Stainless steel bars can experience various forms of intergranular corrosion. These include sensitization, weld decay, and knife-line attack.
1. Sensitization occurs when stainless steel is subjected to prolonged high temperatures. This causes the chromium in the steel to combine with carbon and create chromium carbides along the grain boundaries. As a result, the chromium content in the grain boundaries decreases, making them more susceptible to corrosion. Sensitization is commonly observed in austenitic stainless steels like grades 304 and 316.
2. Weld decay, also known as heat-affected zone corrosion, is a type of intergranular corrosion that takes place in the heat-affected zone of a weld. During the welding process, the elevated temperatures cause the formation of chromium carbides along the grain boundaries, similar to sensitization. Consequently, the corrosion resistance in the heat-affected zone diminishes, making it prone to intergranular corrosion.
3. Knife-line attack is a distinct form of intergranular corrosion that arises along the grain boundaries of stainless steel bars after exposure to specific environments, such as those containing chloride ions. This type of corrosion is commonly observed in welded stainless steel structures, particularly in marine settings. It is named knife-line attack due to its appearance as a narrow, localized corrosion attack along the grain boundaries, resembling a cut made by a knife.
It is crucial to note that proper material selection, heat treatment, and welding techniques can prevent or minimize intergranular corrosion. Using stainless steel grades with low carbon content or stabilized with titanium or niobium can help decrease the risk of sensitization and intergranular corrosion. Additionally, post-weld heat treatment processes, such as solution annealing or stress relieving, can help restore the corrosion resistance of the heat-affected zone.
There are several different types of intergranular corrosion that can occur in stainless steel bars. These include sensitization, weld decay, and knife-line attack.
1. Sensitization: Sensitization occurs when stainless steel is exposed to high temperatures for an extended period of time, causing the chromium in the steel to combine with carbon and form chromium carbides along the grain boundaries. This depletes the chromium content in the grain boundaries, making them more susceptible to corrosion. Sensitization is commonly seen in austenitic stainless steels, such as grades 304 and 316.
2. Weld Decay: Weld decay, also known as heat-affected zone corrosion, is a form of intergranular corrosion that occurs in the heat-affected zone of a weld. During the welding process, the high temperatures can cause chromium carbides to form along the grain boundaries, similar to sensitization. This leads to a decrease in corrosion resistance in the heat-affected zone, making it prone to intergranular corrosion.
3. Knife-line Attack: Knife-line attack is a specific type of intergranular corrosion that occurs along the grain boundaries of stainless steel bars after exposure to certain environments, such as those containing chloride ions. This type of corrosion is often seen in welded stainless steel structures, especially those used in marine environments. It is called knife-line attack because it appears as a narrow, localized corrosion attack along the grain boundaries, resembling a knife cut.
It is important to note that intergranular corrosion can be prevented or minimized through proper material selection, heat treatment, and welding techniques. Using stainless steel grades with low carbon content or stabilized with titanium or niobium can help reduce the risk of sensitization and intergranular corrosion. Additionally, post-weld heat treatment processes, such as solution annealing or stress relieving, can help restore the corrosion resistance of the heat-affected zone.
The different types of intergranular corrosion in stainless steel bars include sensitization corrosion, weld decay corrosion, knife-line attack, and grain boundary attack.
