Views: 0 Author: Site Editor Publish Time: 2022-03-21 Origin: Site
Metal material refers to metal elements or mainly composed of metal elements with metal properties of the material. Metal materials include pure metal, alloy, metal materials intermetallic compounds and special metal materials. (Note: Metal oxides such as alumina are not metallic materials.)
The development of human civilization and social progress are closely related to metal materials. The copper Age and Iron Age, which followed the Stone Age, were marked by the application of metal materials. In modern times, various metal materials have become an important material basis for the development of human society.
Metal materials are usually divided into ferrous metal, non-ferrous metal and special metal materials.
1) Ferrous metals also known as iron and steel materials, including industrial pure iron containing more than 90% iron, cast iron containing carbon 2%-4%, carbon steel containing carbon less than 2%, as well as various uses of structural steel, stainless steel, heat resistant steel, high temperature alloys, stainless steel, precision alloys, etc. Ferrous metals in broad sense also include chromium, manganese and their alloys.
2) Non-ferrous metals refer to all metals and their alloys except iron, chromium and manganese, usually divided into light metals, heavy metals, precious metals, semi-metals, rare metals and rare earth metals. The strength and hardness of non-ferrous alloy are generally higher than that of pure metal, and the resistance is large and the resistance temperature coefficient is small.
3) Special metal materials including structural metal materials and functional metal materials for different purposes. There are amorphous metal materials obtained by rapid condensation process, and quasicrystalline, microcrystalline, nanocrystalline metal materials, etc. There are stealth, hydrogen resistance, superconductivity, shape memory, wear resistance, damping and other special functional alloys and metal matrix composite materials.
3. The performance
It is generally divided into two categories: process performance and service performance. The so-called technological performance refers to the mechanical parts in the process of manufacturing, metal materials in the fixed cold, hot processing conditions of performance. The technological performance of metal material determines its adaptability in manufacturing process. As a result of different processing conditions, the required process performance is also different, such as casting performance, weldability, forging, heat treatment performance, cutting machinability, etc.
Alleged use performance is to point to mechanical part to fall in use condition, the performance that metallic material shows, it includes mechanical performance, physical performance, chemical performance to wait. The performance of metal materials determines its range of use and service life. In the machinery manufacturing industry, the general mechanical parts are used in room temperature, atmospheric pressure and very strong corrosive media, and in the use of the process of mechanical parts will bear different loads. The resistance of metallic materials to damage under load is called mechanical properties (formerly also called mechanical properties). Mechanical properties of metal materials are the main basis of parts design and material selection. Different properties of applied load (such as tensile, compression, torsion, impact, cyclic load, etc.) require different mechanical properties of metal materials. The commonly used mechanical properties include strength, plasticity, hardness, impact toughness, multiple impact resistance and fatigue limit.
4. Metallic material properties
Many mechanical parts and engineering components work under alternating loads. Under the action of alternating load, although the stress level is lower than the yield limit of the material, after a long time of repeated stress cycle, sudden brittle fracture will occur, which is called the fatigue of metal materials.
The characteristics of fatigue fracture of metal materials are:
Load stress is alternating;
The loading time is long;
The fracture is instantaneous;
Both plastic and brittle materials are brittle in the fatigue fracture zone.
Therefore, fatigue fracture is the most common and dangerous fracture form in engineering.
2) The plastic
Plasticity refers to the ability of metal materials to produce permanent deformation (plastic deformation) without being damaged under the action of external load. When a metal material is stretched, both its length and cross-sectional area change. Therefore, the plasticity of a metal can be measured by two indexes: elongation of length (elongation) and shrinkage of section (reduction of section).
The larger the elongation and area shrinkage of metal materials, the better the plasticity of the material, that is, the material can withstand large plastic deformation without damage. Generally, the metal material with elongation rate greater than 5% is called plastic material (such as low carbon steel), and the metal material with elongation rate less than 5% is called brittle material (such as gray cast iron). Good plastic material, it can produce plastic deformation in a larger macro range, and at the same time of plastic deformation so that the metal material due to plastic deformation and strengthening, so as to improve the strength of the material, to ensure the safe use of parts. In addition, good plastic materials can be smoothly processed in some molding processes, such as stamping, cold bending, cold drawing, straightening and so on. Therefore, when selecting metal materials as mechanical parts, certain plastic indexes must be satisfied.
3) The durability
Main forms of building metal corrosion:
Hardness is the ability of a material to resist hard objects pressing into its surface. It is one of the important performance indexes of metal materials. General hardness is taller, wear resistance had jumped over. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.