Welder Red Seal · Question
What is the primary metallurgical reason for preheating a thick section of medium-carbon steel before welding?
Preheating reduces the temperature gradient between the weld and the base metal. This slows down the post-weld cooling rate, which minimizes the formation of ha
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Question: What is the primary metallurgical reason for preheating a thick section of medium-carbon steel before welding?
Answer options:
- To burn off any paint, oil, or rust on the surface.
- To reduce the amount of welding current required.
- To increase the overall tensile strength of the finished weld. ✅ To slow the cooling rate of the weld and HAZ, preventing brittle microstructures.
Correct answer: To slow the cooling rate of the weld and HAZ, preventing brittle microstructures.
Explanation: Preheating reduces the temperature gradient between the weld and the base metal. This slows down the post-weld cooling rate, which minimizes the formation of hard, brittle structures like martensite and reduces the risk of hydrogen-induced cracking in the heat-affected zone (HAZ).
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