What are the feasible measures to prevent and control intergranular corrosion in austenitic stainless steels?
Thread Content
This post was last edited by JFTANG726 on 2010-2-2 11:49. As the title suggests: What are the feasible measures to prevent and control intergranular corrosion in austenitic stainless steels? Austenitic stainless steels generally exhibit a tendency to intergranular corrosion, which mostly occurs after being treated at temperatures between 427 and 816°C.
Intergranular corrosion: According to the chromium-depletion theory, when the welds and heat-affected zones are heated to the sensitization temperature range of 450–850°C, chromium carbide precipitates at the grain boundaries, resulting in chromium-depleted boundaries that are not strong enough to resist corrosion. Preventive measures: (1) Use low-carbon or ultra-low-carbon welding materials such as A002, as well as electrodes containing stabilizing elements like titanium and niobium, such as A137 and A132. (2) A certain amount of ferrite-forming elements are introduced into the weld from the welding wire or electrode, resulting in a dual-phase structure of austenite and ferrite in the weld metal (with the ferrite content generally maintained between 4-12%). (3) Reduce overheating of the weld pool by using a lower welding current and a faster welding speed, thereby accelerating the cooling rate. (4) Perform post-weld stabilization annealing on weldments with high requirements for intergranular corrosion resistance.
Feasible measures to prevent and control intergranular corrosion in austenitic stainless steels include the following: 1. Control of the working environment: this involves controlling the temperature (avoiding the sensitization range of 400–850 degrees) as well as the corrosivity of the medium. 2. Control of material aspects: Use ultra-low carbon stainless steel with a carbon content of 0.03% or less ； The elements in the steel are adjusted to achieve an austenite + ferrite duplex structure, with ferrite accounting for 5%-12%. 3. Control in terms of welding processes: Low-carbon or ultra-low-carbon welding materials such as A002 are used, as well as electrodes containing stabilizing elements like titanium and niobium, such as A137 and A132 ； A certain amount of ferrite-forming elements is introduced into the weld from the welding wire or electrode, resulting in a dual-phase structure of austenite and ferrite in the weld metal; the ferrite content is generally kept between 4-12% ； Reduce overheating of the welding pool by using a lower welding current and a faster welding speed, thereby accelerating the cooling rate. 4. Heat treatment: Solution treatment, stabilization treatment, and stress relief treatment are employed.