The durability and reliability of the mechanisms depend on the material from which they were made, that is, on the combination of all its properties and characteristics, which determine the operational characteristics. Today, the majority of units and parts of machines are made from various grades of steel. Consider this material in more detail.
What is steel
Steel is an alloy of two chemical elements: iron (Fe) and carbon (C), and the content of the latter should not exceed 2%. If there is more carbon, then this alloy belongs to cast iron.
But steel is not only a chemically pure compound of two elements, it contains both harmful impurities, such as sulfur and phosphorus, as well as special additives that give the desired properties to the material — they increase strength, improve workability, ductility, etc.
If the carbon alloy is less than 0.025% and contains a small amount of impurities, then it is considered to be a technical iron. This material differs from steel in all respects, it has high magnetic characteristics, and it is used as a material for the manufacture of electrical components. Pure iron does not exist in nature, it is very difficult to obtain it even under laboratory conditions.
Despite the fact that carbon as a percentage contains quite a bit, it has a significant impact on the mechanical and technical properties of the material. The increase in this substance leads to an increase in hardness, strength increases, but at the same time plasticity sharply decreases. And, as a result, technological characteristics change: with increasing carbon, casting properties decrease, machinability deteriorates. At the same time, low carbon steels are also poorly machined.
Getting steel. Metal science
Steel is the most common alloy on the planet. It is produced industrially from cast iron, from which an excess of carbon and other impurities are burned out under the influence of high temperatures. Steel is mainly obtained in two ways: smelting in open-hearth furnaces and smelting electric furnaces. The material made in an electric furnace is called an electric steel. It turns out more pure in composition. In addition, there are many special processes for producing alloys with special properties, such as electric arc melting in vacuum or electron beam melting.
More information about steels and other alloys can be found in the study of such a science as metallurgy. It is considered one of the branches of physics and covers not only information about steel grades and their composition, but also contains information about the structure and properties of materials at the atomic and structural level.
Students of specialized universities take a special course “Industrial Steel”, where they analyze in detail special-purpose alloys: construction, improved, cemented, for cutting and measuring tools, magnetic, spring-spring, heat-resistant, steel for structures in cold climates, etc.
Steel grades by quality
All steel quality is divided into:
- steel of ordinary quality;
- steel of high quality;
The quality of steel directly depends on the percentage of harmful impurities (composition) and compliance with the stated mechanical and technological characteristics. In industry, all kinds are used, but in different directions: they have become of ordinary quality - for non-critical parts, they have become of improved quality and high-quality - in structures that have special requirements.
Steel according to GOST: classification
- GOST 380-88. Carbonaceous ordinary quality - Art. 1, Art. 2, St3ps, etc. Figures from 0 to 6 denote the brand, with increasing numbers increases the carbon content. Letters ps, kn; cn - indices of the degree of deoxidation of the material: semi-calm, boiling, calm, respectively.
- GOST1050-74. Carbonaceous quality steel - 05; 08; ten; 20 ps; 08 kn. Figures up to 60 are the average C content in hundredths of a percent, the letter ps, kp; ch - the same claim 1.
- GOST 5632-72. High alloy steels and alloys, corrosion-resistant, heat-resistant and heat-resistant - 30HGSA, GN2; 50X; 20XH3A. The first digits are carbon content: 30 - 0.3%; 40 - 0.4%; 45 - 0.45%, letters - the corresponding alloying element (X-chromium; G - manganese; T - titanium; A-nitrogen, etc.), digit by letter - the percentage of the alloying element. If there is no figure, then the proportion of the substance is 1.5%, the letter A at the end means that it is stainless steel. This applies to both tool and alloy steels.
- GOST1435-74. Carbon tool - U7, U8, U10A. Interpretation: V7 - 0.7% С; U8 - 0.8% C; Y - carbon; A - high quality.
- GOST5950-73. Alloy instrumental - 5HGN; X12; 8X3, etc. The interpretation of the brand is similar to paragraph 3, but the content of C is indicated in tenths of a percent. If carbon is less than 0.1%, the numbers are not indicated - XB4; CHC; CVH, etc.
- GOST 801-78. Bearing - SHH4; ШХ15; SHH15SG. ShH - bearing, figure - chromium content: ShH4 - 0.4% chromium, ShH15 - 1.5% chrome, other letters and numbers - the content of additional alloying elements.
- GOST 1414-75. Constructional high and high machinability - A12, A20, A30, A40G. Interpretation of carbon content: A20 - 0.2% C, A12 - 0.12% C, A30 - 0.3% C.