Stainless steel is one of the most versatile and widely used materials in modern engineering, architecture, energy, and manufacturing. Known for its durability, corrosion resistance, and aesthetic appeal, stainless steel comes in many grades and families.
While there are over 150 different stainless steel grades, they can be classified into four main types based on their microstructure and chemical composition. Understanding these four types helps engineers, fabricators, and buyers choose the right alloy for their specific application.
In this detailed article, SAKYSTEEL, a global supplier of premium stainless steel materials, explains the four major types of stainless steel, their properties, applications, and advantages.
Stainless steel is an iron-based alloy that contains at least 10.5 percent chromium. The chromium reacts with oxygen in the atmosphere to form a thin, passive oxide layer that protects the metal surface from corrosion and rust.
By varying the content of chromium, nickel, carbon, molybdenum, and other elements, engineers can develop stainless steels with unique properties suited for different industries such as chemical processing, oil and gas, food production, and marine construction.
All stainless steels are resistant to rust, but their strength, formability, weldability, and corrosion performance vary depending on their microstructure. These variations form the basis of the four main types of stainless steel.
The four main families of stainless steel are:
Austenitic Stainless Steel
Ferritic Stainless Steel
Martensitic Stainless Steel
Duplex (Austenitic-Ferritic) Stainless Steel
Each type has its own metallurgical characteristics, making it suitable for specific applications and environments.
Austenitic stainless steel is the most common and widely used type, representing more than 70 percent of all stainless steels produced worldwide. Its microstructure is face-centered cubic (FCC), giving it excellent ductility, toughness, and corrosion resistance.
Austenitic stainless steels contain high levels of chromium (16–26 percent) and nickel (6–22 percent), with low carbon content. The addition of nickel stabilizes the austenitic structure and enhances corrosion resistance.
Common grades include:
304 and 304L (UNS S30400/S30403)
316 and 316L (UNS S31600/S31603)
321 (stabilized with titanium)
310 and 309 (heat-resistant grades)
Excellent resistance to corrosion and oxidation
Non-magnetic in annealed condition
Excellent formability and weldability
Retains toughness at cryogenic temperatures
Austenitic stainless steels are used in:
Chemical and food processing equipment
Marine fittings and shipbuilding
Heat exchangers and tanks
Architectural facades and handrails
Medical and pharmaceutical instruments
Austenitic stainless steels like 304 and 316 are ideal for environments where corrosion resistance, hygiene, and appearance are critical.
Ferritic stainless steels have a body-centered cubic (BCC) crystal structure and contain chromium as the main alloying element with little or no nickel. They are magnetic and have lower ductility compared to austenitic steels but are more resistant to stress corrosion cracking.
Typical composition includes 10.5–30 percent chromium and very low carbon content (below 0.08 percent).
Common grades include:
409 and 430 (basic ferritic grades)
434 and 436 (with molybdenum for improved corrosion resistance)
446 (high chromium, heat-resistant grade)
Moderate corrosion resistance
Good oxidation resistance
Magnetic and not hardenable by heat treatment
Lower cost due to low nickel content
Limited formability compared to austenitic grades
Ferritic stainless steels are widely used in:
Automotive exhaust systems
Industrial furnaces and heat exchangers
Architectural trim and decorative panels
Appliances and kitchen equipment
Ferritic stainless steels are a cost-effective option for moderately corrosive environments, offering good resistance to oxidation and stress corrosion cracking.
Martensitic stainless steel is known for its high strength and hardness. It has a body-centered tetragonal (BCT) crystal structure formed through heat treatment. Unlike austenitic or ferritic grades, martensitic steels can be hardened by quenching and tempering.
Martensitic grades contain 11–18 percent chromium and higher carbon levels (up to 1.2 percent). Nickel may also be added in small amounts to improve toughness.
Common grades include:
410 and 420 (general-purpose, hardenable grades)
440A, 440B, and 440C (high-carbon tool steels)
High strength and wear resistance
Magnetic
Can be heat-treated to achieve hardness
Lower corrosion resistance than austenitic and duplex grades
Martensitic stainless steels are ideal for:
Cutting tools and blades
Turbine components
Pump shafts and valves
Surgical instruments and bearings
Martensitic stainless steels offer excellent mechanical strength and hardness, making them suitable for wear-resistant and mechanical components.
Duplex stainless steel combines the best features of austenitic and ferritic stainless steels. It contains a balanced microstructure of approximately 50 percent ferrite and 50 percent austenite, resulting in exceptional strength and corrosion resistance.
Typical composition includes 19–28 percent chromium, 3–8 percent nickel, and up to 5 percent molybdenum. The addition of nitrogen further enhances strength and pitting resistance.
Common grades include:
2205 (UNS S32205/S31803)
2507 (super duplex, UNS S32750)
329 (UNS S32900)
Twice the yield strength of austenitic stainless steels
Excellent resistance to pitting, crevice, and stress corrosion cracking
Good weldability and toughness
Moderate cost compared to high-nickel alloys
Duplex stainless steels are widely used in:
Offshore oil and gas platforms
Desalination plants
Chemical processing and petrochemical refineries
Marine pipelines and pressure vessels
Duplex stainless steels are the best choice for environments combining mechanical stress and high corrosion risk, offering outstanding long-term performance.
Each type of stainless steel family has its advantages and trade-offs. Understanding these helps in selecting the right material:
Austenitic: Best corrosion resistance, non-magnetic, easy to form and weld.
Ferritic: Magnetic, cost-effective, moderate corrosion resistance.
Martensitic: Hard and strong, suitable for wear and mechanical parts.
Duplex: Combines high strength with excellent chloride resistance.
For example, if you need stainless steel for food processing equipment, austenitic 316 is ideal. For automotive exhausts, ferritic 409 or 430 offers durability at low cost. For cutlery or blades, martensitic 420 or 440C provides hardness. For offshore pipelines, duplex 2205 or 2507 ensures safety and corrosion resistance.
Selecting the right stainless steel family ensures performance, longevity, and cost efficiency. Choosing the wrong type can result in corrosion failure, mechanical damage, or costly downtime.
Key factors to consider include:
Operating temperature and environment
Required strength and hardness
Weldability and fabrication needs
Cost versus performance balance
Understanding these four main types helps engineers match material properties with real-world conditions.
As an experienced stainless steel manufacturer and exporter, SAKYSTEEL supplies all major stainless steel families — austenitic, ferritic, martensitic, and duplex — in a full range of forms including bars, plates, tubes, and sheets.
Our stainless steels are certified according to ASTM, ASME, EN, and ISO standards, with complete EN 10204 3.1 and 3.2 inspection certificates available.
We serve customers in:
Oil and gas industry
Shipbuilding and marine sectors
Chemical and energy plants
Construction and machinery manufacturing
At SAKYSTEEL, we focus on delivering consistent quality, reliable traceability, and customized solutions for every project.
With industries moving toward sustainability, stainless steel continues to evolve. Modern innovations include lean duplex alloys with reduced nickel content and super-austenitic grades offering improved corrosion resistance.
The trend is toward materials that are:
Recyclable and energy-efficient
Corrosion-proof for longer life
Stronger yet easier to fabricate
This ensures stainless steel remains the material of choice for the future, balancing performance, durability, and environmental responsibility.
So, what are the four types of stainless steel?
They are Austenitic, Ferritic, Martensitic, and Duplex. Each family has unique strengths — from corrosion resistance and weldability to hardness and high strength.
Selecting the right type depends on your operating environment and performance requirements.
Whether you need stainless steel for marine structures, industrial equipment, or precision components, partnering with an expert supplier ensures long-lasting value.
With decades of industry experience, SAKYSTEEL continues to provide high-quality stainless steel products that meet international standards and deliver superior performance across industries.
Contact SAKYSTEEL today to learn more about which stainless steel type best fits your project needs and how we can help you achieve excellence in every application.