Carbon steel grades. Classification, GOST, application
Steel is a product of ferrous metallurgy, the main structural material. It produces building fittings, metal products of various profiles, pipes, parts, mechanisms and tools.
Ferrous metallurgy is engaged in productioncast iron and steel. Cast iron - a solid, but not a strong material. Steel is a durable, reliable, ductile, alloy-prone metal used in foundry, rolling, forging and stamping.
There are several ways of steelmaking:
- Converter. Equipment: oxygen converter. Charge (raw materials): white cast iron, steel scrap, limestone. Only carbon steels are produced.
- Martenovsky. Equipment: Open-hearth furnace. Charge: liquid cast iron, steel scrap, iron ore. Universal for both carbon and alloy steels.
- Electric arc welding. Equipment: electric arc furnace. Charge: steel scrap, cast iron, coke, limestone. The universal method.
- Induction. Equipment: induction furnace. Charge: steel and iron scrap, ferroalloys.
The essence of the steel production process is a decreasethe number of negative chemical inclusions in order to produce a metal that is popularly called "iron", or more precisely, an iron-carbon alloy with a carbon content of not more than 2.14%.
For steel at the final stage of smeltingcharacteristic process of boiling, which is influenced by the inherent nitrogen, hydrogen, carbon monoxide. Such an alloy in the solidified state has a porous structure, which is removed by rolling. It is soft and ductile, but not strong enough.
The deoxidation process is deactivationboiling impurities by introducing into the alloy ferromanganese, ferrosilicon, aluminum. Depending on the amount of residual gases and deoxidizing elements, steel can be semi-calm or calm.
The ready-made steel of the required degree of deoxidation is poured into molds for crystallization and use at subsequent technological stages of manufacturing finished steel products.
Classification of carbon steel
All the steel that exists on the world market can be divided into carbon and alloyed. All grades of carbon steel are divided into different classes of the classifier and the features of the designation.
Proceeding from the main classification characteristics, they distinguish:
- Carbon structural steel. In them, the carbon content is less than 0.8%. They are used for the manufacture of reinforcement, rolling products and casting.
- Carbonaceous tool steels, which contain carbon in the amount from 0,7% to 1,3%. They are used for tools, instrumentation equipment.
By methods of deoxidation:
- boiling - deoxidizing elements (RE) in the composition of less than 0.05%;
- Semi-calm - 0.05% ≤РЭ≤0.15%;
- calm - 0,15% ≤РЕ≤0,3%.
By chemical composition:
- low-carbon (0.3% ≤C);
- medium carbon (0.3 ≤ C ≤ 0.65%);
- High-carbon (0.65 ≤ C≤1.3%).
Steels containing more than 1.3% carbon are not used in industry.
Depending on the microstructure:
- pre-eutectoid - in such a carbon steel in the composition of less than 0.8%;
- eutectoid - steel with a carbon content of 0.8%;
- hypereutectoid - steel with a carbon content of more than 0.8%.
- Ordinary quality. Sulfur here contains less than 0.06%, phosphorus - not more than 0.07%.
- Quality steel. They do not contain sulfur and phosphorus more than 0.04%.
- High-quality. The amount of sulfur here does not exceed 0.025%, and phosphorus - not more than 0.018%.
According to the basic standard, the carbon steel grades are distributed to:
- constructional quality;
- constructional quality;
- instrumental quality;
- high-quality instrumental.
Features of marking of structural steel of ordinary quality
The ordinary quality steel contains: С - up to 0,6%, S - up to 0,06%, P - up to 0,07%. Let's look at how this carbon steel is marked. GOST 380 defines the following nuances of designation:
- A, B, B - group; A - is not indicated in marks;
- 0-6 after the letters "St" - the serial number in which the chemical composition and (or) the mechanical properties are encoded;
- D - presence of Mangan Mn (manganese);
- kp, ps, cn - the degree of deoxidation (boiling, serene, calm).
The figures from 1 to 6 after the indication of the degree of deoxidation through a dash are categories. The first category is not indicated in any way.
The letters M, K at the beginning of the mark can meanmetallurgical method of production: open-hearth or oxygen-converter. Incidentally, carbon steel of ordinary quality is represented by a quantitative composition of brands, about 47 pieces.
Classification of structural steels of ordinary quality
Carbon steel of ordinary quality is divided into groups.
- Group A: Steel, which must exactly match the specified mechanical properties. They are supplied to the consumer most often in the form of sheet and multi-profile rolled products (sheets, brands, I-beams, fittings, rivets and housings). Stamps: Ст0, Ст1 - Ст6 (кп, пс, сп), categories 1-3, including Ст3Гпс, Ст5Гпс.
- Group B: steel, which must be regulated by the necessary chemical composition and properties. Manufacture of castings and rolled products, which will be subjected to additional machining with pressure in the hot state (forging, stamping). Brands: BST0, BST1 (kp-cn), BTS2 (kp, ps), BST3 (kp-cn, including BST3GPS), BS4 (kp, ps), BST 6 (ps, cn), categories 1 and 2.
- Group B: steel, which must correspond to the required chemical, physical, mechanical and technological properties. This group is inherent in a variety of brands, of which plastic sheet metal is manufactured, strong fittings for working in areas of significant temperature differences, critical parts (bolts, nuts, axles, piston fingers). All products of different composition, properties and grades of this group are united by good technological weldability. Brands: ВСт1-ВСт6 (кп, пс, сп), ВСт5 (пс, сп), including ВСт3Гпс, categories 1-6.
Structural steel of ordinary quality - alloys that have a wide variety of uses in the industry.
Marking of carbon quality steel
Carbon content in the steel of the named qualityfrom 0.05% to 0.6%. The melting of the metal of this classification group occurs by open-hearth or electric-arc methods. A wide range of carbon presence diversifies mechanical properties: low-carbon - plastic, medium-carbon - strong.
Carbon steel quality in S and P is not more than 0.04%, respectively.
Marking (GOST 1050-88):
- figures 05-60 - encrypted presence of carbon (minimal - 0.05%, maximum - 0.6%);
- kp, ps, cn - the degree of deoxidation ("cn" is not indicated);
- Г, Ю, Ф - contain manganese, aluminum, vanadium.
Exceptions in the marking
Carbon quality steel in its marking have exceptions:
- 15К, 20К, 22К - qualitative steels, are applicable in boiler construction;
- 20-PV - carbon - 0.2%, steel is applicable in the manufacture of pipes by hot rolling, in boiler construction and the installation of heating systems, contains copper and chromium;
- OsV - steel for the manufacture of car axles, contains nickel, chrome, copper.
For all grades of quality steels, a possible need for the use of thermal (for example, normalization) and chemical-thermal treatment (for example, carburizing) is typical.
Classification of carbonaceous quality steels
This type of carbon steels can be conditionally divided into 4 groups:
- Highly plastic material, suitable for cold machining (rolling), sheet and tube products. Stamps - steel 08ps, steel 08, steel 08kp.
- Metal used in hot rolling and stamping, which will work under thermally aggressive conditions. Stamps - from steel 10 to steel 25.
- Steel, which has found application in the manufacture of critical parts, including springs, springs, couplings, bolts, shafts. Stamps - from steel 60 to steel 85.
- Steel, requiring reliable operation in aggressive conditions (for example, a chain of caterpillar tractor). Stamps are steel 30, steel 50, steel 30G, steel 50G.
It is also possible to divide into 2 groups all the known brands of carbon steel from the class of quality: constructional conventional and constructional manganese-containing.
Application of carbon structural steel
|Steel grade according to quality||Make||Application|
|normal quality||St0||armature, cladding|
|Ст1||brands, I-beams, channels|
|Ст5сп||bushings, nuts, bolts|
|ВСт4кпп||shaped, sheet, long products for strong structures|
|qualitative||Steel10||pipes for boilers, stamping|
|Steel15||details of high plasticity, cams, bolts, nuts|
|Steel 20ps||axles, forks, fingers, unions, branch pipes|
|Steel60||spindles, washers, spring rings|
Carbon tool steel is characterized by high strength and toughness. They are necessarily subject to multistage heat treatment.
Carbon content in steel: 0.7 - 1.3%. For qualitative - up to 0,03%, phosphorus - up to 0,035%. And for instrumental high-quality: sulfur - up to 0.02%, phosphorus - up to 0.03%.
Brand designation (GOST 1435-74):
- U - carbon tool;
- 7 -13 - the carbon content in it is 0.7-1.3%, respectively;
- D - presence of manganese in the composition;
- A - high-quality.
Exceptions from the basic principles of marking carbonaceous tool steels are material for the details of the watch movements A75, ACU10E, AU10E.
Requirements for carbonaceous tool steels
In accordance with GOST, tool steels must meet a number of characteristics.
Necessary physico-chemical and mechanicalproperties: quality indicators of hardness, toughness, strength, resistance to temperature changes during operation (during cutting, drilling, impact loads), resistance to corrosion.
Specified technological properties:
- resistance to negative processes of cutting technology (chip adherence, hardening);
- good machinability by turning and grinding;
- compliance to heat treatment;
- resistance to overheating.
To improve the quality of mechanical and technological indicators, instrumental steels are subjected to multi-stage heat treatment:
- annealing of the raw material before the manufacture of tools;
- quenching (cooling in salt solutions) and subsequent release of finished products (mainly low vacations).
The obtained properties are determined by the chemical composition and the microstructure obtained: martensite with cementite and austenite inclusions.
Use of carbonaceous tool steels
The described steel is used for making all kinds of tools: cutting, percussion, auxiliary.
- Steel U7, U7A - hammers, chisels, axes, chisels, sledge hammers, chisels, fish hooks.
- Steel У8, У8А, У8Г - saws, screwdrivers, punch, countersinks, milling cutters, pliers.
- Steel U9, U9A - metalwork tool, a tool for cutting wood.
- Steel U10, steel U10A, U11, U11A - rasps, taps, spiral drills, auxiliary tools for punching and calibration.
- At 12, V12A - scans, taps, measuring instruments.
- У13, У13А - files, shaving and surgical instruments, stamping punches.
A rational choice of the brand of carbon steel,technology of its heat treatment, understanding of its properties and features is a pledge of long service of manufactured, processed or used structures or tools.