Decoding of steels, alloys and cast irons: table, examples. Deciphering steels by composition
The table of steel interpretation by composition is presented below.
|Chem. element||Name||Designation||Chem. element||Name|
If the name contains the letter "H", then the composition of the alloying elements includes rare earth elements - niobium, lanthanum, cerium.
Cerium (Ce) - affects the strength characteristics and ductility.
Lanthanum (La) and neodymium (Ne) - reduce the sulfur content and reduce the porosity of the metal, leading to a decrease in grain.
Deciphering steels: examples
For an example of decoding, consider the common steel grade 12X18H10T.
The number "12" at the beginning of the brand name is an indicator of the carbon content in this steel, it does not exceed 0.12%. Next comes the designation "X18" - therefore, in steel there is an element of chromium in the amount of 18%. The abbreviation "H10" indicates the presence of nickel in a volume of 10%. The letter "T" indicates the presence of titanium, the lack of digital expression means that it is less than 1.5% there. Obviously, qualified composition of steels in composition immediately gives an idea of its quality characteristics.
If we compare the designations of alloyed and carbon steels, this becomes a noticeable difference, indicating the special properties of the metal, due to the specially introduced alloying additives. Interpretation of steels and alloys indicates their chemical composition. The main alloying additives are:
- Nickel (Ni) - reduces chemical activity and improves the hardenability of the metal;
- chromium (Cr) - increases the tensile strength and yield strength of alloys;
- niobium (Nb) - increases acid resistance and corrosion resistance of welded joints;
- Cobalt (Co) - increases heat resistance and toughness.
Doping - the mechanism of the impact of alloying elements
Difficult to decipher steels. Materials science comprehensively studies this subject.
The content of alloying additives in steel may vary widely, depending on what properties you need to give the metal. Thus, nickel and chromium may be present in the steel in amounts up to 1%, in some cases, and more. Molybdenum, vanadium, titanium and niobium - 0.1-0.5%, manganese and silicon - from 1% or more.
The impact of alloying additives in any case is associated with a distortion of the crystal lattice of iron, the introduction of foreign atoms of a different size into it.
How is the decoding of steels (materials) easier? The table gives useful information.
|Element||Designation||Chem. sign||The influence of the element on the properties of metals and alloys|
Nickel imparts corrosion resistance to alloys through reinforcement of bonds between lattice sites. The enhanced hardenability of such alloys determines the stability of properties for a long time.
|Chromium||X||Cr||Improvement of mechanical properties - increasing the limits of strength and fluidity - due to the increase in the density of the crystal lattice|
|Aluminum||YU||Al||It is fed into the metal stream during casting for deoxidation, most of it remains in the slag, but some of the atoms go into the metal and distort the crystal lattice so much that it leads to a multiple increase in the strength characteristics.|
|Titanium||T||Ti||It is used to increase the heat resistance and acid resistance of alloys.|
Positive aspects of doping
Features of the properties are most clearly manifested after heat treatment, in this regard, all the details of such steel are processed before use.
- Improved alloying of steel and alloys have a higher mechanical properties compared to structural.
- Alloying additives help stabilize austenite, improving the hardenability of steels.
- Due to a decrease in the degree of decomposition of austenite, the formation of quenching cracks and distortion of parts is reduced.
- The toughness increases, which leads to a reduction in cold breakability, and parts made of alloyed steels have a higher durability.
Along with the positive aspects of the alloying of steel has a number of characteristic drawbacks. These include the following:
- In products from alloyed steels reversible temper brittleness of the second kind is observed.
- High-alloyed alloys include residual austenite, which reduces the hardness and resistance to fatigue factors.
- Tendency to the formation of dendritic segregations, which leads to the appearance of line structures after rolling or forging. To eliminate the effect of diffusion is applied.
- Such steels are prone to the formation of flocs.
How is the decryption of steel composition? Materials with less than 2.5% alloying content in their composition are classified as low-alloyed, with an amount from 2.5 to 10% considered to be alloyed, more than 10% - to be high-alloyed.
The carbon content in the composition of the steels due to their separation into:
- high carbon;
- medium carbon;
- low carbon.
The chemical composition determines the separation of steel on:
Cast iron is an alloy of iron and carbon with a content of the latter higher than 2.15%. It is divided into undoped and doped with manganese, chromium, nickel and other alloying additives.
The differences in the structure divide the iron into two types: white (has a silver-white fracture) and gray (a characteristic gray fracture). The form of carbon in white iron is cementite. In gray - graphite.
Gray cast iron is divided into several varieties:
- heat resistant;
- high strength;
- heat resistant;
- corrosion resistant.
Designation of cast iron grades
Different grades of cast iron are designed for various uses. The main ones are the following:
- Pig iron. They are designated as "P1", "P2" and are intended for remelting in the production of steel; cast iron with the designation "PL" is used in the foundry industry for the manufacture of castings; the conversion with a high content of phosphorus, denoted by the letters "PF"; High quality conversion is abbreviated as "PWC".
- Cast iron, in which graphite is in a lamellar form - "MF".
- Antifriction cast iron: gray - "ASF"; high strength - "ACHV"; malleable - "AChK".
- Nodular cast iron used in the foundry industry - "HF".
- Cast iron with alloying additives, endowed with special properties - "H".The alloying elements are labeled in the same way as for steel. The designation of the letter "W" at the end of the name of the brand of cast iron speaks of the spherical state of graphite in such a brand.
- Ductile iron - "RC".
Deciphering steels and cast iron
For cast iron, called gray, the characteristic form of graphite is lamellar. They are marked with letters SCh, the numbers after the letter designation indicate the minimum value of the tensile strength.
Example 1: ChS20 - cast iron gray, has a tensile strength of up to 200 MPa. Gray cast irons are characterized by high casting properties. It is well subjected to machining, has anti-friction characteristics. Products made of gray cast iron are able to extinguish vibrations well.
At the same time, they are not sufficiently resistant to tensile loads, do not have impact resistance.
Example 2: HF50 - high resistance cast iron with tensile strength up to 500 MPa. Having a structure in the form of spherical graphite, it has higher strength characteristics than gray cast iron. They have a certain plasticity and a higher impact strength.Along with gray, high-strength cast iron, good casting characteristics, antifriction and damping properties are characteristic.
These cast irons are used in the manufacture of heavy parts such as press equipment beds or mill rolls, engine crankshafts and so on.
Example 3: KCh35-10 - ductile iron, having a tensile strength of up to 350 MPa and allowing for relative elongation of up to 10%.
Cast iron is malleable, in comparison with gray, have greater strength and ductility. They are used for the production of thin-walled parts experiencing shock and vibration loads: hubs, flanges, crankcases of engines and machine tools, forks, cardan shafts and so on.
The breadth of use of metals in industry requires the ability to quickly navigate the properties and capabilities of products. Such indicators as elasticity, weldability, weariness, are found almost daily in one form or another.
For decades, the production of pig iron and steel per capita was one of the most important factors in assessing the success of the state. It depended on metallurgy, and now it depends, on the successful work of mechanical engineering, automotive, and many other sectors of the national economy.The condition of our only faithful ally - the army and navy - depends on the presence of a large amount of high-quality metal. Metal serves us on the water, under the water and in the air.