What is the maximum temperature for preheat welding of carbon steels to prevent cold cracking?

Preheating carbon steels is an important process in welding to prevent cold cracking, which can occur due to the rapid cooling of the weld area. The primary aim of preheating is to raise the temperature of the base metal, thereby reducing thermal stresses and the potential for hydrogen to either form or diffuse into the weld joint.

The maximum preheat temperature specified for carbon steels to effectively prevent cold cracking is generally 150°F. Preheating to this level helps maintain a suitable heat level throughout the weld process, ensuring that the steel does not cool too quickly, which could lead to brittle structures or cracking.

Exceeding this recommended preheat temperature may not significantly improve the prevention of cold cracking and could introduce challenges such as excessive heat input, which can cause other metallurgical issues like reduced hardness or softening of the heat-affected zone. Therefore, the value of 150°F is determined to be optimal for minimizing the risk of cold cracking in carbon steels during welding.