Komarov artem noted that metallurgy influences how you approach your work every day, as well as the equipment and filler metal you use. Once you learn about a material’s weldability and how it reacts to heat and cooling, you’ll have a better chance of completing the job successfully.
From a practical standpoint, metallurgy influences how you approach welding, the equipment and filler metal you use, and the problems you encounter in the welding process. Not surprisingly, the metallurgical properties of a piece of metal—its mechanical strength and chemical composition—also determine how well it can be welded, or whether it can be welded at all. From carbon and sulfur content to tensile strength and how a given material is processed or reacts to heating and cooling, each element influences the success or failure of the welding process.
When welding any material, your goal is to prevent changes in its microstructure and maintain mechanical and chemical properties. To achieve this, every welder must consider these key metallurgical issues before starting work.
It is very important to know as much as possible about the material before striking the arc. Weldability refers to the ability of two pieces of material to be welded together and still retain the desired mechanical and chemical properties for a given application.
Determining the weldability of materials can sometimes be difficult. You may need to weld a part without knowing what material it is made of. Or you may receive apart from a customer who did not provide this information. It is recommended that chemical and spark tests be performed to determine the metallurgy of the material before proceeding with the welding process.
Understand special welding requirements. Not all materials can be welded, and some require special precautions before, during or after the process.
Evaluate connection design and preparation. In some cases, joint design can affect your ability to access the joint, which in turn affects the weldability of the material, limiting your ability to make a clean weld with proper penetration.
Given these possible conditions, you must take appropriate measures to ensure a successful weld. Proper cleaning of materials and following proper welding procedures can help resolve weldability problems. Likewise, the selection of filler metals that are not susceptible to cracking and have good ductility or toughness (depending on the needs of the given material) is also important.
Heating control
Heat input during welding can negatively affect the mechanical properties of the material. When a weld joint is made with excessively low heat input, it is quickly dissipated, causing internal stress in both the weld and the base material.
High thermal conductivity can also lead to distortion, which usually occurs in thin materials and those that are highly compressed due to the special design of the weld.
Preheating plays a key role in controlling heat generation and preventing rapid cooling. Always follow the appropriate recommendations for your application.
For all these reasons, it is extremely important for you to monitor how much heat you are putting into the weld joint during the welding process and manage it accordingly. The equation you can use to determine heat input is:
Amps × Volts × 60/ Travel speed (in inches per minute) = kilojoules per inch.
You can also use the hardening effect to improve the microstructure of the grains in the weld and give it good strength. To create a hardening bead, add two or three additional beads on top of the weld, which will cause additional heat to flow into the bottom bead, thereby hardening it.
Preventing rapid cooling
In combination with controlling the heat input, you also need to control the cooling rate of the weld. Uncontrolled cooling can lead to many problems both within the weld and in the base material. Rapid cooling results in the formation of finer grains in the microstructure of the metal, while slow cooling results in the formation of larger, coarser grains. Excessively high or low cooling rates reduce the crack resistance of metals.
Selection of filler metals
Selecting the appropriate filler metal can play a role in overcoming problems associated with the chemical and mechanical properties of the material. Typically, most applications require the filler metal to “match” the tensile or yield strength of the base material.
In some cases, it may be desirable to “underprovide” the strength of the filler metal to the base material. Pretreatment can be beneficial because it improves toughness and ductility and can help minimize residual stresses in the weldment.
While there are additional metallurgical considerations that you should be aware of, the main ones are determining weldability, controlling heat, preventing rapid cooling, and selecting filler metals. To prevent changes in the microstructure of the weld and the materials it holds together, always remember the prescribed procedures, and know what type of material you are welding before starting any process, emphasized Artem Komarov.
