Precision engineering experts know how to distinguish and make the most of the properties of different steels. Let’s take a closer look at AISI 420B steel.
Precision engineering uses the properties of different materials to supply the mechanical components needed by a particular sector and working environment. Although steel remains, in most people’s minds, the most used material in precision engineering, it would be a mistake to speak of steel in the singular.
Not steel, then, but steels. AISI 304 is certainly the best known, but different compositions define different types of steel, and AISI 420B is one example.
Martensitic, austenitic or ferritic steel?
The properties of stainless steel can only be fully exploited if you understand what “stainless” means and the difference between martensitic, austenitic and ferritic steels.
When is a steel stainless? When it is an iron-carbon alloy that also contains other elements (e.g. molybdenum, chromium, nickel, silicon, manganese) giving the material high corrosion resistance. Martensitic steel, the family to which AISI 420B belongs, is a magnetic, hardenable steel made of iron, carbon and chromium. Austenitic steel consists of iron alloys with chromium (17–26%), nickel (7–35%) and carbon (max 0.15%), and cannot be hardened. When a steel has a lower carbon content, 11–30% chromium and a mix of aluminium, sulphur and molybdenum, it is called ferritic steel.
AISI 420B: technical data and applications
AISI 420B is a martensitic stainless steel widely used in the production of precision mechanical parts. First of all, its composition makes it ideal for turning, milling and any other type of machining. Among the most valued properties of AISI 420B in the hardened and low-temperature stress-relieved condition are hardness and resistance to both heat and corrosion.
How is 420B steel hardened? Hardening takes place at 980–1040°C followed by rapid oil quenching. Tempering is carried out at 550–750°C. However, being a self-hardening material, it is not used for welding unless it is preheated and annealed immediately afterwards.
The properties of AISI 420B in the quenched and tempered condition make it ideal for surgical instruments, gears, valves and shafts.