Mumbai University > Mechanical Engineering > Sem 4 > Material Technology

Marks: 7M

Year: May 2015

Hardening followed by tempering no doubt gives the best combination of strength and toughness in steel. However the ability of steel to harden depends on its section size, composition, austenitizing temperature, and quenching medium. It is best described by a term called hardenability.

Factors affecting hardenability of steel:

Three most important factors that affect hardenability of steel are austenitic grain size, %C and the presence of additional alloy elements. Hardenability is closely connected with the ease with which diffusion controlled transformation can be suppressed. Diffusion control transformation takes place by nucleation and growth. Grain boundaries are the preferred sites for the nucleation of pro‐eutectoid / eutectoid constituents of steel. Grain boundary area per unit volume decreases as the size of austenite grain increases. It is much easier to suppress the nucleation of ferrite and pearlite in coarse grained steel. Therefore it is expected to have higher hardenability.