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AISI 440A (UNS S44002) is the lowest-carbon variant of the 440-series high-carbon high-chromium martensitic stainless steels, engineered to deliver an optimal balance of hardness, toughness, and corrosion resistance. Unlike higher-carbon 440B and 440C which prioritize extreme hardness at the expense of brittleness, 440A retains the core hardenability of the 440 family while significantly improving impact resistance and corrosion performance. This unique combination makes it the preferred choice for applications where durability, reliability, and dimensional stability are critical, without the high cost and processing challenges of ultra-high-hardness grades.
Product Details
AISI 440A is a heat-treatable martensitic stainless steel that achieves outstanding mechanical properties through precise thermal processing. Its controlled carbon content of 0.60–0.75% enables it to reach 54–57 HRC after quenching and tempering, delivering far better impact toughness than 440C. With 16.00–18.00% chromium addition, it forms a dense passive oxide film, offering the best corrosion resistance among the entire 440 series.
This grade is well suited for components subject to abrasive wear, light impact load and mild corrosive environments. It features excellent polishability for mirror and satin surface finishes. The only compromise is slightly lower maximum hardness compared to 440B/440C, which is fully acceptable for most general wear-resistant and precision component applications.
UNS S44002 Chemical Composition
All limits per ASTM A582 / ASTM A276, UNS S44002.
Note: The following composition is based on authoritative specifications from ATI, Aircraft Materials and ASTM, excluding non-standard erroneous data from third-party sources.
| Element | Specification Limit |
| Carbon (C) | 0.60 – 0.75 % |
| Chromium (Cr) | 16.00 – 18.00 % |
| Manganese (Mn) | ≤ 1.00 % |
| Silicon (Si) | ≤ 1.00 % |
| Molybdenum (Mo) | ≤ 0.75 % |
| Nickel (Ni) | ≤ 0.75 % |
| Phosphorus (P) | ≤ 0.040 % |
| Sulfur (S) | ≤ 0.030 % |
| Iron (Fe) | Balance |
The carbon content differentiates 440A from other 440-series grades, providing sufficient hardenability without excessive brittleness. High chromium ensures reliable corrosion resistance, while molybdenum enhances pitting and crevice corrosion resistance. Sulfur is strictly controlled as an impurity to maintain optimal anti-rust performance, unlike free-machining grades such as 420F with intentional sulfur addition.
Governing standards: ASTM A582 (bar, shapes), ASTM A276 (bar), AMS 5631 (bars/wire/forgings), QQ-S-763
Physical Properties Of 440A Stainless Steel
| Property | Value | Conditions |
| Density | 7.72 g/cm³ | Room temperature |
| Elastic Modulus | 193 – 200 GPa | Room temperature |
| Poisson’s Ratio | 0.27 – 0.29 | — |
| Shear Modulus | ~77 GPa | — |
| Thermal Expansion Coefficient | 10.2 µm/m·°C | 0 – 100 °C |
| Thermal Conductivity | 24.2 W/m·K | ~27 °C |
| Specific Heat Capacity | ~460 J/kg·K | — |
| Electrical Resistivity | ~60 µΩ·cm | — |
| Magnetic Behaviour | Magnetic (ferromagnetic after hardening) | All temperatures |
| Melting Range | 1400 – 1450 °C | Solidus to liquidus |
Mechanical Properties
Annealed Condition (per ASTM A276 / A582)
| Property | Value |
| Tensile Strength (Rₘ) | ≥ 725 MPa (105 ksi) |
| Yield Strength 0.2% (Rₚ₀.₂) | ≥ 415 MPa (60 ksi) |
| Elongation (50 mm gauge) | ≥ 15 % |
| Hardness | ≤ 255 HB (max, annealed) |
Hardened and Tempered Condition (typical values)
| Property | Value |
| Hardness | 54 – 57 HRC |
| Tensile Strength | 1650 – 1900 MPa (depending on temper temperature) |
| Yield Strength | 1450 – 1700 MPa |
| Elongation | 5 – 10 % |
| Fatigue Strength | ~310 MPa |
The hardened and tempered state represents the core performance advantage of 440A. Hardness can be adjusted across 54–57 HRC by varying tempering temperature, allowing designers to balance high hardness, wear resistance and fracture toughness according to actual service conditions.
Heat Treatment Specifications
Annealing: 840 – 870 °C, hold until uniform temperature, furnace cool or slow air cool. Purpose: Soften to ≤255 HB for machining, forming and cold work.
Hardening (Austenitising): 1010 – 1050 °C, hold to achieve uniform temperature throughout section. Quench medium: Oil or pressurised air; air quench acceptable for small sections.
Tempering: 180 – 370 °C, hold 1 – 2 h minimum per 25 mm of section, air cool.
| Temper Temperature | Approximate HRC | Notes |
| 180 – 220 °C | 55 – 57 HRC | Maximum hardness & wear resistance, reduced toughness |
| 230 – 300 °C | 52 – 55 HRC | Balanced hardness, toughness and corrosion resistance |
| 310 – 370 °C | 49 – 52 HRC | Improved impact toughness, slightly lower hardness |
Important: Tempering between 400 – 580 °C produces obvious temper embrittlement and is not recommended for 440-series grades. Always temper either below 400 °C or above 600 °C. Tempering above 600 °C will cause significant hardness decline.
Weldability
440A has poor weldability due to its high carbon content; welding is not recommended unless absolutely necessary. If welding is required:
– Pre-heat: 250 – 300 °C
– Post-weld heat treatment (PWHT): 730 – 780 °C followed by controlled slow cooling to restore ductility and prevent cracking in the heat-affected zone.
Machinability
440A exhibits moderate machinability in the annealed condition, with a machinability rating of approximately 45% relative to the AISI B1112 free-cutting carbon steel baseline. It is significantly easier to machine than 440C (~35% rating) due to its lower carbon content and reduced carbide precipitation, but more challenging than free-machining grades like 420F and 416.
Practical processing recommendations:
– Use carbide or high-speed steel tools with positive rake angles to reduce cutting forces
– Maintain stable chip formation under moderate cutting speeds and feed rates
– Apply adequate cutting fluid to dissipate heat and minimize tool wear
– Excellent polishability, capable of achieving mirror finishes for precision components requiring aesthetic or functional surface quality
Corrosion Resistance
440A delivers the best corrosion resistance in the 440 stainless steel family, with PREN (Pitting Resistance Equivalent) ≈ 16–17, higher than 440C (~14) and moderately lower than 316L austenitic stainless steel.
| Environment | Performance |
| Dry atmosphere, mild indoor service | Excellent |
| Fresh water, neutral pH & room temperature | Excellent; passive film stable |
| Weak organic acids, dilute alkalis | Good; suitable for intermittent exposure |
| Humid or outdoor environments | Good with polishing or plating surface treatment |
| Mild marine splash zones | Adequate for short-term intermittent use |
| Chloride-containing media | Limited; not suitable for long-term continuous exposure |
| Strong acids, alkalis & aggressive chemicals | Not suitable |
Where higher corrosion resistance is the primary requirement, austenitic grades like 316L or duplex stainless steels are recommended. 440A is the optimal choice when a balance of hardness, wear resistance, impact toughness, and mild corrosion resistance is needed, and where the higher cost and brittleness of 440C are not justified.
440A / 440B / 440C Grade Comparison
| Grade | Carbon Range | Typical HRC | Toughness | Corrosion Resistance | Machinability | Cost |
| 440A | 0.60–0.75% | 54–57 | Best | Best | Best | Lowest |
| 440B | 0.75–0.95% | 56–59 | Medium | Medium | Medium | Medium |
| 440C | 0.95–1.20% | 58–62 | Poor | Poor | Poor | Highest |
Equivalent and Related Designations
| Standard | Designation | Notes |
| AISI / ASTM | 440A | |
| UNS | S44002 | |
| EN (European) | 1.4109 (X70CrMo15) | Equivalent |
| JIS (Japan) | SUS 440A | |
| DIN | X70CrMo15 | |
| BS | 440A | |
| GB (Chinese) | 7Cr17 |
Typical Applications
440A is widely adopted for precision and wear-resistant parts requiring balanced hardness, toughness and mild corrosion resistance:
Cutlery & Blades: High-grade kitchen knives, outdoor folding knives, industrial scissors and general cutting tools with good edge retention and anti-chipping performance.
Medical & Dental Instruments: Surgical blades, forceps, dental burs and handpiece components, suitable for repeated high-temperature sterilization.
Pump & Valve Components: Pump shafts, valve cores, valve seats and spindle parts used in non-aggressive fluid medium.
Industrial Wear Parts: Bearings, bushings, gears, pins and precision mechanical fasteners.
Automotive & General Engineering: Fuel system parts, shaft components, hardware and precision tooling gauges.
Consumer & Hardware Products: Watch cases, decorative hardware and polished structural parts.
Available Product Forms
Round bar, hexagonal bar, flat bar (main machining stock), seamless tube, pipe fittings (elbows, tees, reducers, end caps), flanges and custom precision machined components.
Material is supplied in annealed condition as standard; hardened and tempered to custom hardness requirements is available on request.
Why C&N
At C&N (Hongcheng Pipe Fittings Limited), we stock AISI 440A stainless steel complying with ASTM A276 / A582 standards, supplied with full mill test reports traceable to heat number. We serve manufacturers, fabricators and procurement teams across medical, cutlery, automotive and general industrial sectors, providing professional material selection advice and reliable technical support.
C&N Martensitic 440A (UNS S44002)
If you are evaluating 440A for your project, or comparing it with 440B, 440C, 420F and other martensitic grades, contact us for professional technical consultation and competitive quotation.
