Views: 0 Author: Site Editor Publish Time: 2026-08-02 Origin: Site
Buyers are often surprised when a "stainless" ball snaps onto a magnet — isn't stainless steel supposed to be non-magnetic? Not always. Whether a stainless steel ball is magnetic depends entirely on its grade and crystal structure, and 420 stainless steel balls sit firmly on the magnetic side of the family.
In this guide from Changzhou RISHENG Steel Ball Co., Ltd. — an ISO 9001–certified stainless steel ball manufacturer — we answer the magnetism question directly, then walk through the chemical composition, hardness, corrosion resistance, and typical uses of AISI 420 — including a comparison against 440C, 304, and 316 — so you can decide whether 420 is the right grade for your valves, bearings, or magnetic-actuated components.
420 stainless steel balls are ferromagnetic — they are strongly attracted to magnets in both the annealed and the hardened condition. AISI 420 is a martensitic stainless steel: its iron atoms are arranged in a body-centered structure that responds to magnetic fields, just like carbon steel. Magnetism does not mean a ball is "fake stainless"; it simply means the grade is martensitic rather than austenitic.
Stainless steels split into two structural families that behave very differently around a magnet:
Martensitic grades (420, 440C) contain 12 – 18% chromium with enough carbon to be hardened by heat treatment. Their martensitic/ferritic structure is magnetic, and they can reach bearing-level hardness.
Austenitic grades (302, 304, 316) add nickel, which stabilizes a face-centered austenite structure that is essentially non-magnetic. The trade-off: they cannot be hardened by heat treatment, so austenitic balls stay relatively soft.
AISI 420 is the classic "cutlery grade" martensitic stainless steel: roughly 13% chromium with enough carbon (0.15% minimum, and up to ~0.40% in high-carbon 420C variants) to quench-harden. It offers the best-value combination of hardness, wear resistance, and moderate corrosion protection — which is exactly why 420 stainless steel balls are one of the highest-volume products in the stainless steel balls category.
| Element | Content（%） |
| Carbon (C) | ≥ 0.15 (up to ~0.40 in 420C variants) |
| Chromium (Cr) | 12.0 – 14.0 |
| Manganese (Mn) | ≤ 1.00 |
| Silicon (Si) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.040 |
| Sulfur (S) | ≤ 0.030 |
| Country/Standard | Grade |
| USA — AISI / ASTM A276 | 420 |
| Germany / EU — EN 10088 | 1.4021 (X20Cr13) / 1.4028 (X30Cr13) |
| Japan — JIS G4303 | SUS420J1 / SUS420J2 |
| China — GB/T 1220 | 2Cr13 (20Cr13) / 3Cr13 (30Cr13) |
| UK — BS 970 | 420S29 / 420S45 |
After hardening (austenitizing at roughly 980 – 1035 °C, quenching, and low-temperature tempering), 420 stainless steel balls deliver:
Hardness: typically 50 – 55 HRC, with high-carbon 420C variants reaching up to ~58 HRC
Density: ~7.75 g/cm³
Magnetic response: strongly ferromagnetic
Precision grades: G10 – G1000 per ISO 3290 / ABMA Std 10 (G100 – G200 is the workhorse range for valve balls)
Size range: commonly 1 mm – 50 mm, larger diameters on request
Surface treatment: passivation per ASTM A967 to maximize the chromium-oxide layer; ultrasonic cleaning and anti-fingerprint packing for cosmetic and medical uses
420 offers moderate corrosion resistance — a big step up from oiled chrome steel balls, but below the austenitic grades. In practice, 420 stainless steel balls handle:
Fresh water, steam, and humid atmospheres
Alcohols, detergents, foodstuffs, and mild organic acids
Petroleum products and many cosmetic formulations
The 50 – 55 HRC hardness, magnetic response, and rust resistance make 420 balls the default choice across a wide range of industries:
Check valves and pumps — water pumps, dispensing pumps, sprayers, and one-way flow control, where the ball must seal repeatedly without corroding
Magnet-actuated components — magnetically held check valves, position sensors, flow indicators, and detent mechanisms that rely on a ferromagnetic ball
Cosmetic agitator balls — the mixing balls rattling inside nail polish, mascara, and aerosol cans are very often passivated 420 stainless
Bearings in damp environments — appliance, fitness-equipment, and conveyor bearings where oiled chrome steel would rust
Food and beverage equipment — filling machines and dispensers in non-chloride service
Locks, latches, and detents — hardness for wear life plus corrosion resistance for outdoor hardware
Medical and dental instruments — where 440C's extra hardness isn't required
If your application involves continuous rolling contact at high precision, compare 420 against 440C bearing balls; if it involves shock loading or non-stainless duty, our comparison of 52100, 100Cr6 and 8620 alloy steel balls covers that side of the catalog. And for tolerance classes from G10 to G1000, see steel ball precision grades explained.
Are 420 stainless steel balls magnetic?
Yes. AISI 420 is a martensitic stainless steel, so 420 balls are strongly ferromagnetic in both annealed and hardened conditions. They can be picked up, held, or actuated by magnets — unlike austenitic 304 and 316 balls, which are essentially non-magnetic.
Does magnetic mean the stainless steel is fake?
No. Magnetism only indicates the steel's crystal structure. Martensitic stainless grades like 420 and 440C are genuinely stainless (12%+ chromium) and genuinely magnetic. The "stainless steel is never magnetic" rule is a myth that applies only to the austenitic 300 series.
What is the hardness of 420 stainless steel balls?
Hardened 420 stainless steel balls typically measure 50 – 55 HRC; high-carbon 420C variants can reach about 58 HRC. That is softer than 440C (58 – 62 HRC) but far harder than any 304 or 316 ball.
Will 420 stainless steel balls rust?
Under normal conditions — fresh water, humidity, foods, mild chemicals — properly hardened and passivated 420 balls resist rust well. Prolonged exposure to salt water or chlorides can cause pitting; specify 316 stainless steel balls for those environments.
What is the difference between 420 and 440C stainless steel balls?
Both are magnetic martensitic grades. 440C has more carbon and chromium, giving higher hardness (58 – 62 HRC) and better wear and corrosion resistance at a higher price. 420 (50 – 55 HRC) is the economical choice for valves, agitators, and general-purpose components.
Are 420 stainless steel balls food safe?
Passivated 420 stainless steel is widely used in cutlery, dispensing pumps, and food equipment, and is generally acceptable for dry and non-chloride food contact. For high-acid, high-salt, or washdown-intensive food processing, 316 is the safer specification — confirm requirements against your local food-contact regulations.
Changzhou RISHENG Steel Ball Co., Ltd. is a professional 420 stainless steel ball manufacturer and supplier based in Changzhou, China. We produce passivated 420 / 420C balls from 1 mm to 50 mm in precision grades G10 – G1000, alongside 440C, 304, and 316 stainless steel balls — all with material certification, hardness reports, and 100% surface inspection. Whether you need bulk G200 valve balls at factory-direct prices, cosmetic-grade agitator balls, or OEM/ODM support for custom sizes and drilled balls, our engineering team will match the grade to your application.
