Test you: Prevention and control methods of intergranular corrosion

This post was last edited by mopeizhi on 2010-1-31 20:06 1) Solution quenching treatment, heating the German steel that has produced a chromium-depleted area to about 1100C, dissolving the chromium carbide, quenching with water, and quickly passing through the sensitization temperature zone, so that the alloy maintains the uniformity of chromium.； 2) Add a small amount of elements that are more likely to form carbides into steel, such as titanium, niobium, etc. 3) When the carbon content is reduced to less than 0.03%, the amount of chromium precipitated from the grain boundaries will be very small.

This post was last edited by mopeizhi on 2010-1-31 20:07 Intergranular corrosion is a form of corrosion where the corrosion is limited to the grain boundaries and near the grain boundaries, while the corrosion of the grain itself is relatively small. It is caused by the increase or decrease of impurities in the grain boundary or the increase or decrease of a certain alloying element in the grain boundary area. For example, aluminum contains a small amount of iron that precipitates at the grain boundaries, causing intergranular corrosion. The zinc content is relatively high at the grain boundaries of brass, causing intergranular corrosion of brass. Austenitic stainless steel is most prone to intergranular corrosion, and there are three ways to control it: using high-temperature solution treatment, generally called solution quenching; adding stabilizing elements; and reducing the carbon content in the steel to less than 0.03%.

This post was last edited by mopeizhi on 2010-1-31 20:08 Intergranular corrosion is a form of corrosion where the corrosion is limited to the grain boundaries and near the grain boundaries, while the corrosion of the grain itself is relatively small. It is caused by the increase or decrease of impurities in the grain boundary or the increase or decrease of a certain alloying element in the grain boundary area. For example, aluminum contains a small amount of iron that precipitates at the grain boundaries, causing intergranular corrosion. The zinc content is relatively high at the grain boundaries of brass, causing intergranular corrosion of brass. Austenitic stainless steel is most prone to intergranular corrosion, and there are three ways to control it: using high-temperature solution treatment, generally called solution quenching; adding stabilizing elements; and reducing the carbon content in the steel to less than 0.03%. For example, 316TI adds Ti to SUS316 steel to improve intergranular corrosion resistance.

This post was last edited by mopeizhi on 2010-1-31 20:11 ] Reduce the content of carbon, phosphorus, sulfur and other harmful impurity elements; add a small amount of stabilizing element titanium, appropriately increase the chromium content and reduce the nickel content; perform solid solution treatment at 1050-1100°C, rapid cooling, and inhibit the precipitation of carbides at the grain boundaries; perform stabilization treatment at 850-880°C 2-4 h, and then cool slowly; when cold working and treatment at a considerable sensitization temperature are required, follow the principle of cold working first and then heat treatment; the grain size is controlled at level 6-8 through processing and heat treatment.

This post was last edited by mopeizhi on 2010-1-31 20:09.: (1) It is generally believed to be due to the lack of chromium at the grain boundary. Specifically, it has high corrosion resistance, as long as the steel contains a high content of chromium, but the austenite unidirectional structure treated at high temperature (1050-1150 degrees) and subsequently rapidly cooled is in a metastable state. In the future, Carbides will precipitate during the heating process. In the sensitization temperature range of 600-800 degrees, chromium carbides mainly precipitate between crystals. Since the chromium content of this carbide is much higher than the chromium content in the matrix, its formation will inevitably cause aggregation and diffusion in adjacent areas, resulting in chromium deficiency. Intergranular corrosion occurs because chromium deficiency cannot resist corrosion in certain media. (2) Furthermore, corrosion is also related to stress or intergranular heterogeneity. blocking method: Choose titanium niobium and ultra-low carbon stainless steel. Control heat input during welding and avoid heat treatment as much as possible. An effective method to prevent intergranular corrosion of materials is: (1) Reduce the content of harmful impurity elements such as carbon, phosphorus, and sulfur; (2) Add a small amount of stabilizing element titanium ； (3) Appropriately increase the chromium content and reduce the nickel content; (4) Perform solid solution treatment at 1050-1100°C and cool quickly to inhibit the precipitation of carbides at the grain boundaries; (5) Stabilize at 850-880°C for 2-4 hours, and then cool slowly; (6) In situations where cold working and treatment at a considerable sensitizing temperature are required, follow the principle of cold working first and then heat treatment; (7) Control the grain size at level 6-8 through processing and heat treatment ； (8) Choose stainless steel with titanium, niobium and ultra-low carbon ； (9) Control heat input during welding and try not to perform heat treatment.

This post was last edited by mopeizhi on 2010-1-31 20:12 There are currently three main aspects to preventing intergranular corrosion:: 1. Solution treatment 2. Reduce the carbon content in steel 3. Add elements that stabilize carbides

This post was last edited by mopeizhi on 2010-1-31 20:13 Intergranular corrosion of austenitic stainless steel welded structures can be prevented by the following methods: 　　①Use low-carbon grades 00Cr19Ni10 (304L) or 00Cr17Ni14Mo2 (316L), or stable grades 0Cr18Ni11Ti (321, more common in Europe) or 0Cr18Ni11Nb (347, more common in the United States). Using these grades of stainless steel can prevent the amount of carbide precipitation that would cause harmful effects during welding. 　　②If the structural part is small and can be heat treated in a furnace, it can be heat treated at 1040-1150°C to dissolve chromium carbide, and rapidly cooled in the range of 425-815°C to prevent carbon precipitation.

This post was last edited by mopeizhi on 2010-1-31 20:15 ] 1. Reduce the carbon content in steel as much as possible to reduce or avoid the precipitation of carbides on grain boundaries. When the carbon content in steel is less than 0.02%, crystal tip corrosion should not occur. 2. Use appropriate heat treatment to avoid the precipitation of grain boundary precipitation phases or change the type of grain boundary precipitation phases. 3. Add appropriate stabilizing elements titanium or niobium to stainless steel, or add trace amounts of grain boundary adsorption element boron to control intergranular precipitation and grain boundary adsorption. 4. Choose austenite-ferrite (not forming a continuous network) bidirectional stainless steel. This type of steel has good resistance to intergranular corrosion.

This post was last edited by mopeizhi on 2010-1-31 20:17

Methods to prevent intergranular corrosion include: first, reducing the mass fraction of carbon in the steel (<0.03%) so that no carbides are formed in the steel; second, adding elements that can form stable carbides, such as titanium and niobium, to the steel so that TiC/NbC is preferentially formed in the steel instead of chromium carbides to ensure the chromium content in austenite.