Welding Inspection & Metallurgy API ICP Self Study Notes

10.7 HARDENING
Hardening or hardenability is defined as that property of a ferrous alloy that
determines the depth and distribution of hardness induced by quenching.
• It is important to note that there is no close relation between hardenability
and hardness, which is the resistance to indentation.
Hardness depends primarily on the carbon content of the material, where as
hardenability is strongly affected by the presence of alloying elements, such
as chromium, molybdenum and vanadium, and to a lesser extent by carbon
content and alloying elements such as nickel, copper and silicon.
For example at standard medium carbon steel, such as AISI 1040 with no
alloying elements has a lower hardenability then AISI 4340 low-alloy steel
which has the same amount of carbon, but contains small amounts of
chromium, nickel, molybdenum and silicon as alloying elements.