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Due to its strength, excellent machinability, weldability, and flexibility, stainless steel has played a significant role in numerous applications since it was first produced in the early 20th century. This ferrite alloy contains several alloying elements in varying proportions that are responsible for the various grades used in modern industry.

The most versatile grades of stainless steel are SAE 304 and SAE 316 stainless steel. In this article, we'll compare the two grades of stainless steel, their chemical composition, and their various mechanical properties.

SAE 304 Stainless Steel

SAE 304 stainless steel, formerly known as 18/8 (which refers to its chemical composition), is the most versatile and widely used grade of stainless steel worldwide. It's an austenitic stainless steel with 18% to 20% chromium, which gives the steel its corrosion resistance, and 8% to 10.5% nickel, which increases weldability, ductility, and corrosion resistance.

Other elements include 0.08% carbon, as well as silicon and traces of manganese. As austenitic stainless steel, SAE 304 is a non-magnetic type of steel featuring exceptional mechanical properties, like weldability, increased tensile strength, and extreme drawing properties that don't require immediate annealing.

SAE 304L is a low-carbon steel variant of SAE 304 stainless steel and contains 0.03% carbon. It's mostly used in construction and heavy gauge components due to exceptional weldability, as it doesn't require any post-welding heat treatment. SAE 304H is the carbon-rich variant of SAE 304, with up to 0.1% carbon, increasing its strength in high-temperature applications.

SAE 316 Stainless Steel

Just like SAE 304, the SAE 316 stainless steel alloy, often referred to as 18/10 or A4, is among the most versatile types of stainless steel due to its excellent corrosion resistance and increased ductility. In fact, it's one of the most ductile grades of stainless steel.

Its primary alloying elements, after iron and carbon, are chromium (16-18%), nickel (10-12%), and molybdenum (2-3%). Of course, there are traces of other elements, such as silicon, phosphorous, and sulfur, but those are usually present in quantities smaller than 1%.

The addition of molybdenum in SAE 316 provides a superior corrosion resistance than SAE 304, especially in chloridic and sulfuric environments, as it also prevents oxidation caused by salt and chlorides in marine environments. 

This superior corrosion resistance makes SAE 316 suitable for a wide variety of applications, including industrial applications such as food processing equipment, chemical processing, medical equipment, and marine applications. This also includes architectural applications near seashores.

SAE 304 Stainless Steel vs SAE 316 Stainless Steel: The Main Differences

There aren't any visual differences between SAE 304 and SAE 316 stainless steel, but the two types differ chemically. Admittedly, both types share many of their properties with numerous 3xx stainless steel varieties, with only subtle differences in their respective chemical make-ups.

However, those subtle differences in chemical composition can result in varying material properties, and choosing a certain stainless steel grade can either make or break your project. Here are the main differences between SAE 304 and SAE 316:

Chemical Composition

The biggest difference in chemical composition between SAE 304 and SAE 316 lies in varying chromium, nickel, and molybdenum proportions. SAE 304 has approximately 2% more chromium by weight than SAE 316 and approximately 2% less nickel.

The amount of trace elements, such as silicon, phosphorous, sulfur, and nitrogen, remains the same, and any variance in the proportion of trace elements is negligible. The main difference is the addition of molybdenum; SAE 304 lacks molybdenum altogether, while SAE 316 has 2% molybdenum by weight.

These variations lead to the various characteristics and use that each grade displays.

Mechanical Properties

Tensile strength, yield strength, compression strength, and shear modulus are significant mechanical qualities to consider while selecting stainless steel varieties. Here are comparisons of stainless steel 304 and 316 based on each property.

Tensile Strength

The amount of force required to split a material portion, or how far it can be stretched before breaking, is known as tensile strength. 8mm, or 5/16-inch thick SAE 304 stainless steel, has a tensile strength range of 520-720 MPa. SAE 316 of the same thickness has a lower tensile strength, ranging between 530-680MPa.

Yield Strength

The metal's yield strength is the amount of pressure it can withstand before irreversibly changing shape. The yield strength of SAE 316 stainless steel is 290MPa compared to 215MPa for SAE 304 stainless steel. As a result, SS 316 is superior to SS 304 for use in manufacturing items that must withstand more force.

Hardness

The material's hardness determines how well it can resist indentation, penetration, deformation, and abrasion. The hardness of stainless steel 316 is 79 Rockwell B, while that of SAE 304 is 70 Rockwell B. Even though there isn't much of a difference, 316 stainless steel would be better suited for projects that require higher friction.

Modulus of Elasticity

The modulus of elasticity is the correlation between stress, strain, and the metal's reaction to deformation. SAE 304 has a modulus of elasticity of 193-200GPa compared to 164GPa for SAE 316 stainless steel. This demonstrates that SS 304 responds to deformation better.

Corrosion Resistance

As their name implies, stainless steel alloys are corrosion-resistant, not corrosion-proof. SAE 304, generally speaking, has good corrosion resistance. However, the 2% molybdenum content in SAE 316 improves the grade's resistance to acids, alkalis, and chlorine.

This makes SAE 304 more suitable for manufacturing industrial hardware in hygiene-stringent environments. This includes toggle clamps for various enclosures, leveling feet for industrial equipment, various types of hinges, etc.

SAE 316 is also suitable for manufacturing industrial hardware, but it's also suitable for medical applications, such as surgical implants—though they might be surpassed by non-nickel stainless steel alloys.

Weldability

The grade's carbon content affects weldability since more carbon will make it harder to weld. The carbon content of stainless steel 304 and 316 is the same at 0.08%, with a little variation in other constituents. Although both grades are easily welded utilizing arc welding methods, there is little variance in their weldability due to their different elements.

Choosing the Right Stainless Steel Grade

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The main difference between SAE 304 and SAE 316 lies in the different proportions of chromium and nickel, as well as the addition of molybdenum in SAE 316. The addition of the latter element increases the steel's corrosion resistance in chemically harsh conditions, which makes it suitable for a wider application range.

If you want to learn more about stainless steel, visit our Engineer Resource Guides or browse the types of stainless steel industrial parts and components you might need online.