SS 420 stainless steel for blades, moulds and wear parts

Japanese and European standards split 420 into separate grades by carbon content, and Indian buyers often order using those names. The common ones are listed in the varieties table below. Lower-carbon 420 (1.4021, SUS420J1) is tougher and is used for shafts, pump parts and general engineering. Higher-carbon 420 (1.4028, SUS420J2) reaches higher hardness and is the usual choice for blades and cutting tools. Steels such as 1.4034 (X46Cr13) go higher still and are used for better-quality knives.

When you place an order, tell us which variety you need or what hardness you plan to reach after heat treatment. The test certificate will show the actual carbon so you can confirm it.

Annealed, ASTM A276 limits 420 bar to 241 HB maximum, soft enough to turn, mill and drill. After hardening from around 980–1050 °C and a low-temperature temper, the higher-carbon types commonly reach around 48–50 HRC. Tempering at higher temperatures lowers hardness and raises toughness. The exact figure depends on carbon content, section size and the heat treater's cycle.

As with 410, tempering in the range of about 425–600 °C is generally avoided because of reduced toughness and corrosion resistance.

420 is unusual in that it resists corrosion most effectively in the hardened, low-temperature-tempered and polished condition. In the annealed state, much of the chromium is tied up in carbides and the steel is more prone to staining. This is why surgical instruments and scissors are always hardened and polished before use.

Its corrosion resistance is broadly similar to 410: fine for fresh water, mild food acids, steam and dry air, not suitable for salt or strong chemicals. Regular cleaning and drying is part of using any 420 product.

420 is sensitive to how it is heat treated. Heat it evenly, quench in oil or air depending on section size, and temper promptly after quenching. Leaving hardened 420 untempered for long increases the risk of cracking, especially in parts with sharp corners or sudden changes in section.

Protect the surface from scaling and decarburisation during hardening, either in a vacuum or controlled-atmosphere furnace or with a protective wrap. A decarburised skin will not reach full hardness and will also corrode more easily. For moulds and instruments that need a mirror finish, ask your heat treater for vacuum hardening.

Annealed 420 machines reasonably well, a little harder than 410 because of its higher carbon. Rough and semi-finish machine in the annealed state, then harden and finish grind. Hardened 420 grinds and polishes well, which is one reason it is chosen for moulds and cutting edges. Use clean wheels that have not been used on carbon steel to avoid contaminating the surface.

Cutlery, scissors, surgical and dental instruments, and kitchen knives are the classic uses. In engineering, 420 is used for pump shafts, valve components, needle valves and bearings in mild service. Plastic moulding shops use pre-hardened or through-hardened 420 for mould inserts and cavities because it polishes to a high finish and resists corrosion from cooling water and some resins.

If you need still more hardness and wear resistance, look at SS 440. If toughness and corrosion matter more than hardness, SS 431 is usually the better pick.

We supply 420 as round, square and flat bar for machining and moulds, hex bar, and wire for pins and small parts. Bar is normally supplied annealed. Sizes are confirmed at enquiry. For machining shops around Peenya and Bommasandra, we can discuss cut lengths. Every lot comes with a test certificate showing carbon and chromium. See our full range of stainless bars.

For mould steel, mention whether you want annealed or pre-hardened bar.