What is the primary purpose of preheating steel before welding?

The primary purpose of preheating steel before welding is to improve weld quality. Preheating the material helps to minimize the risk of weld defects by reducing thermal stresses during the welding process. When steel is welded, it tends to cool rapidly, particularly at the edges where the molten weld metal solidifies. This rapid cooling can lead to issues such as cracking, especially in high-carbon steels or thicker sections.

By preheating the steel, the material is brought to a more uniform and elevated temperature, which slows down the cooling rate after welding. This more controlled cooling can help to prevent the formation of hard, brittle microstructures and enhances the ductility of the welded joint. Additionally, preheating can help to drive off moisture and contaminants from the surface of the steel, further contributing to a stronger and more reliable weld.

Although options related to cost, speed, and weight may have some relevance in certain contexts, they do not address the critical factors that preheating is designed to mitigate, namely the prevention of weld defects and enhancement of overall weld integrity.