Q1: Preheating prior to welding is done for the purpose of

ANS:A - decreasing cooling rate.

Preheating prior to welding serves multiple purposes, including:

1. Decreasing cooling rate: Preheating helps to slow down the cooling rate of the welded joint after welding. This controlled cooling reduces the risk of cracking, particularly in high-strength or high-alloy steels that are prone to cracking during rapid cooling.
2. Facilitating fusion of high melting metals: Preheating is particularly important when welding high melting point metals or alloys. By preheating the base metal, it becomes easier to achieve proper fusion between the filler metal and the base metal, ensuring a sound weld.
3. Preventing hot cracking: Preheating helps to reduce the thermal gradient between the weld and the surrounding base metal, minimizing the risk of hot cracking during welding. This is especially critical for materials with a high susceptibility to cracking, such as certain alloys and cast irons.
4. Ensuring full penetration: Preheating can aid in achieving full penetration of the weld into the base metal, especially in thick sections or materials with high thermal conductivity. It helps to ensure that the weld metal can flow properly into the joint without solidifying prematurely.