AISI 440A (SUS 440A / UNS S44002 / Grade 440A) Forging Parts — Custom Stainless Steel Forgings from China ISO-Certified Manufacturer

What Is AISI 440A Stainless Steel and What Are Our Forging Capabilities?

Jiangsu Liangyi Co., Limited is a leading China ISO 9001:2015 certified manufacturer of AISI 440A, SUS 440A, UNS S44002, and Grade 440A open die forging parts and seamless rolled steel forged rings. With over 25 years of industry experience, we deliver end-to-end custom forging solutions — from steel melting, precision forging, controlled heat treatment to final machining — with materials manufactured to ASTM, AMS, DIN, EN, JIS and API 6A material specifications.

AISI 440A is a high-carbon martensitic stainless steel, engineered to balance moderate corrosion resistance, exceptional mechanical strength, and the ability to get and keep outstanding hardness (up to 56 HRC) and wear resistance. According to Carpenter Technology’s 440A data sheet, this grade attains maximum toughness when heat treated to Rockwell C 56. This premium material is the best choice for extreme industrial applications that demand high durability, impact resistance, and reliable long-term performance in harsh working environments.

We have advanced forging equipment — including 1600T to 6300T open die forging presses and a diameter 6m ring rolling machine, and we can produce AISI 440A forgings with weight ranges from 30 KGS to 30,000 KGS per single piece. We have 120,000 tons of annual production capacity and can support custom prototypes in small batches and large-scale bulk production for global customers.

What Makes AISI 440A Metallurgically Unique?

Unlike austenitic grades (304, 316) which derive corrosion resistance purely from chromium, AISI 440A achieves its performance through a precisely controlled balance between three competing metallurgical forces: carbon-driven hardness, chromium-driven passivity, and thermal processing-driven microstructure. At 0.60–0.75% carbon — the lowest in the 440 series — 440A deliberately sacrifices some peak hardness to preserve a higher volume of free chromium in the matrix. This chromium remains available to form the protective Cr₂O₃ passive film rather than being consumed by Cr₂₃C₆ carbide precipitation.

In our 25-year production experience, this balance point is what makes 440A the only grade in the 440 family that is consistently forgeable into complex geometries — thick-walled valve bodies, large-bore pump housings, and multi-step transmission shafts — without the centerline cracking risk that plagues 440C in sections above 300 mm. Customers who initially specify 440C for wear resistance frequently switch to 440A after the first rejected batch; 440A's lower crack susceptibility reduces scrap rate by approximately 15–25% in our facility’s production data.

Our Forging Capability at a Glance

Our Jiangyin facility operates seven open-die forging presses ranging from 1600T to 6300T, supported by one ring rolling machine capable of producing seamless rings up to 6 meters outer diameter. All presses are paired with computer-controlled gas-fired furnaces with ±5°C uniformity, ensuring each AISI 440A ingot reaches the correct austenitizing temperature throughout its cross-section before the first hammer blow. This temperature uniformity is not a marketing claim — it is verified by embedded thermocouple records retained with every heat batch certificate.

For AISI 440A specifically, we maintain a minimum forging ratio of 3:1 (typically 4:1 to 6:1 for critical components), which eliminates the original as-cast dendritic segregation of carbon and chromium. This is critical because 440A ingots solidify with carbon-rich centerline segregation that, if not broken down by sufficient forging reduction, produces a heat-treated component with non-uniform hardness across its cross-section. Our process consistently achieves cross-sectional hardness uniformity within ±2 HRC on finished components up to 800 mm diameter.

What Are the International Equivalent Grades of AISI 440A?

AISI 440A stainless steel is designated differently across various international standards. The following table provides a comprehensive cross-reference for engineers and procurement teams worldwide:

Source: Cross-referenced from AZoM Grade 440A data, ATI 440A Technical Data Sheet, and ASTM A276/A479.

Are These Equivalent Grades Truly Identical? Practical Differences You Must Know

While the grades above are described as “equivalent,” our procurement and engineering teams have identified meaningful practical differences that affect purchasing decisions. These are not covered in most technical references because they require direct standard-by-standard comparison and real production experience:

Why Choose AISI 440A Stainless Steel for Forging Applications?

As a main grade of the 440 stainless steel series, AISI 440A has unique advantages over other 440 grades (440B / 440C) for forging applications, so that it is the best choice material for industrial components that need a balance of performance and processability:

• Superior Corrosion Resistance: With moderate carbon content (0.60–0.75%), AISI 440A delivers better corrosion resistance than 440B and 440C in the hardened condition, suitable for mildly corrosive environments in oil and gas, petrochemical and marine industries
• Excellent Forgeability and Toughness: Lower carbon content significantly improves hot forgeability and impact toughness, allowing for complex forging shapes that 440C cannot achieve without cracking
• Controllable Hardness and Wear Resistance: Through precise heat treatment, AISI 440A forgings can reach 50–56 HRC hardness, meeting the wear resistance requirements of most industrial components while maintaining better toughness than 440B/440C
• Stable Mechanical Performance: Consistent material composition and controlled forging process ensure uniform mechanical properties across the entire forging cross-section, critical for high-load rotating and pressure components
• Cost-Effective Solution: AISI 440A provides an optimal balance between performance and cost, offering near-440C wear resistance at a lower raw material cost, with reduced manufacturing risk due to better forgeability

Why Forged AISI 440A Outperforms Bar-Cut or Rolled Plate

A question our engineers frequently receive from new customers: “Can we just machine the part from 440A bar stock instead of ordering a forging?” The answer depends entirely on the application, but for structural and high-fatigue components, forged 440A consistently outperforms machined bar on three critical measures:

What Is the Difference Between AISI 440A, 440B and 440C?

To choose the right material, it’s important to understand the differences between the three grades of the 440 stainless steel family. The following comprehensive comparison highlights why AISI 440A is the best choice for most forging applications:

Source: Compiled from ASTM A276/A479, Carpenter Technology 440A Data Sheet, and ATI Martensitic Stainless Steels Data Sheet.

What AISI 440A Forged Products Can We Manufacture?

We manufacture a complete line of AISI 440A forged steel products in custom sizes and specifications, strictly according to your 2D/3D drawings and technical requirements:

AISI 440A Forged Bars and Rods

We supply AISI 440A forged steel round bars, square bars, flat bars, rectangular bars and step rods, with a maximum forging diameter up to 2 meters and single-piece weight up to 30 tons. All forged bars come with full mill test certificates (MTC) per EN 10204 3.1/3.2 standards. Explore our full forged bars product line.

Standard dimensional tolerances for AISI 440A forged round bars: diameter ±3 mm (as-forged), ±1 mm (rough-machined), ±0.1 mm (finish-machined). Straightness: ≤ 2 mm/m (as-forged), ≤ 0.5 mm/m (machined). Length tolerance: +50 / −0 mm standard. Custom tighter tolerances available per drawing.

SUS 440A Seamless Rolled Forged Rings

We manufacture custom SUS 440A seamless rolled rings and open die forged rings, with a maximum diameter up to 6 meters and single-piece weight up to 30 tons. Engineered for bearing races, valve seat rings, gear rings and turbine seal rings, with full NDT testing. Wall thickness range: 30 mm to 500 mm; height: 20 mm to 2,000 mm. OD/ID ratio: up to 12:1.

Ring tolerances (as-rolled): OD ±5 mm, ID +8/−0 mm, height ±5 mm, wall thickness ±3 mm or ±3% (whichever is greater). Rough-machined rings: OD/ID ±1 mm, height ±1 mm. Face perpendicularity: ≤ 1.5 mm TIR (as-machined).

UNS S44002 Forged Sleeves and Hollow Components

We produce high-precision UNS S44002 forged sleeves, bushes, housings, shells, hollow bars and seamless pipes, all parts are fully machined to meet your custom requirements. Widely used in valve, pump and hydraulic systems. Bore diameter: 50 mm to 1,200 mm. OD: 80 mm to 2,000 mm. Length: up to 3,000 mm (single piece). ID tolerance (machined): H7 or H8 per ISO 286 standard.

Grade 440A Forged Discs, Plates and Custom Components

We also supply Grade 440A forged discs, disks, blocks, plates, gear shafts, spindles and custom forged components, with complete heat treatment and finishing services. We support fully custom solutions for non-standard shapes. Disc diameter: 100 mm to 4,000 mm; thickness: 30 mm to 800 mm. Custom forged flanges, eccentric forgings, and step shafts available with ≤ ±0.5 mm critical dimension tolerances after CNC machining.

Achievable Surface Finish and Delivery Conditions

What Is the Chemical Composition and Mechanical Properties of AISI 440A?

All our AISI 440A forging materials strictly meet the requirements of ASTM A276/A479 standards, and they are fully traceable from steel melting to finished products.

Chemical Composition (per ASTM A276/A479)

Source: ASTM A276/A479; verified against AZoM Grade 440A data.

How Each Alloying Element Works in AISI 440A — Metallurgical Insight

Understanding the role of each element is essential for engineers to specify 440A in important applications. The following is a deeper explanation than what standard data sheets provide, drawn from our metallurgical team’s working knowledge:

• Carbon (0.60–0.75%): The primary hardening element. Carbon dissolves into the iron crystal lattice during austenitizing at 1010–1065°C, then becomes “trapped” during quenching to form the body-centered tetragonal martensite structure. Higher carbon in 440B/440C increases hardness but also increases the volume fraction of chromium carbides, which rob the matrix of free chromium and reduce both corrosion resistance and toughness. 440A’s carbon ceiling at 0.75% is a deliberate engineering decision to preserve this chromium balance.
• Chromium (16–18%): Provides the “stainless” character through a self-healing Cr₂O₃ passive oxide film. In the hardened condition, approximately 1% Cr is consumed for every 0.1% C in the form of M₃₃C₆ carbides. At 0.675% C (midpoint), roughly 6.75% Cr is tied up in carbides, leaving approximately 10.25% free chromium in a 17% Cr heat — still well above the minimum 10.5% needed for stainless behavior. This is the core reason 440A’s corrosion resistance exceeds 440B and 440C in hardened condition.
• Molybdenum (≤ 0.75%): When present, Mo increases pitting resistance by stabilizing the passive film against chloride attack. Mo also refines carbide morphology, distributing smaller, more rounded carbides rather than the coarse, angular Cr₂₃C₆ networks seen in Mo-free heats. Our preferred heats for oil and gas valve applications target Mo at 0.40–0.60% even though the standard only requires ≤ 0.75%. The result is measurably better pitting resistance (higher PREN: see Section 9).
• Manganese (≤ 1.00%): Acts as a deoxidizer during steelmaking and improves hot workability. Mn also bonds preferentially with sulfur to form MnS rather than iron sulfide (FeS); MnS inclusions are less harmful to ductility and toughness. However, Mn above 0.8% can slightly reduce corrosion resistance, so our premium heats target Mn at 0.50–0.70%.
• Silicon (≤ 1.00%): Strong deoxidizer. Reduces the dissolved oxygen content of the melt, preventing porosity. Si also improves the high temperature oxidation resistance, which is beneficial for components operating close to 400 °C. However, excess Si above 0.7% can promote ferrite formation in the annealed structure, reducing hardenability.

Mechanical Properties (Condition-Dependent)

How Tempering Temperature Controls Final Hardness

One of the most practical — and least documented — aspects of AISI 440A is that the final hardness is directly adjustable by tempering temperature. This makes 440A uniquely flexible for applications where the engineer needs to dial in a specific hardness value. The following data is drawn from our in-house heat treatment records and is consistent with published data from Carpenter Technology:

Source: ASTM A276/A479; AZoM 440A data; Carpenter Technology 440A data sheet; Jiangsu Liangyi internal production records.

How Is AISI 440A Forged and Heat Treated?

AISI 440A needs strict process control during forging and heat treatment to avoid carbide precipitation, grain coarsening and cracking. Our process system, refined over 25+ years, guarantees optimal performance:

Precision Forging Process

• Controlled Hot Forging Temperature: Strictly between 1050°C and 1150°C, final forging temperature above 850°C. Per AZoM, preheating to 760°C before slowly increasing to forging range is recommended
• Optimal Forging Ratio: Minimum 3:1 for all products, guaranteeing grain refinement and structural density
• Multi-Pass Forging: Controlled multi-directional forging (upsetting and drawing) to break down as-cast dendritic matrix
• Slow Cooling After Forging: Furnace cooling or sand burial to prevent thermal stress cracking, important for sections exceeding 500 mm

Customized Heat Treatment Process

• Annealing: At 840–900°C (1550–1600°F) with slow furnace cooling to reduce hardness to ≤95 HRB
• Quenching: At 1010–1065°C (1850–1950°F), oil or air quench for uniform martensitic transformation
• Tempering: At 150–370°C (300–700°F), adjustable for target hardness. Avoid 370–600°C (temper embrittlement zone)
• Sub-Zero Treatment (Optional): Cryogenic treatment at −73°C to −196°C for maximum dimensional stability
• Full Data Traceability: All heat treatment recorded digitally, furnace uniformity within ±5°C

Common Forging Defects in AISI 440A — Causes, Detection and Our Prevention Approach

High-carbon martensitic stainless steels like 440A are more prone to specific forging defects than austenitic grades. The following table documents the most frequently encountered defects in 440A forgings from suppliers without adequate process control, and explains exactly how our 25-year process discipline prevents each one. This information is rarely published and represents genuine manufacturing expertise:

What Are the Physical Properties of AISI 440A?

Temperature-Dependent Physical Properties

For design engineers calculating thermal stress in service, the following temperature-dependent property data for AISI 440A is critical. These values are not always published in standard data sheets but are essential for FEA modeling of high-temperature or thermally cycled components:

What Is the Corrosion Resistance of AISI 440A Stainless Steel?

AISI 440A provides moderate corrosion resistance — the highest among the 440 series. According to ATI’s technical data sheet, Types 410, 420, 425 Mod, and 440A exhibit good corrosion resistance to atmospheric corrosion, potable water, and mildly corrosive chemical environments.

The reason 440A outperforms 440B and 440C in corrosion resistance is its lower carbon content. Carbon binds with chromium to form Cr₂₃C₆ carbides; less carbon means more free chromium is available for the protective passive oxide film on the steel surface.

PREN: Pitting Resistance Equivalent Number for AISI 440A

The Pitting Resistance Equivalent Number (PREN) is the most widely used single-number metric for comparing stainless steel pitting corrosion resistance in chloride environments. The formula is: PREN = %Cr + 3.3 × %Mo + 16 × %N.

For AISI 440A at typical composition (17% Cr, 0.5% Mo, ~0% N), the calculated PREN is approximately: PREN = 17 + (3.3 × 0.5) + 0 = 18.7. For heats targeting maximum Mo (0.75%), PREN reaches approximately 19.5. The following table compares 440A against common competitor grades:

Corrosion Resistance by Environment

Where Are AISI 440A Forgings Used? — Applications and Global Industry Cases

Additional applications include: ball bearings, gage blocks, cutlery, measuring instruments, fuel nozzles, shear blades, gear shafts, surgical instruments, dental instruments, molds and dies, aircraft structural parts, and food processing equipment.

Which Standards Do Our AISI 440A Forgings Comply With?

How Do We Ensure Quality of AISI 440A Forgings?

Full-Process Quality Control System

• Raw Material Inspection: OES spectral analysis, inclusion testing (ASTM E45), grain size inspection (ASTM E112)
• Forging Process Control: Pyrometer temperature monitoring, forging ratio verification, real-time data logging
• Heat Treatment Verification: Hardness testing (ASTM E18/E10), metallographic examination, mechanical testing (ASTM A370/E23)
• Finished Product Inspection: 100% dimensional check (CMM), surface quality (visual + Ra), comprehensive NDT

Core Testing Standards

• ASTM E18: Rockwell Hardness Testing (HRC/HRB)
• ASTM E10: Brinell Hardness Testing
• ASTM A370: Mechanical Testing (Tensile, Yield, Elongation)
• ASTM E23: Charpy V-Notch Impact Testing
• ASTM E45: Inclusion Content Determination
• ASTM E112: Average Grain Size Determination
• ASTM A262: Intergranular Corrosion Testing (where required)
• ASTM A967: Passivation Treatment Verification
• ASTM E837: Residual Stress Testing
• AMS 2315: Delta Ferrite Content Determination
• NDT: 100% UT (ASTM A388/EN 10228-3), optional MT (ASTM A275), PT (ASTM E165), RT

All products are supplied with EN 10204 3.1 material test reports including full traceability, heat analysis, mechanical results, heat treatment records, NDT results, and dimensional confirmation. EN 10204 3.2 documents with third-party witness inspection (SGS, Bureau Veritas, Lloyd’s, TUV) available upon customer request and at customer’s arrangement.

What Custom Forging Services Do We Offer for AISI 440A?

• Flexible MOQ: From 30 KGS prototypes to 30,000 KGS bulk production
• Lead Time: 15-25 days standard, 30-45 days custom, expedited service available
• Engineering Support: Free drawing review, process optimization, material selection, FEA simulation
• Trade Terms: EXW, FOB, CIF, CFR, DDP, DAP with door-to-door delivery
• Machining Service: Rough, semi-finish and finish machining on CNC centers
• Account Management: Dedicated project manager for each client

How to Weld and Machine AISI 440A Stainless Steel?

Welding Recommendations

• Pre-Heat: To 200–300°C. Per AZoM, preheating to 260°C and post-weld treating at 732–760°C for 6 hours followed by slow furnace cooling is recommended
• Filler Metal: Matching 440A filler or AWS 309/310 austenitic stainless steel filler
• PWHT: Temper immediately at 150–370°C. Do not cool below 150°C before PWHT
• Interpass Temperature: 200–300°C to prevent untempered martensite
• AISI 440A tends to air harden. For critical applications, forging is always preferred over welding

Machining Guidelines and Recommended Parameters

AISI 440A is generally described as “machinable with care,” but this description understates the practical complexity. The machinability behavior of 440A changes dramatically between its annealed and hardened conditions. The following parameters are drawn from our in-house CNC machining experience and discussions with our tooling suppliers:

• Annealed Condition: Machine at ≤95 HRB. Per AZoM, carbide or ceramic tooling with chip breakers recommended
• Tool Selection: Carbide inserts (C2/C3) or CBN tools for best results
• Cutting Parameters: Turning 40–60 m/min (carbide), feed 0.1–0.3 mm/rev, depth 1–3 mm
• Hardened Machining: CBN or ceramic inserts, 15–25 m/min, 0.1–0.5 mm depth of cut
• Grinding: Aluminum oxide or CBN wheels. Low forces to prevent grinding burn
• Surface Finish: Achievable Ra 0.8 μm or better

Surface Treatment and Post-Processing Options for AISI 440A Forgings

After forging and heat treatment, the surface condition of AISI 440A components is a critical final step that directly determines real-world corrosion resistance and wear life. Unlike austenitic grades where the as-machined surface usually suffices for most environments, 440A forgings frequently benefit from targeted post-processing because the martensitic surface — while very hard — contains microstructural features (carbide exposures, machining stress layers) that can initiate corrosion if untreated.

Material Selection Guide: When to Choose AISI 440A vs. Key Alternatives

Material selection for high-performance forged components involves balancing four competing requirements: corrosion resistance, mechanical strength, wear resistance, and manufacturability. The following decision framework is based on our engineering team’s 25 years of consultation with global clients across oil and gas, power generation, aerospace, and industrial tooling:

Decision Guide: Which Grade for Your Application?

• Choose AISI 440A when: You need hardness 50–56 HRC + moderate corrosion resistance + complex forging geometry + cost-effective solution. Ideal: API valves, pump shafts, turbine seals, precision tooling, railway components.
• Choose AISI 440C when: You need the absolute maximum hardness (58–60 HRC) and the part geometry is simple (thin section, flat, small diameter <150 mm). Ideal: knife blades, gage blocks, ball bearings. Do not use 440C for complex large forgings — cracking risk is unacceptably high.
• Choose 17-4PH (630) when: You need high strength + good corrosion resistance + complex shape + weldability. Ideal: aerospace fasteners, hydraulic cylinders, offshore structural components. Premium cost justified by versatility.
• Choose AISI 316L when: The main requirement is corrosion resistance and there is no need of hardness >30 HRC. It is the best choice for chemical processing equipment, marine fittings, food industry tanks
• Choose Duplex 2205 when: You need superior corrosion resistance (especially chloride pitting) + high strength + NACE MR0175 compliance. Ideal: offshore subsea hardware, desalination equipment, highly corrosive chemical service.

Our engineering team provides free material selection consultation for customers unsure which grade suits their application. Send your operating conditions, environment, required hardness, and part geometry to sales@jnmtforgedparts.com and receive a written recommendation within 48 hours.

Related Stainless Steel Forging Grades

View our complete material grades catalog or forging products overview.

Frequently Asked Questions About AISI 440A Forgings

Contact Us for Custom AISI 440A Forging Solutions

Jiangsu Liangyi Co., Limited  is a top manufacturer of open die forgings and seamless rolled rings in China. We have more than 25 years of experience supplying premium AISI 440A forging parts to customers in more than 50 countries around the world. We can provide standard forged bars and rolled rings and custom complicated parts. We deliver cost-effective, high-quality solutions with short delivery cycles and comprehensive professional technical support.

Send your custom drawings, material requirements and quantity details to get a detailed quotation within 24 hours.