Aside from seasoned sheet metal enthusiasts, many people don’t know about the intricacy of the 304 vs 316 stainless steel comparison and how it affects their applications. Both are austenitic stainless steel and are popular for their excellent heat, abrasion, corrosion resistance, and aesthetic value.
The similarities between the two grades of stainless steel make many people think they have the same applications. However, some slight distinction separates them. This article aims to compare 316 and 304 stainless steel by showing their properties, applications, similarities, differences, and how they all matter before you choose the right one for your project.
What is 304 Stainless Steel?
304 stainless steel or 304 SS is austenitic grade steel that contains 18% chromium and 8% nickel (hence the name 18/8) and other alloying elements such as carbon, phosphorus, sulfur, silicon, and manganese. It has good corrosion resistance properties and is considered the most versatile and common stainless-steel grade in sheet metal fabrication.
304 SS has unique properties making it suitable for different industries. Below are the important physical and mechanical properties of the material flat rolled product (plate, sheet, and coil):
- Melting Point 1450℃
- Density: 8.00 g/cm^3
- Thermal Expansion: 17.2 x10^-6/K
- Modulus of Elasticity: 193 GPa
- Thermal Conductivity: 16.2 W/m.K
- Tensile Strength: 500-700 Mpa
- Elongation A50 mm: 45 Min %
- Stainless Steel Hardness (Brinell): 215 Max HB
304 stainless steel has high formability and considerable corrosion resistance. Hence, it is used in making many products in several industries. Below are a few of its applications:
The food industry uses 304 stainless steel for making fryers and food prep tables. These products require an affordable material with corrosion resistance, heat resistance, and excellent aesthetic value.
304 SS is applicable in making kitchen cookware and silverware. It is a perfect material due to its formability, heat resistance, and abrasion resistance. Due to the increase in desire for kitchen equipment with aesthetics, 304 stainless steel became an important material as it is also abrasion resistance .
The medical industry uses 304 SS for making trays and surgical tools. Here, value is placed on its excellent formability and heat resistance (due to the need for heat sterilization).
What is 316 Stainless Steel?
316 stainless steel or 316 SS is the second most popular austenitic grade of stainless steel, and it comprises iron, 10-14% nickel, and 16-18% chromium. The real distinction in the stainless steel 316 vs 304 SS comparison is the presence of molybdenum (2-3%) alongside the other alloying elements such as carbon, manganese, and silicon.
- Density: 8.00 g/cm3
- Melting Point: 1400°C
- Modulus of Elasticity: 193 GPa
- Electrical Resistivity: 0.74 x 10-6 Ω.m
- Thermal Conductivity: 16.3 W/m.K
- Thermal Expansion: 15.9 x 10-6/K
The mechanical properties depend on the type of 316 stainless steel. There are three categories: 316 Bar and Section (up to 160 mm thick), 316 Sheet (up to 8 mm thick), and 316 Plate (8 – 75 mm thick). Below are the mechanical properties for each category, respectively.
- Tensile strength (Mpa): 500-700, 530-680, 520-670
- Proof Stress (MPa): 200, 240, 220
- Elongation A50 mm: 4 0 Min %, 40 Min %, 45 Min %
- Stainless Steel Hardness Brinell: 215 Max HB, nil, nil
316 stainless steel has high formability and very high corrosion resistance. Due to the presence of molybdenum, it is the most common material in making parts with marine applications. Below are a few applications of the stainless-steel grade.
316 SS is suitable for making parts such as boilers, boat rails, and boat ladders due to its exceptional stability in chloride or sulfuric acid-containing environments. Aside from the corrosion resistance, it is highly weldable and formable, making product manufacturing easier.
Water Handling Product
316 SS heat resistance makes it suitable for making water handling products such as boilers and water heaters. Formability also plays an important role here as the products have complex designs.
Medical and Pharmaceutical Equipment
The medical industry uses 316 stainless steel for medical equipment due to formability and heat resistance (needed for heat sterilization). It is also suitable for pharmaceutical equipment since such equipment work in different environmental conditions and is subjected to chemicals.
304 vs 316 Stainless Steel: Similarities
Based on physical and mechanical properties, 316 and 304 stainless steel are very similar. Both materials have the following similarities:
Both SS are austenitic grades of stainless steel. Consequently, they do not possess any magnetic properties when first formed. However, cold working or welding them can lead to magnetism.
2. Abrasion Resistance
Both grades are resistant to abrasion or scratching. This ensures that the material is not exposed to oxidation or other phenomena. Also, this is an important aesthetic value many consider, especially in making kitchen cookware.
Weldability is the tendency of a metal to be welded together without deformation. This factor depends on the amount of carbon in a stainless-steel grade with low carbon-containing SS having higher weldability. Both grades have high and equal weldability due to the equal amount of carbon present (0.08%) .
Formability is the tendency of a material to undergo plastic deformation without any effect on its ability, such as necking (localized thinning of the sheet metal) and cracking (breakage of the sheet metal). This allows sheet metal fabricators to work with materials and suit them to a design. Both grades have high formability.
Durability measures the strength of a material and the amount of stress it can support. Both grades 316 and 304 are tough. This is visible in their mechanical properties, anti-corrosive properties, and heat resistance, which ensures their use in stringent manufacturing structures.
6. Tensile Strength
Tensile strength defines the energy required to split or stretch a material before it breaks. The SS 304 and SS 316 have a tensile strength of 500-700Mpa, making them suitable for working under the same condition.
304 vs 316 Stainless Steel: Differences
To effectively choose between the 304 SS and 316 SS, you need to know their differences by comparing them. Below are the key differences between both grades of SS.
1. Chemical Composition
304 SS (percentage): Carbon (0.07), Silicon (1), manganese (2), Phosphorus (0.045), Sulphur (0.015), Nitrogen (0.10), Chromium (18), Nickel (8).
316 SS (percentage): Carbon (0.07), Silicon (1.00), manganese (2.00), Phosphorus (0.045), Sulphur (0.015), Nitrogen (0.10), Chromium (16), Nickel (10), and Molybdenum (2.00).
The main difference between 304SS and 316SS is the presence of molybdenum and the percentage of Chromium and nickel they both have. These, in turn, are responsible for the different properties of the grades of stainless steel.
2. Mechanical Properties
Both SS also differ in mechanical properties, including yield strength, stainless steel hardness, and modulus of elasticity.
Yield strength is the maximum force you can use on material before changing its shape permanently. Hence metal strength must always be subjected to forces below the yield strength. SS 304 has a yield strength of 215Mpa, while 316 SS is 205MPa. Although small, the difference is important in high tolerance machining.
This is the ability of a material to resist deformation, penetration, and indentation. The right material must be hard enough to improve durability. It must also be hard enough to ensure a proper manufacturing process.
316 SS hardness is 79 Rockwell B, while 304 SS is 70 Rockwell B. Therefore, 316 stainless steel is more suitable for projects that require a hard material
-Modulus of Elasticity
Modulus of elasticity is the relationship between stress and strain and how a metal responds to deformation. 316 SS modulus of elasticity is 164 GPa, while that of 304 SS is 193-200 GPa. Therefore, SS 304 responds better to deformation.
3. Corrosion resistance
Generally, both grades of stainless steel are corrosion resistant. However, due to the presence of molybdenum in 316 SS, it is more corrosion resistant, especially in chloride or sulfuric acids. The corrosion resistance of 316SS also means that you can easily clean them without worrying about the type of chemical.
4. Heat Resistance
Heat resistance is another distinct factor in comparing 304 vs 316 stainless steel. Based on their melting points, 304 SS has a melting range higher than 316 SS (by 50-100F).
On the one hand, 304 SS can handle heat well. However, continuous use at a temperature between 797-1580 °F can lead to corrosion. On the other hand, 316 SS functions well in temperatures above 1550 ℉ and below 850°F.
316 stainless steel is more expensive than 304 stainless steel due to the higher element content and the addition of molybdenum. Aside from that, the incurred increase in corrosion resistance further makes it more expensive. On average, 316 stainless steel is 40% more expensive than 304 SS.
304 vs 316 Stainless Steel: How to Select the Right One
Benefit-wise, the 316 SS surpasses the 304 SS. However, the 304 SS is more popular in terms of industrial application. Choosing the right one comes from noting the differences between both grades of stainless steel. Below are a few scenarios where both SSs are applicable and how you can choose the right one.
The marine environment contains a high level of chlorides and sulfides. Therefore, the right material should have a high level of corrosion resistance. Due to the presence of molybdenum, 316 stainless steel is the better material.
Products used outdoors are also exposed to corrosion and rust. However, unlike the marine environment, fewer chlorides and other chemicals exist. Therefore, 304 stainless steel is the better option here due to its corrosion resistance and low cost.
Both grades of stainless steel offer near-the-same durability and aesthetic value. However, maintaining the 316 SS is easier than the 304 SS. This is because there is less need to worry about the chemicals used for the cleaning process.
What is the Temperature of Operation?
Temperature can also increase the rate of corrosion. Therefore, if the application site has a high temperature, 316 SS is the better option. Unlike the 304SS, which can experience corrosion at 425-860 °C (797-1580 °F), SS 316 can function at a temperature above 843 ℃ (1550 ℉) and below 454 ℃ (850°F) without corrosion.
Another factor to consider when choosing the right one in the 304 stainless steel vs 316 stainless steel is the cost 304 is the better choice because the 316 SS costs 40% more than it.
By matching your choice to the usage, environment, and cost, you can optimize them for the benefits of your project functionally and cost-wise.
304 and 316 SS are important materials in manufacturing due to corrosion resistance, weldability, formability, and aesthetics. Both are austenitic steels; however, they differ slightly in material composition. This difference in chemical composition is responsible for the difference in their cost and corrosion resistance.
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How to tell 316 SS from 304 SS？
You can’t know the difference between grades of stainless steel by just looking at them. However, subject them to a solution containing chloride or sulfuric acid. 316SS is resistant to these chemicals due to the presence of molybdenum.
Is 316 or 304 SS Stronger?
Both are similar in terms of tensile strength. The main difference between both materials is the cost and the corrosion resistance.
Will a magnet stick to 316 stainless steel?
It should not. Like other austenitic steel, 316 stainless steel is a nonmagnetic SS due to its high nickel composition. Cold working or welding the material can make them magnetic. However, this is only after fresh forming.
Is 316 stainless steel rustproof?
Yes, 316 stainless steel has anti-rust and anti-corrosive properties due to nickel, molybdenum, and Chromium. Therefore, it is suitable for working in an environment that supports rusting and corrosion.