ANS:C - mild steel

Oxyacetylene welding typically uses a neutral flame or a slightly carburizing flame for most common welding applications, including welding on mild steel, alloy steel, and high carbon steel. For welding on alloy steel, mild steel, and high carbon steel, a neutral flame or a slightly carburizing flame is preferred as it provides good control over the welding process and helps achieve strong welds without excessive oxidation or carbon pickup. However, when welding grey cast iron, an oxyacetylene reducing flame is often used. Grey cast iron is sensitive to oxidation and can easily form brittle compounds if exposed to excess oxygen during welding. The reducing flame helps to minimize oxidation and maintain the integrity of the cast iron.