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Pipes and alloys

12 January 2011
Pipes and alloys

Pipes made of steel and non-ferrous metals often have a circular cross-section, but they can also be of square section, rectangular, oval, etc .; Cast-iron and non-metallic pipes (asbestos cement, plastic, glass, etc.) are usually of circular cross-section.

The technologies for the production of metal pipes can be seamless (outer diameter 1-820 mm, special purpose - 1420 mm), made of ingots and tube billets by pressing or rolling (see Tube Rolling), welded (outer diameter 8-1620 mm, special purpose - up to 2500 mm and more) from sheet and strip steel with preforming on presses or forming mills (see Pipe welding mill), cast (outer diameter 50-1000 mm), obtained on pipe-laying machines

Nichrome. The most heat resistant alloys before the appearance of chromals were nichromes with 80% Ni ,. To reduce the cost of nichromes, ferronichromes were proposed in which a significant part of Ni was replaced by Fe. The optimum composition turned out to be 60% Ni, 15% Cr and 25% Fe. The performance qualities of most nichromes are higher than those of ferronichromes, so the latter are used, as a rule, at a lower temperature. Nichrome and ferronichromes have a rare combination of high heat resistance and high electrical resistance (1.05-1.40 mcm). Therefore, together with the chromals, they are most advantageous in the production of wire and tape for the production of high-temperature electric heaters. For electric heaters in most cases, nichromes are doped with silicon (up to 1.5%) and micro additives of rare-earth, alkaline-earth or other metals. The limiting operating temperature of nichrome of this type is, as a rule, 1200 ° C, for a number of grades of 1250 ° C.

Nickel alloys containing 15-30% Cr, Al-doped (up to 4%), are more heat resistant than alloys doped with Si. However, it is more difficult to obtain a homogeneous wire or tape, which is necessary for reliable operation of electric heaters. Therefore, such alloys are mainly for heat-resistant parts that are not subject to high mechanical stresses at temperatures up to 1250 ° C.

Nichrome has a high corrosion resistance under the influence of air or other gaseous media at high temperature. It also has satisfactory processability (ductility in the cold state, weldability) - from nichrome it is possible to obtain wire, tape, rods and other semi-finished products; Sufficient heat resistance - the ability to withstand mechanical loads without significant deformation, without breaking at high temperatures. On the surface of these alloys, oxides are formed that are stable at high temperatures. The oxide film has a high density. These two factors provide high heat resistance of nichrome X20N80 and X15N60.

The alloy Fechral X23Y5T also refers to alloys with high electrical resistance and for it the above mentioned properties and application are also characteristic. But fechral is an iron-chrome-aluminum alloy, nichrome is a chromium-nickel alloy.

Х20Н80 and Х15Н60 combine high heat resistance with good processability (ribbon and thin-chrome wire can be manufactured). These alloys are more heat resistant than ferhral, ​​but unlike the latter contain scarce and expensive nickel. Fechral is cheaper than nichrome and is characterized by increased heat resistance, but it is more solid and brittle than nichrome, and therefore less technologically (ribbon and fine wire can not be manufactured).

Among the various products, nichrome wire, X20N80 and X15N60 tape and wire of fecral X23S5T

Wire - a semi-finished product with a cross-section of constant dimensions, rolled into a coil or wound on a coil, manufactured by rolling, pressing or drawing. (In accordance with GOST 25501-82 )

Ribbon is a semi-finished product of rectangular cross-section with a thickness of more than 0.1 mm in rolls, manufactured by rolling or electrolytic method. (In accordance with GOST 25501-82 )

Fechral and nichrome wires are subdivided by purpose (according to GOST 12766 .1-90):

  • Of alloys of grades Х23Ю5Т:
  • For heating elements - H
  • For tubular electric heaters - TEN
  • For resistance elements - С
  • From alloys of marks Х20Н80-Н, Х15Н60-Н:
  • For heating elements
  • For tubular electric heaters - TEN
  • From alloys of grade Х15Н60:
  • For resistance elements

Inconel, a high-temperature alloy developed in the US based on nickel contains ~ 15% chromium and up to 9% iron. Varieties of Inconel are alloyed depending on the purpose of aluminum, titanium, molybdenum, etc. It goes on details of gas turbine engines, supersonic aircraft, rockets, etc. At temperatures up to 900 ° C, alloys are distinguished by their high strength and toughness, insensitivity to incisions at low Up to -78 ° C) temperatures. Products made of iron well welded, to improve the strength of welded structures subjected to heat treatment. The analogues of iron ore in the USSR were alloys of grades ХН80ТБЮ and ХН73МБТЮ.

Nimonik, a group of high-temperature nickel-based alloys containing Cr, Ti, Al. Developed in the UK (the firm "Mond nickel company", 1941-42). A number of varieties of H. are produced which, depending on the desired combination of properties, contain 10-21% Cr, 0.2-4% Ti, 0.5-6.0% Al; In addition, N is doped with Co (up to 22%), Mo (up to 6%), and other elements. Depending on the chemical composition, the melting point of the alloys is 1310-1390 ° C. The best N. are able to work up to 1000 ° C. Alloys are well suited to hot working with pressure and to a lesser degree of cold working. Are made in the form of forgings, rods, sheets, pipes , etc .; Are used as a structural material for parts of gas turbine engines, rockets , etc. The N. analogues in the USSR were alloys of the brands KhN55VMTFKYU, KhN80TBYU and others in the USA - Inconel.

Hastelloy, the name of the group of Ni-Mo and Ni-Cr-Mo resistant to nickel alloys. Depending on the purpose, X contains different amounts of Mo (up to 30%), Cr (up to 23%), Fe (up to 29%), C (up to 0.15%). Some brands alloy W (about 5%), Si (up to 10%), Co (up to 2.5%), and Cu, V, Ta, Nb, and other elements. For X. characterized by increased resistance to hydrochloric, sulfuric, phosphoric, acetic, formic acids, in media containing ions of chlorine, fluorine, in many organic media , etc. Produced in the form of sheets, rods, wires, castings. They are used mainly for the manufacture of chemical equipment; Some X are used as heat-resistant materials. In the USSR, Kh. Brands N70M28F, Kh15N65M16B and others were produced.

Permalloy 79NM

[Eng. Permalloy, perm (eability), the name of a group of nickel alloys with iron with a high permeability m, a small coercive force Hc, and a small loss in hysteresis. Relate to magnetically soft materials, developed in the United States after the 1-st World War 1914-18; In industry P. began to be used in the 20-ies. There are 2 main groups of P: low-nickel (40-50% Ni, typical representative -permenorm) and high-nickel (70-83% Ni). In the formation of the magnetic properties of semiconductors, an important role is played by the conditions of heat treatment, which are carried out in a vacuum or in a hydrogen environment, sometimes when a magnetic field is applied. To achieve high m and low Hc, high-nickel P is subjected to a sharp cooling (30-80 ° C / s) from 600 ° C, which is due to inhibition of structural transformations, which lead to a deterioration of the magnetic properties. To reduce the rate of cooling and increase the electrical resistivity, high-nickel plating is usually doped with Mo, Cr, Cu, Si, and other elements.

The representative of high-nickel P.-molybdenum P. contains approximately 79% Ni, 17% Fe, 4% Mo and has an initial ma ≥ 22,000, maximum mmax150000, HC ≤ 0.012 A / cm, saturation magnetization 0.85 ml, Curie point 400 ° C. In the alloy superalloy (English super-excellent) containing approximately 79% Ni, 16% Fe, 5% Mo, thanks to the use of the purest charge materials and special care in conducting the heat treatment, the highest among the known magnetically soft materials is achieved: m: ma ³ 100 OQO , Mmax ³ 1 000 000. Alloys of PP type are produced mainly in the form of tapes with a thickness of 0.003-0.5 mm; They are used in radio engineering, communication technology and other fields of application of weak currents. Practical applications in a number of automation and computer devices were also obtained from 65-68% Ni (usually doped with 2-3% Mo), characterized by a rectangular hysteresis loop.

Aljumel,

An alloy used in pyrometry as the negative thermoelectrode of the chromel-alumel thermocouple, and also in the form of compensating wires. The chemical composition of aluminum (in%): 1.8-2.5 aluminum; 0.85-2.0 of silicon; 1.8-2.2 manganese; The rest is nickel and cobalt, and cobalt is present as an impurity in nickel, and to maintain the required thermopower, its content should be in the range of 0.6-1.0%. Thermocouples with A. are used for measuring temperatures up to 1000 ° C. Over 1000 ° C for prolonged exposures, the change in the thermopower becomes very noticeable. Alloys of aluminum alloyed with 0,06-0,1% zirconium or 0,06% zirconium + 0,005-0,03% boron, etc. have been developed and are used. Alloying of A. significantly increases the ductility (at 600-1100 ° С) and prolonged Strength (at 700-900 ° C), and also increases the stability of the thermopower at temperatures up to 1250-1300 ° C.

Chromel, an alloy of nickel with chromium, with a favorable combination of thermoelectric properties and heat resistance. Contains about 10% Cr, about 1% Co, and impurities (up to 0.2% C and up to 0.3% Fe). X. is characterized by a sufficiently large and almost rectilinear change in the thermoelectric power (TEPS) over a wide range of temperatures. The TEPS of the chromel-platinum thermocouple at the junction temperatures of 1000 and 0 ° C is about 33 mV. X. has a constant value of TEPS for long-term operation in air in the temperature range 20-1000 ° C; At higher temperatures, the operational reliability of the alloy is reduced. X is made in the form of a wire and is used in conjunction with Alumel as a positive thermoelectrode for the chromel-alumel thermocouple, which is used for temperature measurement. X is also used as compensating wires. In the USSR, Kh. Grades НХ9.5 and НХ9 were produced.

Kopel,

A copper-nickel alloy containing ~ 43% Ni and ~ 0.5% Mn. The chemical composition, physical and mechanical properties of K. close to the constant, the melting point of K. about 1290 ° C. Of all copper-nickel alloys, K has a maximum thermoelectromotive force in pair with chromel (about 6.95 mV at 100 ° C, 49.0 mV at 600 ° C). It is mainly used in pyrometry as a negative thermoelectrode thermocouple when measuring temperatures up to 600 ° C, e. Also as compensating wires. In the USSR, the brand of MNMts 43-0.5 was manufactured.

Constantan

(From Latin constans, genitive case constantis - constant, unchanged), copper-nickel alloy, differs weak dependence of electrical resistance on temperature. Issued in the USSR, K. contained 39-41% nickel, 1-2% manganese, the rest - copper. The electrical resistivity at 20 ° C. C "0,48mkomxm, temperature coefficient after the special heat treatment (stabilizing annealing) of about 2x10-6 1 / K. The melting temperature of 1260 ° C. K. used in electrical engineering for the manufacture of rheostats, .. instrumentation elements, etc. a disadvantage K. large thermoelectromotive force (about 39 uV / K) is in contact with copper K. therefore rarely used in high-accuracy class devices - random heating contact terminal gives rise to e ktricheskoy circuit current, distorting the readings. Typically, in the most critical cases, a manganin. With copper or iron K thermocouple forms suitable for measuring temperatures up to 500 ° C.

11 January 2011
13 January 2011