Corrosion-resistant steel. Steel grades: GOST. Stainless steel - price

Annually because of corrosion, a lot of metal is lost. However, even more damage is caused by the failure of metal products as a result of corrosion attack. The costs necessary to replace parts or routine maintenance of instruments, cars, sea and river vessels, equipment used in chemical production, many times exceed the cost of material that went into their manufacture.

Indirect losses are also significant. These include, for example, leakage of gas or oil from corrosion-damaged pipelines, spoilage of food, destruction of building structures and much more. Therefore, the fight against corrosion of metal is of paramount importance.

Why is the destruction of metal materials?

Before turning to the question of what corrosion-resistant steel is, let's look at the concept of corrosion and the essence of this process.

In translation from the Latin corroder - corroding. Slow spontaneous destruction of metals and alloys based on them, occurring under the chemical influence of the environment, is called corrosion. The cause of such destruction is the chemical interaction (oxidation-reduction reactions) of metallic materials with the gaseous or liquid medium in which they are located.

What are corrosion-resistant steels and alloys?

Products made of stainless and heat-resistant steel or their alloys are designed to work in corrosive environments at high or ordinary temperatures. Therefore, the main requirement for the materials of this group is heat resistance (resistance to gas medium or high temperature steam) or corrosion resistance (the ability to effectively withstand the effects of aggressive factors at normal temperatures).

Corrosion resistance is characteristic of metal products, on the surface of which an aggressive passive film is formed in the aggressive medium, which prevents penetration into the deeper layers of the metal and the interaction of aggressive substances with them.

In other words, corrosion-resistant steel is a steel with resistance to intergranular, chemical, electrochemical and other corrosion.

Chemical composition

The properties of the metal are determined by its chemical composition. With a chromium content of 12-13%, the steel becomes stainless, that is, stable in the atmosphere and chemical media. Increasing the chromium content to 28-30% makes it stable in aggressive environments.

Other elements used for alloying include manganese, aluminum, titanium, and nickel. The most widely used are alloys, in which the average nickel content is 10%, chromium is 18%, carbon is from 0.08 or 0.12%, titanium is 1% (12Х18Н10Т is corrosion-resistant steel, GOST 5632).

Classification by type of microstructure: austenitic class of stainless steel

The resistance of this class to corrosion is increased due to nickel alloying elements (from 5 to 15%) and chromium (from 15 to 20%). Austenitic alloys are insensitive to intercrystalline corrosion, provided that the content of carbon in them is less than the limit of its solubility in austenite (0.02-0.03% or less). Non-magnetic, well subjected to welding, cold and hot deformation. They have excellent manufacturability. This is the best steel for the manufacture of fasteners, welded structures and applications in various industries.

Martensitic class

Stainless steels entering the martensitic class can be magnetic and have higher values of maximum hardness, compared to austenitic steels. Hardening is achieved by hardening and tempering. Well suited for the production of products intended for use in medium and low intensity environments (for example, a number of food products or the production of razor blades).

The ferritic class

With high corrosion resistance properties of these grades are similar to low-carbon steel. The average chromium content is 11-17%. Used in the manufacture of household appliances, elements of the architectural decor of the interior, kitchen utensils.

Austenitic-ferritic class

Corrosion-resistant stainless steels of this class are characterized by a reduced nickel content and a high chromium content index (from 21 to 28%). As additional alloying elements are niobium, titanium, copper. After the heat treatment, the ratio of ferrite to austenite is approximately one to one.

The strength of austenitic-ferritic steels exceeds the austenitic two times. They are plastic, well resist shock loads, have a low level of corrosion cracking and high resistance to intergranular corrosion. Recommended for use in construction, manufacturing, manufacturing of products that will come into contact with sea water.

Austenitic-martensitic class

The chromium content is from 12 to 18%, nickel is from 3.7 to 7.5%. Additional elements are chrome and aluminum. Hardened by quenching (t> 975 ° C) and subsequent tempering (t = 450-500 ° C). Austenitic-martensitic stainless steels are well welded and have high mechanical properties.

Stainless steel: price (factors affecting the formation)

The composition of corrosion-resistant metals includes expensive alloying elements, such as chromium, nickel, titanium, molybdenum. Their cost is the determining factor in pricing. Since other brands (carbon, structural, ball bearing, tool, etc.) contain the listed elements in much smaller quantities, in comparison with them the cost of corrosion-resistant steels is always higher. However, the price may vary depending on the market conditions and the costs required for the production of stainless steel.

Mechanical properties

Stamps of corrosion-resistant steels shall have mechanical properties meeting the requirements of the established production standards. These include:

• Maximum hardness on the Brinell scale (HB);
• relative extension (%);
• Yield strength (H / mm ² );
• Resistance to tearing (H / mm ² ).

After production, each lot (smelting) of commercial products is checked for compliance of mechanical properties and microstructure of the steel grade with GOST. The results of the laboratory examination of the samples are indicated in the manufacturing certificate.

Steel marking system

In various countries of the world, an extensive range of alloys and steels is produced. At the same time, there is no single international system for their marking.

In the United States of America several naming systems operate at once. This situation, caused by the large number of standardization organizations (AJS, ANSI, ACJ, SAE, AWS, ASTM, ASME), creates certain difficulties for partners, contractors and customers of metal products of American manufacturers from other countries.

In Japan, steel was marked with letters and numbers indicating their group (low-alloy, high-alloy, special-purpose alloys, medium-alloy, high-quality, high-quality, etc.), the serial number in it and the properties of the metal.

In the countries of the European Union, the designation is regulated by the standard EN 100 27, which determines the order according to which the name and serial number are assigned.

In the Russian Federation there is an alphanumeric system developed in the Soviet times, in accordance with which steel grades are designated. GOST prescribes the indication of each alloying chemical element, which is part of the metal, in a capital Russian letter.

For manganese it is Г, silicon-С, chromium-X, nickel-Н, molybdenum-M, tungsten-B, vanadium-Ф, titanium-T, aluminum-Ю, niobium-B, cobalt-K, zirconium-C, boron - R.

The numbers following the letter indicate the percentage of alloying elements. If the content of steel contains less than 1% of the alloying element, the figure is not set, with a content of 1 to 2% after the letter put 1. The two-digit number indicated at the beginning of the mark is necessary to indicate the average carbon content in hundredths of a percent within the brand composition.

The range of products manufactured from stainless steel

Corrosion-resistant steel is used to produce the following products:

• Thermally treated etched and polished sheets;
• Thermally treated untreated sheets;
• Thermally untreated and untreated sheets;
• Heat-, cold- and hot-deformed seamless pipes ;
• Steel hot-rolled strips for general use;
• Calibrated hexahedrons;
• Circles of stainless;
• Stainless steel wire (heat treated and cold drawn);
• Castings with special properties;
• Forgings;
• Other types, for which GOSTs and technical specifications (TU) have been developed.

Application area

Being one of the best samples of strength, aesthetics, resistance to destructive corrosion and high temperatures, recyclability and durability, having an excellent quality of surface treatment meeting all sanitary and hygienic requirements, corrosion-resistant steel is widely used in almost all spheres of economic and economic Activities.

Stainless steel is in high demand in petrochemical, chemical, pulp and paper, food industry, construction industry, electric power, shipbuilding and transport engineering, instrumentation and environmental protection.

The efficiency and durability of products made of stainless steel is determined by the correct choice of its class and brand, the understanding of the physicochemical properties and structure of the microstructure. Using metals that are resistant to the corrosive effects of corrosion, in exact accordance with their properties, we get the opportunity to take advantage of all the undeniable advantages of modern technology.