CSWIP 3.1

Preheating when welding carbon manganese steel is typically done to prevent hydrogen cracking. This is because preheating helps to reduce the cooling rate of the weld, which in turn reduces the risk of hydrogen becoming trapped in the weld and causing cracking. Hydrogen cracking can occur when hydrogen diffuses into the weld metal and becomes trapped as it solidifies, leading to the formation of cracks. By preheating the steel, the cooling rate is slowed down, allowing hydrogen to escape and reducing the likelihood of cracking.

Linear slag inclusion is unlikely to be found by visual inspection because it is a defect that occurs within the weld and is not easily visible on the surface. Slag inclusions are non-metallic materials trapped in the weld metal or between the weld and base metal, and they can be difficult to detect without using non-destructive testing methods such as radiography or ultrasonic testing. Visual inspection alone may not be sufficient to identify linear slag inclusions, making it an unlikely defect to be found through this method.

If the heat input per unit length of weld is excessively high in carbon manganese steel, it can lead to a decrease in toughness. High heat input can cause the formation of coarse grains in the weld zone, which can result in reduced toughness. Coarse grains are more prone to cracking and can lead to brittle behavior, reducing the material's ability to absorb energy and resist fracture. Therefore, toughness is the mechanical property most affected by excessively high heat input in this scenario.

Resistance spot welding uses a resistive heating system to achieve weld metal deposition. In this process, two metal pieces are pressed together and an electric current is passed through them. The resistance of the metal generates heat, which melts the metal at the contact points. As the current continues to flow, the molten metal solidifies, forming a weld. This process is commonly used for joining thin metal sheets or wire mesh, and it is often used in automotive manufacturing and construction industries.

The correct answer is b) Report the occurrence to high authority. This is the first action to take because centerline cracking in a weld is a serious defect that can compromise the structural integrity of the components. Reporting the occurrence to high authority ensures that the issue is brought to the attention of those who have the power to address it and take appropriate actions to prevent further occurrences. Impounding all welding consumables, stopping all welding, and calling for full NDT checks may be necessary steps to investigate and rectify the issue, but reporting it to high authority is the initial action to initiate the process.