As a Welded Stainless Steel Pipes Manufacturer China, share the information with you. Stainless steel is a metal material. Stainless steel refers to steel that is resistant to erosion by weakly corrosive media such as air, steam, and water, and chemically aggressive media such as acid, alkali, and salt. It is also called stainless acid-resistant steel. The steel that is eroded is called stainless steel, and the steel that is resistant to chemical media is called acid-resistant steel. Because of the difference in chemical composition between the two, the former is determined to be resistant to chemical media, and the latter is generally stainless. Stainless steel The corrosion resistance depends on the alloying elements contained in the steel. The basic alloy elements of stainless steel are nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., in order to meet the requirements of various applications on the structure and function of stainless steel, stainless steel is easily attacked by chloride ions, because chromium, nickel, and chlorine are isotopes. Isotopes will be exchanged and assimilated to form stainless steel erosion.
Austenitic Stainless Steel Pipe
Austenitic Stainless Steel Pipe commonly used heat treatment processes are solution treatment, stabilization treatment and stress relief treatment.
(1) Solution treatment. After the steel is heated to 1050 ~ 1150 ℃, it is water quenched. The main purpose is to dissolve carbides in austenite and keep this state to room temperature, so the corrosion resistance of steel will be greatly improved. As mentioned above, in order to prevent intergranular corrosion, solution treatment is usually used to dissolve Cr23C6 in austenite and then quickly cool it. For thin-walled parts, air cooling can be used, and water cooling is generally used.
(2) Stabilizing treatment. Generally, it is carried out after solution treatment. It is usually used for 18-8 steel containing Ti and Nb. After the solution treatment, the steel is heated to 850 ~ 880 ° C and then air-cooled. At this time, the carbides of Cr are completely dissolved and the titanium is removed. The carbides are not completely dissolved, and are fully analyzed during the cooling process, making it impossible for carbon to form chromium carbides again, thus effectively intergranular corrosion.
(3) Destress treatment. The stress relief treatment is a heat treatment process for the residual stress of steel after cold working or welding, which is generally heated to 300 ~ 350 ° C and tempered. For steels that do not contain the stabilizing elements Ti and Nb, the heating temperature does not exceed 450 ° C to prevent the precipitation of chromium carbides and cause intergranular corrosion. For cold-worked and welded parts of ultra-low carbon and Ti and Nb-containing stainless steels, they need to be heated at 500 ~ 950 ° C and then slowly cooled. The stress can increase the intercrystalline corrosion tendency and improve stress corrosion resistance.
On the basis of austenitic stainless steel, appropriately increase the Cr content and reduce the Ni content, and cooperate with the remelting treatment to obtain a dual-phase structure with austenite and ferrite (containing 40 ~ 60% δ-ferrite) ) Stainless steel, typical steel grades are 0Cr21Ni5Ti, 1Cr21Ni5Ti, OCr21Ni6Mo2Ti, etc. Duplex stainless steel pipe has better weldability, no heat treatment is required after welding, and its tendency to intergranular corrosion and stress corrosion is also small. However, due to the high Cr content, it is easy to form a sigma phase. Care should be taken when using it.
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