9.1 State FOUR factors that affect the temperature at which cold-worked steel will recrystallise when heated - NSC Mechanical Technology Welding and Metalwork - Question 9 - 2021 - Paper 1

The type of electrode can greatly influence the thermal properties of the weld. Certain electrodes may provide greater heat input, thus affecting the cooling rate and resulting shrinkage in a welded joint.

The size of the electrode affects heat input during the welding process. A larger electrode can provide more heat, resulting in greater expansion and consequently more shrinkage when it cools.

Welding current directly influences the heat generated during welding. A higher welding current increases the melting temperature, producing more heat which can lead to greater shrinkage upon cooling.

1. Size of work piece: Thicker materials will cool more slowly than thinner materials, affecting the overall cooling rate.

2. Weld thickness: Increased thickness of the weld bead can also influence the cooling rate, as larger volumes retain heat longer.

Weld distortion is the warping of the base metal caused by heat from the welding arc or flame. This results in a change of shape in the welded components.

Weld shrinkage refers to the reduction in size of the welded joint as the weld metal cools and solidifies. This can lead to dimensional changes in the final product.

1. Heating and expansion: When the metal is heated, it expands. If this expansion is restrained during cooling, it can lead to distortion.

2. Cooling and contraction: When the metal cools, contraction occurs. If this is also restrained, it can add residual stresses.

3. Applied stresses: External forces can change the distribution of stresses in a welded joint, impacting both distortion and residual stress.

1. Thermal stresses: The heating and cooling process during welding creates thermal gradients, leading to residual stresses in the joint.

2. Phase changes: As the weld metal cools, it may undergo phase changes that can result in internal stresses.