MaterialPedia

HARDENABILITY STEELS, or H-steels, offer a wide range of mechanical properties that depend on the development of
tempered martensite after quenching and tempering. Typical room-temperature properties of quenched and tempered
steels can vary as follows:

· Hardness values of 130 to 700 HV (30 kgf load)
· Tensile strengths of 400 to 2000 MPa (58 to 290 ksi)
· Yield strengths of 300 to 1800 MPa (43 to 261 ksi)
· Elongation of 8 to 28% in 50 mm (2 in.)

This broad range of properties depends on the maximum (as-quenched) hardness and the degree of softening (tempering)
after quenching.

The maximum (100% martensite) hardness of heat-treated steel depends primarily on the carbon content (Table 1), until
carbon levels reach about 0.50 wt%. Above 0.50 wt%, carbon has little effect on hardness but does improve hardenability.
Alloying elements have little effect on the maximum hardness that can be developed in steel, but they profoundly affect
the depth to which this maximum hardness can be developed in a part of specific size and shape. Thus, for a specific
application, one of the first decisions to be made is what carbon level is required to obtain the desired hardness. The next
step is to determine what alloy content will give the proper hardening response in the section size involved. This is not to
imply that tempered martensitic steels are alike in every respect, regardless of composition, because the alloy content is
responsible for differences in the preservation of strength at elevated temperatures; in abrasion resistance; in resistance to
corrosion; and even, to a certain extent, in toughness. However, the similarities are sufficiently marked to permit
reasonably accurate predictions of mechanical properties from hardness rather than from composition, thereby justifying
the emphasis on hardenability as the most important function of the alloying elements.