18/8 Stainless Steel: How It Is Made, Uses, and Properties
Often delineated as AISI 304, 18/8 stainless steel is an extensively utilized grade offering corrosion resistance, durability, and versatility. It contains 18% chromium and 8% nickel, along with a variety of other alloying elements. Due to its excellent corrosion resistance and toughness, 18/8 stainless steel is used in food processing equipment, kitchenware, architectural structures, automotive components, and medical equipment. Its properties make it suitable for applications requiring resistance to moderately aggressive environments, high temperatures, and high mechanical stress.
This article will discuss 18/8 steel, including how it is made, its uses, and its properties.
What Is 18/8 Stainless Steel?
18/8 stainless steel is a popular and versatile material used in various industries due to its exceptional corrosion resistance, durability, and high aesthetic appeal. 18/8 is a reference to its principal alloy composition of 18% chromium and 8% nickel content by mass.
Chromium forms a self-healing passive oxide layer on the surface of the steel, which acts as an oxygen barrier, protecting it from corrosion and staining, even in moderately harsh environments. Nickel enhances the steel's corrosion resistance and provides enhanced strength, corrosion resistance, formability, and luster. This makes it suitable for applications in which resilience, chemical resistance, strength, and appearance are important, such as: kitchenware, appliance panels, and architectural elements such as handrails and countertops.
What Is the Other Term for 18/8 Stainless Steel?
18/8 stainless steel is also known as Type 304 stainless steel. Multiple nomenclatures are used for stainless steels, with some issues in correlation between them.
The naming system for stainless steels can be complex and is primarily based on a combination of factors including: chemical composition, microstructure, and various standards set by organizations such as the American Iron and Steel Institute (AISI) and the International Organization for Standardization (ISO). Stainless steel grades are typically designated by numbers or alphanumeric codes. These grades relate to the alloy-element composition and properties of the steel. Stainless steels are primarily alloyed with chromium, nickel, molybdenum, titanium, silicon, nitrogen, and copper. Percentages of these elements denote the chemical composition of a stainless steel grade and these are used for designation of type.
How Is 18/8 Stainless Steel Made?
18/8 stainless steel is typically made through smelting in an electric arc furnace (EAF), which is the most common method for producing stainless steel.
The primary raw materials for making stainless steel are steel, chromium, and nickel along with other minor alloying elements such as manganese and molybdenum. In the EAF process, an electric arc furnace melts scrap metal, and alloying elements. The intense heat generated by the electric arc melts the raw materials, liquifying the charge. During smelting, precise amounts of alloy agents are added to achieve the desired composition, to ensure the correct balance of properties. The molten metal then undergoes refining processes to remove impurities and achieve the required cleanliness and homogeneity. Commonly, materials such as charcoal and lime are added to react with impurities and separate them as slag. Once the desired chemical composition is achieved, the molten stainless steel is cast into ingots, billets, or slabs ready for follow-on processing.
How Does 18/8 Stainless Steel Differ From 18/10 Stainless Steel?
18/8 stainless steel and 18/10 stainless steel are both austenitic stainless steels, appreciated for their excellent corrosion resistance and versatility. Both 18/8 and 18/10 stainless steels contain 18% chromium, which delivers the primary corrosion resistance through the formation of a passive oxide layer on the surface. The key difference between 18/8 and 18/10 stainless steels lies in their nickel content. 18/8 stainless steel contains 8% nickel, while 18/10 stainless steel contains 10% nickel. The higher nickel content in 18/10 stainless steel provides enhanced corrosion and reduced staining/pitting in certain environments compared to 18/8 stainless steel. The higher nickel content can contribute to a slightly brighter and more lustrous appearance. Both 18/8 and 18/10 stainless steels are commonly used in kitchenware, cutlery, appliances, and other applications in which corrosion resistance and aesthetics are important. However, 18/10 stainless steel may be preferred in more demanding environments or applications in which a higher level of corrosion resistance justifies the higher material cost.
What Grade Is 18/8 Stainless Steel?
The 18/8 designation corresponds to AISI (American Iron and Steel Institute) grade 304, which is one of the most common and widely used/referenced stainless steel grades.
What Are the Uses of 18/8 Stainless Steel?
18/8 stainless steel is widely used across most industries due to its excellent combination of corrosion resistance, durability, and versatility. Some of its uses include:
- Manufacturing of pots, pans, utensils, and other kitchen appliances due to its hygienic properties and resistance to corrosion, heat, and food acids.
- Used in producing equipment in food processing, such as: tanks, conveyors, piping, and machinery components for corrosion resistance and ease of cleaning.
- Used in architectural elements such as: handrails, door and window frames, facades, and decorative features for its balance of durability and cost.
- Used in many automotive parts, including: exhaust systems, trim, grilles, body panels, and fasteners for its corrosion resistance and strength.
- Used in medical and dental equipment due to its biocompatibility, corrosion resistance, and ease of sterilization.
- Used in construction for structural components, roofing, cladding, and handrails, making use of its strength, durability, and corrosion resistance.
- Used in marine environments due to its resistance to saltwater corrosion. It's used in boat fittings, marine hardware, and offshore structures. Other grades and alloys such as Monel® can offer higher resistance to chloride attack but at a greatly increased cost.
What Industries Utilize 18/8 Stainless Steel?
Most industries employ 18/8 stainless steel (AISI 304) due to its excellent corrosion resistance, durability, formability, and application versatility. Some examples are listed below:
- Food, Brewing, and Beverage: Use 18/8 stainless steel for equipment such as: tanks, piping, processing machinery, storage containers, and tools. Its corrosion resistance and hygienic properties make it ideal for applications in which food contact is involved.
- Automotive: Used for various components such as: exhaust systems, trim elements, grilles, fasteners, and decorative parts.
- Construction: Used for architectural elements like: handrails, door and window frames, façades, cladding, roofing, grilles, and decorative features.
- Medical and Pharmaceutical: Extensively used for manufacturing equipment, instruments, and sundry devices due to its biocompatibility, corrosion resistance, and ease of sterilization.
Why Use 18/8 Stainless Steel?
18/8 stainless steel is widely chosen for a huge range of applications for its balance of resistance to corrosion, heat, chemical damage, aesthetic appeal, and cost. It is often the preferred material due to its ease of fabrication, hygienic properties, and low maintenance requirements, contributing to its popularity across industries.
Is 18/8 Stainless Steel Suitable for Cookware?
Yes, 18/8 or 304 stainless steel is widely used for cookware and kitchen equipment due to its combination of toughness, moderate ductility in forming, and good resistance to both heat and corrosion in use and cleaning.
Can 18/8 Stainless Steel Be Used for CNC Machining?
Yes, 18/8 stainless steel is very commonly used for CNC machining components for many sectors and industries. Its excellent machinability characteristics suit it for various machining processes, including CNC processing.
18/8 stainless steel can be precisely machined to produce intricate components with tight tolerances. It exhibits good chip formation and chip evacuation properties, reducing the risk of tool wear and ensuring smooth machining operations. It maintains its mechanical properties and corrosion resistance after machining. However, appropriate machining parameters and cutting tools should be selected to optimize the machining process and minimize tool wear.
To learn more, see our full guide on CNC Machining Manufacturing.
What Are the Properties of 18/8 Stainless Steel?
Table 1 below shows a selection of important properties for 18/8 or 304 stainless steel:
| Property | Value |
|---|---|
Property Density | Value 8.0 g/cm³ |
Property Melting Point | Value 1,400–1,450 °C |
Property Thermal Conductivity | Value 16.2 W/m·K at 100 °C |
Property Electrical Resistivity | Value 720 nΩ·m at 20 °C |
Property Modulus of Elasticity | Value 193 GPa |
Property Poisson's Ratio | Value 0.29 |
Property Tensile Strength | Value 515 MPa |
Property Yield Strength | Value 205 MPa |
Property Hardness (Rockwell B) | Value 70–85 HRB |
Property Hardness (Brinell) | Value 201–262 HB |
Property Corrosion Resistance | Value Excellent |
Property Magnetic Properties | Value Non-magnetic |
These values are greatly affected by processing conditions and relatively small changes in alloying elements, so some variation between manufacturers and cold and hot rolling can be expected.
Are 18/8 Stainless Steels Weldable?
Yes, 18/8 stainless steel is generally considered weldable using common welding techniques such as: TIG (tungsten inert gas), MIG (metal inert gas), arc (stick) welding, as well as laser welding methods. However, there are some considerations to keep in mind. Preheating the material before welding and applying post-weld heat treatment may be necessary to prevent cracking and ensure proper weld integrity. Matching or slightly overmatching filler materials with a similar composition to the base metal (304 stainless steel) is recommended. Proper selection of welding parameters such as: heat input, travel speed, and shielding gas composition is crucial to achieving sound welds. To prevent contamination and maintain corrosion resistance, it's essential to use clean equipment, filler materials, and appropriate welding techniques.
Are 18/8 Stainless Steels Good Quality?
Yes, 18/8 stainless steel is generally perceived as a good-quality material. However, much depends on the nature of the application, so its suitability for aggressive chemical environments, extreme heat, marine applications, and high-stress/fatigue uses may render it unsuitable.
Does 18/8 Stainless Steel Have a High Rust Resistance?
In non-aggressive environments and with low exposure to high concentrations of chloride ions, 18/8 stainless steel is highly resistant to corrosion.
It is vulnerable to pitting corrosion when exposed to salt and some other chemistries, which can lead to brown spots, point-corrosion-forming pits, and the staining of surrounding materials with brown iron-oxide residues. Examples of this are pinhole failures in marine fuel tanks when exposed to saltwater, and brown point staining of the uncoated 304 or 18/8 sheet stainless steel used in Tesla vehicles (according to various internet-based discussions).
How Much Does 18/8 Stainless Steel Cost?
Typical prices for 18/8 stainless steel vary somewhat with process conditions. Cold-rolled coil sheets of a range of thicknesses are priced between $950 and $1,200 per tonne depending on the volume of bulk order. Small sheet purchases can be considerably more expensive, with 20 gauge ranging up to $100 per sheet (size variable). Rolled and welded tube prices vary between $1,100 and $4,300 per tonne.
Is 18/8 Stainless Steel Expensive?
Yes. 18/8 is among the more expensive grades of basic stainless steel, as it has a relatively high nickel and chromium content. Other grades such as the 400 series have either low- or zero-nickel content, making them lower cost. They also have quite different properties and are not necessarily interchangeable in most applications.
What Are the Advantages of 18/8 Stainless Steel?
18/8 stainless steel offers several advantages that make it a popular choice in various industries. Such advantages include:
- Has excellent corrosion resistance, particularly in environments in which exposure to moisture, chemicals, and corrosive substances is common.
- Offers high tensile strength and excellent durability, making it capable of withstanding heavy loads, impacts, and mechanical stresses.
- The surface of 18/8 stainless steel is non-porous, making it resistant to bacterial growth, easy to clean, and offering a low risk of cross-contamination and taint of the product.
- Has a bright, silver metallic finish that adds aesthetic appeal to products and structures, even after prolonged exposure to harsh environments.
- It is highly versatile and can be easily formed, machined, welded, and fabricated into complex and precise shapes and products.
- Recyclable, with no degradation in properties through multiple melt/reform cycles.
What Are the Disadvantages of 18/8 Stainless Steel?
While 18/8 stainless steel offers many advantages, there are also some potential drawbacks to consider, including:
- Can be relatively expensive because of the relatively high nickel content.
- Although 18/8 stainless steel is generally non-paramagnetic in its annealed state, it can become slightly magnetic after cold working or during certain machining processes, which is not desirable in some applications.
- While 18/8 stainless steel performs well under normal operating temperatures, it may not be suitable for applications involving high temperatures. It can experience reduced mechanical properties and potential flaky oxidation.
- In certain environments, it may require regular maintenance to preserve its surface finish and prevent staining or corrosion, particularly in highly corrosive or chlorinated environments.
What Are the Differences Between 18/8, 316, and 304 Stainless Steel?
18/8, 316, and 304 stainless steel are commonly used grades of stainless steel, but they differ in terms of composition, properties, and applications.
18/8 stainless steel contains 18% chromium and 8% nickel, with small amounts of manganese and silicon. 316 stainless steel contains 16–18% chromium, 10–14% nickel, 2–3% molybdenum, and small amounts of manganese and silicon. 304 stainless steel is closely related to 18/8 stainless steel, containing 18% chromium and 8% nickel, but commonly with slightly different trace-element compositions.
18/8 stainless steel offers good corrosion resistance in most environments but may be susceptible to pitting, stress corrosion cracking, and staining in chloride-rich environments. 316 stainless steel has superior corrosion resistance, particularly in chloride-rich environments such as coastal areas and marine applications, due to the addition of molybdenum. 304 stainless steel offers good general corrosion resistance, similar to 18/8 but cannot match 316, particularly in chloride-rich environments.
18/8 stainless steel offers good strength and toughness, suitable for a wide range of applications. 316 stainless steel generally has higher tensile and yield strength than 304. 304 stainless steel is essentially identical in strength to 18/8 stainless steel but may have slightly divergent mechanical properties.
In application terms, 18/8 and AISI 304 are used whenever corrosion resistance is required but environments offer lower chloride-ion exposure. 316 offers additional resistance to chlorides and acids.
To learn more, see our full guide on 18/8, 316, and 304 Stainless Steels.
What Are the Differences Between 18/8, 18/10, and 18/0 Stainless Steel?
The differences between 18/8, 18/10, and 18/0 stainless steel primarily lie in their nickel content, which affects their corrosion resistance and other properties:
18/8 stainless steel contains approximately 18% chromium and 8% nickel. It offers good corrosion resistance and durability. It is suitable for a wide range of applications including: kitchenware, cookware, appliances, and architectural structures.
18/10 stainless steel contains approximately 18% chromium and 10% nickel. Its higher nickel content provides generally enhanced properties and higher luster in polished finishes. It offers enhanced corrosion resistance, particularly in aggressive environments. It is often preferred for applications requiring superior resistance to corrosion and staining, such as high-end kitchenware and cutlery.
18/0 stainless steel contains approximately 18% chromium and no nickel. It offers good corrosion resistance in mild environments, but lower than 18/8 and 18/10 stainless steel. It is generally less expensive than 18/8 and 18/10 stainless steel due to the absence of nickel. It is suitable for applications in which corrosion resistance is less critical, such as: utensils, flatware, and certain architectural elements that will get no salt exposure or are distant from view.
The choice between these materials depends on the specific requirements of the application, including: environmental conditions, aesthetics, and budget considerations.
Summary
This article presented 18/8 stainless steel, explained it, and discussed how it is made and its various uses. To learn more about 18/8 stainless steel, contact a Xometry representative.
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