A Brief Introduction To The Classification Of Steel.

The concept of part steel is introduced as follows:

(1) high quality carbon structural steel (GB/ t699-1999)

In addition to contain carbon (C) elements in steel and for DNA containing a certain amount of silicon (Si) (generally no more than 0.40%), manganese (Mn) (generally no more than 0.80%, to 1.20%) higher alloy elements, excluding other alloying elements (except for residual element).

Such steel must also ensure chemical composition and mechanical properties. The contents of sulfur (S) and phosphorus (P) are generally controlled below 0.035%. If it is controlled below 0.030%, it is called superior quality steel. After its brand name, "A" should be added, such as 20A; If P is controlled below 0.025% and S is controlled below 0.020%, it is called premium grade steel, and the brand name should be marked with "E" to distinguish it. For other residual alloy elements brought into steel by raw materials, such as Cr, Ni, Cu, etc. are generally controlled in Cr less than 0.25%, Ni less than 0.30%, and Cu less than 0.25%. Some of the brand manganese (Mn) content reaches 1.40%, which is called manganese steel.

This type of steel is used to improve the mechanical properties of steel by adjusting the amount of carbon (C). Therefore, according to the carbon content, such steel can be divided into:

Low carbon steel -- carbon content is generally less than 0.25%, such as 10, 20 steel, etc.

Medium carbon steel -- carbon content is generally between 0.25 and 0.60%, such as 35, 45 steel, etc.

High carbon steel - carbon content is generally greater than 0.60%. Such steel is generally not used to make steel pipes.

In fact, there is no obvious boundary between their carbon content.

This kind of steel production is bigger, the use is more wide, general more rolling (forging) make round, square, flat and so on section material, plank and seamless steel tube. It is mainly used for the manufacture of general structure and mechanical structure, components and construction structures and pipes for conveying fluids. It is sometimes used after heat treatment (normalizing or tempering) according to the requirements.

(2) carbon structural steel (GB/700-1999)

This kind of steel is generally smelted by converter or open-hearth furnace, its main raw material is molten iron and scrap steel, the content of sulfur and phosphorus in steel is higher than that of high quality carbon structure steel, general sulfur is less than 0.050% and phosphorus is less than 0.045%. From raw materials into the other content of alloy elements in steel, such as chromium, nickel, copper is generally not more than 0.30%, according to the composition and performance requirements, this kind of steel grades by Q195, Q215A, B, Q235A, B, C, D, Q255A, B, Q275 steel grade said.

Note: "Q" is the yield of "bending" Chinese pinyin "capital", followed by Numbers for the brand minimum yield point (sigma s) value, followed by symbol is according to the steel impurity element content from high to low (sulfur, phosphorus, and along with the change of the carbon, manganese element is divided into A, B, C, D four grades.

This kind of steel production is the biggest, the use is very wide, the many rolling makes sheet, the section material (round, square, flat, work, groove, Angle and so on) and the special-shaped material and the manufacture welded steel pipe. Mainly used in buildings, Bridges, ships and other construction structures and general flow pipes. This type of steel is not normally used for heat treatment.

(3) low alloy high-strength structural steel (GB/ t1591-1994)

In addition to a certain amount of silicon or manganese, the steel contains other elements suitable for our country's resources. Such as vanadium (V), niobium (Nb), titanium (Ti), aluminum (Al), molybdenum (Mo), nitrogen (N), and rare earth (RE), etc. According to chemical composition and performance requirements, its brand by the Q295A, B, Q345A, B, C, D, E, Q390A, B, C, D, E, Q420A, B, C, D, E, Q460C, D, E grade steel, said the meaning with carbon structural steel.

V, Nb, Ti, Al and other refined grain trace elements, except for A and b-grade steel in such steel, at least one of them should be included in C, D and E steel. In order to improve the performance of steel, A and B can also be added. In addition, Cr, Ni and Cu residual elements of such steel are not greater than 0.30%. Q345A, B, C, D and E are the representatives of such steel, among which A and b-grade steel are commonly referred to as 16Mn; More than one microelement must be added to grade C steel, and a low temperature impact performance is added to its mechanical properties.

This kind of steel is compared with carbon structural steel. It has the advantages of high strength, good comprehensive performance, long service life, wide application range and comparative economy. It is widely used in Bridges, ships, boilers, vehicles and important building structures.

(4) alloy structural steel (GB/ t3077-1999)

This type of steel is based on high quality carbon structural steel and is suitable for adding one or several alloy elements to improve the mechanical properties, toughness and hardenability of steel. Products made from such steel usually require heat treatment (normalizing or tempering); Before the use of the components, they usually need to be treated with the chemical treatment (carburizing, nitriding, etc.), surface quenching or high frequency quenching. Therefore, according to the different chemical composition (mainly carbon content), heat treatment technology and use, this kind of steel can be divided into three kinds: carburizing, tempering and nitride.

This kind of steel rolling, forging more made into round, square, flat profile and seamless steel pipe, used to make mechanical products more and more important in the larger size of parts, components and high pressure pipe, containers, etc., the high quality carbon structural steel has more excellent comprehensive mechanical properties.

The seamless steel pipe made by this kind of steel is widely used in hydraulic support, high-pressure gas cylinder, high-pressure boiler, chemical fertilizer equipment, oil cracking, automobile axle sleeve, diesel engine, hydraulic pipe fitting and so on.

(5) stainless steel (GB/ t1220-92, GB/ t1221-92)

According to the main use of industry, stainless steel is divided into stainless steel and refractory steel.

A, stainless steel and acid-resistant steel are divided into two types: stainless steel and acid-resisting steel. Stainless steel which can resist corrosion in air; Steel that can resist corrosion in various corrosive medium is called acid-resisting steel. Stainless steel does not have acid corrosion, but acid-resistant steel has good rust resistance.

This kind of steel contains five elements (C, Si, Mn, P, S), mainly containing chromium and nickel alloy elements. Such as chromium steel (Cr13), chromium nickel steel (18-8); There are also one or more of the elements including molybdenum, niobium, titanium and nitrogen.

This kind of steel is widely used in chemical equipment, medical equipment, food industry equipment and household utensils, hotel and hotel decoration, etc.

B. Refractory steel is divided into two types: heat resistant and non-starter. Steel that is resistant to dielectric erosion at high temperature without peeling steel; Steel that is resistant to dielectric erosion at high temperature and has sufficient strength without peeling is called heat resistant steel.

In addition to chromium and nickel in stainless steel, this type of steel also contains one or more of the alloying elements such as aluminum (Al), tungsten (W), cobalt (Co), vanadium (V), etc. The circle, plate, belt and tube are widely used in petrochemical equipment, power station boilers, gas turbine and industrial heating furnace components and components working in high temperature.