annually due to corrosion lost a lot of metal.However, even greater damage causing failure of metal products due to corrosion effects.Costs necessary for replacement parts or maintenance equipment, vehicles, sea and river vessels, equipment used in the chemical industry, many times the cost of the material that went to their production.Significant
there are indirect losses.To those include, for example, the leakage of gas or oil from corroded pipelines, food spoilage, destruction of building structures and more.Therefore, the fight against metal corrosion is paramount.
Why is the destruction of metallic materials?
Before turning to the question of what is stainless steel, let's deal with the concept of corrosion and the essence of the process.
Translated from the Latin corroder - corrosive.Slow spontaneous destruction of metals and their alloys, which occurs under the influence of the chemical environment is called corrosion.The reason for this failure is the chemical reaction (redox reaction) of metallic material with a gaseous or liquid medium in which they are located.
What is corrosion-resistant steels and alloys?
Stainless and heat resistant steel or their alloys are designed for operation in hostile environments or at high ambient temperatures.Therefore, the main requirement for the content of this group - the heat resistance (resistance to the gaseous medium or high temperature steam) and corrosion resistance (having the ability to effectively resist the corrosive factors at ordinary temperature).
inherent corrosion resistance of metal products on the surface of which is formed in hostile environments solid passivating film that prevents the penetration into the deeper layers of metal and interact with aggressive substances.
other words, corrosion-resistant steel - is steel, is resistant to intergranular, chemical, electrochemical and other corrosion.
chemical composition
properties of metals are determined by its chemical composition.When the chromium content becomes 12-13% stainless steel, that is resistant to atmospheric and chemical environments.Increasing the chromium content up to 28-30% makes it resistant to aggressive environments.
Other elements used for doping include manganese, aluminum, titanium, nickel.Most widely used alloys, as part of which the average nickel content of 10% chromium - 18% of carbon - between 0.08 and 0.12% titanium - 1% (12X18H10T - corrosion-resistant steel, GOST 5632).
Classification by type of microstructure: austenitic stainless steel
Resistance to the corrosive action of this class is increased by alloying elements nickel (from 5 to 15%) and chromium (15 to 20%).Austenitic alloys insensitive to intercrystalline corrosion provided that the content of carbon is less than the limit of its solubility in austenite (0.02-0.03% and less).Nonmagnetic, well exposed to welding, cold and hot deformation.Has excellent processability.This is the best steel for manufacturing of fastener elements, welded structures and applications in various industries.
martensitic grades of stainless steel, included in the martensitic grades, can be magnetic and have higher - compared to austenitic - indicators of maximum hardness.Hardening is achieved by quenching and tempering.Well suited for the production of products intended for use in environments of medium and low intensity (for example, a number of products the food industry or the production of blades for razors).
ferritic grades
With high corrosion resistance properties of these grades are similar to the low-carbon steel.The average content of chromium is 11-17%.Used in the manufacture of household appliances, elements of architectural decor, kitchen utensils.
austenitic-ferritic class
Corrosion-resistant stainless steels of different classes reduced nickel content and a high rate of chromium (21 to 28%).As additional alloying elements protrude niobium, titanium, and copper.After the heat treatment the ratio of ferrite and austenite - approximately one to one.
On the strength of austenitic-ferritic steels, austenitic exceed twice.At the same time they are flexible, well withstand shock loads, have a low level of stress corrosion cracking, and high resistance to intergranular corrosion.Recommended for use in the construction, manufacturing, for the manufacture of products that will be in contact with sea water.
austenitic-martensitic grades
chromium content of 12 to 18%, nickel - from 3.7 to 7.5%.Additional elements - chromium and aluminum.Hardening by quenching (t & gt; 975 ° C) and subsequent tempering (t = 450-500 ° C).Austenitic-martensitic stainless steels are welded well and have good mechanical properties.
Stainless steel: the price (factors influencing the formation)
The composition of corrosion-resistant metals include expensive alloying elements such as chromium, nickel, titanium, molybdenum.Their value is decisive in pricing.Since other brands (carbon, structural, ball bearing, and so tool. D.) Comprise the elements listed in much smaller quantities, compared with the cost of them stainless steels are always higher.However, the price may vary depending on market conditions and the cost required for the production of stainless steel.
mechanical properties
Stamps stainless steels should have mechanical properties that meet established standards for manufacturing.These include:
- maximum hardness scale Brinell (HB);
- elongation (%);
- yield strength (H / mm2);
- tensile strength (H / mm2).
after each batch production (fusion) of marketable products checked for compliance with the mechanical properties and microstructure of the steel grade GOST.The results of laboratory studies of samples specified in the certificate for manufacturing.
Notation steels
in different countries produced an extensive assortment of alloys and steels.Thus while there is no single international system of marking.
The United States operates several systems of notation.This situation is due to the presence of a large number of standards organizations (AJS, ANSI, ACJ, SAE, AWS, ASTM, ASME), creates difficulties for partners, suppliers and customers of US steel producers from other countries.
in Japan were marked with letters and numbers indicating their group (low-alloyed, high-alloyed, special purpose alloys, srednelegirovannye, quality, quality, etc.), The serial number in it, and the properties of the metal.
The European Union regulates the designation of standard EN 27 100, which determines the order in which assigned the name and number.
The Russian Federation has developed during the Soviet era alphanumeric system, according to which the designated steels.Standard prescribes specify each alloying element, which is part of the metal, Russian capital letter.
for manganese is H, silicon - C chromium - X, Ni - H, Mo - M, tungsten - B, vanadium - F, titanium - T aluminum - U, Nb - B, cobalt - K, Zr - C, boron - R.
numbers following the letter indicates the content of alloying elements as a percentage.If the steel composition contains less than 1% of the alloying elements, the digit is not affixed at levels of from 1 to 2% after the letter put 1. Said mark the beginning digit number necessary to refer to the average carbon content in hundredths of a percent within grade composition.
Range of products manufactured from stainless steel
corrosion-resistant steel is used for the production of the following products:
- etched heat treated and polished sheets;
- netravlenyh heat-treated sheets;
- thermally untreated and netravlenyh sheets;
- heat-, cold- and hot-rolled seamless pipes;
- hot-rolled strip steel, general purpose;
- calibrated hexagons;
- Stainless circles;
- stainless wire (heat-treated and cold-drawn);
- castings with special properties;
- forgings;
- other types, which are designed to state standards and technical guidance (TU).
Scope
Being one of the best examples of strength, aesthetics, resistance to the destructive power of corrosion and high temperatures, the suitability for re-use and longevity of operation, having met all sanitary requirements excellent quality surface finish, corrosion-resistant steel is widely usedalmost all spheres of economic activities.
Stainless steel is in high demand in the petrochemical, chemical, pulp and paper, food industry, construction industry, power industry, shipbuilding and transport engineering, instrument-making, and in the areas of environmental protection.
efficiency and durability of products made of stainless steel, is determined by the best one for her class and brand, understanding the physicochemical properties and structure of the microstructure.Using metals that are resistant to the ravages of corrosion, in strict accordance with their properties, we are able to take advantage of all the undeniable advantages of modern technology.
