Material Science Simplified

Knife Line Attack on Stabilized Austenitic Stainless Steel (ASS): A Welding Engineer's Perspective Introduction As a welding engineer, it is crucial to understand the various challenges associated with different types of steels and their welding processes. One such challenge is the occurrence of knife line attack on stabilized Austenitic Stainless Steel (ASS). In this blog, we will delve into the causes, consequences, and possible remedies for this issue. Understanding Knife Line Attack Knife line attack refers to a very narrow band or line that forms in an area adjacent to the fusion boundary during the welding process. This phenomenon specifically occurs in stabilized ASS. The affected area experiences a thermal cycle close to the fusion boundary, where temperatures rise significantly above the solidus temperature. Causes of Knife Line Attack Knife line attack in stabilized ASS is primarily attributed to the behavior of titanium (Ti) and niobium (Nb) carbides. Normall...

  Sensitization in austenitic stainless steel occurs when the material is exposed to temperatures within the sensitization range for an extended period. This can happen during welding or heat treatment processes. The formation of chromium carbides at the grain boundaries due to the combination of carbon and chromium atoms leads to a depletion of chromium in the surrounding regions. This depletion creates a chromium-depleted zone along the grain boundaries, making the steel susceptible to intergranular corrosion.   The implications of sensitization in welded structures are significant. Intergranular corrosion weakens the material and can result in localized failures and reduced structural integrity. In critical applications where corrosion resistance is vital, such as in the chemical, petrochemical, and food processing industries, the avoidance of sensitization is crucial to maintain the reliability and longevity of welded components.   To mitigate sensitization, w...