Low carbon steel is ubiquitous. Its popularity is based on physical, chemical properties and low cost. This alloy is widely used in industry and construction. Let us consider in more detail this type of steel.
Structure
Steel is iron enriched in carbon during the smelting process. Carbon smelting is characterized by the presence of carbon, which determines the basic 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 not more than 0.25% carbon.
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 cracking of the alloy during heat treatment, phosphorus - in the cold.
Production methods
The production of a low-carbon alloy can be decomposed into several stages: loading pig iron and scrap (charge) into the furnace, heat treatment to the melting state, and removing impurities from the mass.
Further, steel casting or additional processing may occur: slag or vacuum and inert gases.
To execute such processes, three methods are used:
- Open-hearth furnaces. The most common equipment. The melting process takes several hours, which allows the laboratories to monitor the quality of the resulting composition.
- Convection ovens. It is produced by purging with oxygen. It should be noted that the alloys obtained in this way do not differ in high quality, since they contain a greater amount of impurities.
- Induction and electric furnaces. The production process is using slag. In this way, high-quality and specialized alloys are obtained.
Consider the features of the classification of alloys.
Kinds
Mild steel can be of three types:
- The usual quality. In such alloys, the sulfur content does not exceed 0.06%, phosphorus 0.07%.
- High quality . As part of the presence of: sulfur up to 0.04%, phosphorus up to 0.035%.
- High quality. Sulfur content up to 0.025%, phosphorus up to 0.025%
- Of particular quality. Low impurity content: sulfur up to 0.015%, phosphorus up to 0.025%.
As mentioned earlier, the less impurities, the better the quality of the alloy.
Low-carbon steel GOST 380-94 of ordinary quality is divided into three more groups:
- A. Determined by its mechanical properties. The form of delivery to the consumer is most often found in the form of multi-profile and sheet metal.
- B. Key indicators - chemical composition and properties. Optimal for mechanical impact by pressure under the thermal factor (forging, stamping).
- B. For these types of alloys, the following properties are important: technical, technological, physical, chemical, and, accordingly, composition.
According to the process of deoxidation, steel is divided into:
- Calm. The hardening process is calm. No gases are emitted during this process. Shrinkage occurs in the middle of an ingot.
- Soothing. An intermediate type of steel between still and boiling compositions.
- Boiling. Hardening occurs with the release of gas. Concealed shrink basin.
Basic properties
Low-carbon steel is characterized by high ductility, it is easily deformed in the cold state and in the hot state. A distinctive feature of this alloy is its good weldability. Depending on the additional elements, the properties of steel may vary.
Most often, low-carbon alloys are used in construction and industry. This is due to the low price and good strength properties. Such an alloy is also called structural. The properties of low carbon steel are encrypted in the marking. Below we consider its features.
Labeling Features
Ordinary mild steel has the letter designation ST and digital. The number should be divided by 100, then the percentage of carbon will be clear. For example, CT15 (carbon 0.15%).
Consider the marking and decipher the notation:
- The first letters or their absence indicates belonging to a particular quality group. It can be B or C. If there is no letter, then the alloy belongs to category A.
- St stands for the word steel.
- Digital designation - encrypted carbon percentage.
- kp, ps - denotes a boiling or semi-quiet 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 included in the composition, and their percentage. For example, G - manganese, Yu - aluminum, F - vanadium.
For high-quality low-carbon steels, the lettering “St” is not indicated in the marking.
Color coding is also used. For example, grade 10 low carbon steel is white. Special steels may be indicated by additional letters. For example, “K” - is used in boiler building; OSV - used for the manufacture of car axles, etc.
Manufactured products
There are several groups of steel products:
- Sheet steel. Subspecies: plate (GOST 19903-74), sheet (GOST 19904-74), broadband (GOST 8200-70), strip (GOST 103-76), corrugated (GOST 8568-78)
- Corner profiles. Equal-shelf (GOST 8509-93), unequal (GOST 8510-86).
- Channel bars (GOST 8240-93).
- I-beams. Beams ordinary I-beams (GOST 8239-89), Beams wide I-beams (GOST 26020–83, STO ASChM 20–93).
- Pipes.
- Profiled flooring.
Secondary profiles are added to this list, which are formed due to welding and machining.
Fields of application
The scope of use of low carbon steel is wide enough and depends on the marking:
- St 0, 1, 3 GSP. Widespread use in construction. For example, reinforcing wire of low carbon steel,
- 05kp, 08, 08kp, 08yu. Good for stamping and cold drawing (high ductility). They are used in the automotive industry: body parts, fuel tanks, coils, parts of welded structures.
- 10, 15. 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. Widely used for the production of fasteners. Couplings, cam followers, frames and other parts of agricultural machinery.
- 30, 35. Axes, on which there is a small load, sprockets, gears, etc.
- 40, 45, 50. Parts experiencing moderate stress. For example, crankshafts, friction discs.
- 60-85. High-stress parts. It can be rails for the railway, wheels for cranes, springs, washers.
As you can see, the manufactured assortment is vast - it is not only low-carbon steel wire. These are also details of complex mechanisms.
Low alloy and low carbon steel: differences
Alloying elements are added to improve any characteristics of the alloy .
Steels that contain a low amount of carbon in the chaeb (up to a quarter percent) and alloying additives (total percentage up to 4%) are called low alloyed. This product retains high weld qualities, but at the same time different properties are enhanced. For example, durability, 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.
Welding Features
Welding low carbon steels has high rates. The type of welding, the electrodes and their thickness are selected based on the following technical data:
- The connection must certainly be firmly bonded.
- There should be no defects in the seams.
- The chemical composition of the seam must be carried out in accordance with the standards specified in GOST.
- Welded joints must comply with the operating conditions (resistance to vibrations, mechanical stress, temperature conditions).
Various types of welding can be used, from gas welding to welding in a carbon dioxide medium with a consumable electrode. When selecting take into account the high fusibility of low carbon and low alloy alloys.
As for the specific scope, low-carbon steel is used in construction and engineering.
Steel grade is selected based on the physical and chemical properties required at the outlet. The presence of alloying elements can improve some properties (resistance to corrosion, temperature differences), but also worsen others. Good weldability is another advantage of such alloys.
So, we found out what are the products of low carbon and low alloy steel.