Carbon steel grades. Classification, GOST, application

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Steel is a ferrous metallurgy product, the main structural material. It is used to produce construction fittings, rolled metal of various profiles, pipes, parts, mechanisms and tools.

Steel production

Ferrous metallurgy is engaged in the production of iron and steel. Cast iron is a hard but not durable material. Steel is a strong, reliable, ductile, alloy-prone metal used in foundry, rolling, forging and stamping.

There are several ways to make steel:

1. Converter. Equipment: oxygen converter. Charge (raw materials): white cast iron, steel scrap, limestone. Only carbon steels are produced.
2. Martenovsky. Equipment: open-hearth furnace. Charge: liquid pig iron, steel scrap, iron ore. Universal for both carbon and alloy steels.
3. Electric arc. Equipment: electric arc furnace. Charge: steel scrap, cast iron, coke, limestone. Generic method.
4. Induction. Equipment: induction furnace. Charge: steel and cast iron scrap, ferroalloys.

The essence of the steel production process is to reduce the amount of negative chemical inclusions in order to obtain a metal that is popularly called "iron", or rather, an iron-carbon alloy with a carbon content of no more than 2.14%.

Deoxidation processes

For steel at the final stage of smelting, a boiling process is characteristic, which is influenced by the nitrogen, hydrogen, and carbon oxides inherent in it. Such an alloy in the solidified state has a porous structure, which is removed by rolling. It is soft and plastic, but not strong enough.

The deoxidation process consists in the deactivation of boiling impurities by introducing ferromanganese, ferrosilicon, and aluminum into the alloy. Depending on the amount of residual gases and deoxidizing elements, the steel can be semi-quiet or quiescent.

Finished steel of the required degree of deoxidation is poured into molds for crystallization and use at subsequent technological stages in the manufacture of finished steel products.

Classification of carbon steel

All steel existing on the world market can be divided into carbon and alloy. All grades of carbon steel are divided into different classifier groups and designation features.

Based on the main classification features, they distinguish:

1. Carbon structural steels. They contain less than 0.8% carbon. They are used for making rebar, rolling products and castings.
2. Carbon tool steels that contain carbon inamount from 0.7% to 1.3%. They are used for tools, instrument equipment.

By deoxidation methods:

• boiling - deoxidizing elements (RE) in the composition of less than 0.05%;
• semi-calm - 0.05%≦RE≦0.15%;
• calm - 0.15%≦RE≦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 carbon above 1.3% are not used in industry.

Depending on microstructure:

• hypoeutectoid - in such steel, carbon content is less than 0.8%;
• eutectoid - these are steels with a carbon content of 0.8%;
• hypereutectoid - steels with a carbon content over 0.8%.

Quality:

1. Regular quality. Sulfur here contains less than 0.06%, phosphorus - no more than 0.07%.
2. Quality steels. They do not contain more than 0.04% sulfur and phosphorus.
3. High quality. The amount of sulfur here does not exceed 0.025%, and phosphorus - no more than 0.018%.

According to the main standard, carbon steel grades are divided into:

• Constructional regular quality;
• construction quality;
• instrumental quality;
• instrumental high quality.

Features of marking structural steel of ordinary quality

Steels of ordinary quality contain: From - to0.6%, 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, C - group; A - not indicated in stamps;
• 0–6 after the letters "St" - a serial number in which the chemical composition and (or) mechanical properties are encrypted;
• G - the presence of Mangan Mn (manganese);
• kp, ps, cn - degree of deoxidation (boiling, semi-calm, calm).

The numbers from 1 to 6 after the degree of deoxidation through a dash are categories. In this case, the first category is not indicated in any way.

The letters M, K at the beginning of the brand can mean a metallurgical method of production: open-hearth or oxygen-converter. By the way, carbon steels of ordinary quality are represented by a quantitative composition of grades, approximately 47 pieces.

Classification of ordinary quality structural steels

Common quality carbon steels are divided into groups.

• Group A: steels that must exactly match the specified mechanical properties. They are supplied to the consumer most often in the form of sheet and multi-section rolled products (sheets, tees, I-beams, fittings, rivets and cases). Grades: St0, St1 - St6 (kp, ps, sp), categories 1-3, including St3Gps, St5Gps.
• Group B: steels that must be regulated by the necessary chemical composition and properties. Casting and rolled products are produced, which will be subjected to additional machininghot pressure (forging, stamping). Marks: Bst0, Bst1 (kp-sp), Bst2 (kp, ps), Bst3 (kp-sp, including Bst3Gps), Bst4 (kp, ps), Bst 6 (ps, sp), categories 1 and 2.
• Group B: steels that must meet the required chemical, physical, mechanical and technological properties. This group is characterized by a variety of grades from which plastic sheet products are made, durable fittings for working in areas of significant temperature differences, critical parts (bolts, nuts, axles, piston pins). All products of different composition, properties and grades of this group are united by good technological weldability. Grades: VSt1-VSt6 (kp, ps, sp), VSt5 (ps, sp), including VSt3Gps, categories 1-6.

Structural steels of ordinary quality are alloys that have a wide variety of uses in industry.

Marking carbon quality steel

The carbon content in steel of the named quality is from 0.05% to 0.6%. Smelting of metal of this classification group occurs by open-hearth or electric arc methods. A wide range of carbon presence diversifies the mechanical properties: low-carbon - ductile, medium-carbon - strong.

Carbon quality steels have an S and P content of no more than 0.04%, respectively.

Marking (GOST 1050-88):

• numbers 05-60 - encrypted presence of carbon (minimum - 0.05%, maximum - 0.6%);
• kp, ps, cn - the degree of deoxidation ("sp" is notindicated);
• G, Yu, F - contain manganese, aluminum, vanadium.

Marking exceptions

Carbon quality steels have exceptions in their marking:

• 15K, 20K, 22K - high-quality steels, applicable in boiler building;
• 20-PV - carbon - 0.2%, steel is applicable in the manufacture of pipes by hot rolling, in boiler building and installation of heating systems, contains copper and chromium;
• OSV - steel for the manufacture of wagon axles, contains nickel, chromium, copper.

For all grades of quality steels, the possible need to use thermal (for example, normalization) and chemical-thermal treatment (for example, carburizing) is typical.

Classification of carbon quality steels

This kind of carbon steel can be roughly divided into 4 groups:

1. Highly plastic material applicable for cold machining (rolling), sheet and pipe rolling. Grades - steel 08ps, steel 08, steel 08kp.
2. Metal used in hot rolling and stamping that will perform under thermally aggressive conditions. Grades - from steel 10 to steel 25.
3. Steel, which has found application in the manufacture of critical parts, including springs, springs, couplings, bolts, shafts. Grades - from steel 60 to steel 85.
4. Steels that require reliable operation in aggressive conditions (for example, the chain of a caterpillar tractor). Grades steel 30, steel 50, steel 30G, steel 50G.

It is also possible to divide everything into 2 groupswell-known grades of carbon steel from the quality class: structural conventional and structural manganese.

Application of carbon structural steel

Steel grade by quality	Brand	Application
regular quality	St0	reinforcement, sheathing
	St1	tas, I-beams, channels
	St3Gsp	construction steel
	St5sp	bushings, nuts, bolts
	St6ps	construction scrap
	ST4kp	shaped, sheet, long products for durable structures
quality	Steel10	pipes for boilers, stampings
	Steel15	high ductility parts, cams, bolts, nuts
	Steel18kp	welded structures
	Steel 20ps	axles, forks, pins, fittings, pipes
	Steel50	gears, clutches
	Steel60	spindles, washers, spring rings

Carbon tool steels have high strength and toughness. They are necessarily subject to multi-stage heat treatment.

Carbon content in steel: 0.7 – 1.3%. For high-quality - up to 0.03%, phosphorus - up to 0.035%. And for the instrumentalhigh quality: sulfur - up to 0.02%, phosphorus - up to 0.03%.

Brand designation (GOST 1435-74):

• U - carbon instrumental;
• 7 -13 - the carbon content in it is 0.7-1.3%, respectively;
• G - the presence of manganese;
• A is high quality.

Exceptions to the basic principles of marking carbon tool steels are the material for parts of watch movements A75, ASU10E, AU10E.

Requirements for carbon tool steels

In accordance with GOST, tool steels must comply with a number of characteristics.

Required physical, chemical and mechanical properties: quality indicators of hardness, impact strength, strength, resistance to temperature changes during operation (during cutting, drilling, shock loads), corrosion resistance.

Specified technological properties:

• resistance to negative processes of cutting technology (chip sticking, hardening);
• good turning and grinding machinability;
• susceptibility to heat treatment;
• overheat resistance.

To improve the quality of mechanical and technological indicators, tool steels are subjected to multi-stage heat treatment:

• annealing of raw material before making tools;
• hardening (cooling in s alt solutions) and subsequent tempering of finished products (mainly low tempering).

Receivedproperties are determined by the chemical composition and the resulting microstructure: martensite with cementite and austenite inclusions.

Using carbon tool steels

The described steels are used for the manufacture of all kinds of tools: cutting, percussion, auxiliary.

• Steel U7, U7A - hammers, chisels, axes, chisels, sledgehammers, chisels, fishhooks.
• Steel U8, U8A, U8G - saws, screwdrivers, center punches, countersinks, cutters, pliers.
• Steel U9, U9A - metalwork tool, wood cutting tool.
• Steel U10, steel U10A, U11, U11A - rasps, taps, twist drills, auxiliary tools for punching and sizing.
• U 12, U12A - reamers, taps, measuring tools.
• U13, U13A - files, shaving and surgical instruments, stamping punches.

Rational choice of carbon steel grade, technology of its heat treatment, understanding of its properties and features is the key to a long service life of structures or tools produced, processed or used.