The development of human civilization and social progress are closely related to metal materials. After the Stone Age, the bronze age and the iron 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. Our understanding of metal materials should start from the following aspects:
I. Classification:
Metal materials are usually divided into ferrous metals, nonferrous metals and special metal materials.
(1) ferrous metals, also known as steel materials, include industrial pure iron containing more than 90% iron, cast iron containing 2% ~ 4% carbon, carbon steel containing less than 2% carbon, and various structural steels, stainless steels, heat-resistant steels, superalloys and precision alloys. The generalized ferrous metals also include chromium, manganese and their alloys.
(2) Non-ferrous metals refer to all metals except iron, chromium and manganese and their alloys, which are usually divided into light metals, heavy metals, precious metals, semi-metals, rare metals and rare earth metals. Generally, the strength and hardness of non-ferrous alloys are higher than those of pure metals, with large resistance and small temperature coefficient of resistance.
③ Special metal materials include structural metal materials and functional metal materials with different uses. Among them, there are not only amorphous metal materials obtained by rapid condensation process, but also quasicrystal, microcrystalline and nanocrystalline metal materials. There are also special functional alloys such as stealth, hydrogen resistance, superconductivity, shape memory, wear resistance, vibration reduction and damping, and metal matrix composites.
Metal materials are divided into casting metal, deformed metal, spray forming metal and powder metallurgy material according to production and forming technology.
Casting metal is formed by casting process, mainly including cast steel, cast iron and casting nonferrous metals and alloys.
Deformed metal is formed by forging, rolling and stamping, and its chemical composition is slightly different from that of the corresponding cast metal.
Spray forming metal is a part and blank with a certain shape and microstructure made by spray forming process.
The properties of metal materials can be divided into two types: process performance and service performance.
Second, performance.
In order to use metal materials more reasonably and give full play to their functions, it is necessary to master the performance (service performance) of parts made of various metal materials under normal working conditions and the performance (process performance) of materials during cold and hot processing.
The properties of materials include physical properties (such as specific gravity, melting point, electrical conductivity, thermal conductivity, thermal expansion, magnetism, etc. ), chemical properties (durability, corrosion resistance and oxidation resistance), and mechanical properties are also called mechanical properties.
The technological performance of materials refers to the ability of materials to adapt to cold and hot processing methods.
Third, the production process:
In the production of metal materials, metal is generally extracted first and then melted.
Some metals need to be further refined, adjusted to the appropriate composition, and then processed into products of various specifications and properties. In order to extract metals, steel usually adopts pyrometallurgical process, that is, converter, open hearth furnace, electric arc furnace, induction furnace and cupola (ironmaking) are used for smelting and smelting; Non-ferrous metals use pyrometallurgical and hydrometallurgical processes; High-purity metals and metals requiring special properties also adopt regional melting, vacuum melting and powder metallurgy processes. After melting and adjusting the composition, metal materials are made into ingots and blanks by casting or powder metallurgy, and then plastic processing is carried out to make products of various shapes and specifications. For some metal products, specific internal structure and mechanical properties are required, and heat treatment technology is often used. Commonly used heat treatment processes include quenching, normalizing, annealing and aging treatment (the quenched metal parts are kept at room temperature or higher for a proper time to improve their strength and hardness).
Fourth, the development trend:
The development of metallic materials has got rid of pure metal and gold. With the progress of material design, process technology and performance testing, traditional metal materials have developed rapidly, and new high-performance metal materials have been continuously developed. Such as rapidly solidified amorphous and microcrystalline materials, Al-Li alloys with high specific strength and high specific modulus, ordered intermetallic compounds and mechanical alloying alloys, oxide dispersion strengthened alloys, directionally solidified columnar crystals and single crystal alloys, metal matrix composites and new functional metal materials such as shape memory alloys, NdFeB permanent magnet alloys and hydrogen storage alloys, have been applied to aerospace, energy, electromechanical and other fields respectively, and have produced huge economic benefits.