Question 1

What is an AISI 420A / 420B stainless steel ball?

Accepted Answer

An AISI 420A / 420B stainless ball is a martensitic stainless steel ball with 12-14 % chromium and controlled carbon. 420A contains ~0.15 % C (softer, more ductile) and 420B ~0.20-0.30 % C (harder after heat treatment). They offer a balance of moderate corrosion resistance, magnetic response and lower cost than 420C / 440C, common in hardware and light bearing duty.

Question 2

What is the chemical composition of 420A / 420B?

Accepted Answer

420A: ≤0.15 % C, ≤1.00 % Mn, ≤1.00 % Si, 12.0-14.0 % Cr, ≤0.04 % P, ≤0.03 % S. 420B: 0.15-0.30 % C, same manganese, silicon, chromium range. The lower carbon of 420A gives better weldability and formability; 420B takes a slightly higher hardness (HRC 48-52) without brittleness.

Question 3

How hard can 420A / 420B stainless balls be?

Accepted Answer

420A reaches HRC 35-45 after hardening; 420B reaches HRC 48-52, both softer than 420C or 440C. They are often supplied annealed (HRB 90-95) for machining and later hardened. For higher hardness with similar corrosion resistance, switch to 420C or 440C; for higher corrosion resistance at moderate hardness, switch to 304 or 316.

Question 4

420A / 420B vs 440C stainless ball - which should I choose?

Accepted Answer

Choose 420A / 420B for magnetic applications needing moderate hardness, decent corrosion resistance and lower cost (about 25 % cheaper than 440C). Choose 440C when you need precision grade G25 or finer, hardness above HRC 58, or the best corrosion performance of any martensitic grade. 420A is also preferred for cold heading.

Question 5

How corrosion-resistant are 420A / 420B balls?

Accepted Answer

420A / 420B offer fair corrosion resistance, better than chrome steel but inferior to 440C or 316. They withstand mild atmospheres, fresh water, weak acids, and brief food contact, but pit and stain when exposed to chlorides, salt water, or strong acids. Passivation per ASTM A967 significantly improves performance.

Question 6

Are 420A / 420B balls magnetic?

Accepted Answer

Yes. 420A / 420B are martensitic and therefore ferromagnetic in all conditions. They strongly attract a magnet and are unsuitable for non-magnetic applications. If you need stainless with magnetic neutrality, choose austenitic 304 or 316.

Question 7

What precision grades are 420A / 420B supplied in?

Accepted Answer

420A / 420B balls are typically produced in AFBMA / ISO 3290 grades G200, G500, G1000. Tight grades below G100 are achievable but uneconomical compared with 440C, so we recommend 440C for G100 or finer requirements. Manufacturing tolerance, surface finish and lot diameter variation follow the standard grade definitions.

Question 8

What sizes of 420A / 420B balls do you supply?

Accepted Answer

Standard 420A / 420B ball diameters span 1 mm to 100 mm. The most common stocked sizes are 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 15 mm, 20 mm. Custom diameters and large balls above 150 mm are produced by forging plus machining with extended lead time.

Question 9

What are 420A / 420B balls typically used for?

Accepted Answer

420A / 420B balls are widely used in drawer slides, cabinet hardware, magnetic catches, safety locks, oil burners, pump components, decorative trim, valve trim, food-processing hardware, bicycle parts, and low-load bearings with intermittent exposure to moisture. They are the workhorse 'cheap-magnetic-stainless' of hardware.

Question 10

How should 420A / 420B balls be heat treated?

Accepted Answer

Austenitize at 980-1030 °C, oil or air quench, then temper at 200-300 °C to reach the target hardness. 420A tolerates faster cooling; 420B benefits from oil quench to avoid ferrite retention. Stress relieve large balls (>50 mm) after rough grinding to minimize distortion before final lap.

Question 11

Can 420A / 420B balls be welded?

Accepted Answer

Yes. 420A is weldable using 420 filler wire with preheat ~150 °C and post-weld temper at 200-300 °C to restore corrosion resistance. 420B is harder to weld because of higher carbon; usually brazing or mechanical fastening is preferred. In both cases, the weld HAZ may have reduced corrosion resistance, so apply post-weld passivation.

Question 12

What passivation is required for 420A / 420B balls?

Accepted Answer

Standard passivation by citric acid (preferred over nitric for environmental reasons) per ASTM A967 restores the chromium oxide layer after heat treatment or grinding. We passivate every 420A / 420B lot before packaging to ensure rust-free arrival. A passivation certificate accompanies each shipment.

Question 13

What surface finishes are available for 420A / 420B?

Accepted Answer

We supply mirror polish (Ra ≤0.05 µm) for decorative and food-grade use, standard lap (Ra 0.1 µm), and bright-ground (Ra 0.2-0.4 µm) for industrial hardware. Black-oxide or chrome plating is available for appearance or extra corrosion protection. Dry-blasted matte finishes suit architectural projects.

Question 14

What is the minimum order quantity for 420A / 420B balls?

Accepted Answer

Stocked 420A / 420B diameters (3-25 mm) carry a 200 kg MOQ. Custom sizes, special temper, or precision grade finer than G200 require 500 kg. Trial orders of 100 pieces are available ex-stock with a sample surcharge.

Question 15

What is the lead time for 420A / 420B ball orders?

Accepted Answer

Stocked sizes ship in 7-10 days. Custom sizes or non-standard lots take 25-35 days. Repeat orders with confirmed tooling run 15-25 days. We confirm dispatch dates in the order acknowledgement.

Question 16

What documents accompany 420A / 420B ball shipments?

Accepted Answer

All shipments include an EN 10204 2.1 compliance certificate and, on request, a 3.1 mill certificate with chemical composition and hardness. Surface finish, dimensional, and salt-spray test reports are issued against purchase-order requirements. Independent third-party inspection (SGS / BV) is available.

Question 17

How are 420A / 420B balls packaged for export?

Accepted Answer

Anti-rust VCI bags inside steel drums (25-100 kg) or cartons (20-25 kg), palletized and stretch-wrapped. Stainless balls for hardware often ship in bulk cartons with foam dividers. Labels list size, grade, lot number, net/gross weight, HS code 8482.91.

Question 18

What drives 420A / 420B ball pricing?

Accepted Answer

Pricing depends on diameter, grade, hardness targets, lot size, surface finish, and inspection level. 420A is ~5 % cheaper than 420B because of lower carbon and softer temper. Compared to 440C the grade is 20-30 % cheaper, making it attractive for large-volume hardware lines.

Question 19

420A / 420B vs carbon steel ball - which is better?

Accepted Answer

420A / 420B offer noticeably better corrosion resistance than carbon steel and a brighter appearance, at roughly 2-3× the unit price. Choose stainless for any application exposed to occasional moisture or visible to end users; choose carbon steel for sealed, dry, hidden hardware where price dominates.

Question 20

How long does a 420A / 420B ball last in service?

Accepted Answer

Lifespan depends on load, lubrication and environment. Properly lubricated, lightly loaded applications such as drawer slides or oil-burner nozzles yield 5-15 years of service. In dry, abrasive, or wet conditions the life drops sharply. We can recommend grade, hardness, and lubrication based on your duty cycle and target hours.

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