What preheating or interpass conditions are typically recommended for high-carbon steels to minimize cracking in GMAW?

• A. Preheat to higher temperature (commonly 150–200°C or more depending on carbon content), maintain controlled interpass temperature, and use low-hydrogen filler and slower cooling.
• B. No preheating required.
• C. Preheat to 500°C.
• D. Use high-hydrogen filler.

Answer: (D)

Minimizing cracking in high-carbon steels during GMAW hinges on reducing hydrogen effects and controlling cooling and thermal stresses. Preheating the workpiece lowers the cooling rate and keeps the metal more ductile as it solidifies, which helps prevent delayed cracks that form in brittle, high-carbon microstructures. A moderate preheat is typical—around 150–200°C, with interpass temperatures kept in that range (adjusted for carbon content and thickness)—to slow hydrogen diffusion and reduce thermal gradients that drive cracking. Using a low-hydrogen filler metal minimizes the amount of hydrogen introduced into the weld, a major factor in hydrogen-induced cracking for these steels. Slower cooling after welding further reduces residual stresses and allows constructive microstructural changes toward toughness. Conversely, practices like no preheat, excessively high preheat (such as 500°C), or using a high-hydrogen filler would increase cracking risk rather than mitigate it.