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In addition to iron and carbon in alloy steel alloysteel steel, other alloying elements are called alloy steel. An iron-carbon alloy composed of an appropriate amount of one or more alloying elements added to ordinary carbon steel. Depending on the added elements and appropriate processing techniques, special properties such as high strength, high toughness, wear resistance, corrosion resistance, low temperature resistance, high temperature resistance and non-magnetic properties can be obtained.
Category editing 1, according to the content of alloying elements
1) The total content of low alloy steel alloy elements is less than or equal to 5%;
2) The total content of alloying alloy alloy elements is between 5% and 10%;
3) The total content of high alloy steel alloy elements is greater than or equal to 10%;
2. According to the types of alloying elements, there are chrome steel, manganese steel, chromium manganese steel, chrome nickel steel, chromium nickel molybdenum steel, silicon manganese molybdenum vanadium steel.
3. According to the main purpose (1) structural steel
1) Structural steel for construction and engineering
2) Structural steel for machine building (2) Tool steel (3) Special performance steel [1] General classification Alloy steel alloy steel has many types, usually divided into low alloy steel according to the content of alloying elements (content <5%), medium alloy Steel (content 5%~10%), high alloy steel (content >10%); divided into high-quality alloy steel and special alloy steel according to quality; divided into alloy structural steel, stainless steel, acid-resistant steel and wear-resistant according to characteristics and use Steel, heat-resistant steel, alloy tool steel, rolling bearing steel, alloy spring steel and special performance steel (such as soft magnetic steel, permanent magnet steel, non-magnetic steel).
In addition to iron, carbon and a small amount of unavoidable silicon, manganese, phosphorus and sulfur, steel also contains a certain amount of alloying elements. The alloying elements in steel are silicon, manganese, molybdenum, nickel, niobium, tantalum and titanium. One or more of bismuth, bismuth, boron, lead, rare earth, etc., this steel is called alloy steel. The alloy steel systems of different countries vary with their respective resources, production and use conditions. In the past, nickel and tantalum steel systems were developed in foreign countries. In China, silicon, manganese, vanadium, titanium, niobium, boron, lead and rare earth were found. The main alloy steel system alloy steel accounts for about 10% of the total steel output. Generally, the alloy steel can be divided into 8 categories according to the purpose of smelting in the electric furnace. They are: alloy structural steel, spring steel, Bearing steel, alloy tool steel, high speed tool steel, stainless steel, heat-resistant steel, silicon steel for electricians.
Quenched and tempered steel Medium carbon alloy steel, low alloying element content; 2. High intensity; 3. Used for high temperature bolts, nut materials, etc.
Spring steel 1, carbon content is higher than quenched and tempered steel; 2 after quenching and tempering treatment, higher strength and higher fatigue strength; 3 for spring materials.
Rolling bearing steel 1 high carbon alloy steel, high alloy content; 2 with high and uniform hardness and wear resistance; 3 for rolling bearings.
Alloy tool steel measuring steel 1 high carbon alloy steel, low alloying elements; 2 with high hardness and wear resistance, good machining performance, good stability; 3 for measuring materials.
Special performance steel stainless steel 1 low carbon high alloy steel; 2 good corrosion resistance; 3 for corrosion resistance, some can be used as heat resistant materials.
Heat-resistant steel 1 low-carbon high-alloy steel; 2 good heat resistance; 3 for heat-resistant materials, some can be used as corrosion-resistant materials.
Low-temperature steel 1 low-carbon alloy steel, according to the low temperature resistance alloy elements are high and low; 2 low temperature resistance; 3 for low temperature materials (special steel is nickel steel).
According to the tendency of carbides, the tendency of alloy steels to form carbides in steel according to various elements can be divided into three categories:
Alloy steel 1 strong carbide forming elements, such as vanadium, titanium, niobium, zirconium and the like.
As long as there is sufficient carbon, such elements form their respective carbides under appropriate conditions; they enter the solid solution in an atomic state only under conditions of carbon deficiency or high temperature.
2 carbide forming elements such as manganese, chromium, tungsten, molybdenum, and the like. Some of these elements enter the solid solution in the atomic state, and the other part forms the replacement alloy cementite, such as (Fe, Mn) 3C, (Fe, Cr) 3C, etc., if the content exceeds a certain limit (except manganese), The respective carbides are formed, such as (Fe, Cr) 7C3, (Fe, W) 6C, and the like.
3 does not form carbide elements such as silicon, aluminum, copper, nickel, cobalt, and the like. Such elements are generally present in an atomic state in a solid solution such as austenite or ferrite. Some of the more active elements of alloying elements, such as aluminum, manganese, silicon, titanium, zirconium, etc., are easily combined with oxygen and nitrogen in steel to form stable oxides and nitrides, generally in the form of inclusions in steel. in. Elements such as manganese and zirconium also form sulfide inclusions with sulfur. Steels can form different types of intermetallic compounds when they contain a sufficient amount of elements such as nickel, titanium, aluminum, and molybdenum. Some alloying elements such as copper, lead, etc., if the content exceeds its solubility in steel, it exists in a relatively pure metal phase.
The properties of steel depend on the phase composition of the steel, the composition and structure of the phases, the volume components of the various phases in the steel and the relative distribution of each other. Alloying elements work by affecting the above factors. The influence on the phase transition point of steel is mainly to change the position of the phase transition point in steel, which can be roughly summarized into the following three aspects:
1 Change the phase change point temperature. In general, the elements in the γ phase (austenite) region, such as manganese, nickel, carbon, nitrogen, copper, and zinc, are enlarged to lower the temperature at the a3 point and increase the temperature at the a4 point; instead, the elements in the γ phase region are reduced. For example, zirconium, boron, silicon, phosphorus, titanium, vanadium, molybdenum, tungsten, rhenium, etc., the temperature of a3 is increased, and the temperature of a4 is lowered. Only cobalt increases the temperature at both a3 and a4. The effect of chromium is special. When the chromium content is less than 7%, the temperature of a3 is lowered, and when it is more than 7%, the temperature of a3 is increased.
2 Change the position of the embedding point S. Reducing the elements of the γ phase region increases the temperature of the eutectoid point S; expanding the elements of the γ phase region is reversed. In addition, almost all alloying elements reduce the carbon content of the eutectoid point S, shifting the S point to the left. However, carbide-forming elements such as vanadium, titanium, niobium (including tungsten, molybdenum), after the content is high to a certain limit, the S point is shifted to the right.
3 Change the shape, size and position of the γ phase region. This effect is more complicated and generally causes a significant change when the alloying element content is high. For example, when the content of nickel or manganese is high, the γ phase region can be extended to below room temperature, so that the steel becomes a single-phase austenite structure; and when the content of silicon or chromium is high, the γ phase region can be reduced to a small or even completely disappeared. To make the steel ferrite structure at any temperature.
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