1. Chemical properties

      The property of metals and other substances causing chemical reactions is called the chemical properties of metals. In practical applications, the main consideration is the corrosion resistance and oxidation resistance of metals (also called oxidation resistance, which especially refers to the resistance or stability of metals to oxidation at high temperatures), as well as between different metals, metal and The influence of compounds formed between non-metals on mechanical properties and so on. Among the chemical properties of metals, especially the corrosion resistance is of great significance to the corrosion fatigue damage of metals.

2. Physical properties

      The main considerations of the physical properties of metals:

      (1) Density (specific gravity): ρ=P/V in grams/cubic centimeter or ton/cubic meter, where P is weight and V is volume. In practical applications, in addition to calculating the weight of metal parts based on the density, it is important to consider the specific strength of the metal (the ratio of the strength σb to the density ρ) to help select materials, as well as the acoustic impedance in acoustic testing related to non-destructive testing. (The product of the density ρ and the speed of sound C) and the materials with different densities in radiographic testing have different absorption capabilities for ray energy, and so on.

       (2) Melting point: The temperature at which a metal changes from a solid state to a liquid state, which has a direct effect on the smelting and thermal processing of metal materials, and has a great relationship with the high-temperature performance of the material.

       (3) Thermal expansion. The phenomenon that the volume of the material changes (expansion or contraction) as the temperature changes is called thermal expansion. It is usually measured by the coefficient of linear expansion, that is, when the temperature changes 1°C, the ratio of the increase or decrease in the length of the material to its length at 0°C . Thermal expansion is related to the specific heat of the material. In practical applications, specific volume (the increase or decrease of the volume per unit weight of the material when the material is affected by external influences such as temperature, that is, the ratio of volume to mass), especially for working in a high-temperature environment, or in cold or hot conditions. Metal parts working in alternate environments must consider the influence of their expansion properties.

       (4) Magnetism. The property that can attract ferromagnetic objects is magnetism, which is reflected in the magnetic permeability, hysteresis loss, residual magnetic induction, coercive force and other parameters, so that metal materials can be divided into paramagnetic and reverse magnetic, soft magnetic and hard magnetic materials .

     (5) Electrical performance. Mainly consider its electrical conductivity, which has an impact on its resistivity and eddy current loss in electromagnetic nondestructive testing.

4. Process performance

      The adaptability of metal to various processing methods is called process performance, which mainly has the following four aspects:

　 (1) Cutting performance: It reflects the difficulty of cutting metal materials with cutting tools (such as turning, milling, planing, grinding, etc.).

　 (2) Forgeability: reflects the difficulty of forming metal materials during pressure processing, such as the degree of plasticity when the material is heated to a certain temperature (expressed as the resistance to plastic deformation), and the allowable temperature range for hot pressure processing Size, thermal expansion and contraction characteristics, critical deformation limits related to microstructure and mechanical properties, fluidity of the metal during thermal deformation, thermal conductivity, etc.

     (3) Castability: Reflects the difficulty of melting and casting of metal materials into castings, manifested as fluidity, gas absorption, oxidation, melting point, and uniformity, compactness, and coldness of the casting microstructure in the molten state. Shrinkage etc.

     (4) Solderability: It reflects the difficulty of the metal material in the local rapid heating, so that the joint part is melted or semi-melted quickly (pressure is required), so that the joint part is firmly joined together to form a whole, which is expressed as melting point, Inhalation, oxidation, thermal conductivity, thermal expansion and contraction properties, plasticity and the correlation with the microstructure of the joints and nearby materials during melting, and the impact on mechanical properties.