At Goodfellow, we understand that the foundation of innovation lies in thoughtful material selection. Among the most versatile and essential materials in modern engineering are stainless steels, renowned for their exceptional strength, corrosion resistance, and adaptability across a wide range of environments. These attributes make stainless steels vital to industries such as chemical processing, medical technology, aerospace, construction, and energy.
Stainless steels comprise a versatile group of high-performance alloys defined by a minimum chromium content of 10.5%, which facilitates the formation of a protective passive oxide layer that resists corrosion. Their wide-ranging properties arise from differences in alloy composition and heat treatment, which shape their internal microstructure. At room temperature, stainless steels are generally categorized into five main types: austenitic, ferritic, martensitic, duplex, and precipitation-hardening. Each class offers unique combinations of hardness, ductility, corrosion resistance, and magnetic properties, allowing engineers to select and customize materials for specific functional requirements.
Fundamental Microstructure
Solid metals and alloys consist of grains, each possessing a distinct crystalline lattice. In stainless steels, these lattices can take several forms and form the foundation of stainless-steel performance, linking composition, processing, and properties:
| Crystal Type | Structure | Typical Phase | Magnetism |
|---|---|---|---|
| FCC | Face-Centered Cubic | Austenite | Non-magnetic |
| BCC | Body-Centered Cubic | Ferrite | Magnetic |
| BCT | Body-Centered Tetragonal | Martensite | Magnetic |
| FCC + BCC | Mixed | Austenite + Ferrite | Magnetic |
| BCT (precipitated) | Body-Centered Tetragonal or Body-Centered Cubic lath | Austenite + Martensite | Magnetic |
Key Alloying Elements & Their Effects
Stainless steel contains a variety of alloying elements, each added to enhance specific mechanical, chemical, or physical properties such as corrosion resistance, strength, and formability. The most critical element is chromium, but others play vital roles depending on the grade and application.
| Element | Role and Effects |
|---|---|
| Chromium (Cr) | All SS has minimum of 10.5% of Cr, forms a passive oxide film for corrosion resistance, oxidation resistance at high temperature, stabilize ferritic structure. |
| Nickel (Ni) | Stabilizes austenitic microstructure; improves ductility, toughness, and corrosion resistance especially in acidic environment. |
| Carbon (C) | Increases hardness and strength; excessive amounts can reduce weldability. |
| Manganese (Mn) | Enhances strength and hot workability; can substitute for nickel in some grades. |
| Molybdenum (Mo) | Boosts resistance to uniform and localised corrosion, increase mechanical strength, promotes ferritic microstructure. |
| Silicon (Si) | Improves oxidation resistance, increase strength, stabilize ferritic microstructure. |
| Nitrogen (N) | Increases mechanical strength and localised corrosion resistance, stabilizes austenitic structure. |
| Titanium (Ti) | Stabilizes ferrite structure, prevents carbide precipitation, improves weldability, corrosion resistance, improves mechanical properties at high temperature. |
| Niobium (Nb) | Similar to titanium, used in stabilization and precipitation hardening, improves corrosion resistance and enhance properties at high temperature. |
| Aluminum (Al) | Enhances oxidation resistance in heat-resistant grades. |
| Copper (Cu) | Improves corrosion resistance in certain acidic environments, decrease work hardening, improves formability. |
| Cobalt (Co) | Increase hardness and tempering resistance in martensitic steels, stabilizes austenitic phase. |
| Phosphorus (P) | Strengthens steel but can reduce toughness if excessive. |
| Sulfur (S) | Improves machinability but can reduce corrosion resistance. |
Classification & Characteristics
Austenitic Stainless Steels
Austenitic grades represent the largest and most versatile family of stainless steels with 17-18% Cr and 8-11% Ni. Their microstructure, face-centred cubic (FCC), is stabilized by nickel, manganese, and nitrogen additions.
Key Properties
- Non-magnetic in the annealed state.
- Excellent ductility, toughness, and formability.
- Good to excellent corrosion resistance, enhanced by molybdenum in grades such as 316.
- Hardenable only by cold work.
- Superior performance at cryogenic temperatures due to their good impact strength.
Typical Applications
Chemical plants, food processing, marine structures, cryogenic systems, aerospace, exhaust systems, medical devices, seismic applications.
Representative Grades
| UNS | EN | AISI | Composition & Properties |
|---|---|---|---|
| S30400 | 1.4301 | 304 | The standard 18Cr-8Ni grade (18-8 stainless); used in piping and kitchen equipment. |
| S30403 | 1.4307 | 304L | Low-carbon variant for improved weldability; used in welded structures and tanks. |
| S31600 | 1.4401 | 316 | Mo-alloyed for improved pitting resistance; used in marine hardware, medical implants, and chemical processing. |
| S31603 | 1.4404 | 316L | Low-carbon 316; widely used in welded fabrications, marine piping, and surgical tools. |
| S31703 | 1.4438 | 317L | Higher Mo for aggressive environments; used in marine and coastal structures, petrochemical, and refinery applications. |
| S32100 | 1.4541 | 321 | Ti-stabilized against intergranular corrosion for high-temperature use; employed in exhaust systems, aerospace, and heat exchangers. |
| S34700 | 1.4550 | 347 | Nb-stabilized; excellent corrosion resistance and suitable for elevated temperatures; used in turbine engine components, reactor vessels, and boiler tubes. |
| N08904 | 1.4539 | 904L | Super austenitic, high-alloyed, excellent chloride and acid resistance; used in battery components, acid-resistant connectors, pressure vessels, and structural components. |
| S31254 | 1.4547 | 254 SMO® | Super austenitic, resists pitting, crevice, and stress corrosion cracking; used in seawater piping, chemical processing equipment, and flue gas scrubbers. |
Ferritic Stainless Steels
Ferritic steels have a body-centred cubic (BCC) structure. They are iron-chromium alloys containing 10.5-18% chromium and minimal nickel and cost-effective.
Key Properties
- Magnetic; strengthened by cold work.
- Highly resistant to chloride induced stress corrosion cracking (SCC).
- Lower thermal expansion and higher thermal conductivity than austenitic grades.
- Moderate strength and formability.
Typical Applications
Automotive components, heat exchangers, furnace components and domestic appliances.
Representative Grades
| UNS | EN | AISI | Composition & Properties |
|---|---|---|---|
| S43000 | 1.4016 | 430 | Standard ferritic grade; 16–18% Cr; used in kitchen appliances and architectural panels. |
| S40900 | 1.4512 | 409 | Low Cr, good oxidation resistance; used in automotive exhaust systems and catalytic converter housings. |
| S43932 | 1.4510 | 439 | Ti-stabilized with improved corrosion resistance and weldability; used in automotive fuel tanks, heat exchangers, and solar water heaters. |
| S44400 | 1.4521 | 444 | ~18% Cr; Mo-alloyed for pitting corrosion resistance; used in marine environments and hot water tanks. |
| S44600 | 1.4749 | 446 | ~24% Cr; excellent oxidation and heat resistance; used in furnace parts and heat exchangers. |
| S43035 | 1.4017 | 434 | ~16–18% Cr, 1% Mo; enhanced corrosion resistance; used in automotive trim and kitchen appliances. |
Martensitic Stainless Steels
Martensitic steels possess a body-centred tetragonal (BCT) structure and derive their strength from heat treatment. They contain higher carbon content than ferritic grades.
Key Properties
- Magnetic and hardenable by heat treatment.
- High strength and hardness, high wear resistance but limited formability and weldability.
- Moderate corrosion resistance and good wear resistance.
Typical Applications
Cutlery, turbine blades, valves, pump shafts, and surgical instruments, aircraft parts.
Representative Grades
| UNS | EN | AISI | Composition & Properties |
|---|---|---|---|
| S41000 | 1.4006 | 410 | ~12% Cr; good wear and moderate corrosion resistance; used in turbine blades, fasteners, and bolts. |
| S42000 | 1.4021 | 420 | Higher C for improved hardness; used in surgical tools. |
| S41600 | 1.4005 | 416 | Sulphur-added variant for enhanced machinability; used in gears and bolts. |
| S43100 | 1.4057 | 431 | ~16% Cr, ~2% Ni; high strength and toughness with better corrosion resistance; used in marine and aircraft parts. |
Duplex Stainless Steels
Duplex steels combine both ferrite and austenite phases in roughly equal proportions, providing a superior balance of strength and corrosion resistance.
Key Properties
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High yield strength (typically twice that of austenitic steels).
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Excellent resistance to corrosion and cost effective.
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Moderate toughness and limited-service temperature range (-40 °C to ~300 °C).
Typical Applications
Desalination equipment, offshore platforms, chemical processing, and structural components in chloride-rich environments, heat exchangers.
Representative Grades
| UNS | EN | Common Name | Composition & Properties |
|---|---|---|---|
| S32205 | 1.4462 | 2205 | ~22% Cr, 3% Mo, and 5–6% Ni; high strength with excellent resistance to pitting and stress corrosion cracking; used in marine structures, oil and gas tanks. |
| S32101 | 1.4162 | 2101 | ~21% Cr; lean duplex, cost-effective with good strength; used in bridges and storage tanks. |
| S32304 | 1.4362 | 2304 | ~23% Cr; lean duplex, economical with balanced corrosion resistance; used in structural components. |
| S32750 | 1.4410 | 2507 | ~25% Cr; super duplex with exceptional resistance to pitting and stress corrosion cracking; used in offshore platforms. |
| S32760 | 1.4501 | 4501 | Super duplex with W and Cu additions; excellent corrosion resistance and high strength; used in marine structures, oil and gas platforms, and heat exchangers. |
Precipitation Hardening Stainless Steels
PH steels are a class of stainless steel strengthened through precipitation hardening (ageing), forming fine intermetallic compounds that obstruct dislocation movement.
Key Properties
-
Magnetic.
-
High yield and tensile strength after ageing with good corrosion resistance.
-
Strengthened by precipitation of fine particles.
Typical Applications
Aerospace components, energy systems, petrochemical hardware, and precision instruments, medical, marine applications.
Representative Grades
| UNS | EN | Common Name | Composition & Properties |
|---|---|---|---|
| S17400 | 1.4542 | 17-4PH / 630 | ~17% Cr, ~4% Ni, Cu and Nb alloyed; combines strength and corrosion resistance with excellent weldability; used in medical, nuclear, and chemical processing applications, as well as aerospace. |
| S17700 | 1.4568 | 17-7PH | ~17% Cr, ~7% Ni; good formability and high strength; used in automotive, aerospace, and industrial equipment. |
| S15700 | 1.4574 | 15-7PH | ~15% Cr, ~7% Ni, Mo alloyed; used in high-performance displays, catalyst carriers in emission control systems, and precision components in turbine and heat exchanger assemblies. |
Fabrication & Processing of Stainless Steel
Stainless steel fabrication involves transforming raw stainless steel into finished components through cutting, forming, welding, machining and finishing processes.
- Cutting is one of the foundational steps in stainless steel fabrication, and it encompasses several techniques depending on the precision, thickness, and finish required. Techniques involve plasma or laser cutting, mechanical sawing, punching.
- Forming stainless steel involves shaping it through mechanical processes like bending, drawing, spinning, roll forming and press forming. These techniques require careful control due to stainless steel’s strength and tendency to work harden.
- Welding stainless steel is a critical process in fabrication, known for its strength, corrosion resistance, and clean finish. Stainless steel can be welded using several methods, each suited to different applications and material thicknesses. It could be fusion where, base metals are melted to form a joint, often with the addition of a filler material (manual metal arc, metal inert gas, tungsten inert gas, laser beam welding) or pressure welding, where metals are joined by applying mechanical force, with or without heat, to create a bond through plastic deformation (resistance spot, seam welding and high frequency welding).
- Machining stainless steel involves removing material from a workpiece using tools like drills, mills, and lathes. Common machining processes are turning, milling, drilling, grinding and tapping.
- Finishing processes in stainless steel fabrication enhance appearance, improve corrosion resistance, and prepare surfaces for specific applications. Common methods include mechanical polishing, chemical treatments, and specialized coatings.
Selecting the Appropriate Stainless Steel
When selecting a stainless steel, engineers must balance mechanical performance, fabrication requirements, cost requirements and corrosion environment. Key considerations include:
- Operating temperature and exposure conditions.
- Fabrication method (welding, forming, machining).
- Mechanical strength and hardness requirements.
- Required resistance to specific corrosion types (pitting, SCC, intergranular).
- Regulatory or hygiene standards, surface aspects (e.g., food, medical, or aerospace compliance).
- Availability, life cycle cost, recyclability and standards.
Goodfellow’s technical experts provide consultation to ensure the correct alloy and form are selected for your application.
Goodfellow Stainless Steels in Research
Goodfellow Grades |
Research Papers |
|
| AISI 304 | Mondal J, Marandi M, Kozlova J, Merisalu M, Niilisk A, Sammelselg V. Protection and functionalizing of stainless steel surface by graphene oxide-polypyrrole composite coating. J. Chem. Chem. Eng. 2014;8(8):786-93. | Research Paper Link |
| Polanco R, De Pablos A, Miranzo P, Osendi MI. Metal–ceramic interfaces: joining silicon nitride–stainless steel. Applied surface science. 2004 Nov 15;238(1-4):506-12. | Research Paper Link | |
| AISI 310 | long Li X, Wei X, Lu J, Ding J, Wang W. Corrosion resistance of 310S and 316L austenitic stainless steel in a quaternary molten salt for concentrating solar power. Energy Procedia. 2017 Dec 1;142:3590-6. | Research Paper Link |
| AISI 316 | Hoppius JS, Kukreja LM, Knyazeva M, Pöhl F, Walther F, Ostendorf A, Gurevich EL. On femtosecond laser shock peening of stainless steel AISI 316. Applied Surface Science. 2018 Mar 30;435:1120-4. | Research Paper Link |
| Polanco R, De Pablos A, Miranzo P, Osendi MI. Metal–ceramic interfaces: joining silicon nitride–stainless steel. Applied surface science. 2004 Nov 15;238(1-4):506-12. | Research Paper Link | |
| AISI 316L | long Li X, Wei X, Lu J, Ding J, Wang W. Corrosion resistance of 310S and 316L austenitic stainless steel in a quaternary molten salt for concentrating solar power. Energy Procedia. 2017 Dec 1;142:3590-6. | Resarch Paper Link |
| Tardio S, Abel ML, Carr RH, Watts JF. The interfacial interaction between isocyanate and stainless steel. International Journal of Adhesion and Adhesives. 2019 Jan 1;88:1-0. | Resarch Paper Link | |
| Taer E, Deraman M, Talib IA, Awitdrus A, Hashmi SA, Umar AA. Preparation of a highly porous binderless activated carbon monolith from rubber wood sawdust by a multi-step activation process for application in supercapacitors. International journal of electrochemical science. 2011 Aug 1;6(8):3301-15. | Resarch Paper Link | |
| AISI 321 | Polanco R, De Pablos A, Miranzo P, Osendi MI. Metal–ceramic interfaces: joining silicon nitride–stainless steel. Applied surface science. 2004 Nov 15;238(1-4):506-12. | Research Paper Link |
Why Partner with Goodfellow?
- Extensive Alloy Portfolio: Access an unparalleled range of stainless steels and specialty alloys, from standard engineering grades to super austenitic, duplex, and precipitation-hardening compositions. Each material is supported by precise specification data and quality assurance documentation.
- Flexible Supply Options: Choose from a wide selection of product forms, wire, foil, sheet, tube, powder, and rod, available in both laboratory-scale quantities and production volumes. This flexibility ensures continuity from research and prototyping to industrial application.
- Technical Collaboration: Our in-house materials scientists and metallurgists provide expert guidance on alloy selection, processing, and application matching, helping customers select the most suitable stainless-steel grade or alloy for their performance requirements.
- Global Logistics and Traceability: With worldwide distribution, rapid delivery, and fully traceable materials, Goodfellow ensures consistent quality and reliability for both academic and industrial research customers.
References & Further Reading
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Tuthill, A. H., & Covert, R. A. (2000). Stainless steels: An introduction to their metallurgy and corrosion resistance. Dairy Food and Environmental Sanitation, 20, 506–517.
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Outokumpu. (n.d.). Outokumpu stainless steel handbook. https://steel-sci.com/assets/outokumpu-stainless-steel-handbook.pdf
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Afshan, S., Arrayago Luquin, I., Gardner, L., Gedge, G., Jandera, M., Real Saladrigas, E., Rossi, B., Stranghoner, N., & Zhao, O. (n.d.). Design manual for structural stainless steel.
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Bhadeshia, H. K. D. H., & Honeycombe, R. W. K. (2017). Steels: Microstructure and properties. Butterworth-Heinemann.
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Baddoo, N. R. (2008). Stainless steel in construction: A review of research, applications, challenges and opportunities. Journal of Constructional Steel Research, 64(11), 1199–1206.
