In many people’s minds, stainless steel seems like a single type of material—just iron and steel that doesn’t rust easily. In fact, it’s a large family of metallic materials, including hundreds of grades with different compositions and properties. Choosing the right stainless steel material directly affects a product’s service life, safety, and cost control.
Today, let’s get to know some “star members” of the stainless steel family: 304, 316, 410, 420, and 17-4PH. We’ll take a look at their unique strengths and the scenarios each is suitable for.
The Three Major Families of Stainless Steel
Based on their microstructures and heat treatment characteristics, stainless steels can be mainly divided into three categories. They are: austenitic, martensitic, and precipitation-hardening stainless steels.
Austenitic Stainless Steel (Represented by the 300 Series)
Austenitic stainless steel is currently the most widely used type. Its characteristics are:
- Non-magnetic (may have slight magnetism after cold working)
- Excellent corrosion resistance
- Good toughness and formability
- Cannot be strengthened by heat treatment, but its strength can be improved through cold working
Common grades and applications:
304 stainless steel: Also known as 18/8 stainless steel (containing 18% chromium and 8% nickel). It has good corrosion resistance and formability, and is the preferred material for kitchenware, household items, architectural decorations, food industry equipment and chemical containers.
316 stainless steel: Added with molybdenum (Mo) based on 304. This significantly enhances its resistance to chloride ion corrosion (e.g., seawater, salt spray). Therefore, it is often used in marine components, medical equipment, coastal building exteriors and chemical pipelines.
| Property | 304 Stainless Steel | 316 Stainless Steel |
| Main Composition | Cr18 – Ni8 | Cr16 – Ni10 – Mo2 |
| Tensile Strength | ≥515 MPa | ≥515 MPa |
| Corrosion Resistance | Excellent | Extremely excellent (especially resistant to pitting corrosion) |
| Main Applications | Kitchenware, home appliances, building materials | Ships, medical care, chemical industry |
Martensitic Stainless Steel (Represented by the 400 Series and Tool Steels)
The characteristics of martensitic stainless steel are:
- Magnetic
- Can be strengthened through heat treatment to achieve high strength and hardness
- Good wear resistance
- Corrosion resistance is relatively poorer than that of austenitic stainless steel
Common grades and applications:
410 stainless steel: The most basic type of martensitic stainless steel. It can gain relatively high strength via heat treatment and is often used to make stress-resistant and wear-resistant parts, such as valves, shafts, and bolts.
420 stainless steel: Has a higher carbon content than 410. Thus, it can reach higher hardness (up to HRC 50 and above) through heat treatment. It is commonly used in manufacturing cutlery, surgical instruments, and molds.
Precipitation-Hardening Stainless Steel (Represented by the PH Series)
This type of stainless steel is an “all-rounder”—it combines the excellent corrosion resistance of austenitic stainless steel and the high strength of martensitic stainless steel.
- Extremely high strength can be achieved through simple aging heat treatment
- Corrosion resistance is close to that of austenitic stainless steel
- Good workability
Representative grade and applications:
17-4PH (Grade: S17400): Contains approximately 17% chromium, 4% nickel, and 4% copper. Precipitation hardening is achieved by adding elements like copper and niobium. Its tensile strength can reach up to 1310 MPa, which is more than twice that of 304 stainless steel, while maintaining good corrosion resistance. It is widely used in fields with strict requirements for both strength and corrosion resistance, such as aerospace, petrochemical, and medical equipment.
| Property | 17 – 4PH Stainless Steel |
| Main Composition | Cr17 – Ni4 – Cu4 – Nb |
| Tensile Strength after Heat Treatment | Up to 1310 MPa |
| Corrosion Resistance | Good (better than martensite) |
| Main Applications | Aerospace components, high – strength structural parts |
How to Select Materials for Your Project?
When faced with numerous stainless steel grades, you can follow this systematic material selection approach:
1. Corrosion Resistance Requirement: The Primary Consideration
The environment where a product is used determines the required level of corrosion resistance. It is necessary to clarify which media the part will come into contact with:
- Mild environments: For parts used in indoor dry environments, ordinary atmosphere, or short-term contact with fresh water (such as decorative parts, furniture, and general structural parts), 304 stainless steel becomes the most common choice due to its excellent cost-effectiveness and sufficient corrosion resistance.
- Severe environments: If the product will come into contact with chemicals, acids, alkalis, or be used in environments prone to chloride ion corrosion (such as marine areas, coastal regions, food processing, and pharmaceuticals), 316 stainless steel is a more reliable option. The added molybdenum (Mo) element can effectively resist pitting and crevice corrosion.
- Special environments: For scenarios requiring higher strength while maintaining good corrosion resistance (such as pump and valve parts, turbine blades), precipitation-hardening stainless steels like 17-4PH have more advantages. While providing high strength, their corrosion resistance is far superior to that of martensitic stainless steel.
2. Strength/Hardness/Wear Resistance Requirements
The strength potential varies significantly among different series of stainless steel:
- High strength and wear resistance: When manufacturing components that need to withstand high loads and high wear (such as gears, shafts, and cutters), martensitic stainless steels (e.g., 410, 420) — which can be strengthened by heat treatment — are ideal choices.
- Ultra-high strength with corrosion resistance: When a project requires both extremely high strength and good corrosion resistance, precipitation-hardening stainless steels (e.g., 17-4PH) are the best option.
- Good formability and general strength: If the design focuses on complex forming, deep drawing, or welding, and has no high requirements for absolute strength, austenitic stainless steels (304/316) — with excellent ductility — are the first choice.
3. Budget and Total Cost
Material selection must align with the project’s economy:
- Initial material cost: Typically, 304 has the lowest cost. 316 is more expensive due to its molybdenum content. Specialized materials like 17-4PH are the most costly.
- Total cost consideration: Never focus solely on unit price. Choosing more corrosion-resistant or wear-resistant materials may mean a longer product lifespan and lower maintenance costs, which significantly reduces the total cost over the entire lifecycle.
The most reliable way is to communicate in depth with your casting supplier. Clearly explain the final service environment, performance requirements, and budget range of the parts. Professional foundries like QD can provide one-stop solutions from material selection, process design to final forming based on your needs, ensuring you get castings that best meet the requirements at the most reasonable cost.
Conclusion
Stainless steel is by no means a single type of metal. Instead, it is a large family with different properties and respective strengths. From daily-use kitchenware to aircraft flying in the sky, all rely on the precise selection of materials.
QD Foundry has rich experience in stainless steel casting production. From common grades like 304 and 316 to high-performance 17-4PH, we can provide you with high-quality castings that meet standards. We also offer professional material selection advice and technical support. Feel free to contact our technical team at any time—we will support your next project.
FAQ
1. Is stainless steel definitely rust-proof?
No. The “rust-resistance” of stainless steel is relative. Its corrosion resistance depends on the alloy composition and the environment. In certain harsh environments (such as high chloride ion environments), even 316 stainless steel may suffer from pitting corrosion. Correct material selection and maintenance are the keys.
2. Can a magnet be used to judge the quality of stainless steel?
No. It can only distinguish between austenitic stainless steel (usually non-magnetic) and other types (magnetic). 304 and 316 are non-magnetic but have excellent performance; 410 is magnetic but is also a widely used and effective material.
3. Why is 316 stainless steel widely used in medical devices?
Because 316 stainless steel is not only resistant to corrosion by human body fluids but also resistant to corrosion by disinfectants used repeatedly. It also has better biocompatibility.
4. Why is 17-4PH material so expensive?
Because it contains more types and quantities of alloying elements (such as nickel, copper, niobium), its production process is more complex, and its heat treatment technology requires high standards. Therefore, the cost is higher.
5. What information do I need to provide to get accurate material selection advice and a quotation?
Please provide as much as possible: the application scenario of the part, working environment (contact medium, temperature), stress conditions, precision requirements, and estimated production volume. The more detailed the information, the more accurate our advice and quotation will be.