Low-carbon steel: composition and properties

Low-carbon steel is found everywhere. Its popularity is based on physical, chemical properties and low cost. This alloy is widely used in industry and construction. Let us consider this type of steel in more detail.

Composition

Steel - iron, enriched with carbon in the process of melting. Carboniferous smelters are characterized by the presence of carbon, which determines the main properties of the metal, and impurities: phosphorus (up to 0.07%), silicon (up to 0.35%), sulfur (up to 0.06%), manganese (up to 0.8% ). Thus, low-carbon steel contains no more than 0.25% carbon. As for other additives, manganese and silicon serve to deoxidize (remove oxygen from the liquid metal, which reduces brittleness during hot deformation). But an increased percentage of sulfur can lead to the cracking of the alloy during heat treatment, phosphorus - for cold.

Methods of obtaining

Production of low-carbon alloy can be decomposed into several stages: charging of iron and scrap (charge) into the furnace, thermal exposure to the melting state, removal of impurities from the mass. Further, steel casting or additional processing can occur: slag or vacuum and inert gases.

There are three ways to execute such processes:

• Marten furnaces. The most common equipment. The melting process takes place within a few hours, which makes it possible to track the quality of the resulting composition to the laboratories.
• Convector ovens. Produced by purging with oxygen. It should be noted that alloys obtained in this way are not of high quality, since they contain more impurities.
• Induction and electric furnaces. The process of production is using slag. In this way, high-quality and specialized alloys are obtained.

Consider the features of the classification of alloys.

Kinds

Low-carbon steel can be of three types:

• Ordinary quality. In such alloys, the sulfur content does not exceed 0.06%, phosphorus 0.07%.
• Quality . In the presence of: sulfur to 0.04%, phosphorus to 0.035%.
• High-quality. The sulfur content is up to 0.025%, phosphorus is up to 0.025%
• Special quality. Low content of impurities: sulfur up to 0.015%, phosphorus - up to 0.025%.

As mentioned earlier, the fewer impurities, the better the quality of the alloy. Low-carbon steel GOST 380-94 of ordinary quality is divided into three groups:

• A. It is determined by its mechanical properties. The form of delivery to the consumer is most often found in the form of multi-profile and sheet products.
• B. The main indicators - the chemical composition and properties. Optimal for the mechanical effect of pressure under the thermal factor (forging, stamping).
• B. For such types of alloys, such properties are important: technical, technological, physical, chemical and, accordingly, composition.

By the process of deoxidation, steel is divided into:

• Calm. The solidification process is calm. Gases in this process are not allocated. Shrinkage occurs in the middle of the ingot.
• Semi-calm. Intermediate steel between calm and boiling compounds.
• Boiling. Curing occurs with the release of gas. Shrouded sink.

Basic properties

Low-carbon steel is highly ductile, easily deformed in the cold and hot state. A distinctive feature of such an alloy is good weldability. Depending on the additional elements, the properties of the steel can vary. Most often low-carbon alloys are used in construction and industry. This is due to the low price and good strength properties. This alloy is also called structural. Properties of low-carbon steel are coded in the marking. Below we consider its features.

Features of the marking

Usual low-carbon steel has the letter designation CT and digital. The number should be divided by 100, then the percentage of carbon will be understood. For example, CT15 (carbon 0.15%).

Consider marking and decipher the notation:

• The first letters or their absence indicate the belonging to a particular group of quality. It can be B or B. If there is no letter, then the alloy belongs to the category A.
• St stands for the word "steel".
• The digital notation is the encrypted percentage of carbon.
• Kp, ps means a boiling or semi-quenched alloy. The absence of a designation indicates that the steel is calm (cn).
• The letter designation and the digital one after it reveal what impurities are in the composition and their percentage. For example, Г - manganese, Ю - aluminum, Ф - vanadium.

For qualitative low-carbon steels, the lettering "St" is not included in the marking. The color designation is also used. For example, low-carbon steel grade 10 has a white color. Special-purpose steel can be indicated by additional letters. For example, "K" - is used in the boiler industry; OsV - used for the manufacture of car axles, etc.

Let out products

Several groups of steel products can be distinguished:

• Sheet steel. Subspecies: thick-leaf (GOST 19903-74), thin-sheeted (GOST 19904-74), wide-leaf (GOST 8200-70), strip (GOST 103-76), corrugated (GOST 8568-78)
• Corner profiles. Equal (GOST 8509-93), unequal (GOST 8510-86).
• Channel bars (GOST 8240-93).
• I-beams. I-beam ordinary beams (GOST 8239-89), I-beam broad-gauge beams (GOST 26020-83, STO ACHM 20-93).
• Pipes.
• Profiled flooring.

To this list, the secondary profiles are added, which are formed by welding and machining.

Applications

The area of use of low-carbon steel is wide enough and depends on the marking:

• St 0, 1, 3Gsp. Wide application in construction. For example, reinforcing wire made of low-carbon steel,
• 05kp, 08, 08kp, 08yu. Good for stamping and cold drawing (high ductility). Used in the automotive industry: body parts, fuel tanks, coils, parts of welded structures.
• 10, 15. They are used for parts not subject to high loads. Pipes for boilers, stamping, couplings, bolts, screws.
• 18kp. Typical applications are structures that are produced by welding.
• 20, 25. It is widely used for the production of fastening materials. Couplings, valve tappets, frames and other parts of agricultural machinery.
• 30, 35. The axes to which there is a small load, sprockets, gears, etc.
• 40, 45, 50. Details experiencing medium loads. For example, crankshafts, friction discs.
• 60-85. Parts subject to high load. These can be rails for the railway, wheels for cranes, springs, washers.

As can be seen, the range being produced is extensive - it's not just a wire of low-carbon steel. Also these are details of complex mechanisms.

Low-alloy and low-carbon steel: differences

To improve any characteristics of the alloy, alloying elements are added . Steels that contain a low amount of carbon (up to a quarter of a percent) and alloying additives (the total percentage - up to 4%) are called low-alloy steels. Such rolling preserves high welded qualities, but at the same time different properties are strengthened. For example, strength, anti-corrosion characteristics and so on. As a rule, both types are used in welded structures, which must withstand the temperature range from minus 40 to plus 450 degrees Celsius.

Features of welding

Welding of low-carbon steels has high performance. The type of welding, electrodes and their thickness are selected on the basis of the following technical data:

• The connection must be firmly secured.
• There should be no stitching defects.
• The chemical composition of the joint must be carried out in accordance with the standards specified in the GOST.
• Welded joints must meet the operating conditions (resistance to vibration, mechanical stress, temperature conditions).

Various types of welding from gas to welding in a carbon dioxide medium with a consumable electrode can be used. At selection allow for high fusibility of low-carbon and low-alloy alloys.

As for the sphere of application, low-carbon steel is used in construction and machine building. The steel grade is selected on the basis of the physical and chemical properties required at the output. The presence of alloying elements can improve some properties (resistance to corrosion, temperature changes), but also worsen others. Good weldability is another advantage of such alloys.

So, we found out what are products from low-carbon and low-alloy steel.