Metallurgical science is the study of internal structure of the metal, and the relationship between this structure and properties of metals. In metallurgical science, we are primarily interested in various changes that occur in metals when they are welded together. In particular, this applies to those changes that affect the mechanical properties of metals.
In this regard, the welding inspector should know the fundamentals of welding metal science. It seems unlikely that the welding inspector will be responsible for developing the technical conditions for alloys of base metals and weld metals, as well as for processing them. However, the understanding of the welding metal fundamentals science not only helps the inspector in work, but also, in many cases, is a necessary condition for performing various control functions. One of the reasons is that the metallurgical changes that occur as a result of welding affect the mechanical properties of metals, such as strength, hardness, ductility, toughness, and fatigue strength and abrasion resistance.
These properties can vary under the influence of various factors related to metallurgy, including the addition of alloying elements, heat treatment and machining. The welding inspector, who knows these parameters, will be able to better understand the need for performing certain operations during the welding operations. The number of procedures that must be performed during welding, including preheating, heating after welding, monitoring the weld metal temperature before applying the subsequent layer, monitoring the running energy, seam sealing, removing thermal stresses, and other types of heat treatment may lead to certain changes of metallurgical properties, which, in turn, is affect the mechanical properties of metals.
Metallurgical science is a very versatile field of knowledge, so we need to focus our attention on the most significant changes that can occur during the welding. These changes can be divided into two main categories.
The first category includes those changes that occur when the metal is heated from room temperature to high temperatures, as well as changes that occur during cooling. The second category includes the effect of these temperature changes on the properties of the metal, taking into account the rate at which these changes occur. In particular, we are interested in the rate at which the heated metal is cooled to room temperature.
Further in the articles, we will consider the specific changes that occur with metals when they are uniformly heated and cooled. At the same time, it should be noted that when performing welding operations, local heating of individual parts of the metal surface occurs, creating special problems. Due to the uneven heating and cooling, there is a need to take into account a number of the additional factors.