What are the differences between 304 and 316 stainless steel?

For machining enthusiasts, tool selection is a daily task. Tools are essential for removing excess surface material, and there are many material options. When it comes to stainless steel, there are various types, such as 304 and 316. How much do you know about these two grades?

304 and 316 stainless steel are the two most widely used stainless steel grades globally. Both offer excellent corrosion resistance and practical value.

304 stainless steel contains 16% to 24% chromium, with small amounts of carbon and manganese. The most common form is 18-8 stainless steel, which contains 18% chromium and 8% nickel. The 316 grade has nearly the same physical and mechanical properties as 304 stainless steel. The primary difference is that 316 stainless steel contains about 2% to 3% molybdenum. This addition enhances corrosion resistance, particularly against chlorides and other industrial solvents.

When comparing 304 and 316 stainless steel, there's no definitive answer to which one is "better." Different stainless steel materials have different uses. Today, let's explore the differences between 304 and 316 stainless steel.

1. Differences in Chemical Composition Between 304 and 316 Stainless Steel

The most significant difference between 304 and 316 stainless steel is the 2-3% molybdenum content in 316 stainless steel, which helps resist corrosion from chlorides like seawater and de-icing salts.

The molybdenum content in alternative 300 series grades can reach up to 7%, providing better chloride resistance. However, this heavy-duty resistance is only required in industrial or high-concentration exposure conditions.

2. Differences in Performance Between 304 and 316 Stainless Steel

304 stainless steel is the most common steel type. It is widely used for its good corrosion resistance, heat resistance, low-temperature strength, and mechanical properties. It has good hot workability, such as stamping and bending. There is no heat treatment hardening phenomenon (non-magnetic, usable temperature -196°C to 800°C / -320°F to 1472°F).

316 stainless steel, due to its molybdenum content, has excellent corrosion resistance, atmospheric corrosion resistance, and high-temperature strength. It can be used in harsh conditions and has excellent work hardening properties (non-magnetic).

3. Differences in Applications Between 304 and 316 Stainless Steel

304 Applications:

• Kitchen fixtures, such as sinks, splashbacks, cookware, cutlery, cabinets.
• Kitchen appliances like refrigerators and dishwashers.
• Home goods, including indoor plumbing, water heaters, boilers, bathtubs.
• Heat exchangers.
• Commercial food processing equipment, breweries, pharmaceutical production equipment.
• Manufacturing nuts, bolts, screws, and fasteners.
• Pipes, tanks, interior electrical enclosures, automotive interior parts.
• Decorative trim.

316 Applications:

• Chemical piping.
• Pharmaceutical equipment.
• Medical devices and tools.
• Stainless steel floats.
• Structural steel and components in marine environments.
• Equipment for food, chemical, and oil production.
• Construction of laboratory benches and equipment.
• Building cladding in coastal areas.
• Marine hardware and pipes.

4. Differences in Corrosion Resistance Between 304 and 316 Stainless Steel

316 stainless steel has better corrosion resistance than 304 stainless steel. It performs well in pulp and paper production and can resist erosion from marine and corrosive industrial atmospheres.

Generally, 304 and 316 stainless steel have similar chemical resistance. However, there are some differences in certain environments.

304 stainless steel was originally developed and is sensitive to pitting in some conditions. The addition of 2-3% molybdenum reduces this sensitivity, leading to the development of 316 stainless steel. The additional molybdenum also reduces corrosion in certain heated organic acids.

316 stainless steel has almost become the standard material for the food and beverage industry. Due to the shortage of molybdenum and the nickel content in 316 stainless steel, it is more expensive than 304 stainless steel.

Pitting corrosion is caused by deposits on the surface of stainless steel that prevent the formation of a chromium oxide protective layer when oxygen is scarce.

Small valves, for example, are unlikely to accumulate deposits, so pitting corrosion is rare. Various water media, such as distilled water, drinking water, river water, boiler water, and seawater, can lead to this issue.

In most cases, the corrosion resistance of 304 and 316 stainless steel is quite similar unless there is a high chloride content. In such cases, 316 stainless steel is more suitable.

In general, the corrosion resistance of 304 and 316 stainless steel may be similar, but it can vary significantly in specific conditions. A detailed analysis is necessary.

Valve users, for instance, should understand this as they choose materials for containers and pipes based on the medium.

5. Heat Resistance

316 stainless steel has good oxidation resistance when used intermittently below 1600°F (870°C) and continuously below 1700°F (927°C). However, 316 stainless steel should not be used continuously within the 800°F - 1575°F (427°C - 857°C) range.

When used outside of this temperature range, it exhibits excellent heat resistance. Ultra-low carbon stainless steel, 316L, has better resistance to carbide precipitation than SS316, making it suitable for use within this temperature range.

6. Heat Treatment

The annealing process for heat treatment is performed in the temperature range of 1850°F to 2050°F (1010°C to 1120°C). The material is then rapidly cooled by quenching. 316 stainless steel cannot be hardened by heat treatment.

7. Welding

Between 304 and 316 stainless steel, 316 stainless steel exhibits good weldability. All standard welding methods can be used for welding.

When welding, 316Cb, 316L, or 309Cb stainless steel filler rods or electrodes can be used depending on the application.

For optimal corrosion resistance, SS316 weldments require post-weld annealing. If using 316L stainless steel, post-weld annealing is unnecessary.

8. Cost Difference

The cost of stainless steel largely depends on its alloy composition.

All stainless steels require at least 10.5% chromium content and are iron-based alloys. However, various other elements can significantly affect performance, characteristics, and final cost.

316 contains at least 2.0% molybdenum and is more resistant to corrosion than 304 stainless steel. Molybdenum is a more expensive element, and this typically makes 316 a more expensive grade.

9. Low Carbon Grades

Austenitic stainless steel’s corrosion resistance comes from a chromium oxide protective layer formed on the metal’s surface. When heated to a temperature between 450°C and 900°C (842°F to 1652°F), the structure changes, and carbides form along the grain boundaries. As a result, a chromium oxide protective layer cannot form along these boundaries, reducing corrosion resistance. This type of corrosion is called "intergranular corrosion."

304L and 316L stainless steels were developed to counteract this type of corrosion. Both have lower carbon content than standard 304 and 316 stainless steel, preventing carbide precipitation and intergranular corrosion.

It's important to note that higher intergranular corrosion sensitivity does not necessarily mean non-low-carbon materials are more prone to corrosion. This sensitivity increases, especially in high-chloride environments.

This phenomenon occurs due to high temperatures (450°C - 900°C / 842°F - 1652°F). Welding is usually the direct cause of reaching this temperature. For soft-seated butterfly valves, using low-carbon stainless steel is not very significant since we don’t weld on the valve plates. However, most specifications call for 304L or 316L stainless steel.

Nebu Precision is a manufacturing leader providing on-demand manufacturing services for prototypes and mass production. Specializing in CNC, sheet metal, and plastic injection, we have successfully collaborated with diverse sectors, including Aerospace, Energy, Automotive Manufacturing, Medical Devices, and General Machinery Manufacturing. We consistently deliver high-quality products with precision, on-time reliability, and quality assurance.