quenched from the austenitizing temperature. It describes how far through a cross-section a given cooling regime can produce a hardened region, and is distinct from the instantaneous hardness of a surface.
Factors determining karkaisukyky:
- Chemical composition: carbon content and alloying elements (Cr, Ni, Mo, V, Mn, Si) that influence hardenability.
- Austenitizing condition: temperature, time, and prior austenite grain size.
- Geometry and cooling: section size and quenching medium determine the effective cooling rate.
Measurement and representation:
- The Jominy end-quench test yields a hardenability curve, showing hardness as a function of distance from
- Common practical metric is the hardness-depth at a specified threshold, used to compare grades.
Significance and applications:
- Higher karkaisukyky enables deeper hardening for thicker sections, improving wear resistance without surface-only hardening.
- Material selection for gears, shafts, and cutting tools often relies on hardenability values.
- It informs heat-treatment design to balance hardness, strength, and toughness.
- Excessive hardenability can cause distortion or quench cracks; related to brittleness if not tempered appropriately.
- In Finnish technical literature, karkaisukyky equals hardenability in metallurgy.