420 Stainless Steel
420 is a high carbon steel with at least a 12% chromium content. The material presents a good level of ductility while annealed. The corrosion properties of 420 are excellent once it is hardened, polished or ground. 420 corrosion properties are due to the high level of (12%) chromium. 420 can achieve a good hardness once heat treated. This steel is often used in the medical and optical industries due to its properties.
420 Applications
420 has a wide range of uses but typically finds use in plastic moulds due to the materials ability to resist abrasion thanks to its high hardness and the fact that acidic plastics wont damage the material. Its also used in the medical industry thanks to the materials ability to be polished to a high surface finish as well as previously mentioned properties (this also applies to the optical industry)
420 Typical Chemical Properties
| Carbon 0.40% | Manganese 0.50% |
| Silicon 0.75% | Chromium 12.00 - 14.00% |
| Physical Properties | Value |
|---|---|
| Density | 7.75 g/cm³ |
| Thermal Expansion | 10.3 x10^-6 /K |
| Modulus of Elasticity | 20 0 GPa |
| Thermal Conductivity | 24.9 W/m.K |
| Electrical Resistivity | 0.055 x10^-6 Ω .m |
420 Forging and Annealing
420 stainless can be forged but its important to heat the material slowly and uniformly to 1000 Celsius. Once forged cool the material slowly and uniformly preferably in a furnace.
To anneal 420 heat the steel slowly to 780 Celsius and then allow the steel to cool slowly to 600 Celsius once at this temperature allow the steel to cool in the air. Do bear in mind that the material is supplied annealed typically and will only require annealing if its has been forged or hardened.
420 Heat Treatment
Heat Treatment temperatures, including the rate of heating, cooling and soaking times will vary due to factors such as the shape and size of each 420 stainless steel component. Other considerations during the heat treatment process include the type of furnace, quenching medium, and workpiece transfer facilities. Please consult your heat treatment provider for full guidance on heat treatment of 420 stainless steel.
Hardening
With 420 its very important that the temperature is consistent throughout the work piece. Initially pre-heat the steel to around 650 Celsius ensuring that this temperature is consistent through the material. Then take the material to the final hardening temperature of 1000 - 1050 Celsius again ensure that the material temperature is equal throughout the piece. 420 is very susceptible to decarbonisation so its imperative to protect against this by using a controlled atmosphere furnace, salt bath, or by quenching in oil.
Tempering
To temper 420 ensure that the material is heated uniformly to the required temperature, generally allow one hour for every 25 mm of total thickness. Tempering twice is advised. To achieve the best all round result its recommended to temper at 250 Celsius .
| Temperature | 100 | 200 | 300 | 400 | 500 | 600 |
| Hardness HRC | 56 | 54 | 52 | 54 | 53 | 34 |
Machining and Sawing
420 is typically supplied in an annealed form which will cut and machine with no trouble, once hardened however it becomes very challenging to manipulate it is still possible with the correct equipment.
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