630 stainless steel round bar, widely known as 17-4PH precipitation hardening stainless steel (UNS S17400 / EN 1.4542), is the most popular martensitic precipitation hardening stainless steel. It achieves ultra-high strength and hardness through simple aging heat treatment, combining the high mechanical strength of alloy steel and moderate corrosion resistance close to conventional austenitic stainless steel. With excellent mechanical properties, good toughness, superior wear resistance, easy machining and welding performance, 630 round bar is widely used in aerospace, petrochemical, food machinery, marine equipment, valve pump parts and high-precision structural components requiring high strength and anti-corrosion performance.
2. International Equivalent Grade
| USA Standard | European Standard | Japanese Standard | Chinese Standard | ISO Standard |
| AISI 630, 17-4PH, UNS S17400, ASTM A564 / A693 | EN 1.4542,
X5CrNiCuNb17-4-4 |
JIS SUS630 | GB 05Cr17Ni4Cu4Nb / 0Cr17Ni4Cu4Nb | X5CrNiCuNb16-4 |
3. 630/17-4PH Chemical Composition (Weight % / ASTM A564 Standard)
Copper and niobium are the core precipitation hardening elements, ensuring stable aging strengthening effect and balanced corrosion resistance.
| Carbon (C) | Silicon (Si) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Chromium (Cr) | Nickel (Ni) | Copper (Cu) | Niobium+Tantalum (Nb+Ta) | Iron (Fe) |
| ≤0.07% | ≤1.00% | ≤ 1.00% | ≤ 0.040% | ≤ 0.030% | 15.50 – 17.50% | 3.00 – 5.00% | 3.00 – 5.00% | 0.15 – 0.45% | Balance |
4. Basic Physical Properties
Density: 7.80 g/cm³
Melting Temperature Range: 1390 – 1430°C
Modulus of Elasticity: 196 GPa
Thermal Conductivity: 18.0 W/m·K (20°C)
Thermal Expansion Coefficient: 16.0 × 10⁻⁶ /°C
Magnetic Property: Magnetic (typical martensitic stainless steel feature)
Max Continuous Service Temperature: 300°C
5.Mechanical Properties (Different Heat Treatment Conditions)
630/17-4PH can obtain different strength and hardness grades through different aging treatments to adapt to various load requirements.
| CONDITION | Solution Annealed | H900 (Aging Hardened, Highest Strength Grade) | H1025 (Balanced Strength & Toughness Grade) | H1150 (High Toughness & Anti-Fatigue Grade) |
| Tensile Strength | ≥ 1100 MPa | ≥ 1310 MPa | ≥ 1100 MPa | ≥ 930 MPa |
| 0.2% Offset Yield Strength | ≥ 965 MPa | ≥ 1170 MPa | ≥ 1000 MPa | ≥ 725 MPa |
| Elongation | ≥ 10% | ≥ 6% | ≥ 8% | ≥ 12% |
| Hardness | ≤ 38 HRC | 44 – 48 HRC | 37 – 42 HRC | 28 – 33 HRC |
| Feature | Uniform internal structure, good machinability, suitable for subsequent secondary aging treatment and conventional mechanical processing | Maximum strength and hardness, excellent wear resistance, applicable for high-load, high-strength structural parts | Balanced mechanical properties of strength, hardness and toughness, the most widely used universal grade for industrial applications | Excellent toughness and ductility, strong anti-fatigue and anti-cracking performance, suitable for dynamic load and impact-resistant parts |
6.Surface Finishes & Diameter Tolerance Classification
6.1 Common Surface Types
Black Hot Rolled Surface: Original hot rolling oxide surface, low cost, suitable for forging, rough machining and heavy structural parts
Pickled Matte Surface: Uniform silver-gray finish without oxide scale, clean surface, standard industrial finished surface for general machining
Cold Drawn Bright Surface: Smooth and bright surface, consistent roundness and diameter, no surface defects, directly usable for precision machining
Precision Ground Mirror Surface: Fine grinding treatment, ultra-smooth surface, high dimensional accuracy, suitable for high-end precision shafts, valve cores and aerospace parts
6.2 Diameter Tolerance Standard
Hot Rolled Round Bar: ±0.3mm ~ ±0.8mm
Cold Drawn Round Bar: ±0.05mm ~ ±0.15mm
Precision Ground Bar: h8 / h9 / h10 high precision tolerance (±0.01mm ~ ±0.03mm)
6.3 Size Range
Diameter: Φ2mm – Φ300mm
Standard Length: 3000mm / 6000mm, customized fixed length available
7.Core Product Advantages
Ultra-High Mechanical Strength: After simple aging treatment, the strength is far higher than 304 and 316L austenitic stainless steel, reaching alloy steel level, which can reduce product wall thickness and save material cost
Good Moderate Corrosion Resistance: Better anti-rust and anti-corrosion performance than ordinary martensitic stainless steel (410/420), resistant to atmospheric corrosion, fresh water, weak acid and weak alkali media
Excellent Wear & Fatigue Resistance: High surface hardness and structural stability, suitable for long-term dynamic load and friction working conditions
Simple Heat Treatment Process: No complex quenching process required, low deformation rate after aging hardening, stable dimensional accuracy
Superior Machinability & Weldability: Easy for cutting, turning, drilling and welding, low processing difficulty and high production efficiency
Good Temperature Stability: Maintains stable mechanical properties below 300°C, not easy to soften and deform
8.Main Application Fields
Aerospace & Military Industry: High-strength structural parts, aircraft fittings, hydraulic components, military precision parts
Petrochemical & Energy Equipment: High-pressure valve parts, pump shafts, fluid control components, oilfield mechanical accessories
Food & Pharmaceutical Machinery: Sanitary equipment structural parts, high-strength conveyor shafts, food processing anti-rust components
Marine & Offshore Facilities: Marine mechanical parts, ship equipment fasteners, salt spray corrosion-resistant structural components
Precision Machinery & Molds: High-strength wear-resistant shafts, precision mechanical parts, instrument components, mold accessories
Automotive & General Industry: High-load engine parts, mechanical equipment fasteners, hydraulic and pneumatic system parts
9.Production & Quality Inspection Standards
Executive Standards: ASTM A564, ASTM A693, EN 10088, JIS G4303
Full Inspection Items: Spectrum chemical composition analysis, multi-state mechanical tensile & hardness test, ultrasonic internal flaw detection, dimensional tolerance full inspection, surface defect visual inspection, grain structure detection
10.Export Packaging
Round bars are bundled and fixed with steel strips, coated with anti-rust oil, wrapped with waterproof plastic film and woven bags. Both ends are protected by plastic caps to prevent collision deformation and surface scratches. Custom labels, logos and personalized export packaging are supported for long-distance ocean transportation.
