Welding characteristics of steel and copper

Welding characteristics of steel and copper

  The welding characteristics of steel and copper-copper welding:
Red copper welding is the material of the workpiece to be welded (here refers to red copper). By heating steel and pouring copper or pressurizing or both, and with or without filling materials, the material of the workpiece is made of copper to form a permanent connection between atoms. The process is generally used in the industrial copper welding process. The workpiece and the solder are melted to form a molten area, and the molten pool is cooled and solidified to form a connection between the materials. During this process, pressure is usually applied. There are many energy sources for copper welding, including gas flame, electric arc, laser, electron beam, friction and ultrasonic waves. Before the end of the 19th century, the only red copper welding process was the metal forge welding that blacksmiths have used high-strength brass for hundreds of years. The earliest modern copper welding technology appeared at the end of the 19th century, first arc welding and oxygen gas welding, and later resistance welding.

Classification of copper welding: metal copper welding is divided into three categories: fusion welding, pressure welding and brazing according to the characteristics of the process.

Fusion welding is a method in which the interface of the workpiece is heated to a molten state during the copper welding process, and the copper welding is completed without pressure. During welding, the heat source rapidly heats and melts the joint of the two workpieces to be welded, forming a molten pool. The molten pool moves forward with the heat source and forms a continuous weld after cooling to connect the two workpieces into one.

  In the fusion welding process, if the atmosphere is in direct contact with the high-temperature molten pool, the oxygen in the atmosphere will oxidize metals and various alloying elements. Atmospheric nitrogen, water vapor, etc. enter the molten pool, and will also form pores, slag inclusions, cracks and other defects in the weld during the subsequent cooling process, deteriorating the quality and performance of the weld.

Classification of copper welding: metal copper welding is divided into three categories: fusion welding, pressure welding and brazing according to the characteristics of the process.
In order to improve the quality of copper welding, various protection methods have been developed. For example, gas shielded arc welding is to use argon, carbon dioxide and other gases to isolate the atmosphere to protect the arc and molten pool rate during copper welding; another example is to add iron titanium powder with a high affinity for oxygen to the electrode coating when welding copper. Deoxidation can protect the beneficial elements such as manganese and silicon in the welding rod from oxidation and enter the molten pool. After cooling, high-quality welds can be obtained.

  Pressure welding is to make two workpieces realize interatomic bonding in a solid state under pressure, which is also called solid copper welding. The commonly used pressure welding process is resistance butt welding. When the current passes through the connecting end of the two workpieces, the temperature rises due to the large resistance. When heated to a plastic state, the connection becomes a whole under the action of axial pressure.

  The welding characteristics of steel and copper-carbon steel welding
Weldability refers to the ability of a material to be welded into a component according to the specified design requirements under limited construction conditions, and to meet the expected service requirements. Weldability is affected by four factors: material, welding method, component type and usage requirements. Carbon steel is based on iron element, iron-carbon alloy, carbon is the alloying element, the mass fraction of carbon does not exceed 1%, in addition, the mass fraction of manganese does not exceed 1.2%, and the mass fraction of silicon does not exceed 0.5%. Both are not used as alloying elements. Other elements such as Ni, Cr, Cu, etc. are controlled within the limit of the residual amount, let alone alloying elements. Impurity elements such as S, P, O, N, etc., are strictly restricted according to different steel varieties and grades. Therefore, the weldability of carbon steel mainly depends on the carbon content. As the carbon content increases, the weldability gradually deteriorates. Among them, low carbon steel has the best weldability.
Welding characteristics of steel and copper:

The atomic radius, lattice type, lattice constant and number of electrons in the outer layer of Fe and Cu are relatively close, which is more advantageous for welding between steel and copper. However, the fusion welding of steel and copper still has certain difficulties, mainly as follows:

(1). The physical properties of steel and copper are different, and the melting point and linear expansion coefficient are different. The coefficient of linear expansion of red copper is large, which will produce greater welding stress during the welding process.

(2). The thermal conductivity of copper is more than 8 times that of steel. The cooling rate of the molten pool is much greater than that of steel. The diffusion and escape of hydrogen and the floating conditions of water are worse, and the sensitivity of forming air and air is increased.

(3). Hot cracks are likely to occur in the weld or near the seam area, which affects the strength and air tightness of the joint. This is a key problem to be solved in the welding process. Because steel and copper contain a certain amount of impurities, such as oxygen, sulfur, and phosphorus. In the welding process, these impurity elements are easy to form various low-melting eutectic and brittle compounds, which are stored at the grain boundaries of the weld, which severely weakens the intergranular bonding force of the metal at high temperatures and is the main cause of thermal cracks in the weld. the reason. In addition, the iron element in the weld has a greater influence on the tendency of hot cracking. According to relevant information, when the iron content is 10 to 43%, the weld has the best crack resistance. Therefore, it is very important to control the fusion ratio of the weld.