Structural steel

The quality of structural carbon steels is determined by the presence of harmful impurities of phosphorus (P) and sulfur (S) in the steel. Phosphorus gives the steel cold brittleness (brittleness). Sulfur - the most harmful impurity - makes steel red-cracked . The content of harmful impurities in steel:

• Of ordinary quality - P and S - up to 0.05% (marking St ).
• Quality - P and S - up to 0.035% ( Steel marking).
• High quality - P and S - up to 0.025% (marking A at the end of the mark).
• Particularly high quality - P and S - up to 0.015% (marking Ш at the end of the mark).

Widely used in construction and engineering as the cheapest, most technologically advanced , with the necessary properties in the manufacture of structures for mass purposes. Basically, these steels are used in a hot rolled state without additional heat treatment with a ferrite - pearlite structure.

Depending on the subsequent purpose, structural carbon steels of ordinary quality are divided into three groups: A, B, C.

Group A Steel

Delivered with certain regulated mechanical properties. Their chemical composition is not regulated. These steels are used in structures whose units are not subjected to hot working - forging , hot stamping , heat treatment, etc. In this regard, the mechanical properties of hot-rolled steel are preserved.

Group B steels

They are delivered with a specific regulated chemical composition, without guarantee of mechanical properties. These steels are used in products subjected to hot processing, the technology of which depends on their chemical composition, and the final mechanical properties are determined by the processing itself.

Steel Group B

They are supplied with regulated mechanical properties and chemical composition. These steels are used for the manufacture of welded structures. Their weldability is determined by the chemical composition, and the mechanical properties outside the weld zone are determined in the delivery state. Such steels are used for more critical parts.

The degree of deoxidation is determined by the silicon (Si) content in this steel. According to the degree of deoxidation, carbon steels of ordinary quality are divided into:

• calm (SP) - not less than 0.12% (Si)
• semi-calm (PS) - 0.07-0.12% (Si)
• boiling (KP) - not more than 0.07% (Si)

Marking

The main grades of structural carbon steels of ordinary quality:

St1kp2; BSt2ps; VSt3Gps; St4-2; ... VSt6sp3.

• The letter in front of the mark indicates a group of steel. Group A steel is not indicated by a letter.
• St - indicates that the steel is of ordinary quality.
• The first digit is the number according to GOST (from 0 to 6).
• The letter G after the first digit is the increased content of manganese (Mn) (serves to increase the hardenability of steel).
• cn; ps; kn - the degree of deoxidation of steel (For steel of group A, the absence of a designation implies "cn").
• The second digit is the steel category number (from 1 to 6 - the main mechanical properties). Steel of the 1st category is not indicated by a number.
• A dash between the numbers indicates that the customer did not make requirements for the degree of deoxidation of steel.

Application

• St1; St2 - wire , nails , rivets .
• St3; St4 - fasteners, fittings.
• St5; St6 - lightly loaded shafts , axles .

High-quality carbon steels are steel grades: Steel08; Steel10; Steel15 ...; Steel78; Steel80; Steel85,

Also belong to this class with a high content of manganese (Mn - 0.7-1.0%): Steel 15G; 20G ... 65G having increased hardenability .

Marking

• Steel - the word "Steel" indicates that this carbon steel is of high quality. (At present, the word "Steel" is not written, only the index and subsequent letters are indicated)
• The number indicates the carbon content in the steel (C) in hundredths of a percent.

Application

Low-carbon steels of the grades Stal08, Stal08KP, Stal08PS belong to mild steels, most often used in the annealed state for the manufacture of parts by cold stamping - deep drawing. Steel grades Steel10, Steel15, Steel20, Steel25 are usually used as cemented, and high-carbon Steel60 ... Steel85 - for the manufacture of springs , springs , high-strength wire and other products with high elasticity and wear resistance .

Steel30 ... Steel50 and similar steels with a high content of manganese Steel30G, Steel40G, Steel50G are used for the manufacture of a wide variety of machine parts.

Steels with high machinability or automatic steels include steels with a high content of sulfur and phosphorus, as well as steels specially alloyed with selenium (Se), tellurium (Te) or lead (Pb). These elements help to increase the cutting speed, reduce the cutting force and tool wear, improve the cleanliness and dimensional accuracy of the machined surface, facilitate the removal of chips from the cutting zone, etc. These steels are used in mass production for the manufacture of parts on automatic machines .

Steel with a high content of sulfur and phosphorus have reduced mechanical properties and they are used for the manufacture of lightly loaded non-essential parts (for example, hardware ).

As laser cutting technology developed, special structural steels for laser cutting were developed. Their distinguishing feature is a more predictable behavior of the sheet after cutting (reduced level of internal stresses in the metal) ^[1] .

Marking

At the beginning of the designation of the grade of automatic steel is always the letter "A", for example A12, A20, A35.

Alloyed structural steels are used for the most critical and heavily loaded machine parts. Almost always, these parts undergo final heat treatment — quenching , followed by high tempering in the region of 550–680 ° C (improvement), which ensures the highest structural strength.

Alloying elements are chemical elements that are added to structural steels to give them the required properties. The leading role of alloying elements in structural steels lies in a significant increase in their hardenability . The main alloying elements of this group of steels are chromium (Cr), manganese (Mn), nickel (Ni), molybdenum (Mo), vanadium (V) and boron (B). The carbon content (C) in alloy structural steels is within 0.25-0.50%.

Marking

• The two numbers at the beginning of the marking indicate structural steels. This is carbon content in hundredths of a percent.
• A letter without a number is a specific alloying element with a steel content of less than 1%. (A - nitrogen, P - boron, F - vanadium, G - manganese, D - copper, K - cobalt, M - molybdenum, N - nickel, C - silicon, X - chromium, P - phosphorus, H - rare earth metals, B - tungsten, T - titanium, U - aluminum, B - niobium)
• The letter and number after it is a certain alloying element with a percentage content (number).
• The letter A at the end of the marking indicates stainless steel.

For example, 38X2H5MA is a medium alloyed high-quality chromium-nickel structural steel. Chemical composition: carbon - about 0.38%; chromium - about 2%; nickel - about 5%; molybdenum - about 1%.

Heat-resistant structural steels include steel used in power engineering for the manufacture of boilers , vessels, steam heaters , steam pipes , as well as in other industries for working at elevated temperatures. The working temperatures of heat-resistant steels reach 600-650 ° C, and the details of them must work without replacement for a long time (up to 10000-20000 hours).

At pressures of 6 MPa and temperatures up to 400 ° C, carbonaceous boiler steels (12K, 15K, 18K, 20K) are used. For parts of power units operating at pressures up to 25.5 MPa and temperatures up to 585 ° C, steels alloyed with chromium, molybdenum, and vanadium are used. The carbon content is 0.08-0.27%. The heat treatment of these steels consists in hardening or normalization with a mandatory high tempering.

A feature of the operation of bearings are high local loads. In this regard, extremely high requirements are imposed on the purity of steel, especially for nonmetallic inclusions of carbide heterogeneity. Ensuring high static load capacity is achieved by using as a material for bearings hypereutectoid alloyed with chromium steels, machined for high hardness .

Marking

SHX9, SHX15 .

• The carbon content is about 1%;
• Chromium content in tenths of a percent (for example: ШХ15 - chromium - about 1.5%)

14XH4A, 38X2H5M, 20XH3A.

The general requirement for spring-spring steels is to provide high resistance to small plastic deformations (elastic limit) and relaxation resistance (stress relaxation resistance). These characteristics ensure the accuracy and reliability of the springs and the constancy in time of such operational properties as torque , power parameters. Spring steel in the form of wire and tape is reinforced with cold plastic deformation and quenching on martensite with subsequent tempering. Finished springs are subjected to stabilizing tempering.

• Converter production
• Automatic steel
• Stainless steel
• Tool steel
• Heat resistant steel
• Heat resistant steel
• Steelmaking
• Steelmaking process
• Steel foam
• Cast iron

• Steel and alloys. Marochnik. Ref. ed. / V. G. Sorokin et al. Scientific. C77. V. G. Sorokin, M. A. Gervasyev - M .: "Intermet Engineering", 2001 - 608s, ill. ISBN 5-89594-056-0

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