What is duplex stainless steel?
1. Introduction of Duplex Stainless Steel
Duplex Stainless Steel (Duplex Stainless Steel) is an important branch of stainless steel. It refers to a stainless steel whose metallographic structure is composed of two phases of ferrite and austenite. In its solid solution structure, the ferrite phase and the austenite phase each account for approximately 50%. Generally, the content of the lesser phase should be at least 30% or more. This type of stainless steel is called ferrite-austenite duplex stainless steel. Duplex stainless steel combines the good corrosion resistance, excellent ductility and weldability of austenitic stainless steel with the higher strength and chloride stress corrosion resistance of ferritic stainless steel, making it both iron The advantages of elemental stainless steel and austenitic stainless steel. It has good comprehensive mechanical properties, not only has high yield strength and fatigue strength, but also has good toughness.
According to chemical composition, the duplex stainless steel commonly used in forging and rolling products at home and abroad can be divided into the following four categories: Mo-free economic duplex stainless steel, standard duplex stainless steel, advanced duplex stainless steel, super duplex stainless steel kind.
SAF2205 duplex stainless steel is a duplex stainless steel composed of 22% chromium, 3% molybdenum and 5-6% nickel-nitrogen alloy. It is currently the most commonly used duplex stainless steel in foreign countries. This steel grade was first developed by Sweden in the 1980s. , It is a typical N, low-carbon, dual-phase ferritic-austenitic stainless steel. This steel has broad application prospects in petrochemical industry, seawater utilization and neutral chloride environment. Therefore, the research on the weldability of 2205 duplex stainless steel is of great significance.
2. Application of duplex stainless steel at home and abroad
Foreign duplex stainless steels are relatively mature in terms of production, processing and application, and are widely used
In industrial territories, such as papermaking, petroleum, chemical, transportation, pharmaceutical, food and construction industries, it is mostly used in manufacturing
Reaction vessels, industrial equipment and pipelines.
Oil and gas industry:
It is widely used in this field abroad, and the application of duplex stainless steel in sour oil and gas fields is gradually increasing. It is mainly used as production pipe lining, pipeline transportation system and heat exchanger. Duplex stainless steel is an ideal structural material, especially in acidic environments containing a large amount of CT, CO2 and some H2S. Duplex stainless steel can not only resist high flow rate wear and corrosion, but also can replace carbon steel with corrosion inhibitors. , Reduce the amount and weight of materials. At present, most oil pipelines use SAF2205 grade duplex stainless steel. Oil and gas well production, offshore oil production platform facilities and oil and gas pipelines in Alaska, North Sea, Gulf of Mexico and other places even use SAF2507 stainless steel. Most of them contain a large amount of CI, CO2 and some H2S. The acidic environment. Domestic oil fields use duplex stainless steel relatively few, and the oil refining industry is the first sector to use domestic duplex stainless steel.
Chemical and petrochemical processing industry:
The working conditions in this field are complex and diverse, and it is also the field where duplex stainless steel is used earlier and more frequently. Under the conditions of high temperature and high concentration of acetic acid, the corrosion resistance of high-alloy austenitic stainless steels and even corrosion-resistant alloys is not ideal, while super duplex stainless steels can be used as coolers, coal contact regeneration equipment, etc. Especially in a gas ion environment, austenitic stainless steel cannot be used due to stress corrosion fracture. Duplex stainless steel can solve this problem. Due to its corrosion resistance and high strength, duplex stainless steel is used in the chemical and petrochemical fields to manufacture reaction vessels, heat exchangers, cooling tanks, etc., and it is widely used in this field in China.
Pulp and paper industry:
The application of duplex stainless steel in the pulp and paper industry has a history of 30 to 40 years. This is the earliest
It is one of the most widely used fields. At present, almost all pressure vessels in pulp and paper mills abroad are
It is made of duplex stainless steel and has very few domestic applications.
Neutral chloride environment:
Duplex stainless steels are widely used in industry, especially in the presence of chloride ions that are prone to local corrosion. In the presence of gas ions, AISI 304L, 316L and other austenitic stainless steels often have stress corrosion cracking (SCC), while duplex stainless steels have strong resistance to chloride ion corrosion and can be substituted Austenitic stainless steel is commonly used to solve this problem, especially for the occasion of stress corrosion cracking caused by pitting corrosion, the application of duplex stainless steel is necessary. Years of use experience has shown that duplex stainless steel is used in a neutral chloride medium, especially as a large number of pipes for contacting heat exchangers containing CI cooling water, and there are few cases of damage. However, stress corrosion cracking will occur in places where chloride ions are enriched or in acid chloride solutions containing H2S.
Sea water environment:
Seawater is the most corrosive medium in the natural environment. Especially when microorganisms are present on the metal surface, the metal surface changes and the metal’s corrosion potential increases. As a result, the probability of pitting and crevice corrosion increases. In the hot sea water medium, the loss of thermal efficiency of the sea water heat exchanger is due to the continuous thickening of the microbial layer on the metal surface. As early as the 1970s, Japan began to use steel materials to manufacture heat exchangers or cooler bundles for petrochemical plants and ships. In the 1980s, a catalyst regeneration cooler was made of 00Cr25NiMo3 WCuN duplex stainless steel in China, which was applied to the ethylene plant. At present, the 25Cr-3Mo duplex stainless steel is the most widely used for hot sea water steel.
Pharmaceutical, salt, food and beverage industries:
The production and processing of food and beverages are generally carried out in hot aqueous solutions containing gas ions, but in gas-containing
The austenitic stainless steel in the hot aqueous solution of ions is prone to stress corrosion and even fracture, so many
Duplex stainless steel is used in heaters, coolers, and storage tanks in breweries, sugar factories, and milk factories. Biphasic not
Rusty steel is also used in steaming towers and other equipment in the pharmaceutical industry. Since duplex stainless steel is in neutral chloride solution
China has good local corrosion resistance. The domestic application of duplex stainless steel has developed vacuum salt and nitric acid joints.
Production equipment, the large-scale brine and mirabilite tanks of the 200,000-300,000-ton salt factory are made of duplex stainless steel.
Linhe composite board material.