Comparison between Duplex Steel and 316 Stainless Steel

Difference Between Duplex Steel and 316 Stainless Steel

The user or seeker must first understand what stainless steel is and why there are several sorts before learning about that steel. The term “stainless steel” refers to a steel category distinguished by its corrosion to resistance. There are many different kinds of stainless steel, but they all have a low amount of chromium. Ferritic, martensitic, austenitic, and duplex are some of the stainless steel varieties. As duplex and 316 stainless steel are being considered in this article, they each have distinctive characteristics.

The fundamental distinction between duplex and 316 stainless steel is how corrosion-resistant each alloy is. The 300 family’s 316 has the most excellent resilience to corrosive conditions, with the duplex having greater resistance to corrosive pitting in the presence of chlorides. The alloys’ chemical make-ups vary significantly from one another. 316 stainless steel has a chromium content of 16% and a nickel content of 8%, while duplex has a chromium content of 18 to 28% and 4 to 8%.

What is Duplex Steel?

The graticule and austenitic stainless steel comprise the two-phase microstructure of duplex stainless steel. The ferritic grains split in two at room temperature, becoming austenitic grains. As duplex steel starts to melt, it transforms from a liquid condition to a ferritic one.

What is 316 Stainless Steel?

This type of stainless steel is called austenitic stainless steel. Because of its 2-3% molybdenum concentration, 316 stainless steel is well recognized. Adding molybdenum to the metal makes it more durable and resistant to high temperatures and corrosion.

Duplex Steel VS 316 Stainless Steel


Duplex Steel

316 Stainless Steels

1. Corrosion Resistance

Duplex stainless steel has excellent corrosion resistance. They have significant intergranular corrosion resistance. Duplex stainless steel has excellent stress corrosion cracking resistance, especially in chloride and sulfide conditions.

Super duplex grades offer significantly more corrosion resistance.

In various hostile conditions and media, stainless steel 316 exhibits high corrosion resistance. People often call it “marine grade” stainless steel, but it doesn’t hold well in warm seawater. Pitting and pitting may occur in a hot chloride atmosphere. Over 60°C, grade 316 is also susceptible to corrosion cracking.


2. Heat Resistance

Temperatures beyond around 300°C might result in burning due to the high chromium concentration in duplex stainless steel, which protects against corrosion.

The ductility of duplex stainless steels is higher at low temperatures than that of ferritic and martensitic grades. Duplex grades may be utilized at temperatures as low as -50°C.

In intermittent use, stainless steel 316 has excellent resistance to oxidation up to 870°C, and in continuous service, up to 925°C. If, on the other hand, resistance to corrosion in water is essential, it is not advisable to use the material continuously at temperatures ranging from 420 to 860 degrees Celsius. In this situation, 316L is recommended because it prevents carbides from forming.

The 316H grade is suitable for high-strength applications at temperatures exceeding 500°C.


3. Welding

Weldability is excellent in duplex stainless steel. All conventional welding methods are compatible. While they are more difficult to weld than austenitic grades, duplex grades’ reduced thermal expansion after welding minimizes deformation and residual stress.

With or without fillers, the fusion welding performance of 316 stainless steel is outstanding. For stainless steel 316 and 316L, the recommended filler rods and electrodes are the same as for the base metals 316 and 316L, respectively. Post-weld annealing may be necessary for heavy welded parts. In heavy section welds, grade 316Ti may be used instead of stainless steel 316.

For connecting stainless steel 316, oxyethylene welding has not proven effective.


4. Machining

While machinable, duplex stainless steel’s high strength makes machining challenging. The machining of 2205, for example, is about 20% less than that of 304.

The following guidelines may be used to improve machining.

Sharpening cutting edges is essential. More labour is made more difficult by dull edges.

The incisions should be thin but deep enough to prevent driving over the material’s surface from hardening the job.

Chip breakers should be utilized to assist in guaranteeing that swarf from the job is kept clean.

Since austenitic alloys have limited thermal conductivity, heat is focused near the cutting edges. This necessitates the use of significant volumes of coolants and lubricants.

Machinability is excellent in stainless steel 316. Following these guidelines will improve machining:

It’s important to maintain sharp cutting edges. More labour is made more difficult by dull edges.

Chip breakers should be utilized to assist in guaranteeing that swarf from the job is kept clean.

Since austenitic alloys have a limited thermal conductivity, heat is focused on the cutting edges.


5. Applications

Duplex stainless steel is often used in the following applications:

Processing, transportation, and storage of chemicals

Exploration for oil and gas, as well as offshore rigs

Pollution Control Devices for Oil and Gas Refining Marine Environment

Stainless steel 316 was created for use in paper mills; however, it is now widely used in:

Processing equipment for food

Brewing, dairy, and pharmaceutical equipment

Equipment for the Chemical and Petrochemical Industries

Laboratory equipment and benches

Architectural Paneling for the Coast

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