Applications of Advanced Ferritic Stainless Steels
Ferritic stainless steel is an iron-chromium alloy with a chromium content of 10%-30% in stainless steel materials. This traditional stainless steel material is rarely used in industrial products due to its limited toughness, high brittle transition temperature, and weak processing capabilities.
Through advanced smelting technology, the content of interstitial elements can be effectively reduced and other alloying elements can be added to enhance the toughness of the material and enhance the corrosion resistance of ferritic stainless steel, thereby developing super-ferritic stainless steel and high-performance ferritic stainless steel. Ferritic stainless steel is some of the modern ferritic stainless steel we see now.
Because the chemical composition of this stainless steel saves or even contains no nickel, its price is lower than that of austenitic stainless steel, and it also has very good resistance to stress corrosion cracking and pitting corrosion. Moreover, modern ferritic stainless steel can replace austenitic stainless steel in some fields, and can even replace titanium materials, so its economic significance is relatively prominent.
Due to factors such as the shortage of nickel ore and rising prices, how to use less or no nickel metal is a key issue that needs to be solved in domestic industrial products. The use of modern ferritic stainless steel to partially replace austenitic stainless steel can effectively solve this problem.
Modern ferritic stainless steel is widely used in the petrochemical industry, and there are many types of modern ferritic stainless steel used in the petrochemical industry. The first is 00Cr18Ti ferritic stainless steel, which is 430 or 439 stainless steel. It is an ultra-low carbon ferritic stainless steel stabilized with titanium. Its chemical composition removes sensitivity to intergranular corrosion and does not form a martensite structure in the welding heat affected zone. This steel type can replace 304 stainless steel to a certain extent and can be used to make various condensers, feed water heaters and lubrication system coolers as heat exchange tubes.
The welding, crimping, pipe expansion and other processing methods of this steel type are similar to those of 304 stainless steel. However, the disadvantage of this steel type is that the transition temperature from plastic to brittle is relatively high, and it may become brittle in the range of 260°C to 650°C for a long time. However, heating to 815°C and rapid cooling can restore a certain degree of toughness.
The second type is 0000Cr26Mo stainless steel, which is a high-purity ferritic stainless steel, also known as XM27 stainless steel. This type of steel uses vacuum induction combined with electron beam melting or electroslag remelting for refining to control the mass fraction of interstitial elements carbon and nitrogen to no more than 0.02%, thereby improving plasticity and reducing the brittle transition temperature to -60°C. Because this steel type has relatively high chromium and molybdenum elements, it has excellent corrosion resistance in many environments, especially in chlorides, organic acids, oxidizing acids and hot concentrated alkali solutions. corrosion.
The third type is 00Cr27Mo4Ni3NbT stainless steel, which uses titanium and niobium as stabilizing elements and is refined by the green AOD method to achieve ultra-low carbon content. It has the characteristics of high strength, good ductility, and low work hardening rate. Because of the addition of nickel, its plastic-brittle transition temperature is as high as -84°C, which is lower than similar ferritic stainless steels that do not contain nickel. Its characteristics enable it to have both high design allowable stress and excellent processing performance. . This type of steel can be used to make power plant condensers and feed water heaters, as well as seawater desalination heat exchangers.
The last type is low chromium stainless steel. Because the cost of ferritic stainless steel with a chromium content of 18%-30% is relatively high, the development and use of low-chromium stainless steel is more in line with demand. This type of steel can be used to make automobile exhaust, purification treatment devices and mufflers. It can also be used to make furnace tubes, heat exchangers, reactors and pipes for refinery atmospheric and vacuum, catalytic cracking, delayed coking, hydrocracking and other equipment.
