Which ordinary quality steel is classified as semi-quiet?

The figure below shows eight typical states of industrial steel ingots that have been cast into identical, tapered molds. They are arranged and numbered according to the degree of suppression of gas emission during solidification. The dashed lines indicate the level to which the steel was initially poured in each mold. Depending on the carbon content, and even more so on the oxygen content, the structure of the ingots varies. Number 1 is completely calmed steel, calmed steel

, and number 8 - steel to which deoxidation operations were not applied, highly
boiling steel
.

Figure - Eight typical states of industrial steel ingots with varying degrees of deoxidation

When cast into ingots, steels are classified into three main types depending on the degree of deoxidation or, which is the same, according to the amount of gases released during the solidification of the ingot.

These four types include: - mild steel; - semi-quiet steel

; - boiling steel.

Carbon steel - classification, marking and application

Steel is an alloy consisting of two essential components - iron and carbon. Additional elements: silicon less than 1%, manganese less than 1%, sulfur less than 0.05%, phosphorus less than 0.06%. Carbon content no more than 2.14%. Alloys with a C percentage greater than 2.14% are classified as cast iron. Based on their chemical composition, steel grades are divided into carbon and alloy, which contain additional additives that give the material the desired characteristics. Carbon steel alloys are classified according to the degree of deoxidation, carbon content, and quality.

Semi-quiet steel

In semi-quiet steel, the release of gases during its deoxidation is not completely suppressed, since the steel is only partially deoxidized. In English it is called semikilled
steel
. The degree of gas evolution in these steels is greater than in calm steels, but less than in boiling steels. Before the release of gases begins, a crust of considerable thickness forms in the ingot. A properly “semi-deoxidized” steel ingot does not have a shrinkage cavity, but there are bubbles widely dispersed throughout the thickness in the central zone of the upper part of the ingot. These bubbles, however, are sealed when the ingot is rolled. Semi-quiet steels typically have a carbon content of 0.15 to 0.30%. They are widely used in the production of long products, strips and pipes.

The main differences between semi-quiet steels are: 1) different degrees of heterogeneity of the chemical composition - average between the degrees of calm and boiling steels; 2) less segregation of chemical elements than in plain steel; 3) a pronounced tendency for positive chemical segregation in the center of the upper part of the ingot (figure).

Classification of carbon steels by degree of deoxidation

Calm

Such alloys have the most uniform structure. For deoxidation, aluminum, ferrosilicon and ferromanganese are used, which almost completely remove the gases present in the melt. The combination of the almost complete absence of gases with a fine-grained structure due to the presence of residual aluminum ensures good quality of the metal. These grades are suitable for the manufacture of parts, products and structures for critical purposes. The main disadvantage is the high cost.

Boiling

This is the cheapest and least quality group. Due to the use of a minimal amount of additives for deoxidation, dissolved gases are present in the material, which cause heterogeneity in the structure, chemical composition, and therefore mechanical properties. Such metals have poor weldability, since due to the presence of gases there is a high probability of cracks forming at the seams.

Semi-calm

The group occupies an intermediate position in terms of cost and characteristics. Much fewer gas bubbles form in the casting compared to boiling steels. When rolling, internal defects in the bulk are eliminated. Such materials are often used as structural alloys.

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Types of unalloyed carbon steels by carbon content

Low carbon with a C content of no more than 0.25%

Most of these products are produced in the form of cold-rolled or annealed sheets and strips. Properties, and therefore the scope of its application, depend on the percentage of components:

• Up to 0.1% C, Mn less than 0.4%. High ability to hot deformation and cold drawing. The materials are in demand in the production of wire, very thin sheets used in the manufacture of containers, and also for the manufacture of car bodies.

C 0.1-0.25%. The ability to deform is lower than that of the group described above, but the hardness and strength are higher. Often these grades are in demand for the production of parts with a cemented surface layer. The carburization process produces a wear-resistant surface layer combined with a tough core. This is true for shafts and gears.

• C at 0.25%, Mn and Al – up to 1.5%. They have high viscosity. Aluminum is not added to metals intended for stamping, forging, the production of seamless tubes and sheets for boilers.
• C at 0.15%, Mn - up to 1.2%, Pb up to 0.3% or without it, minimum amount of Si. This group is used in mass production on automatic lines of parts not intended to withstand severe mechanical and temperature loads. For products with high requirements for ductility, toughness, and corrosion resistance, alloys are not used.

Medium carbon with C0.2-0.6%

The manganese content is usually in the range of 0.6-1.65%. They are used in the production of products intended for use under high loads. They are usually produced calm. They are strengthened by cold hardening or heat treatment. All steels in this group can be forged. These metal products are widely used in mechanical engineering. Grades with a high carbon content (0.4-0.6%) are in demand in the production of railway rails, wheels and car axles.

High carbon – 0.6-2.0%

Increasing the amount of carbon to 1% leads to an increase in strength and hardness with a gradual decrease in the yield strength and plasticity. When the percentage of C increases above 1%, the formation of a coarse network of secondary martensite begins, leading to a decrease in the strength of the material. Therefore, steels with a C content of more than 1.3% are practically not produced.

High-carbon grades have a high manufacturing cost, have low ductility, and are difficult to weld. The scope of application of this group is quite limited - the production of cutting tools, including those intended for earthmoving and agricultural machinery, and the production of high-strength wire.

Characteristics

To obtain semi-quiet steels, alloys with a carbon content of 0.15-0.3% of ordinary quality and high quality are usually used. In the production of semi-deoxidized metal, before the release of gases, the ingot is covered with a crust of considerable thickness. If the steel is deoxidized correctly, then there is no shrinkage cavity, and widely scattered air bubbles are concentrated in the central upper part of the ingot, which roll up during rolling in the mills. If a sink is present, the waste is approximately 8%.

Classification of structural carbon steels by quality, their marking and application

Structural steels of ordinary quality

They are produced in accordance with GOST 380-2005 and supplied for sale in the form of sheets, sections and shaped products. GOST implies the release of the following brands:

• St0;
• St1ps, St1sp, St1kp;
• St2ps, St2sp, St2kp;
• St3ps, St3sp, St3kp, St3Gsp, St3Gps;
• St4ps, St4sp, St4kp;
• St5ps, St5sp, St5Gps;
• St6ps, St6sp.

Alphanumeric marking of this group of alloys:

• St – steel;
• numbers 0-6 indicate the brand number;
• the presence of the letter “G” in the designation indicates the presence of manganese in an amount of 0.8% or more;
• the last two letters characterize the degree of deoxidation, sp - calm, ps - semi-calm, kp - boiling.

High-quality structural steel

Manufactured in accordance with GOST 1050-2-13 of the following grades - 05, 08, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 58, 60, as well as grades 55PP, 60PP, 60PP " select” – reduced hardenability. The marking of such alloys indicates the degree of deoxidation if they are boiling or semi-quiet, for example 10 kp or 10 ps. The cn index is not indicated in the designation of quality construction grades.

Main Applications:

• production of long products (sheets, strips, circles, hexagons), profiles (angles, channels, I-beams);
• production of strip, which is a blank for pipe production;
• the most common grade of carbon steel of ordinary quality, St3ps, is used for load-bearing and non-load-bearing elements of welded structures designed to operate at temperatures above zero, structures operated under variable loads;
• St5ps – for riveted structures, bolts, nuts, rods, handles, stops, sprockets, designed to operate at positive temperatures up to +425°C.

Semi-quiet steel grades

• carbon semi-quiet steels of ordinary quality are manufactured according to GOST 380-2005, designation - “ps”;
• high-quality and high-quality are produced in accordance with GOST 1050-88, letter designation - “ps”;
• rarely - low alloy steels.

Differences between semi-quiet steel and calm steel

In relation to fully deoxidized steel, semi-deoxidized steel is characterized by:

• greater degree of heterogeneity of chemical composition;
• high yield;
• lower cost.

The presence of a certain amount of free oxygen reduces the strength and ductility of semi-quiet steel.

Source of the article: https://metallz.ru/articles/poluspokojnaya_stal/

Deoxidizers: types and functions

Ferrosilicon is used as deoxidizers in an amount of 0.12-0.3% by weight, ferromanganese, aluminum - up to 0.1%, and titanium.

A negative consequence of deoxidation is the formation of a large shrinkage cavity. To remove it, you have to cut off up to 16% by weight from the ingot of mild steel. Due to this loss of metal, as well as the cost of deoxidizing additives, the cost of calm steel significantly exceeds the price of boiling metal.

Deoxidizing additives, combining with free oxygen found in the alloy, solve the following problems:

• reduce the negative impact of free oxygen on the developing structure of the ingot;
• maintain high steel temperature for a long period, which ensures maximum slag and gas removal;
• contribute to the production of metal with a fine-grained, homogeneous structure, since the resulting silicates and aluminates increase the number of crystallization centers. This causes grain refinement and improves the quality and mechanical characteristics of the metal.

Mild steel grades

Full deoxidation alloys are divided into the following groups:

• mild carbon steels of ordinary quality - regulated by GOST 380-2005, designated “sp”;
• high-quality and high-quality - produced in accordance with GOST 1050-88, they do not have a letter index according to this standard;
• All alloy and low-alloy steels are usually made calm and do not have a letter index.

Attention! Steels produced by continuous casting are completely deoxidized during the process.

Steel deoxidation - You know how

Steel smelted by any method contains dissolved oxygen, which significantly impairs its strength and plastic properties. To reduce its content, the steel is deoxidized. In steelmaking practice, several deoxidation methods are used.

Precipitation deoxidation

The most common way to reduce dissolved oxygen is achieved by binding it with deoxidizing elements: Mn, Si, Ti, Al, Ca, REE, which is possible due to their greater affinity for oxygen than iron. When adding deoxidizing agent R

interaction takes place in metal

[O] + yR = Ry

Ox(gas, liquid, TV)

with the formation of insoluble deoxidation products, which must separate (precipitate) into a gaseous or slag phase. The deoxidation products remaining in the steel sometimes cause less harm than dissolved oxygen, but they clog the metal with non-metallic inclusions, the accumulation of which makes the steel unsuitable for further use. Therefore, it is necessary to provide conditions for the removal of deoxidation products, which depends on their size, ability to coarse, metal viscosity, and particle density.

The enlargement of deoxidation products and the ability to float are created and enhanced by the formation of liquid, fusible formations. From this point of view, and especially due to the fact that strong deoxidizers, like their deoxidation products, are difficult to melt, it is advisable to use complex deoxidizers. Complex deoxidizers are alloys that contain several deoxidizers, proportioned so that the deoxidation products acquire specified properties that favor their separation from the steel. Complex deoxidizers include silicomanganese, silicocalcium, AMS (an alloy of aluminum, manganese and silicon), etc.

The deoxidizing power of deoxidizers is determined by the isobaric potential of oxide formation or the residual concentrations of the deoxidizer and dissolved oxygen in the steel.

Deoxidation with manganese (in the form of ferromanganese) is carried out before the metal is released from the furnace. Manganese is a weak deoxidizer, so deoxidation with it is preliminary. The deoxidation products—MnO—form xMnO complexes in the metal. • y

FeO• z

SiO2 with a lower melting point and high fluid mobility.

Silicon is a stronger deoxidizing agent. The deoxidation products—SiO2—melt at a temperature of 1710° C, so inclusions of solid silica are first formed. Subsequent fusion of SiO2 with FeO and MnO gives low-melting silicates mSKVFeO'&MnO, which coarse well and float easily. Blast furnace-poor ferrosilicon is used to deoxidize the metal in a furnace. The final deoxidation with silicon occurs at the outlet, when rich ferrosilicon is released into the stream.

Aluminum has a high affinity for oxygen. Deoxidation products are solid fine particles of Al2O3. Aluminum is introduced into a ladle, and the metal is partially deoxidized when poured into molds.

Tool steels

Tool steels are products without alloying that are durable. Additives are used to seal some areas. They are subject to special requirements related to their specific use.

Tool steels are also divided into several subtypes:

• for cutting tools;
• for measuring instruments;
• stamped;
• roller

For cutting tools

Steels for cutting tools are quite expensive, so not everyone can create products from them. Typically, some parts of the tools are made from constitutional steel, such as plates or blades.

Steel of this type, in turn, is divided into the following subtypes:

• carbon tool alloys (usually contain 0.5-1.3% carbon, common for use in the manufacturing process);
• alloyed tool tools (from which you can make cutters, drills and broaches);
• high-speed (can create products with heat resistance up to -660 degrees).

Steels for measuring instruments

Steel for measuring instruments must have stable shape and dimensions during alteration and storage. Also, its surface must be perfectly smooth, well processed and polished.

Such steel can be carbon and alloyed with chromium, nickel and other elements. To increase wear resistance and improve surface quality, products are cemented and hardened. Steel is still in demand in the manufacture of the most modern measuring instruments.

Die steels

Die steel is characterized by hardness, resistance to temperature changes and hardenability. It must be wear-resistant and have a permanent shape. These alloys include the following:

• cold stamping (in addition to hardness, wear resistance, stability of dimensions and shape, a high level of viscosity and resistance to temperature changes are added; they can work under conditions of impact and high pressure; they are produced on the basis of alloys with chromium and other elements);
• hot stamping (they must have increased strength and toughness when heated to 500 degrees and high thermal conductivity in order to avoid overheating; they are subject to an alloying procedure with chromium, nickel, vanadium, etc.).

Roll steels

Rolling steel is used to produce rolling mills, dies, punches, and blades for working with metal products. They can also be used to produce components for mining and paper-making equipment.

Basic requirements for roll steel:

• high level of hardenability for product strength (hardening of steel is carried out slowly, immersing it in oil for cooling);
• high wear resistance (it allows the entire rolling mill to operate for a long time and without interruption, ensuring stable parameters);
• contact strength (it must be greater than the voltage that occurs during the process, taking into account the load from the resistance and the mass of the device).

Advantages of mild steel

Due to the homogeneity and fine-grained structure, deoxidized steels have the following advantages:

• good resistance to dynamic impacts and brittle fracture, due to which they are used in the manufacture of critical structures for which static and dynamic impacts are planned;
• steel, for the deoxidation of which aluminum additives were used, is not subject to aging, which implies a change in the properties of the material without a noticeable change in the microstructure. Plasticity, resistance to brittle fracture, and the threshold of cold brittleness are reduced, and strength is slightly increased;
• uniform distribution of sulfur and phosphorus;
• good weldability.