17-4PH (UNS S17400, also known as grade 630) is a martensitic precipitation-hardening stainless steel that offers an exceptional combination of high strength, good corrosion resistance, and ease of fabrication. With a tensile strength that can exceed 1300 MPa in the H900 condition, it is one of the most widely used stainless steels in the aerospace, chemical, and oil & gas industries. Its ability to be heat-treated to a wide range of strength levels makes it highly versatile for CNC machined components.
1. Basic Information of 630 (17-4PH)
17-4PH is a martensitic stainless steel hardened by the precipitation of copper-rich phases. Unlike semi-austenitic grades, 17-4PH is martensitic in the annealed condition, which gives it a baseline hardness of approximately 30 HRC. Through a simple single-step aging heat treatment (typically 900°F to 1150°F), the hardness can be increased to 44 HRC or higher. The alloy is supplied in Condition A (annealed) and is then aged by the end user to achieve the desired mechanical properties. It is magnetic in all conditions.
2. Chemical Composition
The composition of 17-4PH is designed to provide a balance of corrosion resistance and hardenability. Copper is the primary precipitation-hardening element, while niobium (columbium) refines the grain structure and enhances toughness.
| Element | Composition Range (wt%) |
|---|---|
| Carbon (C) | ≤ 0.07 |
| Manganese (Mn) | ≤ 1.00 |
| Silicon (Si) | ≤ 1.00 |
| Chromium (Cr) | 15.00 – 17.50 |
| Nickel (Ni) | 3.00 – 5.00 |
| Copper (Cu) | 3.00 – 5.00 |
| Niobium + Tantalum (Nb+Ta) | 0.15 – 0.45 |
| Phosphorus (P) | ≤ 0.040 |
| Sulfur (S) | ≤ 0.030 |
| Iron (Fe) | Balance |
3. Mechanical Properties
The mechanical properties of 17-4PH are highly dependent on the aging temperature. Lower aging temperatures (e.g., H900) produce maximum strength, while higher temperatures (e.g., H1150) improve toughness and stress corrosion cracking resistance.
| Condition | Tensile Strength (MPa) | Yield Strength 0.2% (MPa) | Elongation (%) | Hardness (HRC) |
|---|---|---|---|---|
| Condition A (Annealed) | ≤ 1100 | ≤ 760 | ≥ 10 | ≤ 38 |
| H900 (482°C) | 1310 – 1480 | 1170 – 1380 | ≥ 10 | 40 – 47 |
| H1025 (552°C) | 1070 – 1240 | 1000 – 1170 | ≥ 12 | 35 – 42 |
| H1150 (621°C) | 930 – 1070 | 720 – 860 | ≥ 16 | 28 – 36 |
4. Typical Applications
17-4PH is used across a broad range of industries due to its strength and corrosion resistance. Key applications include:
- Aerospace: Turbine engine components, landing gear parts, and structural brackets.
- Oil & Gas: Valve stems, pump shafts, and downhole tool components exposed to sour gas (NACE MR0175 compliant in H1150 condition).
- Chemical Processing: Impellers, shafts, and fasteners in corrosive environments.
- Medical Devices: Surgical instruments and orthopedic implants requiring high strength and biocompatibility.
- CNC machined parts: Precision gears, shafts, and housings for industrial equipment.
5. CNC Machining Performance
17-4PH is considered one of the most machinable precipitation-hardening stainless steels. It machines best in the annealed condition (Condition A) with a hardness of approximately 30 HRC. Machining in the aged condition (H900+) is possible but requires reduced speeds and rigid setups.
| Operation | Cutting Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Tool Material |
|---|---|---|---|---|
| Turning (Annealed) | 90 – 140 | 0.20 – 0.40 | 2.0 – 5.0 | Carbide (C5/C6) |
| Turning (H900) | 45 – 75 | 0.10 – 0.20 | 0.5 – 2.0 | Carbide (TiAlN coated) |
| Milling (Annealed) | 80 – 120 | 0.12 – 0.25 (per tooth) | 1.0 – 4.0 | Carbide (AlTiN coated) |
| Drilling | 25 – 50 | 0.08 – 0.15 | N/A | HSS-Co or Carbide |
Key Machining Tips:
- Use sharp tools with positive rake angles to minimize work hardening.
- Apply flood coolant with a concentration of 8-10% for optimal chip evacuation.
- For threading, use single-point threading with carbide inserts; avoid chaser taps in hardened material.
- Surface finish in the annealed condition can achieve Ra ≤ 0.8 µm; in H900, Ra ≤ 0.4 µm is achievable with finishing passes.
6. Our Services
Dongguan Stirling Metal Products Co., Ltd. specializes in providing 630 material + CNC machining One-Stop Service:
- ✅ Material procurement: Genuine product guarantee, complete material certificates (MTC per AMS 5604/5643)
- ✅ CNC machining: Precision ±0.01mm, surface finish down to Ra 0.2 µm
- ✅ Heat treatment: In-house aging from H900 to H1150 with full hardness testing
- ✅ Sample production: Fast delivery in 3-5 days for design verification
- ✅ Batch production: Delivery in 7-15 days with ISO 9001 quality control
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