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, a wide variety of metal materials has become an important material basis for the development of human society.
Metal materials are usually divided into ferrous metals, non-ferrous metals and special metal materials.
① Ferrous metals are also called steel materials, including industrial pure iron with more than 90% iron, cast iron with 2% to 4% carbon, carbon steel with less than 2% carbon, and structural steel, stainless steel, heat-resistant for various purposes Steel, high temperature alloy
Stainless steel, precision alloy, etc. Ferrous metals in a broad sense also include chromium, manganese and their alloys.
②Non-ferrous metals refer to all metals and their alloys except iron, chromium, and manganese, which are usually divided into light metals, heavy metals, precious metals, semi-metals, rare metals and rare earth metals. The strength and hardness of non-ferrous alloys are generally higher than that of pure metals, and the resistance is large and the temperature coefficient of resistance is small.
③Special metal materials include structural metal materials and functional metal materials for different purposes. Among them are amorphous metal materials obtained by rapid condensation process, as well as quasicrystalline, microcrystalline, nanocrystalline metal materials, etc.; as well as special functional alloys such as stealth, hydrogen resistance, superconductivity, shape memory, wear resistance, vibration reduction and damping And metal matrix composite materials.
Generally divided into two types: process performance and use performance. The so-called process performance refers to the performance of metal materials under the specified cold and hot processing conditions during the processing and manufacturing of mechanical parts. The process performance of metal materials determines its adaptability in the manufacturing process. Due to the different processing conditions, the required process performance is also different, such as casting performance, weldability, forgeability, heat treatment performance, machinability, etc. The so-called service performance refers to the performance of metal materials under the conditions of use of mechanical parts, which include mechanical properties, physical properties, chemical properties, etc. The performance of metal materials determines its use range and service life. In the machinery manufacturing industry, general mechanical parts are used in normal temperature, normal pressure and very strong corrosive media, and each mechanical part will bear different loads during use. The ability of metal materials to resist damage under load is called mechanical properties (also known as mechanical properties in the past). The mechanical properties of metal materials are the main basis for the design and material selection of parts. The nature of the applied load is different (such as tension, compression, torsion, impact, cyclic load, etc.), and the required mechanical properties of the metal material will also be different. Commonly used mechanical properties include: strength, plasticity, hardness, impact toughness, multiple impact resistance and fatigue limit. For example:
Platinum has good ductility and can be drawn into filaments with a diameter of only 1/5 000 mm; gold has good ductility and can be pressed into thin sheets with a thickness of only 1/10 000 mm. The difference in properties determines the different uses of metals.