Stainless pipe fitting,stainless fitting,duplex stainless,31803,32750,32760,we are one of largest sour service stainless fitting supplier according to ISO 10156.
High-carbon, high-chromium martensitic grade — engineered for maximum hardness, superior wear resistance, and moderate corrosion protection in demanding industrial environments.
| UNS | AISI | EN | Max Hardness | Cr Content | Standard |
| S44004 | 440C | 1.4125 | 60 HRC | 16 – 18 % | ASTM A276 / A484 |
Standard Overview
Grade 440C is covered under ASTM A276 / A276M (Standard Specification for Stainless Steel Bars and Shapes) and ASTM A484 / A484M (General Requirements for Stainless Steel Bars, Billets, and Forgings). The equivalent European designation is EN 10088-3 1.4125, while the Japanese standard JIS G4303 lists it as SUS440C.
440C is the highest-carbon member of the 440-series martensitic family. Its elevated carbon content (0.95 – 1.20 %) combined with a chromium range of 16.00 – 18.00 % produces carbide networks that deliver the hardest condition achievable among standard stainless steels after heat treatment. The grade is supplied in bar, rod, wire, shape, and seamless tubular forms.
Applicable Product Forms: Hot-finished and cold-finished bars; seamless mechanical tube; forgings; wire. Welded construction is generally not recommended for this grade due to its high carbon content and susceptibility to carbide precipitation at grain boundaries.
Core Characteristics
Highest Hardness in Stainless Family
Excellent Wear & Abrasion Resistance
Moderate Corrosion Resistance
Good Dimensional Stability
High Compressive Strength
Magnetic in All Conditions
Grade Introduction
Operating Temperature Range
440C performs reliably at continuous service temperatures up to approximately 425 °C (800 °F) in the hardened-and-tempered condition when maximum hardness is not the priority. For applications requiring hardness above 58 HRC, service temperatures should be kept below the tempering temperature used during heat treatment — typically 150 – 200 °C for bearing applications. The grade is not recommended for cryogenic or sub-zero service where impact toughness is critical.
Max Service Temp (H+T) 425 °C
Austenitizing Temp 1010 – 1065 °C
Annealing Temp 845 – 900 °C
Max Hardness (H+T) 60 HRC
Product Specification Range
| Product Form | Diameter / Thickness | Length | Finish |
|---|---|---|---|
| Round Bar (Hot-Finished) | Ø 6 – 300 mm | Up to 6 m | Black / Peeled |
| Round Bar (Cold-Finished) | Ø 3 – 100 mm | Up to 6 m | Bright Drawn / Ground |
| Flat Bar / Plate | 3 – 100 mm thick | Custom | Hot-Rolled / Annealed |
| Seamless Tube | OD 10 – 273 mm, WT 1 – 30 mm | Up to 12 m | Bright Annealed / Pickled |
| Wire | Ø 0.5 – 12 mm | Coil | Cold-Drawn / Annealed |
Typical Application Industries
Precision Bearings & Races
Knife & Cutting Tool Blades
Valve Balls & Seats
Nozzles & Wear Plates
Surgical Instruments
Pump Shafts & Sleeves
Aerospace Structural Parts
Die Components
Dental Equipment
Chemical Composition
Per ASTM A276 / UNS S44004. All values are weight percent (%). Compliance is verified by heat analysis and product analysis where specified.
| Element | Min (%) | Max (%) | Notes |
|---|---|---|---|
| Carbon (C) | 0.95 | 1.20 | Primary hardening element |
| Chromium (Cr) | 16.00 | 18.00 | Corrosion resistance |
| Manganese (Mn) | — | 1.00 | Max only |
| Silicon (Si) | — | 1.00 | Max only |
| Phosphorus (P) | — | 0.040 | Max only |
| Sulfur (S) | — | 0.030 | Max only |
| Molybdenum (Mo) | — | 0.75 | Optional; improves pitting resistance |
| Iron (Fe) | Balance | ||
Note on Carbon: The high carbon content of 0.95 – 1.20 % is essential to forming iron and chromium carbide precipitates that contribute to the extreme hardness after hardening. This is the key differentiator between 440C and the lower-carbon 440A (max 0.75 % C) and 440B (max 0.95 % C) variants.
Mechanical Properties
Annealed Condition
Minimum guaranteed values per ASTM A276 for the annealed (softened) delivery condition.
| Property | Value | Unit | Test Standard |
|---|---|---|---|
| Tensile Strength (UTS) | 758 | MPa (110 ksi) | ASTM E8 |
| Yield Strength (0.2% offset) | 448 | MPa (65 ksi) | ASTM E8 |
| Elongation in 50 mm | 14 | % | ASTM E8 |
| Reduction of Area | 25 | % | ASTM E8 |
| Hardness (max) | 269 | HBW | ASTM E10 |
| Hardness (approx. Rockwell) | 27 | HRC | ASTM E18 |
Hardened & Tempered — Typical Values
Values depend on tempering temperature. The following data represents typical (not guaranteed minimum) results from commercial heat treatment practice.
| Temper Temp. | UTS (MPa) | YS 0.2% (MPa) | Elong. (%) | RA (%) | Hardness |
|---|---|---|---|---|---|
| As-Quenched | — | — | — | — | 60 – 61 HRC |
| 150 °C (300 °F) | 1970 | 1480 | 2 | 10 | 58 – 60 HRC |
| 205 °C (400 °F) | 1930 | 1450 | 2 | 10 | 57 – 59 HRC |
| 260 °C (500 °F) | 1900 | 1420 | 3 | 12 | 55 – 57 HRC |
| 315 °C (600 °F) | 1830 | 1370 | 4 | 14 | 53 – 55 HRC |
| 370 °C (700 °F) | 1760 | 1310 | 5 | 18 | 50 – 52 HRC |
| 480 °C (900 °F) | 1720 | 1290 | 4 | 15 | 50 – 52 HRC* |
* Secondary hardening peak — see chart below.
Fig. 1 — Hardness (HRC) vs. Tempering Temperature for 440C (UNS S44004). Oil-quenched from 1038 °C. Note the secondary hardening effect near 480 °C.
Fig. 2 — Comparative mechanical properties across four heat treatment conditions: annealed and three hardened-and-tempered states.
Physical Properties
The following data is representative of the annealed condition unless otherwise stated. Physical properties vary only moderately between annealed and hardened conditions.
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Density | 7.75 | g/cm³ | Room temperature |
| Melting Range | 1370 – 1480 | °C | Solidus–Liquidus |
| Elastic Modulus (E) | 200 | GPa | Room temperature |
| Shear Modulus (G) | 77 | GPa | Room temperature |
| Poisson’s Ratio | 0.28 | — | Room temperature |
| Thermal Conductivity | 24.2 | W / m · K | at 100 °C |
| Specific Heat Capacity (Cp) | 460 | J / kg · K | 0 – 100 °C |
| Electrical Resistivity | 600 | nΩ · m | 20 °C |
| CTE (0 – 100 °C) | 10.2 | µm / m · °C | Avg., 20 °C baseline |
| CTE (0 – 315 °C) | 11.0 | µm / m · °C | Avg., 20 °C baseline |
| Magnetic Permeability | > 600 | µ (rel.) | H+T condition |
Fig. 3 — Coefficient of Thermal Expansion (CTE) vs. temperature for 440C, with austenitic 316L and carbon steel shown for reference.
Heat Treatment
Fig. 4 — Recommended heat treatment process flow for 440C (UNS S44004) from raw material to final inspection and dispatch.
Sub-Zero (Cryogenic) Treatment — Optional
To minimize retained austenite and maximize hardness after quenching, parts may be cooled to –73 °C (–100 °F) within 2 hours of quenching, held for 8 – 24 hours, and then returned to room temperature before tempering. This step is particularly recommended for precision bearing races requiring dimensional stability.
Step 01 Stress Relieve
620 – 650 °C; air cool; prior to final hardening
Step 02 Preheat
790 °C; equalize temperature throughout cross-section
Step 03 Austenitize
1010 – 1065 °C; hold 30 min / 25 mm of section
Step 04 Quench
Oil quench or positive-pressure gas (vacuum furnace)
Step 05 Temper
150 – 370 °C; 2 × 1–2 h cycles; air cool between
Tempering Caution: Avoid tempering in the 425 – 565 °C range where chromium carbide precipitation at grain boundaries can sensitize the steel and reduce both toughness and corrosion resistance. This zone is sometimes termed the “temper embrittlement range.”
Corrosion Resistance
440C offers moderate corrosion resistance — markedly better than carbon tool steels, but not comparable to austenitic grades (e.g., 316L) or duplex grades in wet or chloride-rich environments. Its performance is closely tied to surface condition and heat treatment state.
| Environment | Performance | Notes |
|---|---|---|
| Mild atmospheric (dry) | Good | Recommended without protection |
| Mild aqueous / fresh water | Moderate | Ground / polished finish preferred |
| Dilute organic acids | Limited | Short-term exposure only |
| Chloride-containing media | Poor | Pitting risk; consider higher-alloy grade |
| Fuel / lubricating oils | Good | Common in bearing applications |
Maximizing corrosion resistance requires a smooth, oxide-free, fully hardened surface. Electropolishing or passivation per ASTM A967 is recommended for critical applications.
Inspection & Testing Requirements
Standard Tests (ASTM A276 / A484)
| Test Type | Standard Reference | Frequency | Acceptance Criterion |
|---|---|---|---|
| Chemical Analysis (Heat) | ASTM A751 | Per heat | Composition limits above |
| Chemical Analysis (Product) | ASTM A751 | Per lot if required | Table 1 tolerances |
| Tensile Test | ASTM E8 | Per lot | UTS / YS / Elong. min. |
| Hardness Test | ASTM E10 / E18 | Per piece (if specified) | See condition table |
| Dimensional Inspection | A276 Table 5 | 100 % | Size tolerances per product form |
| Visual / Surface Inspection | A484 §14 | 100 % | Free of cracks, seams, laps |
Supplementary Non-Destructive Tests (on request / customer spec)
| Method | Standard | Application |
|---|---|---|
| Ultrasonic Testing (UT) | ASTM A388 / EN 10308 | Internal defects in bars > 40 mm Ø |
| Magnetic Particle (MT) | ASTM E1444 / EN 10228-1 | Surface / near-surface cracks |
| Eddy Current (ECT) | ASTM E309 | Seamless tube, wire — surface discontinuities |
| Positive Material ID (PMI) | XRF or OES | Grade verification at delivery |
| Microstructure Examination | ASTM E45 / A751 | Carbide distribution, grain size (on request) |
Documentation
Mill Test Report (MTR) — EN 10204 Type 3.1 or 3.2Chemical Composition CertificateMechanical Test CertificateHeat Treatment RecordDimensional Inspection Report
Machinability & Fabrication Notes
440C is best machined in the annealed condition (HB ≤ 269). Machinability is roughly 50 % that of AISI 1212 free-machining carbon steel. Recommended practices include the use of carbide tooling, reduced cutting speeds versus carbon steel, positive-rake geometry, and the consistent application of cutting fluid (sulfurised or sulfochlorinated oil).
Cold working in the annealed condition is feasible for moderate reductions. Extensive cold forming should be followed by a full anneal cycle to restore ductility and relieve residual stresses before hardening.
Welding: Not generally recommended. When unavoidable, preheat to 200 – 300 °C, use matching filler metal or 309L as buffer, and perform a full post-weld anneal or hardening cycle. The high carbon content makes the heat-affected zone susceptible to martensite cracking if welding is done without adequate precautions.
About C&N — HONGCHENG PIPE FITTINGS LIMITED
C&N has spent years building a supply chain focused on one thing: putting the right material in your hands with the documentation to back it up. Our 440C inventory covers bars, seamless tubes, and machined blanks across a broad size range — stocked in annealed condition and available with full EN 10204 3.1 mill certification.
Whether your application is precision bearings, valve trim, surgical tooling, or wear-critical pump components, our team can advise on grade selection, size tolerancing, and heat treatment scheduling. We understand that in critical applications, traceability is not optional — every shipment from C&N comes with a complete documentation package.
Reach out with a drawing, a specification, or just a requirement — we work from all three.
EN 10204 Type 3.1 / 3.2ASTM A276 / A484PED 2014/68/EUISO 9001UT / MT on RequestPMI Verified
