Article
inflash butt weldingOr in resistance butt welding work, due to the influence of the resistance heat source that changes the workpiece port section from solid to liquid to fused solid, the structure and properties of metals and alloys after welding will undergo some changes. Therefore, if we understand the chemical composition and properties of metal and alloy welded joints, we can grasp the rules of structural changes that may occur during welding, so as to obtain high-quality metal welded joints faster.
metal structure The properties of metals and alloys are closely related to their internal organizational structures. Differences in ingredients and changes in heat treatment conditions willAffects the organizational structure of metals and alloys, causing the materials to exhibit very different performance states.
metal crystal structure
Crystalline and amorphous
All matter is made up of atoms. If the elements are ordered and arranged regularly, the substance is called a crystal; if the elements are arranged in a regular manner, the substance is called a crystal;If the columns are scattered, disordered and irregular, they are called amorphous. Take a piece of metal (pure iron) and polish it at the grain and grain boundaries to make a metallographic sample. Put it under a metallographic microscope and observe it under magnification. You can see that the microstructure of the metal is composed of many small particles with irregular shapes. In metallography, these small particles are called grains, and the interface between the grains is called the grain boundary. If the grains are analyzed with more advanced technology, it can be found that the atoms (molecules, ions) in the grains are all in aArranged regularly in a fixed pattern, these grains are all small crystals.
alloy structure
1. Most metals are not used in a pure metal state, but are composed of two or more metals or metals and non-metal elements. This substance with metallic characteristics becomes an alloy. Carbon steel, alloy steel and rails are alloys of iron, carbon and other elements. 2. Alloys can roughly have three structural types: solid solution, intermetallic compound and mechanical mixture.
1) Solid solution: In a solid solution, the atomic diameters of the solute and solvent elements are similar. When forming a solid solution, the solvent atoms partially occupy the solvent atomic lattice. Most solid solutions formed when alloying elements dissolve into iron belong to this type. For example, in steel rails, manganese dissolves into iron, and carbon melts into iron.
2) Intermetallic compounds: The solute and solvent atoms are composed in a certain proportion to form a new crystal structure, which is completely different from the structure of the atoms that originally made up the alloy. It is called an intermetallic compound. The nature of intermetallic compounds is generally relatively hard and brittle, and the melting point of some intermetallic compounds is quite high. They play a role in improving the strength and hardness of the alloy, but also reduce the toughness of the alloy.
3) Mechanical mixture When the grains of two or more crystal structures neither dissolve each other nor form a compound in the solid state, but are uniformly mixed and each retains its original crystal structure, it is called a mechanical mixture. For example, the pearlite in carbon steel is a mixture of ferrite (a solid solution of carbon dissolved in iron) and cementite FegC.
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