The difference between stainless steel 316 and 316L

Introduction

What is stainless steel? Alloy steel that contains more than 12% chromium or more than 8% nickel is typically referred to as stainless steel.

This kind of steel has a certain corrosion resistance in the atmosphere or corrosive media and has higher strength at higher temperatures (>450℃). Steel with a chromium content of 16% to 18% is called acid-resistant steel or acid-resistant stainless steel and is usually called stainless steel. When the chromium content in steel is more than 12%, a layer of chromium-rich passivation film quickly forms on the surface due to electrochemical action in contact with oxidizing media to protect the inside of the metal from corrosion; but in non-oxidizing corrosive media, it is still difficult to form a solid passivation film. To improve the corrosion resistance of steel, the proportion of chromium is usually increased, or alloy elements that can promote passivation are added, such as Ni, Mo, Mn, Cu, Nb, Ti, W, Co, etc.

These elements not only improve the corrosion resistance of steel but also change the internal organization and physical and mechanical properties of steel. The different contents of these alloy elements in steel have different effects on the properties of stainless steel.

Some are magnetic, some are non-magnetic, some can be heat-treated, and some cannot be heat-treated. Due to the above characteristics of stainless steel, it is increasingly widely used in aviation, aerospace, chemical, petroleum, construction, food and other industrial sectors and daily life. The alloy elements contained in it have a great influence on the machinability, and some are even difficult to cut.

To help readers better understand and select the material that works for them, this article will go into great detail on the differences between 316 and 316L stainless steel. 316 is a low-carbon stainless steel with the domestic grade 0Cr17Ni12Mo2, while 316L is an ultra-low-carbon stainless steel with the domestic grade 00Cr17Ni14Mo2. It is evident that while 316L is more resistant to corrosion, 316 has superior mechanical qualities.

The differences between 316 and 316L stainless steel are as follows:

The stainless steels 316 and 316L are those that contain molybdenum. 316L stainless steel contains a little more molybdenum than 316 stainless steel. Compared to stainless steels 310 and 304, this steel performs better overall because of the molybdenum it contains. When the sulfuric acid content is between 15% and 85% at high temperatures, 316 stainless steel can be used for a variety of purposes. Marine areas frequently use 316 stainless steel because of its strong resistance to chlorine corrosion.

When the highest corrosion resistance and annealing after welding are needed, 316L stainless steel, which has a maximum carbon content of 0.03 percent, can be utilized.

316 VS 316L Chemical composition (mass fraction, %)

Corrosion resistance:

In the pulp and paper production process, it has good corrosion resistance, outperforming 304 stainless steel. Furthermore, corrosion from corrosive industrial environments and maritime environments cannot erode 316 stainless steel.

Heat resistance:

316 stainless steel resists oxidation well when used continuously below 1700 degrees and intermittently below 1600 degrees. 316 stainless steel has good heat resistance when used constantly outside of the 800-1575 degree temperature range, although it is preferable not to use it in this range throughout the day. The upper temperature range is suitable for 316L stainless steel, which is more resistant to carbide precipitation than 316 stainless steel.

Heat treatment:

Anneal between 1850 and 2050 degrees, then anneal quickly before cooling quickly. Overheating won't harden 316 stainless steel.

Welding:

316 stainless steel performs well when it comes to welding. All common welding techniques can be used to weld it. Depending on the application, stainless steel electrodes or filler rods made of 316Cb, 316L, or 309Cb can be used for welding. After welding, the 316 stainless steel section must be annealed to get the highest level of corrosion resistance. Post-weld annealing is not necessary when using 316L stainless steel.

Typical uses:

316 and 316L Stainless Steel vs. 304

A common stainless steel used to create equipment and parts that need to have good overall qualities (such as corrosion resistance and formability) is 304.

Regarding chemical corrosion resistance, 304 and 316 stainless steel rarely differ from one another, although there are some media-specific variations.

Under some conditions, 304, the first stainless steel to be created, is susceptible to pitting corrosion. A further 2-3% molybdenum addition might lessen this sensitivity, resulting in 316. This extra molybdenum can also lessen corrosion caused by some hot organic acids.

In the food and beverage business, 316 stainless steel is practically a standard material. 316 stainless steel is more costly than 304 stainless steel because of the global scarcity of molybdenum and the increased nickel content of 316 stainless steel.

Because of the absence of oxygen and the incapacity to generate a protective layer of chromium oxide, pitting corrosion is mostly caused by deposition corrosion on the surface of stainless steel.

Pitting corrosion is rare, especially in small valves, because there is little chance of depositing on the valve plate.

304 and 316 stainless steel have nearly equal corrosion resistance in a variety of water media (drinking water, distilled water, river water, boiler water, seawater, etc.); however, 316 stainless steel is better suited if the medium contains exceptionally high levels of chloride ions.

Although the corrosion resistance of 304 and 316 stainless steel is often not substantially different, there may occasionally be a significant variation that calls for more investigation. Since they will be selecting the pipeline and container material based on the medium, valve users should generally have a clear concept. We don't advise users on any materials.

Chemical composition (304,304L,316,316L)

Mechanical properties (304,304L,316,316L)

Introduction to other stainless steels

304 is a general-purpose stainless steel that is widely used to make equipment and parts that require good comprehensive properties (corrosion resistance and formability).

301 stainless steel exhibits obvious work hardening when deformed and is used on various occasions that require higher strength.

302 stainless steel is essentially a variant of 304 stainless steel with a higher carbon content, which can be made to have higher strength through cold rolling.

302B is a stainless steel with a higher silicon content, which has higher resistance to high-temperature oxidation.

303 and 303Se are free-cutting stainless steels containing sulfur and selenium respectively, which are used in places where free-cutting and high surface finish are mainly required. 303Se stainless steel is also used to make parts that require hot upsetting because it has good hot workability under such conditions.

304L is a variant of 304 stainless steel with a lower carbon content, which is used in places where welding is required. The lower carbon content minimizes the precipitation of carbides in the heat-affected zone near the weld, which may cause intergranular corrosion (weld erosion) of stainless steel in certain environments.

305 and 384 stainless steels contain high nickel content and low work hardening rate and are suitable for various occasions with high requirements for cold formability.

308 stainless steel is used to make welding rods.

309, 310, 314 and 330 stainless steels have relatively high nickel and chromium content in order to improve the oxidation resistance and creep strength of steel at high temperatures. 30S5 and 310S are variants of 309 and 310 stainless steels, the only difference being that the carbon content is lower in order to minimize the carbides precipitated near the weld. 330 stainless steel has a particularly high resistance to carburization and thermal shock.

316 and 317 stainless steel contain aluminum, so their resistance to pitting corrosion in marine and chemical industrial environments is much better than that of 304 stainless steel. Among them, 316 stainless steel has variants including low-carbon stainless steel 316L, and high-strength stainless steel containing nitrogen.

316N and free-cutting stainless steel 316F with a high sulfur content.

321, 347, and 348 are stainless steels stabilized with titanium, niobium, and tantalum, respectively, and are suitable for welding components used at high temperatures. 348 is a stainless steel suitable for the nuclear power industry and has certain restrictions on the amount of tantalum and cobalt.

When choosing, you should consider factors such as specific application requirements, environmental conditions, and cost budget.