5919 is Alloyed case hardening steel for highly strained parts and good toughness at core tensile strength of 900 – 1200 N/mm².

Characteristic
5919 is a low carbon low alloy steel. With tensile strength 780-1,060 N/mm2 (after heat treatment). Available for case hardening by carburizing (surface hardening 58-60 HRC, core hardness 25-32 HRC)

Case Hardening APPLICATION
Structural parts requiring good wear resistant surface and a very tough core e.g. stems, shafts, axles, connecting rods, crank shafts, pinion gears and machinery parts.

What is case hardened steel?
Case–hardening or surface hardening is the process of hardening the surface of a metal object while allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal at the surface. … The term face hardening is also used to describe this technique, when discussing modern armour.

What is the difference between hardening and case hardening?
The biggest difference between each process is that case hardening creates a thin layer on the surface. Surface hardening hardens the outer surface and keeps the core soft throughout the entire process.