431 vs 17-4PH stainless steel:Strength & Hardness
Jul 13, 2026
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When selecting stainless steel for high-strength applications, buyers often compare 431 stainless steel and 17-4PH stainless steel because both are precipitation-hardening or martensitic-type stainless steels known for excellent mechanical performance.
For procurement engineers, understanding 431 vs 17-4PH stainless steel strength and hardness helps avoid over-specification, reduce maintenance costs, and select the most cost-effective grade for shafts, fasteners, aerospace parts, marine equipment, and industrial components.
What is ASTM A276 Type 431 stainless steel bar?
ASTM A276 Type 431 is a martensitic stainless steel featuring excellent hardenability. Available in hot-worked or cold-worked bar forms, it can achieve a tensile strength of 850 to 1000 MPa along with high yield strength under heat-treated conditions, with hardness significantly increased to HRC 35–45. Although its corrosion resistance is inferior to that of austenitic stainless steels like Grade 304, it offers outstanding resistance to fresh water, marine mist, and various acidic or alkaline environments within this high-strength category. It is ideal for high-strength, high-demand applications such as shafts, bolts, and pumps in marine or corrosive environments.
What Is 17-4PH Stainless Steel round Bar?
17-4PH round bar is a cylindrical metal bar made from high-strength, precipitation-hardening (PH) martensitic stainless steel. In the initial annealed condition (Condition A), the material is relatively soft and easy to machine, yet it can achieve extremely high tensile strength through heat treatment. Its corrosion resistance is superior to standard hardenable martensitic stainless steels (such as the 400 series). By selecting different aging treatment temperatures (such as H900, H1025, or H1150), the ultimate tensile strength under the H900 condition can reach as high as approximately 1310 MPa.
431 vs. 17-4 PH Stainless Steel: Key Differences
| Feature | SUS431 (Martensitic) | 17-4PH / SUS630 (PH) |
| Hardening Method | Quench & Temper (Q&T) | Precipitation Hardening (Aging) |
| Corrosion Resistance | Moderate to High (Best of 400 series) | High (Approaching Grade 304) |
| Tensile Strength | 800-1000 MPa | 930-1300 MPa |
431 vs. 17-4 PH Stainless Steel: Chemical Composition (wt %)
| Grade | C | Cr | Ni | Cu | Nb + Ta |
| SUS431 |
≤0.20 |
15.0 – 17.0 | 1.5 – 2.5 | - | - |
| 17-4PH |
≤0.07 |
15.0 – 17.5 | 3.0 – 5.0 | 3.0 – 5.0 | 0.15 – 0.45 |
431 vs. 17-4 PH Stainless Steel: Mechanical Properties (Typical Condition)
Note: 431 is shown in Quenched & Tempered (Q&T) condition; 17-4PH is shown in H900 (High Strength) and H1150 (High Ductility) conditions.
| Property | SUS431 (Typical Q&T) | 17-4PH (H900) | 17-4PH (H1150) |
| Tensile Strength |
≥ 850 MPa |
≥ 1310 MPa |
≥ 930 MPa |
| Yield Strength |
≥ 650 MPa |
≥ 1170 MPa |
≥ 725 MPa |
| Elongation |
≥ 15% |
≥ 10% |
≥ 16% |
| Hardness (HRC) | 30 – 40 HRC | 40 – 47 HRC | 28 – 37 HRC |
International Equivalent Standards
| Grade | USA (ASTM) | Japan (JIS) | Germany (DIN/EN) | China (GB) |
| AISI 431 | ASTM A276 | JIS G4303 (SUS431) | 1.4057 (X17CrNi16-2) | 14Cr17Ni2 |
| 17-4PH | ASTM A564 (630) | JIS G4303 (SUS630) | 1.4542 (X5CrNiCuNb16-4) | 05Cr17Ni4Cu4Nb |
431 vs. 17-4 PH Stainless Steel: Heat Treatment
| Grade | Condition Code | Description | Typical Hardness |
| AISI 431 | Annealed (A) | Softened for machining. |
≤ 285 HBW |
| QT 800 / 900 | Quenched & Tempered for high torque. | 28 – 36 HRC | |
| 17-4PH | Condition A | Solution Annealed (Required before aging). |
≤ 363 HBW |
| H900 | Aged at 900°F (482°C) - Max Strength. | 40 – 47 HRC | |
| H1025 | Aged at 1025°F (552°C) - Balanced. | 35 – 42 HRC | |
| H1150 | Aged at 1150°F (621°C) - Max Ductility. | 28 – 37 HRC |
431 vs 17-4PH stainless steel: Corrosion resistance
Due to its 15%–17% chromium content, 431 stainless steel exhibits good corrosion resistance, making it suitable for atmospheric, fresh water, and mild marine environments. However, its martensitic microstructure results in lower resistance to chloride corrosion compared to 17-4PH stainless steel. In salt spray and marine applications, 17-4PH typically provides a longer service life if properly heat-treated.
431 vs 17-4PH stainless steel: Machinability
Grade 431 stainless steel typically exhibits good machinability in the annealed or tempered condition, with a machinability rating approximately 40%–50% that of AISI 1212 carbon steel. Due to its lower alloy content, the material is easier to turn, drill, and mill. In contrast, 17-4PH stainless steel has poorer machinability due to its precipitation-hardened microstructure, particularly in the H900 condition (with a Hardness of approximately HRC 40–47.
431 vs. 17-4PH Stainless Steel: Applications
431 stainless steel is commonly used for aerospace shaft components, pump shafts, and golf club heads.
17-4PH is the standard choice for high-stress applications requiring wear resistance, such as valve stems, marine shafting, aircraft components, and heavy-duty fasteners.
How to Select Between 431 and 17-4PH Stainless Steel?
| Requirement | Recommended Grade |
|---|---|
| Tensile strength below 1000 MPa | 431 Stainless Steel |
| Tensile strength above 1300 MPa | 17-4PH Stainless Steel |
| Marine shafts | 431 |
| Aerospace components | 17-4PH |
| High wear resistance | 17-4PH |
| Cost-sensitive projects | 431 |
| Precision mechanical parts | 17-4PH |
Can 431 stainless steel replace 17-4PH?
In some moderate-strength applications, yes. However, 431 cannot fully replace 17-4PH where extremely high strength, hardness, and fatigue performance are required.
AISI 431 / 17-4PH Stainless Steel Bar Suppliers and Manufacturers
| Product Form | Diameter / Size Range (mm) | Length (m) | Standard Finishes |
| Round Bar (Cold Drawn) | 2.0 – 50.0 mm | 3.0 – 6.0 m | Bright, Polished (h8, h9, h10) |
| Round Bar (Hot Rolled) | 10.0 – 250.0 mm | 4.0 – 6.0 m | Black, Peeled, Rough Turned |
| Round Bar (Forged) | 200.0 – 600.0 mm | 2.0 – 5.0 m | Black, Rough Machined |
| Hexagonal Bar | 5.0 – 75.0 mm | 3.0 – 4.0 m | Bright, Cold Drawn (h11) |
| Square Bar | 10.0×10.0 – 150 ×150 mm | 3.0 – 6.0 m | Hot Rolled, Cold Drawn |
| Flat Bar | (T) 5 – 100×(W) 20 – 400 mm | 3.0 – 6.0 m | HRAP (Hot Rolled Annealed & Pickled) |
Quality Control
Each batch of bars is typically accompanied by the following documentation: MTC (Material Test Certificate) compliant with EN 10204 3.1 (including heat number, chemical composition, and mechanical properties).
Ultrasonic Testing (UT): Performed on forged bars to ensure the absence of internal defects (compliant with ASTM A388 or SEP 1921 standards).
Dimensional Inspection: Verification of diameter, length, and roundness.
PMI Testing: Positive Material Identification to prevent grade mix-ups.
Macro-etching Test: Inspection of grain structure uniformity (commonly used for 17-4PH grade steel).
Export Packaging
Small-diameter bars: Bundled with steel wire and wrapped in heavy-duty plastic film or woven bags.
Bright/Precision bars: Individually sleeved in plastic or paper and packed in seaworthy wooden cases to prevent scratches and corrosion.
Large-diameter bars: Secured to steel frames or wooden pallets using nylon slings.
Identification: Each bar or bundle is labeled with the grade, specifications, heat number, net weight, and country of origin.
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