17-7PH stainless steel vs. 304: Key Differences
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Does your project require stainless steel? In short, if your application demands extremely high strength and heat resistance (such as aerospace components), then 17-7 PH stainless steel is the preferred choice. If cost-effectiveness and excellent corrosion resistance are key factors (such as kitchen equipment or architectural trim), then 304 stainless steel is the industry standard.
17-7PH stainless steel vs. 304: Key Differences
What is 17-7 PH material?
17-7 PH stainless steel (UNS S17700) is a precipitation-hardening, semi-austenitic alloy known for its high strength, high hardness, excellent fatigue life, good corrosion resistance (similar to 304 stainless steel), and minimal distortion after heat treatment. Therefore, it is ideal for applications in aerospace, springs, and demanding food/chemical processing industries.
What are the advantages of 304 stainless steel?
SAE 304 stainless steel is the most common type of stainless steel. It is an alloy of iron, carbon, chromium, and nickel. It is an austenitic stainless steel and therefore non-magnetic. It has lower electrical and thermal conductivity than carbon steel. It has higher corrosion resistance than ordinary steel and is widely used due to its ease of forming into various shapes.
What is the differences between 17-7PH stainless steel and 304 stainless steel?
17-7PH (631) is a high-strength precipitation-hardening (PH) stainless steel that, after heat treatment, exhibits excellent strength, hardness, and fatigue resistance, making it suitable for aerospace and spring manufacturing; while 304 is a versatile austenitic stainless steel widely used for general purposes such as kitchenware, and is more cost-effective and easier to form than 17-7PH.
304 Stainless Steel vs 17-7 PH Stainless Steel Equivalent Grade
| Standard / Country | 304 Stainless Steel Equivalent Grade | 17-7 PH Stainless Steel Equivalent Grade |
|---|---|---|
| AISI / ASTM (USA) | 304 (ASTM A240 / A276) | 17-7 PH (ASTM A693 Type 631) |
| UNS (Unified Numbering System) | S30400 | S17700 |
| EN / DIN (Europe / Germany) | 1.4301 | 1.4568 |
| JIS (Japan) | SUS304 | SUS631 |
| GB (China) | 06Cr19Ni10 | 0Cr17Ni7Al |
| BS (UK) | 304S15 / 304S31 | 17-7PH |
| AFNOR (France) | Z7CN18-09 | Z8CN17-07 |
| GOST (Kazakhstan) | 08Х18Н10 | 07Х17Н7А |
| ISO | X5CrNi18-10 | X7CrNiAl17-7 |
17-7 Stainless Steel vs. 304 Stainless Steel： Composition
| Element | 17-7 Stainless Steel (%) | 304 Stainless Steel (%) |
|---|---|---|
| Cr | 16.0-18.0 | 18.0-20.0 |
| Ni | 6.5-7.8 | 8.0-10.5 |
| Al | 0.75-1.50 | – |
| C | 0.09 max | 0.08 max |
| Mn | 1.00 max | 2.00 max |
| Si | 1.00 max | 0.75 max |
| P | 0.04 max | 0.045 max |
| S | 0.03 max | 0.03 max |
17-7 Stainless Steel vs. 304 Stainless Steel:Mechanical Properties
| Property | 17-7 Stainless Steel | 304 Stainless Steel |
|---|---|---|
| Tensile Strength | Up to 1035 MPa (after heat treatment) | Approximately 515 MPa |
| Yield Strength | Up to 960 MPa (after heat treatment) | Approximately 205 MPa |
| Elongation | Approximately 11-15% (after heat treatment) | Approximately 40% |
| Hardness | Up to 375 HV (after heat treatment) | Approximately 201 HB |
17-7 Stainless Steel vs. 304: Corrosion Resistance
304 stainless steel generally shows better corrosion resistance in chloride and acidic environments, while 17-7 stainless steel provides adequate corrosion resistance for atmospheric and mild chemical exposure but prioritizes strength over corrosion performance.
17-7 Stainless Steel vs. 304: Magnetism
17-7 stainless steel becomes magnetic after heat treatment due to its martensitic structure, whereas 304 stainless steel remains non-magnetic in the annealed condition.
17-7 Stainless Steel vs. 304: Hardness
After precipitation hardening, 17-7 stainless steel can reach Rockwell C 40–45, while 304 stainless steel typically remains around Rockwell B 70–90 even after cold working.
17-7 Stainless Steel vs. 304: Machinability
17-7 stainless steel has lower machinability than 304, especially in hardened conditions, and is best machined in Condition A, while 304 offers more stable and forgiving machining performance in the annealed state.
GNEE Stainless Steel is an independent stockist and processor of 17-7ph/304 stainless steel. With our extensive inventory and superior processing capabilities, we can meet the needs of most projects, whether for stock products or custom orders. We offer: stock size plates and sheets, stock length round bars, custom-cut plates and sheets, custom-cut round bars, cold forming of plates, sheets, and round bars, and any other necessary processing services. For any inquiries, please email info@gneestainless.com
