What are the Advantages of welding Preheating?

What are the Advantages of welding Preheating?

Welding holds some of the most violent changes of temperature in the manufacturing industry. Pre-heating the metal can help prevent weld cracking caused by these extremities.

One of the main reasons for weld cracking has to do with the properties of the metal, which change during the welding process. As the weld cools, the steel undergoes multiple phases with different molecular structures, depending on the rate of cooling. If the steel cools too fast it can result in the formation of a hard and brittle structure called martensite. This structure can easily allow for weak welds and cracking. As the picture shows, the structure is formed in the adjacent base metal, and not so much in the weld metal, so the base metal is where the cracks will form.

Preheating the entire base metal, or even the base metal local to the weld, will help prevent cracking. The more area around the weld that is preheated, the longer it will take the weld to cool down, just because there is more material that needs to release heat. Preheating is very important for controlling the cooling rate of the weld area.