As one of the most common materials in industrial applications, stainless steel can be found in both everyday uses and high-end sectors. While stainless steel types with different applications may appear visually identical, they may actually belong to distinct categories. If your project is considering stainless steel as a production material, selecting the appropriate type from the wide range available could directly determine its success or failure. This article provides a brief overview of various stainless steel types, listing common grades and their characteristics to offer guidance for your reference.
What is Stainless Steel
Stainless steel, simply put, is an iron-based alloy containing at least 10.5% chromium, renowned for its exceptional corrosion resistance. The corrosion resistance of stainless steel primarily stems from the chromium-based passivation layer formed on its surface due to its high chromium content, which prevents erosion by external corrosive agents. Beyond chromium, elements like molybdenum, carbon, and nickel are often alloyed into stainless steel to enhance specific properties such as corrosion resistance, strength, and formability.
Primary Types of Stainless Steel
Stainless steel is primarily divided into five major categories. Based on their microstructures at room temperature, stainless steels can be classified as austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and duplex stainless steel. The final category, precipitation-hardening stainless steel, is named according to the heat treatment process it employs. These five categories of stainless steel are also referred to as alloy families, each possessing unique properties.
Austenitic Stainless Steels
As the largest family within stainless steel, austenitic stainless steel offers comprehensive properties and accounts for approximately 70% of all stainless steel production. The addition of nickel, manganese, or nitrogen results in a face-centred cubic crystal structure. Typically containing 17% to 25% chromium and 8% to 20% nickel, grades exceeding 6% molybdenum are termed super austenitic steels, offering enhanced resistance to crevice corrosion and cracking.
Austenitic stainless steel exhibits excellent ductility, creep resistance, tensile strength, and fatigue resistance, making it highly suitable for welding. Generally non-magnetic, it can become magnetic through cold forming processes. Austenitic stainless steel cannot be heat-treated but achieves higher strength through cold working.
Austenitic stainless steel finds extensive applications across aerospace, chemical processing, automotive, food processing, and household hardware sectors. Common grades include 303, 304, 316, 310, and 321.
Ferritic Stainless Steels
As the second major category of stainless steel, ferritic stainless steel possesses a body-centred cubic crystal structure. It typically contains 10.5% to 27% chromium with minimal or no nickel content, offering excellent cost-effectiveness.
Ferritic stainless steel is magnetic, exhibiting excellent ductility and weldability, along with good tensile strength, creep resistance, and fatigue resistance. Its formability and corrosion resistance are inferior to austenitic stainless steel, and its strength is generally moderate. Like austenitic stainless steel, it cannot be hardened through heat treatment but can be strengthened through cold working.
Ferritic stainless steel is commonly used in automotive components and building structures. It also appears in food processing equipment, kitchen appliances, and certain chemical processing applications. In summary, when cost and performance are primary considerations for your project, ferritic stainless steel is a solid choice. Common grades include 409, 429, and 430.
Martensitic Stainless Steels
Martensitic stainless steel is the least common type of stainless steel, characterised by its lower chromium content and body-centred tetragonal crystal structure. Generally, its physical properties resemble those of ferritic and austenitic stainless steels, with the distinction lying in its chemical composition. It offers an exceptionally diverse range of properties, making it suitable for use as stainless engineering steel, stainless tool steel, and creep-resistant steel.
Martensitic stainless steel exhibits outstanding strength and can be hardened through heat treatment and cold working, making it highly suitable for applications requiring high tensile strength. It possesses excellent machinability and is magnetic under all conditions. However, its ductility is limited, and its weldability and formability are poor. Its corrosion resistance is inferior to that of austenitic and ferritic stainless steels, so coatings are often applied to its surface to enhance corrosion resistance during use.
Martensitic stainless steel is widely used in medical devices, serving as a common medical-grade stainless steel. Beyond this, it finds applications in jet engines, petrochemical equipment, and industrial components. Common grades include 410, 420, and 440.
Duplex Stainless Steels
Duplex stainless steel possesses a mixed microstructure of austenite and ferrite phases, thereby combining partial properties of both. The ideal ratio is 50:50, but the phase proportions in commercial duplex stainless steel typically fluctuate between 40% and 60%. It contains relatively high chromium levels, typically ranging from 19% to 32%, with molybdenum content reaching up to 5%. Nickel content is lower, and nitrogen is added to stabilise the austenitic structure and enhance corrosion resistance. Based on varying corrosion resistance, it can be classified into economical duplex steel, standard duplex steel, super duplex steel, and extra-super duplex steel.
Due to its ferritic internal structure, duplex stainless steel exhibits magnetic properties. Its yield strength is twice that of austenitic stainless steel, coupled with superior corrosion resistance, particularly against chloride pitting and crevice corrosion. However, its higher hardness and strength result in poorer machinability compared to austenitic or ferritic stainless steels.
Initially adopted in the papermaking industry, it has gradually become the material of choice for demanding applications in sectors like oil and gas, marine engineering, and petrochemical storage tanks, piping systems, and coastal structures. Common duplex stainless steel grades include 2205 and 2507.
Precipitation Hardening (PH) Steels
Precipitation-hardening stainless steel is renowned for its exceptional strength. Typically containing 12% to 16% chromium and 3% to 9% nickel, it incorporates trace amounts of aluminium, copper, niobium, titanium, and other elements as precipitation hardeners. Its corrosion resistance rivals that of austenitic stainless steel, yet its yield strength can reach four times that of austenitic grades while offering superior ductility and weldability compared to martensitic stainless steel.
Metallographically, precipitation-hardening stainless steels are primarily classified into three categories: martensitic, semi-austenitic, and austenitic. Among these, martensitic grades like 17-4PH are the most commonly used.
Their exceptional strength makes them ideal for nuclear power, aerospace, petrochemical, and other high-tech industries, including applications such as landing gear, structural components, reactor parts, and valve stems.
Comparison
| Tensile Strength | Corrosion Resistance | Machinability (Cutting/Forming) | Classic Grade | |
| Austenitic Stainless Steels | Low（~200-300 MPa） | Excellent (especially against uniform corrosion) | Excellent (Excellent ductility, suitable for cold working) | 304, 316 |
| Ferritic Stainless Steels | Medium（~250-350 MPa） | Moderate (good stress corrosion resistance, average pitting resistance) | Good (Easy to machine, but limited deep drawing capability) | 430, 444 |
| Martensitic Stainless Steels | High（>1000 MPa） | Low (suitable only for mild environments) | Poor (High hardness, prone to brittle fracture) | 410, 440 |
| Duplex Stainless Steels | High（~450-600 MPa） | Excellent (particularly against pitting and SCC) | Average (High strength results in high cutting forces) | 2205, 2507 |
| Precipitation Hardening (PH) Steels | Very High（ >1100 MPa） | Good (close to 304) | Poor (Extremely high hardness after age hardening) | 17-4PH, 15-5PH |
Common Grades of Stainless Steel
301
301 contains 16%-18% chromium and 6%-8% nickel, offering outstanding ductility, corrosion resistance, high-temperature performance, and weldability. It exhibits excellent work-hardening properties and is commonly used in medical devices and tableware.
304
304 stainless steel possesses higher nickel and chromium content, typically 18%-20% chromium and 8%-10.5% nickel. It exhibits outstanding tensile strength, excellent corrosion resistance, good ductility, temperature resistance, and weldability. It can be cold-work hardened but cannot be heat-treated. 304 stainless steel is commonly used in marine components, surgical instruments, offshore projects, and kitchenware.
316
316 stainless steel contains 16%-18% chromium and 10%-14% nickel, with an additional 3%-4% molybdenum. This composition provides exceptional resistance to chloride corrosion. It also offers good temperature resistance, ductility, and weldability, and can be hardened through cold working. 316 stainless steel is an ideal material for the marine industry and is also commonly used in medical, petrochemical, and food processing applications.
317
317 stainless steel contains slightly higher levels of chromium, nickel, and molybdenum than 316 stainless steel. Consequently, it exhibits exceptional resistance to chloride pitting corrosion. It also possesses excellent weldability, ductility, and high-temperature performance, and can undergo cold working and heat treatment. Its common applications include shipbuilding, petrochemicals, food processing, and papermaking industries.
321
321 stainless steel contains 17%-19% chromium and 9%-12% nickel. It exhibits outstanding high-temperature performance, maintains strength at low temperatures, and possesses excellent corrosion resistance, ductility, and weldability. 321 stainless steel can be work-hardened, offering superior stress-crack resistance compared to 304 stainless steel. It is commonly used for manufacturing aerospace engine components and accessories for food processing equipment.
410
410 stainless steel contains approximately 11.5%-13.5% chromium, with nickel content typically below 0.75%. It maintains strength at low temperatures, though its ductility and corrosion resistance are moderate. However, its corrosion resistance can be enhanced through heat treatment. 410 stainless steel is commonly used in knives, cutlery, mechanical parts, automotive components, pumps, valves, and similar products.
420
420 stainless steel contains 12%-14% chromium, with nickel content below 0.75% like 410. It is the hardest grade among all stainless steels, offering excellent cold-weather performance, good corrosion resistance, and ductility, though its weldability is poor. It can also be heat-treated. 420 stainless steel is commonly used for cutlery, knives, pumps and valves, hand tools, and similar applications.
430
430 stainless steel contains 16%-18% chromium and less than 0.75% nickel. It offers good resistance to nitric acid and excellent ductility, though its tensile strength is lower than most austenitic alloys. Its high-temperature performance and weldability are average, and it cannot be hardened through heat treatment. Common applications include architectural decoration, household appliances, kitchen equipment, and automotive components.
434
434 stainless steel offers higher strength than 430, with superior pitting resistance and high-temperature performance due to its 0.75%-1.25% molybdenum content. However, its ductility and weldability are average, and it can be hardened through heat treatment. It is commonly used in manufacturing automotive trim components, including door mouldings and bumpers.
2205
2205 stainless steel contains 22%-23% chromium, 4.5%-6.5% nickel, 3%-3.5% molybdenum, and 0.14%-0.2% nitrogen. It exhibits outstanding resistance to pitting and crevice corrosion, with corrosion resistance nearly double that of other austenitic stainless steels. 2205 stainless steel is an ideal material for demanding conditions, commonly used in marine engineering components, petrochemical pipeline systems and chemical equipment, wastewater management systems, and paper manufacturing equipment.
17-4
17-4 stainless steel contains 15%-17.5% chromium, 3%-5% nickel, and 3%-5% copper as key components. It combines outstanding strength with excellent corrosion resistance, making it common in aerospace, chemical, and petroleum industries.
15-5
15-5 stainless steel contains 14%-15.5% chromium, 3.5%-5.5% nickel, and 2.5%-4.5% copper. Its superior corrosion resistance, strength, and ductility make it an ideal choice for components in demanding industries such as aerospace.
Price of Different Types of Stainless Steel
The price of stainless steel is primarily determined by three factors: the nickel and molybdenum content of different grades, and the costs associated with their processing techniques. Due to its significant price volatility, nickel serves as the benchmark for stainless steel costs. Although nickel constitutes only 8% by weight in 304 stainless steel, its cost often accounts for over 50%-60% of the total. Molybdenum’s price fluctuations can sometimes exceed those of nickel, directly influencing the alloy surcharge (Alloy Surcharge).
When comparing per-ton prices of mainstream market products, precipitation-hardening stainless steel claims the top spot due to its high smelting and processing costs. Next comes high-molybdenum, high-nitrogen super duplex steel. Austenitic (molybdenum-containing) stainless steel occupies the mid-range price bracket, yet its dual reliance on nickel and molybdenum still positions it as a high-cost material. Standard austenitic stainless steel represents the largest market volume with the most frequent price fluctuations. Following this are economical duplex grades with low nickel content, along with nickel-free ferritic and martensitic stainless steels, which exhibit exceptionally stable pricing.
Beyond these factors, market supply and demand dynamics, macroeconomic conditions, and material specifications all influence stainless steel pricing.
Choosing the Right Type of Stainless Steel
When selecting the appropriate stainless steel type for your project, multiple factors must be considered. The following aspects can guide your choice of stainless steel suitable for your project.
Operating Environment
Analysing your project’s target operating conditions is the first step in selecting the right stainless steel type. This includes the working environment’s temperature, load conditions, pH level, and whether it involves abrasive conditions. For instance, if your environment is marine or otherwise corrosive, you need a stainless steel type with strong corrosion resistance, particularly seawater resistance. If your application requires bearing significant loads, a high-strength stainless steel type is necessary.
Formability & Weldability
If your product requires deep drawing, bending, stamping, or similar processes, the formability of the stainless steel must be considered. For instance, deep drawing and expansion bending require austenitic stainless steel with high ductility. If you plan to weld stainless steel to other metals, the weldability of the steel must also be evaluated.
Cost
Cost is undoubtedly a critical operational factor for all projects. However, beyond the initial purchase price, we recommend adopting a total lifecycle cost perspective to assess the long-term benefits of higher-priced materials.
Conclusion
This article provides a comprehensive overview of the primary stainless steel families and common stainless steel grades. If you are selecting the appropriate grade for your stainless steel project, we hope this article offers valuable guidance. Similarly, if you still have questions regarding material selection, we—Pingheng Machinery, a professional investment casting foundry with 26 years of expertise in stainless steel investment casting—are delighted to assist you. We can cast a wide range of stainless steel grades, including 304 and 316. Simply send us your project details, and our technical team will provide you with the most professional solution.
FAQ
Will Stainless Steel Get Rust?
Although stainless steel exhibits outstanding corrosion resistance among alloys, if its surface passivation layer is continuously compromised, it may eventually succumb to pitting corrosion, crevice corrosion, or rusting over time. For more information on stainless steel corrosion, please read our blog post “Why Does Stainless Steel Rust?”
What is the main difference between the most commonly used 304 and 316 stainless steels?
The key distinction lies in the presence of approximately 2-3% molybdenum (Mo) in 316 stainless steel. This significantly enhances its resistance to chloride corrosion, particularly against pitting and general corrosion, compared to 304 stainless steel. If your project demands superior corrosion resistance, 316 stainless steel would be the better choice. If you want to know more about the differences and similarities between 304 and 316 stainless steel, please click “304 vs 316 Stainless Steel – the Ultimate Guide for Beginners and Experts”.
Which is more expensive between duplex stainless steel 2205 and 316, and how should one choose?
Duplex stainless steel 2205 carries a higher price tag than 316 stainless steel, reflecting its superior performance. If your project demands both high strength and excellent resistance to chloride stress corrosion cracking, 2205 is the superior choice. Its yield strength is nearly double that of 316 stainless steel, delivering superior performance in demanding conditions — particularly in harsh environments like seawater chemical processing. While the initial cost is higher, its lifecycle cost proves more advantageous in the long run.
Which stainless steel is more suitable for extremely high-temperature conditions?
For products requiring long-term operation in high-temperature environments, the material’s oxidation resistance and creep resistance are critical. Generally, 430 stainless steel and 310S stainless steel are common choices.
What are the Advantages of Stainless Steel？
Corrosion-Resistant
This is the most prominent characteristic of stainless steel. Its high chromium content enables stainless steel to react with oxygen when exposed to air, forming an extremely thin, dense, and self-repairing passivation layer. This layer can rapidly regenerate using atmospheric oxygen after damage, effectively shielding the underlying material from external corrosive agents.
Heat Resistant
Austenitic stainless steels generally exhibit excellent high-temperature performance, with 310S standing as a benchmark material for high-temperature applications, maintaining good creep rupture strength at elevated temperatures. While ferritic and martensitic stainless steels are inferior to austenitic grades in high-temperature performance, they remain suitable for typical high-temperature working environments.
High Strength
Austenitic stainless steels, duplex stainless steels, and precipitation-hardening stainless steels all achieve outstanding strength after cold working.
Excellent Surface Finish
Stainless steel surfaces are smooth, and their modern silver-white appearance offers both aesthetic appeal and exceptional hygienic properties. The smooth (low roughness) surface makes bacterial adhesion difficult, providing inherent antibacterial characteristics.
Recyclable
Recyclability is a standout feature in today’s sustainability-focused environment. Stainless steel is theoretically 100% recyclable, and recycling does not compromise its properties.
Low Life Cycle Cost (LCC)
This is a standout characteristic of stainless steel in infrastructure and industrial equipment, making it the preferred material over carbon steel for numerous projects. Although its initial cost is higher, its simple maintenance and long service life result in a significantly lower life cycle cost over the long term.
Biocompatibility
In food processing and biomedical applications, stainless steel is utilised for manufacturing food processing equipment and medical implants due to its non-toxicity and absolute inertness in liquid environments. This makes it the industry standard for food-grade and implant-grade materials.
