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AISI 440C Stainless Steel Balls are high-carbon, high-chromium martensitic stainless steel balls produced for applications where hardness, wear resistance, and precision are more important than maximum corrosion resistance. After heat treatment, 440C can achieve one of the highest hardness levels among common stainless steel grades, making it suitable for stainless bearing applications, valve seating elements, pump parts, and repeated-contact mechanical assemblies.

Compared with AISI 52100 chrome steel balls, 440C stainless steel balls provide better corrosion behavior in many mild environments while maintaining high hardness. Compared with AISI 304 or AISI 316 stainless steel balls, 440C provides much higher hardness and wear resistance but lower corrosion resistance, especially in chloride-rich, seawater, or acidic conditions.

Material Selection & Technical Positioning

AISI 440C is a hardened martensitic stainless steel. It is selected when the buyer needs a stainless steel ball with high hardness, strong wear resistance, magnetic properties, and dimensional stability for precision rolling or seating functions. It should not be positioned as the best stainless grade for marine or chemical corrosion resistance. For those environments, AISI 316/316L, ceramic balls, or other corrosion-focused materials may be more suitable.

The correct industry terminology includes: AISI 440C stainless steel balls, 440C stainless balls, hardened martensitic stainless steel balls, bearing-grade stainless steel balls, high hardness stainless steel balls, and stainless bearing balls.

Specifiche tecniche

Proprietà	Recommended Content
Material Grade	AISI 440C / UNS S44004
Equivalent Names	SUS440C, X105CrMo17 / 1.4125, 9Cr18Mo, 440C martensitic stainless steel
Diameter Range	0.5 mm – 150.00 mm；other sizes subject to production confirmation
Gradi di precisione	G20 – G1000 final range confirmed by size and order specification
Durezza	Typical HRC 57-65
Densità	Approx. 7.70 g/cm3
Young’s Modulus	Approx. 210 GPa
Resistenza alla trazione	Approx. 1900-2000 MPa, depending on heat treatment and material condition
Supply Condition	Hardened, polished, passivated or oiled according to order requirements
Magnetismo	Magnetic
Resistenza alla corrosione	Good in mild environments; not recommended as the first choice for seawater, chloride-rich, or acidic environments
Finitura superficiale	Polished, passivated, oiled, or other finish upon request

Chemical Composition Reference

Grado	Fe	C %	Cr %	Mo %	Mn max %	Si max %	P max %	S max %
AISI 440C	Balance	0.95-1.20	16.00-18.00	0,75 massimo	1.00	1.00	0.040	0.030

Note: Composition ranges are reference values. Final specification should follow the agreed material standard, purchase order requirements, and customer-approved drawing or datasheet.

International Grade Equivalents

Standard / Region	Common Equivalent
AISI / ASTM	440°C
UNS	S44004
JIS	SUS440C
EN / DIN	X105CrMo17 / 1.4125
Chinese reference	9Cr18Mo / related high-carbon chromium martensitic stainless grade

Heat Treatment, Hardness & Performance

AISI 440C stainless steel balls are normally heat treated to develop a hardened martensitic structure. This allows the balls to reach high hardness and strong wear resistance for repeated rolling contact, seating, and anti-friction applications.

• Typical hardness: HRC 57-65, depending on diameter, heat treatment and order requirement.
• High hardness supports wear life and dimensional stability in precision bearings, valves, pumps, rollers, and coupling mechanisms.
• Martensitic structure makes the balls magnetic, which can support automatic handling and feeding in assembly lines.
• 440C offers better corrosion behavior than chrome steel in many mild environments, but it is not equal to 304/316 stainless steel for corrosion resistance.
• For seawater, chloride-rich liquids, strong acids, or aggressive chemical exposure, buyers should confirm the media and consider 316/316L, ceramic, or other corrosion-focused alternatives.

Surface Finishes & Corrosion Resistance

Standard 440C stainless steel balls can be supplied with a polished metallic surface. Passivation may be used to remove free iron contamination and support formation of the stainless passive surface film. Anti-rust oil or customized cleaning and packing can also be discussed according to the application and shipping route.

Environment / Media	General Suitability	Buyer Note
Fresh water / mild humidity	Bene	Confirm exposure time, temperature and cleaning condition.
Steam, oil, gasoline, alcohol	Generally suitable within normal operating limits	Confirm media concentration and operating temperature before final selection.
Food-related equipment	Application-dependent	Suitable where hardness and wear resistance are required and media exposure is mild; confirm food-contact and cleaning requirements.
Medical instruments / devices	Application-dependent	Confirm regulatory, passivation, cleaning, traceability and documentation requirements.
Seawater / chloride-rich environment	Limited	440C may pit; consider 316/316L, ceramic or special corrosion-resistant grades.
Acidic chemical environment	Not recommended as first choice	Select material according to actual chemical concentration, temperature and exposure time.

Applications & Application Fit

AISI 440C stainless steel balls are best used where the application requires high hardness, excellent wear resistance, dimensional precision, and moderate stainless corrosion behavior. They are not the first choice for low-cost general hardware or for aggressive corrosion environments.

Applicazione	Fit Level	Why It Fits	Buyer Note
Precision bearings / anti-friction bearings	Very good	High hardness, dimensional stability and wear resistance support repeated rolling contact.	Confirm grade, noise, vibration, lubrication and fatigue requirements.
Pumps and valves	Very good	Hard surface supports seating, checking and repeated contact in fluid-control components.	Confirm media, pressure, temperature and corrosion conditions.
Quick couplings and fittings	Bene	Stable geometry and hardness support repeated engagement and release.	Confirm surface finish and contact stress.
Conveyor rollers and industrial movement systems	Bene	Wear resistance supports repetitive contact in mechanical systems.	Confirm load, lubrication and environmental exposure.
Ballpoint pens and precision consumer mechanisms	Bene	Fine finish and controlled diameter support smooth movement.	Confirm surface roughness, grade and cleanliness requirement.
Food-related equipment	Application-dependent	Useful where wear resistance is needed and exposure is mild.	Confirm cleaning chemicals, food-contact expectations and corrosion risk.
Medical instruments	Application-dependent	Precision and stainless behavior can be useful in selected device components.	Confirm documentation, traceability and regulatory needs.
Marine / acidic environments	Limited	440C can suffer pitting or corrosion in aggressive media.	Consider 316/316L, ceramic or special stainless alternatives.

Material Selection Guide

Material Option	Typical Strength	Limitation	When to Recommend
AISI 440C stainless steel balls	Highest hardness among common stainless ball grades, excellent wear resistance, bearing-grade precision.	Moderate corrosion resistance; not ideal for seawater or acidic media.	Precision bearings, pumps, valves, anti-friction components, high-wear stainless applications.
AISI 420C stainless steel balls	Good hardness and wear resistance with practical stainless performance.	Lower hardness and bearing performance than 440C.	Cost-sensitive martensitic stainless applications with moderate wear demand.
AISI 304 / 304L stainless steel balls	Good general corrosion resistance, non-hardened austenitic stainless, non-magnetic or slightly magnetic after processing.	Much lower hardness and wear resistance than 440C.	Food, cosmetic, general corrosion-resistant and non-hardened stainless applications.
AISI 316 / 316L stainless steel balls	Better corrosion resistance, especially in chloride and marine-like environments.	Lower hardness; not ideal for high-wear bearing loads.	Marine, chemical, medical, food-contact or corrosion-critical environments.
AISI 52100 chrome steel balls	Very high bearing performance, hardness and fatigue resistance at lower cost.	Not stainless; poor corrosion resistance without protection.	High-speed bearings, motors, precision rolling assemblies in protected environments.

Manufacturing & Process Control

SDBALLS controls 440C stainless steel ball production through raw material selection, wire drawing, cold heading, flashing, heat treatment, grinding, lapping or polishing, cleaning, passivation or oiling when required, inspection and packing. The production route is selected according to the required diameter, precision grade, surface finish and application requirement.

For precision applications, control of heat treatment, diameter variation, roundness, surface quality and final cleanliness is especially important. For valve, pump, coupling, food-related or medical equipment projects, SDBALLS can discuss additional inspection, cleaning, documentation and packing requirements before production.

Quality Control & Inspection

Typical inspection items for AISI 440C stainless steel balls include material verification, diameter, grade, roundness, surface appearance, hardness, surface roughness, corrosion-related requirements when specified, cleaning condition and packing condition.

• Dimensional inspection according to agreed precision grade and drawing requirement.
• Hardness inspection to confirm HRC range after heat treatment.
• Surface appearance control for scratches, dents, rust marks, stains and visible defects.
• Roundness and lot consistency control for precision rolling or seating applications.
• Optional passivation, cleaning, RoHS request, third-party testing or customer-specific report when required.
• Batch labeling and export packing control for traceability and international shipment.

Packing Options

SDBALLS can supply AISI 440C stainless steel balls in bulk industrial packing or customized OEM packing according to order quantity, ball size, cleanliness requirement and shipping method.

• Small-size balls: inner plastic bags, cartons, bottles, pails or drums depending on quantity.
• Bulk industrial orders: bag, carton, steel drum, plastic pail, wooden case or palletized export packing.
• Precision or clean applications: additional inner protection, labeling, batch separation or anti-contamination packing can be discussed.
• Customized label: material, diameter, grade, quantity, batch number, customer item number, barcode or OEM label upon request.

How to Specify for Quotation

To quote accurately, please confirm: material grade, diameter in mm or inch, precision grade, hardness requirement, surface finish, passivation or oiling requirement, corrosion environment, application, quantity, packing method, inspection documents, destination port and trade term.

For replacement or engineering projects, buyers are encouraged to provide drawings, current supplier specification sheets, photos, samples, media exposure, temperature, load, speed, lubrication condition and failure history if available.

Technical FAQ

Q: What is AISI 440C stainless steel ball?

A: AISI 440C stainless steel ball is a hardened martensitic stainless steel ball with high carbon and high chromium content. It is selected for high hardness, excellent wear resistance and bearing-grade stainless performance.

Q: Is AISI 440C stainless steel ball magnetic?

A: Yes. 440C is martensitic stainless steel and is magnetic. This is normal and can be useful for automatic sorting, feeding and assembly.

Q: What hardness can SDBALLS supply for 440C balls?

A: Typical hardness is HRC 57-65 after heat treatment. The final hardness range should be confirmed according to ball diameter, precision grade and purchase order specification.

Q: Is 440C better than 304 or 316 stainless steel balls?

A: It depends on the application. 440C is much harder and more wear resistant, making it better for bearings, valves and high-wear mechanisms. 304 and 316 are softer but offer better corrosion resistance, especially 316 in chloride or marine environments.

Q: Can 440C stainless steel balls replace chrome steel balls?

A: In some applications, yes. 440C can provide high hardness and better mild-environment corrosion resistance than chrome steel. However, chrome steel may still be preferred for cost-sensitive protected bearing applications.

Q: Are 440C stainless steel balls suitable for seawater?

A: Usually not as the first choice. 440C can suffer pitting in seawater or chloride-rich environments. For marine or chemical corrosion, 316/316L, ceramic, or special corrosion-resistant grades should be evaluated.

Q: Can SDBALLS supply passivated or polished 440C balls?

A: Yes. SDBALLS can supply polished, passivated, oiled, cleaned or specially packed 440C balls according to application and order requirements.

Q: What information is needed for quotation?

A: Please provide material, diameter, precision grade, hardness, surface finish, application, corrosion environment, quantity, packing, inspection documents, destination and trade term. Drawings or samples are helpful for replacement projects.