The phenomenon of weld decay is found in case of

ANS:D - cast iron

Cast iron is not typically associated with the phenomenon of weld decay. Instead, it is commonly known for its own unique characteristics and challenges in welding. Cast iron is a ferrous alloy known for its high carbon content, typically between 2% and 4%, along with silicon and other alloying elements. When cast iron is welded, it presents several challenges due to its high carbon content and the formation of graphite flakes or nodules within its microstructure. Here are some key points about welding cast iron:

1. Brittleness: Cast iron can be brittle, especially in its as-cast state. During welding, the rapid heating and cooling cycles can induce stresses in the material, leading to cracking, particularly if proper preheating and cooling procedures are not followed.
2. Graphitization: The carbon in cast iron exists in the form of graphite flakes or nodules dispersed throughout the metal matrix. During welding, the high temperatures can cause some of the carbon to migrate, resulting in changes to the microstructure, such as the formation of harder phases like martensite in the heat-affected zone.
3. Preheating and Post-Weld Heat Treatment: Preheating the cast iron before welding and applying post-weld heat treatment can help reduce the risk of cracking and improve the overall integrity of the weld joint. Preheating helps to reduce thermal gradients and minimize stresses, while post-weld heat treatment can relieve residual stresses and promote the formation of a more ductile microstructure.
4. Welding Processes: Various welding processes can be used for welding cast iron, including shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), and oxyacetylene welding. Each process has its advantages and limitations, and the selection depends on factors such as the thickness of the material, accessibility, and desired weld quality.

In summary, while cast iron does not exhibit weld decay in the same way as stainless steel, it does present its own challenges during welding due to its high carbon content and unique microstructure. Proper welding techniques, including preheating, selection of appropriate filler materials, and post-weld heat treatment, are essential for achieving successful welds in cast iron.