More than just a shiny metal, stainless steel is one of the most common materials in modern manufacturing. It offers a unique blend of strength, hygienic properties, and resistance to corrosion, heat, chemicals, and acidity. It is very common in several industries, from industrial food processing and healthcare to at-home appliances.
In this post, we will explore what stainless steel is, its history and production, its mechanical properties, and its applications across a variety of industries.
What is Stainless Steel?
It is a ferrous, or iron-based alloy containing a minimum of 10.5% chromium by mass. Chromium is what gives it its defining rust- and corrosion-resistance. Chromium gives the metal its shine by forming a thin, passive coating of chromium oxide, which in turn protects the underlying material from damage.
Additionally, it can contain other elements, such as manganese, molybdenum, and nickel, as well as nitrogen. Each additional element enhances specific properties, such as strength and various forms of resistance.
An Overview of the Families
The composition of each grade or type of this metal is for specific applications. Each of these grades is standardized and identified by its number, such as 304, 316, 409, and 430. The numbers indicate the alloy’s exact composition and properties. Common types include:
- Austenitic Stainless Steel: The makeup of this alloy is high in chromium and nickel. It is non-magnetic and has exceptional corrosion resistance. Austenitic includes the grades 304 and 316.
- Ferritic Stainless Steel: These grades are high in chromium and low in carbon. It is magnetic and has good corrosion resistance. Ferritic grades include 409 and 430.
- Martensitic Stainless Steel: These grades include 410 and 420 and contain moderate to high chromium and higher carbon. They are magnetic and can undergo hardening.
- Duplex Stainless Steel: A mixture of austenitic and ferritic formats, duplex delivers high strength, stress resistance, corrosion resistance, and resistance to cracking.
- Precipitation Hardening Stainless Steel: These grades can be heat-treated to harden and are ideal for high-strength applications such as aerospace.
A Comparison Table of the Stainless Steel Families
| Family | Microstructure | Key Alloying Elements | General Characteristics | Typical Applications |
|---|---|---|---|---|
|
Austenitic |
FCC |
Cr, Ni, Mo |
Excellent corrosion resistance, non-magnetic, formable. |
Food, Chemical, and Architecture |
|
Ferritic |
BCC |
Cr |
Good corrosion resistance, magnetic, and moderate strength. |
Automotive and Appliances |
|
Martensitic |
BCC |
Cr, C |
High strength/hardness, magnetic, and moderate corrosion. |
Cutlery, Tools, and Surgical Instruments |
|
Duplex |
Mixed FCC and BCC |
Cr, Ni, Mo, N |
High strength, excellent corrosion, and magnetic. |
Oil and Gas, Marine, and Chemical |
|
Precipitation Hardening (PH) |
Varies |
Cr, Ni, Cu, Al, Ti |
Very high strength after heat treatment and good corrosion. |
Aerospace and High-Strength Components |
What is the History of Stainless Steel?
British metallurgist Harry Brearley discovered stainless steel in 1913. Harry found that a chromium-iron alloy is resistant to corrosion while working on solutions to gun barrel erosion. This invention was initially called “rustless steel” and later came to be known as “stainless steel”. This breakthrough came after a century of experiments with steel-chromium alloys by scientists such as Michael Faraday. Brearley commercialized the first true stainless steel. Following the commercialization, rapid advancements led to the development of types such as 18-8 (18% chromium and 8% nickel) and duplex steels. These grades expanded their uses from cutlery and architectural structures to surgical implants and chemical processing equipment.
The Manufacturing and Fabrication Process Chain
There are several steps in manufacturing stainless steel, including the following:
- Melting and Refining: Raw materials such as stainless steel scrap, iron ore, nickel, and chromium are heated in an Electric Arc Furnace above 2800° F. The result is a molten bath. An Argon Oxygen Decarburization converter refines impurities, reduces carbon while limiting chromium loss, and achieves precise alloying of the materials.
- Casting: Continuous casting produces slabs, billets, or blooms for additional processing, while ingot casting is common for specialty or large-section products.
- Hot and Cold Rolling: Hot rolling reduces thickness, refines the grain structure, and produces plates, sheets, or structural shapes. On the other hand, cold-rolling reduces thickness while improving surface finish and dimensional accuracy. The largest difference between the two is strength – cold-rolled stainless steel wins; formability – hot-rolled stainless steel is more malleable; appearance – cold-rolled provides a superior aesthetic finish; and cost – hot-rolled is more cost-effective.
- Sheet Metal Fabrication: Cutting, shearing, blanking, bending, and forming require sharp tools and proper lubrication to prevent galling and excessive tool wear. Prototek’s laser cutting and waterjet cutting services, along with press brake services, can provide precise bends and cutting.
- Machining: Prototek offers CNC machining services, including turning, milling, and drilling, for shaping stainless steel with sharp carbide or HSS tools at slow speeds and high feed rates.
- Welding: TIG and MIG welding services are acceptable for stainless steel projects. They are especially relevant in automotive component and appliance manufacturing.
- Surface Finishing: There are several finishes for stainless steel. They include passivation, electropolishing, pickling, and brushing. These finishes can enhance aesthetics, improve corrosion resistance, and create uniform finishes.
- Heat Treatments: Annealing, solution treating, and stress relieving can restore ductility, relieve stresses, and optimize the material’s properties. Not all grades respond equally to heat treatments, and some cannot be hardened.
Stainless Steel Properties
Chemical Properties
- Corrosion/Oxidation Resistance: When chromium reacts with oxygen, a thin protective layer is formed (Cr2O3). This protective layer resists rust and corrosion, except under specific conditions, such as saltwater and low-oxygen environments.
- Self-Healing: If stainless steel is scratched or damaged, the protective layer reforms in the presence of oxygen.
- Biologically Inert: It’s hygienic and non-reactive, making stainless steel acceptable for surgical implants and medical devices. While generally inert, it can release small amounts of nickel and chromium.
- Chemical Stability: With a few exceptions (mentioned above), stainless steel is stable around chemicals.
- Alloying Elements: These elements can increase properties like nickel, which increases the resistance to acidic environments; molybdenum boosts resistance to pitting, nitrogen enhances yield strength, titanium acts as a stabilizer during welding, and manganese increases strength.
Physical Properties
- Density: Generally ranges between 7,500 and 8,000 kg/m3
- Melting Point: Generally ranges between 1,370° C and 1,540° C
- Thermal Properties: Low thermal conductivity, high thermal expansion, and high melting point.
- Magnetism: Varies based on the microstructure. Non-magnetic austenitic stainless steel to strongly magnetic ferritic and martensitic.
- Strength and Ductility: Tensile strength ranges from 483 to over 2,400 MPa, and yield strength from 170 to over 1,000 MPa.
- Appearance: The coloring is bright, silvery, and sleek with a range of matte to highly reflective/mirror-like finish.
Which Industries Use Stainless Steel?
Every major industry uses stainless steel. It offers a lot of important properties that make it valuable.
| Industry | Typical Applications | Recommended Grades | Key Standards/Regulations |
|---|---|---|---|
|
Food and Beverage |
Tanks, piping, conveyors, and work surfaces. |
304 and 316 |
3-A Sanitary, FDA, and ANSI/3-A |
|
Bioreactors, WFI systems, and surgical instruments. |
316/316L, 304, 420, and 440 |
FDA cGMP, ASME BPE, 3-A |
|
|
Exhausts, trim, pressure tanks, and structural parts. |
Content321, 347, 409, 430, and 434 |
ASTM, ASME, and ISO 9001 |
|
|
Storage tanks, piping, and reactors. |
316, 317, 309S, and 310S |
ASME BPVC and ASTM |
|
|
Construction and Architecture |
Cladding, roofing, railings, and supports. |
304, 316, and 430 |
ANSI/AISC 370 and AISC 313 |
|
Appliance exteriors, cutlery, and hardware. |
304, 420, and 430 |
ASTM |
|
|
Marine |
Boat fittings, seawater components, and pool equipment. |
316 |
ASTM A312/A778 |
Stainless Steel vs Other Materials
| Property | Stainless Steel | Carbon Steel | Aluminum | Titanium |
|---|---|---|---|---|
|
Corrosion Resistance |
Excellent |
Poor |
Good |
Excellent |
|
Strength/Durability |
High |
High |
Moderate |
Very High |
|
Hygienic |
Excellent |
Moderate |
Good |
Good |
|
Aesthetic Appeal |
High |
Moderate |
High |
Moderate |
|
Recyclability |
Very High |
High |
High |
Moderate |
|
Lifecycle Cost |
Low (Long-Term) |
High |
Moderate |
High |
|
Machinability |
Moderate |
Easy |
Easy |
Difficult |
|
Welding Complexity |
High |
Low |
Moderate |
High |
|
Thermal Expansion |
High |
Moderate |
High |
Moderate |
Stainless Steel In Review
With a polished and easy-to-clean surface, stainless steel also offers several other valuable attributes, such as corrosion and temperature resistance. The metal’s use spans domestic components and commercial applications, ranging from automotive to kitchenware and medical instruments. Its recyclability ensures its continued use.
FAQs
Define: Stainless Steel
It is a corrosion-resistant alloy of iron, chromium, and other elements, known for its durability, strength, and aesthetic appeal.
What industries use stainless steel?
It is common in most industries, such as food processing, pharmaceuticals, aerospace, and construction, due to its corrosion resistance and durability.
Which applications are stainless steel suitable for?
It is suitable for many applications. Food processing, medical equipment, and marine components are a few appexamples lications, dtheirto its corrosion resistance and durability.
How can stainless steel components be finished?
Stainless steel components can be finished through processes like polishing, passivation, and electroplating to enhance appearance and corrosion resistance.
What are the advantages of stainless steel?
It offers corrosion resistance, durability, and aesthetic appeal. It is highly resistant to rust, staining, and pitting. Its strength and toughness make for long-lasting performance, while its sleek, modern appearance enhances the visual appeal of products and structures.
What are the disadvantages of stainless steel?
It may corrode in certain environments, is more expensive than other materials, and can be more difficult to machine or weld.
What is the cost of stainless steel compared to other metals?
It is commonly more expensive than carbon steel but less expensive than metals like titanium and aluminum. The cost of stainless steel can vary. It really depends on the grade and market conditions.
