What is comparable to 304 stainless steel?

18/8, 316, and 304 stainless steels are all very similar. Their differences lie in their composition, properties, applications, and cost.

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This article will discuss the differences between 18/8 vs. 316 vs. 304 stainless steel in terms of composition, how they are made, and their advantages.

What Is 18/8 Stainless Steel?

18/8 stainless steel refers to a group of stainless steels that are often used in cookware, kitchen utensils, and food processing equipment. The "18/8" designation indicates the composition of the steel, specifically the percentages of chromium and nickel alloyed with the iron base. In this case, 18/8 stainless steel contains approximately 18% chromium and 8% nickel. It also sometimes contains around 0.08% carbon (e.g., 304 stainless steel) and 50'70% iron. The chromium in the steel forms a passive layer of chromium oxide on the surface, which helps to prevent further corrosion. The nickel enhances the corrosion resistance and also provides a smooth and polished finish.

18/8 stainless steel covers a family of stainless steel grades. This includes: 302, 304, 305, and 384. 304 stainless steel is the standard 18/8 grade, whereas all the others are non-standard grades that fall within the 18/8 family. 18/8 stainless steel is very durable and also easy to fabricate. Compared to the 400 series, 18/8 stainless steel has better corrosion resistance. It becomes harder through cold working and lacks magnetic properties. Although 18/8 stainless steel offers improved corrosion resistance, it is susceptible to damage from chloride exposure, making it less suitable for use in marine environments.

How Is 18/8 Stainless Steel Made?

18/8 stainless steel is made through a series of processes. First, the different metals in its composition are melted in the right amounts (18% chromium, 8% nickel, 50'70% iron, and around 0.08% carbon). Once melted, the mixture is cast into solid forms, such as ingots or billets. These are then subjected to various forms of hot and cold working processes such as: rolling, forging, and annealing to produce the desired shape and size of the final product, ensuring the metal has the proper structure and mechanical properties. 

What Are the Advantages of 18/8 Stainless Steel?

18/8 stainless steel offers several advantages. Here are some of its key benefits:

1. Offers good resistance to corrosion and oxidation.
2. Has a non-reactive surface, making it food-safe.
3. Has good durability, as well as abrasive and impact resistance.
4. Can maintain strength when exposed to high temperatures.
5. Is relatively inexpensive compared to 316 stainless steel.

What Are the Disadvantages of 18/8 Stainless Steel?

18/8 stainless steel has the following disadvantages:

1. Susceptible to corrosion when chlorides are present. This makes it unsuitable for use in marine environments. Generally considered non-magnetic, making it unsuitable for applications in which magnetism is required.
2. Under certain conditions, such as the presence of chlorides and high tensile stresses, 18/8 stainless steel can be susceptible to stress corrosion cracking.

What Is 316 Stainless Steel?

316 stainless steel is the second most popular stainless steel grade, after grade 304. It is known for its enhanced corrosion resistance compared to 304 and 18/8 stainless steel, especially in chloride environments. This increased resistance is due to the addition of molybdenum (typically 2'3%) to the alloy, which significantly improves its resistance to pitting and corrosion in saline or chloride-exposed conditions. 316 stainless steel has a tensile strength of up to 621 MPa and an operating temperature of up to 800 °C.

Like 18/8 stainless steel, 316 stainless steel also contains chromium (about 16'18%) and nickel (about 10'14%), but the key differentiator is the presence of molybdenum. This composition makes 316 stainless steel particularly useful in environments exposed to chemical corrodents, as well as marine atmospheres. Additionally, it maintains its strength at high temperatures and resists atmospheric corrosion, as well as moderately oxidizing and reducing environments.

There are a lot of different types of 316 stainless steel. Some common variants include: F, H, L, and N. Each of these has its own set of attributes that make it unique. For example, 316L is known for its lower carbon content, which offers even better corrosion resistance after welding or when higher resistance to carbide precipitation is needed. 316H, on the other hand, is the higher-carbon-content variant, and it has better creep resistance and thermal stability. 

To learn more, see our full guide on 316 Stainless Steel Properties.

How Is 316 Stainless Steel Made?

316 stainless steel is made in the same way as 18/8 stainless steel, only here the raw materials include: iron, chromium, nickel, molybdenum, and carbon, along with small amounts of manganese, silicon, and sometimes nitrogen. These are melted together in an electric arc furnace or a blast furnace. The exact proportions are carefully controlled to achieve the desired chemical composition, particularly the 16'18% chromium, 10'14% nickel, and 2'3% molybdenum characteristic of 316 stainless steel.

The molten steel is then cast into forms such as: blooms, billets, or slabs, depending on the final product's required shape and size. This casting process can involve continuous casting or ingot casting. The cast steel is then formed into its final shape through a series of hot and cold working processes. This can include: rolling, pressing, or forging to produce sheets, bars, rods, or other shapes.

After forming, the steel undergoes heat treatment, such as annealing, to relieve stresses from the forming process, improve ductility, and refine its microstructure. This step is crucial for achieving the desired mechanical properties. The surface of the steel is then cleaned to remove scale (oxidation) and other impurities. This is typically achieved through pickling (acid washing) or by blasting with an abrasive. Finally, the steel is cut to size and finished according to the specific requirements of the application. This can include: polishing, grinding, or applying surface finishes to enhance corrosion resistance or aesthetic appeal.

What Are the Advantages of 316 Stainless Steel?

316 stainless steel offers several advantages that make it highly sought after for various applications. Here are some of its key benefits:

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1. Exhibits excellent corrosion resistance. The addition of molybdenum makes it resistant to saltwater corrosion, as well as corrosion due to harsh chemicals and acids.
2. Maintains its strength and mechanical properties even at higher temperatures.
3. It offers excellent durability and strength, making it suitable for heavy-duty applications.
4. The non-reactive nature of 316 stainless steel makes it suitable for medical and surgical applications.

What Are the Disadvantages of 316 Stainless Steel?

316 stainless steel has the following disadvantages:

1. Relatively more expensive compared to 304 and 18/8 stainless steel.
2. Relatively difficult to machine. This is due to its hardness, as well as a tendency to work-harden. This can reduce tool life, and increase machining time.
3. Can be welded, but is prone to weld decay. This weakens the corrosion resistance at the point at which the steel is welded.
4. Is less malleable than 304 stainless steel. 

What Is 304 Stainless Steel?

304 stainless steel is a widely used austenitic (non-magnetic) stainless steel known for its corrosion resistance and durability. It is the most popular and versatile austenitic type of stainless steel. 304 stainless steel contains a high percentage of chromium (around 18%) and nickel (around 8%) along with iron and small amounts of carbon, silicon, and manganese. The high chromium content provides a passive film of chromium oxide on the surface, which helps to prevent surface corrosion by inhibiting oxygen diffusion to the steel's surface and stopping corrosion from spreading into the metal's internal structure. Nickel enhances corrosion resistance and provides a high degree of formability and weldability. 304 stainless steel also has a fairly high tensile strength with an operating temperature of up to 870 °C. This stainless steel generally has around 0.08% carbon in its composition. There are also variations of 304 stainless steel, such as 304L, in which the "L" stands for 'low carbon' (around 0.03%), which offers even greater resistance to weld decay and intergranular corrosion. The 304H grade has a higher carbon content with a maximum percentage of 0.1%. 

This type of stainless steel is highly versatile and is used in a variety of applications ranging from kitchen appliances, cutlery, and food processing equipment to architectural facades, automotive parts, and medical devices. Its excellent balance of corrosion resistance, workability, and cost-effectiveness make it the most commonly used form of stainless steel.

To learn more, see our full guide on What is 304 Stainless Steel.

How Is 304 Stainless Steel Made?

The manufacturing of 304 stainless steel begins with melting the raw materials'iron, chromium (about 18%), nickel (about 8%), and small amounts of carbon'in an electric arc or blast furnace to achieve its specific composition. This molten steel is then cast into forms like billets or slabs. The next step involves hot rolling these forms into the desired shapes and thicknesses. Subsequently, the steel undergoes annealing, a heat-treatment process to relieve internal stresses and improve ductility, which involves heating the steel and then cooling it slowly. To remove the scale that forms during annealing, the steel is pickled in a mixture of nitric and hydrofluoric acids. Finally, the steel is cut to size and undergoes finishing processes, such as polishing, to achieve the desired surface quality. 

What Are the Advantages of 304 Stainless Steel?

The advantages of 304 stainless steel include:

1. Compared to 316 stainless steel, some grades of 304 stainless steel have a higher tensile strength. 
2. Is easily processed, shaped, and welded, allowing for the creation of a wide range of product shapes. It boasts excellent plasticity and machinability.
3. Most widely used stainless steel and is used for a wide range of products from kitchenware to water piping to medical devices, and more. 
4. If you are not looking for the higher corrosion resistance of 316, you can get 304 stainless steel with similar performance in most areas and longevity at a lower price point. 

What Are the Disadvantages of 304 Stainless Steel?

The disadvantages of 304 stainless steel are as follows:

1. Compared with 316 stainless steel, its corrosion resistance is poor'especially in marine environments. 
2. Even though 304 stainless steel handles high heat well, continuous use at temperatures between 425 and 860 °C may cause corrosion. 
3. The smooth surface of 304 stainless steel, despite its appearance, is quite soft and prone to scratching, making it less ideal for applications in which resistance to scratches is a necessity.
4. Offers only moderate resistance to wear, necessitating the consideration of alternative materials in scenarios demanding higher durability.
5. While 304 stainless steel exhibits respectable oxidation resistance at elevated temperatures, its performance may diminish under conditions of extreme heat or cold.

How To Choose Between 18/8, 316, and 304 Stainless Steel?

Choosing between these three grades of stainless steel comes down to the environment the chosen metal will be exposed to, the desired properties of the product, and of course budget constraints. 316 outperforms 18/8 and 304 in terms of corrosion resistance, especially in saltwater environments and also when exposed to other corrosives. However, if the product will not be facing such harsh environments, it's best to go with 18/8 or 304 stainless steel, which can give similar performance in other categories than corrosion resistance but for a much lower price point. 304 and 18/8 are sometimes used interchangeably due to the overlap of properties. 304 is one of the standard grades in the 18/8 group. Other grades like 301, 302, 305, and 384 are non-standard grades within this family since they have additional chromium or nickel, and other elements, added to their composition. In terms of material hardness in less corrosive environments, 304L can be used when a softer material is needed, whereas 304H will be better suited when a harder material is desired.

How Do 18/8, 316, and 304 Stainless Steels Differ in Properties?

The properties of 18/8, 316, and 304 stainless steels are outlined in Table 1:

There are more than 60 grades of stainless steel. Stainless steel is essentially low-carbon steel that contains chromium of 10% or more by weight. It is the addition of chromium that gives the steel its unique stainless, corrosion-resisting properties. Austenitic 304 and 316 stainless steels are considered surgical or medical-grade stainless steels, they are the most common stainless steels. The key difference between 304 and 316 stainless steel that makes them different is the addition of molybdenum, an alloy that drastically enhances corrosion resistance, especially for more saline or chloride-exposed environments. 316 stainless steel contains molybdenum, but 304 does not.

Both of these 300-grade steels are known for their excellent welding and forming properties, which give them applications across many industries. These alloys cannot be hardened by heat treatment, but they can develop high strength by cold working.

304 vs 316 Stainless Steel

In pharmaceutical, power generation and chemical process applications, austenitic stainless steels like 304 are typically the first choice. Molybdenum is mainly used for added corrosion resistance in 316, make it ideal for more acidic environments. Certain critical petroleum, chemical processes and marine applications with corrosive chloride gas require the improved pitting and crevice corrosion resistance of 316 molybdenum-modified stainless steels.

300 Series Austenitic ' Typical Grade: 304 Chromium (17-25%); nonmagnetic, not heat treatable. Can develop high strength by cold working. Molybdenum (up to 7%) can increase corrosion resistance ' especially pitting and crevice corrosion resistance.

Typical Use: Food & beverage, cryogenic, chemical process, medical (hypodermic needles, implants, stents), instrumentation/chromatography tubing, oil & gas, hydraulic tubing and marine applications. Super austenitic grades (high nickel) extend performance for applications requiring extreme corrosion & oxidation/scaling resistance or higher strengths.

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