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What is the difference between 304, 304L, 316 and 316L? Finally got it!

What is the difference between 304, 304L, 316 and 316L? Finally got it!

What exactly are “steel” and “iron”, what are their characteristics, and what is their relationship? Where do the 304, 304L, 316, and 316L we usually call come from, and what are the differences between them?

  • Steel: A material with iron as the main element, carbon content generally below 2%, and other elements. ——GB/T 13304-91 “Steel Classification”
  • Iron: A metallic element with atomic number 26. Iron materials have strong ferromagnetism and good plasticity and thermal conductivity.
  • Stainless steel: Steel that is resistant to weak corrosive media such as air, steam, water, etc. or is stainless. Commonly used steel types are 304, 304L, 316, and 316L, which are 300 series steels of austenitic stainless steel.
PBA Aluminum Bending Machine Rolling SUS Pipe

304 stainless steel

  • Performance introduction: 304 stainless steel is the most common type of steel. As a widely used steel, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; it has good hot workability such as stamping and bending, and no heat treatment hardening phenomenon (non-magnetic). , operating temperature -196℃~800℃).
  • Scope of application: Household supplies (categories 1 and 2 tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs)

Auto parts (windshield wipers, mufflers, molded products)

Medical equipment, building materials, chemicals, food industry, agriculture, ship parts

304L stainless steel

(L is low carbon)

  • Performance introduction: As a low-carbon 304 steel, its corrosion resistance is similar to that of 304 steel under normal conditions. However, after welding or stress relief, its resistance to intergranular corrosion is excellent; it can also maintain good performance without heat treatment. Excellent corrosion resistance, operating temperature -196℃~800℃.
  • Scope of application: It is used in outdoor machines in the chemical, coal, and petroleum industries that require high resistance to grain boundary corrosion, as well as heat-resistant building material parts and parts that are difficult to heat treat.

316 stainless steel

  • Performance introduction: Due to the addition of molybdenum, 316 stainless steel has excellent corrosion resistance, atmospheric corrosion resistance and high temperature strength, and can be used under harsh conditions; it has excellent work hardening properties (non-magnetic).
  • Scope of application: Seawater equipment, chemicals, dyes, papermaking, oxalic acid, fertilizer and other production equipment; photography, food industry, coastal area facilities, ropes, CD rods, bolts, nuts.

316L stainless steel

(L is low carbon)

  • Performance introduction: As a low carbon series of 316 steel, in addition to having the same characteristics as 316 steel, it has excellent resistance to grain boundary corrosion.
  • Scope of application: Products with special requirements for resistance to grain boundary corrosion.

Performance comparison

Chemical composition

What is the difference between 304, 304L, 316 and 316L? Finally got it!
What is the difference between 304, 304L, 316 and 316L? Finally got it!

316 and 316L stainless steel are molybdenum-containing stainless steels. The molybdenum content in 316L stainless steel is slightly higher than that of 316 stainless steel. Due to the molybdenum in the steel, the overall performance of this steel is better than that of 310 and 304 stainless steel. Under high temperature conditions, when the concentration of sulfuric acid is lower than 15% and higher than 85%, 316 Stainless steel has a wide range of uses. 316 stainless steel also has good resistance to chloride attack, so it is often used in marine environments. 316L stainless steel has a maximum carbon content of 0.03 and can be used in applications where annealing cannot be performed after welding and where maximum corrosion resistance is required.

Corrosion resistance

The corrosion resistance of 316 stainless steel is better than that of 304 stainless steel, and it has good corrosion resistance in the pulp and paper production process. Moreover, 316 stainless steel is also resistant to corrosion from the ocean and corrosive industrial atmosphere.

Generally speaking, there is not much difference in chemical corrosion resistance between 304 stainless steel and 316 stainless steel, but there are differences in some specific media.

The stainless steel originally developed was 304. Under certain circumstances, this material is sensitive to pitting corrosion (Pitting Corrosion). Adding an additional 2-3% of molybdenum can reduce this sensitivity, and thus 316 was born. Additionally, this additional molybdenum can reduce corrosion by certain hot organic acids.

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

Pitting corrosion is a phenomenon mainly caused by deposited corrosion on the surface of stainless steel, which is due to the lack of oxygen and the inability to form a protective layer of chromium oxide.

Especially in small valves, the possibility of deposits on the valve plate is very small, so pitting corrosion is also rare.

In various types of water media (distilled water, drinking water, river water, boiler water, sea water, etc.), the corrosion resistance of 304 stainless steel and 316 stainless steel is almost the same, unless the content of chloride ions in the medium is very high, in which case 316 stainless steel more suitable.

In most cases, there is not much difference in the corrosion resistance of 304 stainless steel and 316 stainless steel, but in some cases there may be a big difference, which requires specific analysis of the specific situation. Generally speaking, valve users should be aware of this, because they will choose the materials of containers and pipes based on the medium, and it is not recommended to recommend materials to users.

Heat resistance

316 stainless steel has good oxidation resistance in intermittent use below 1600 degrees and continuous use below 1700 degrees. In the range of 800-1575 degrees, it is best not to continuously use 316 stainless steel, but when 316 stainless steel is used continuously outside this temperature range, the stainless steel has good heat resistance. The resistance to carbide precipitation of 316L stainless steel is better than that of 316 stainless steel, and it can be used in the above temperature range.

Heat treatment

Annealing is performed in the temperature range of 1850-2050 degrees, followed by rapid annealing and then rapid cooling. 316 stainless steel cannot be hardened by heat treatment.


316 stainless steel has good welding properties. Welding can be carried out using all standard welding methods. When welding, 316Cb, 316L or 309Cb stainless steel filler rods or welding rods can be used for welding according to the purpose. In order to obtain the best corrosion resistance, the welded section of 316 stainless steel needs to be annealed after welding. If 316L stainless steel is used, post-weld annealing is not required.

Mechanical behavior

What is the difference between 304, 304L, 316 and 316L? Finally got it!
What is the difference between 304, 304L, 316 and 316L? Finally got it!

Austenitic stainless steel has the lowest yield point of all steels. Therefore, from the perspective of mechanical properties, austenitic stainless steel is not the best material to use for the valve stem, because to ensure a certain strength, the diameter of the valve stem will increase. The yield point cannot be increased by heat treatment but can be increased by cold forming.


Due to the widespread use of austenitic stainless steel, people are given the wrong impression that all stainless steel is non-magnetic. For austenitic stainless steel, it can basically be understood as non-magnetic, and this is indeed the case for quenched forged steel. However, 304 processed by cold forming will be somewhat magnetic. For cast steel, if it is 100% austenitic stainless steel, it is not magnetic.

Low carbon type of stainless steel

The corrosion resistance of austenitic stainless steel comes from the protective layer of chromium oxide formed on the metal surface. If the material is heated to a high temperature of 450°C to 900°C, the structure of the material will change and chromium carbide will form along the edge of the crystal. In this way, a protective layer of chromium oxide cannot be formed on the edge of the crystal, resulting in reduced corrosion resistance. This corrosion is called “intergranular corrosion”.

304L stainless steel and 316L stainless steel were developed to combat this corrosion. The carbon content of 304L stainless steel and 316L stainless steel is low. Because the carbon content is reduced, chromium carbide will not be produced, and intergranular corrosion will not occur.

It should be noted that higher susceptibility to intergranular corrosion does not mean that non-low carbon materials are more susceptible to corrosion. This sensitivity is also higher in high chlorine environments.

Please note that this phenomenon is caused by high temperatures (450℃-900℃). Usually welding is the direct cause of reaching this temperature. For soft-seat conventional butterfly valves, since we are not welding on the valve plate, it doesn’t make much sense to use low-carbon stainless steel, but most specifications will require 304L stainless steel or 316L stainless steel.