Mechanical properties of steel and its metallic materials
Classification of steel
Steel is an alloy of iron, carbon as the main component of the alloy, its carbon content is generally less than 2.11%. Steel is one of the most important metal materials in economic construction. According to the chemical composition of the steel is divided into carbon steel and alloy steel (or steel) two categories. Carbon steel is an alloy obtained by smelting pig iron, iron, carbon for its main components, but also contains a small amount of manganese, silicon, sulfur, phosphorus and other impurities. Carbon steel has a certain mechanical properties, but also has a good technical performance, and the price is low. Therefore, carbon steel has been widely used. However, with the rapid development of modern industry and science and technology, the performance of carbon steel can not completely meet the needs, so people developed a variety of alloy steel. Alloy steel is a multicomponent alloy obtained by adding some elements (called alloying elements) on the basis of carbon steel. Compared with the carbon steel, the properties of the alloy steel are greatly improved, so the application is more and more widely.
Because of the wide variety of steel, in order to facilitate the production, storage, selection and research, must be classified. According to the use of steel, chemical composition, the quality of different, can be divided into many types of steel:
Classification by use
According to the use of steel can be divided into structural steel, tool steel, special properties of steel three categories.
Structural steel: 1 steel for various machine parts. It includes carburizing steel, Quenched and tempered steel, spring steel and rolling bearing steel.
2 steel used as engineering structure. It includes carbon steel in a and B, the special class of ordinary steel and low alloy steel.
Tool steel: steel used to make tools. According to the use of different tools can be divided into tool steel, die steel and tool steel.
Special performance steels: steels with special physical and chemical properties. Can be divided into stainless steel, heat-resistant steel, wear-resistant steel, steel etc..
Two) by chemical composition
According to the chemical composition of the steel can be divided into two categories of carbon steel and alloy steel.
Carbon steel: according to carbon content can be divided into low carbon steel (carbon content less than 0.25%);
Medium carbon steel (0.25% < carbon content < 0.6%);
High carbon steel (carbon content more than or equal to 0.6%).
Alloy steel: according to the contents of alloy elements can be divided into low alloy steel (alloy element content is less than or equal to 5%);
Medium alloy steel (alloy element total content =5%--10%);
High alloy steel (alloy element content > 10%).
In addition, according to the steel contains main alloy elements are different, can be divided into manganese steel, chrome steel, nickel chromium steel, chromium, manganese, titanium and other.
Three) by quality
According to the steel harmful impurity phosphor and sulfur content can be divided into ordinary steel (phosphorus is equal to or less than 0.045%, sulfur content is less than or equal to 0.055%; or the content of sulphur, phosphorus were is less than or equal to 0 0_.050%); quality steel (phosphorus and sulfur contents were less than or equal to 0.040%); senior high quality steel (phosphorus is equal to or less than 0.035%, sulfur content is less than or equal to 0.030%).
In addition, according to the type of smelting furnace, steel is divided into open hearth steel (acid open hearth furnace, basic open hearth), air converter steel (Bessemer, basic converter, oxygen top blown converter steel) and electric furnace steel. According to the degree of the smelting, the steel is divided into the boiling steel (not completely), killed steel (more completely) and semi killed steel.
Steel in the name of the product to the steel, the use of the use, composition, quality of these three classification methods combined. If the steel is known as ordinary carbon structural steel, quality carbon structural steel, carbon tool steel, high quality carbon tool steel, alloy structural steel, alloy tool steel, etc..
Four. Mechanical properties of metallic materials
The properties of metal materials are generally divided into two categories of process performance and performance. The so-called process performance refers to the performance of mechanical parts in the process of manufacturing, metal materials in the set of cold and hot processing conditions. The process performance of the metal material is good or bad, which determines its ability to adapt to the forming process in the manufacturing process. Due to the different processing conditions, the requirements of the process performance is also different, such as casting properties, can be welding, forging, heat treatment, machining, etc.. The so-called performance is the use of mechanical parts in the use of the conditions, the performance of metal materials, including mechanical properties, physical properties, chemical properties, etc.. The use of metal materials is good or bad, which determines its scope of use and service life. In the mechanical manufacturing industry, the general mechanical parts are in normal temperature, normal pressure and the use of non corrosive medium, and in the use of mechanical parts will be under different load. The performance of a metal material under the action of a load, called mechanical properties (or mechanical properties).
The mechanical properties of metallic materials are the main basis for the design and material selection of the parts. The mechanical properties of metallic materials are different, such as tensile, compression, torsion, impact, cyclic loading, and so on. Commonly used mechanical properties include: strength, plasticity, hardness, impact toughness, repeated impact resistance and fatigue limit, etc.. A variety of mechanical properties will be discussed below.
Strength refers to the performance of the metal material under static load to resist damage (excessive plastic deformation or fracture). The mode of action of the load is tensile, compression, bending, shear, etc., so the strength is also divided into tensile strength, compressive strength, bending strength, shear strength and so on. There is always a certain link between the various strength, use in general more with tensile strength as the most basic strength index.
Plasticity refers to the plastic deformation (permanent deformation) under the load of the metal materials.