🔍 Key Concepts

• Effect of temperature gradient across a weld during heating and cooling • Relationship between thermal stresses and how fast or unevenly metal heats and cools • Why welders use preheat/postheat on thick or high‑strength steels (e.g., to control cracking)

💭 Think About

• Think about whether preheating makes the weld and base metal heat and cool more evenly or more sharply from hot to cold. • If the metal experiences a sharp temperature difference in a small area, what happens to internal stresses and the risk of cracking? • If the heating process is more gradual and uniform, what usually happens to internal stresses in the welded joint?

✅ Before You Answer

• Decide whether preheating makes the temperature gradient larger or smaller across the weld and base metal. • Decide whether larger temperature gradients usually increase or relieve internal stresses in metals. • Match the combination: (increase/decrease) in gradient with (intensify/relieve) stresses to pick the best choice.