What is a typical interpass temperature range for carbon steels in many codes?

What is a typical interpass temperature range for carbon steels in many codes?

• A. 50-100°C
• B. 150-250°C
• C. 400-450°C
• D. 300-350°C

Answer: (B)

Interpass temperature defines how hot the joint can be between passes in a multi-pass weld. Controlling this temperature is crucial because it shapes how the weld and heat-affected zone cool and reheat, which in turn affects the microstructure, hardness, and the ability of hydrogen to diffuse out. For carbon steels, many codes settle on a middle ground of 150 to 250°C because this range provides enough heat to ensure good fusion with the previous pass while keeping the cooling rate from being too fast (which can create brittle, hard microstructures) and not too slow (which can lead to excessive reheating and distortion or softening). Too cool a temperature (like 50–100°C) can trap hydrogen and promote cracking; too hot (such as 300–350°C or 400–450°C) can over-temper or distort the weld and surrounding metal, compromising strength and toughness. Therefore, 150–250°C is the standard interpass range.

Interpass temperature defines how hot the joint can be between passes in a multi-pass weld. Controlling this temperature is crucial because it shapes how the weld and heat-affected zone cool and reheat, which in turn affects the microstructure, hardness, and the ability of hydrogen to diffuse out. For carbon steels, many codes settle on a middle ground of 150 to 250°C because this range provides enough heat to ensure good fusion with the previous pass while keeping the cooling rate from being too fast (which can create brittle, hard microstructures) and not too slow (which can lead to excessive reheating and distortion or softening). Too cool a temperature (like 50–100°C) can trap hydrogen and promote cracking; too hot (such as 300–350°C or 400–450°C) can over-temper or distort the weld and surrounding metal, compromising strength and toughness. Therefore, 150–250°C is the standard interpass range.