Steel structures / | Cast and articles thereof |
Cast - an alloy of iron with carbon (more than 2%), divided into unalloyed and alloyed, containing chromium, nickel, manganese, and other alloying elements.
cast iron used in the manufacture of products for municipal hozyatsstva (covers, gratings), certain parts, sewerage equipment and household items (bath, kitchen utensils, etc.).
Pig iron.
Pig iron for further recast into steel or melting in iron foundries at casting production. Depending on the application is made:
for steelmaking
Foundry
Cast iron foundry.
Cast iron is intended for further processing in the iron foundries in the production of moldings.
When used for smelting iron iron ores containing Cr, Ni, Ti, and others. alloying elements receive prirodnolegirovanny iron . In the production of cast iron in iron foundries divided: depending on the degree of graphitization, determines the type of fracture - on the gray, white and half (or bleached); depending on the form of graphite inclusions – pig iron with lamellar, nodular (ductile iron), compacted and flaky (ductile iron) graphite; depending on the nature of the metal bases - in the pearlite, ferrite, pearlite-ferritic, austenitic, martensitic and bainitic; depending on the application - in the construction and cast iron with special properties; chemical composition - on alloyed and unalloyed.
Cast iron - the most widely used form of iron (engineering, plumbing, building construction) - is the inclusion of graphite plate shape. For details of cast iron are characterized by low sensitivity to the influence of external stress concentrators under cyclic loading and a higher absorption coefficient fluctuations during the vibrations of parts (2-4 times higher than that of steel). Important design features of cast iron - higher than that of steel, the ratio of the yield tensile strength. The presence of graphite improves the lubrication conditions in friction, which increases the frictional properties of cast iron. Properties of cast iron are dependent on the structure of the metal substrate, shape, size, quantity and distribution of graphite. Pearlitic gray cast iron has high mechanical properties and is used for cylinders, bushings and others. Loaded engine components, machine beds and etc. For less critical parts used gray cast iron with ferrite-pearlite metallic base.
White iron is an alloy in which the excess carbon that is not in solid solution of iron is present in the bound state in the form of iron carbide Fe 3 C (cementite) or r. n. special carbides (in alloy cast). Crystallization white irons metastable system occurs with the formation of cementite and pearlite. White cast iron because of the low mechanical properties and brittleness has limited use for parts of simple configuration, working in conditions of high abrasive wear. Alloying white iron carbide forming elements (Cr, W, Mo and others.) Increases its durability.
Half Iron contains a portion of the carbon in the free state in the form of graphite, and some - in the bound in the form of carbides. It is used as a friction material, working in conditions of dry friction (brake pads) as well as for parts of increased wear resistance (rolling, paper, flour rolls).
called ductile iron in the castings made of white iron and subjected to a subsequent graphitizing annealing, causing cementite decomposes and the resulting graphite takes the form of flakes. Ductile cast iron has a better damping capacity than a steel, and less notch sensitivity, operates satisfactorily at low temperatures. Mechanical properties of the ductile iron structure defined by the metal substrate, the amount and degree of compactness of graphite. Ductile iron base metal depending on the type of heat treatment may be ferrite, pearlite and ferrite-pearlite.
The highest the properties of ductile iron that has a matrix with the structure of the granular perlite; they can replace the cast or forged steel. In those cases where a high ductility, ferritic ductile cast iron is used. To intensify the process of graphitization during the heat treatment ductile iron modified Te, In, Mg, and other elements.. Ductile cast iron is used mainly in the automotive, tractor and agricultural machinery. The tendency (especially in the automotive industry) to replace a high-strength ductile iron with nodular graphite in order to increase the strength of the castings, reducing the duration of a work cycle and simplify the manufacturing technology.
Ductile Iron , characterized by spherical or close to the form of graphite, obtained by modifying the liquid iron additives Mg, Ce, Y, Ca and certain other elements. (alone or in alloys). Spherical graphite least weakens the metal matrix, which leads to a sharp increase in the mechanical properties of pure iron with a pearlitic or bainitic structure, properties closer to those of carbon steel. For purely ferritic matrix (cast and heat treated condition) provides increased ductility. Ductile Iron has good casting and processing properties (fluidity, linear shrinkage, machinability), but the value of volumetric shrinkage centered approaches to steel. This iron is used to replace the cast steel and forged parts (crankshafts engines, compressors and etc.), As well as details of a conventional ductile or gray iron. ductile iron , with the inclusion t. n. vermicular graphite (when viewed in optical microscope - thickened curved plates with rounded edges) on the properties occupy an intermediate position between ductile and cast iron with lamellar graphite. This cast iron has good processing properties at low volumetric shrinkage and a high thermal conductivity (almost the same as that of gray iron). Cast iron with vermicular graphite is used in diesel building and other fields of engineering.
alloy cast . To improve the strength, performance or make pig iron functions (wear resistance, heat resistance, heat resistance, corrosion resistance, nonmagnetic and etc.) In its composition is introduced alloying elements (Ni, Cr, Cu, Al, Ti, W, V, Mo and etc.). Alloying elements may also serve at the Mn content of > 2% and when the content of Si > 4%. Alloyed cast irons are classified according to the major alloying elements - chromium, nickel, aluminum and etc. According to the degree of doping distinguish low-alloy (the total amount of alloying elements < 2,5%), srednelegirovannye (2.5-10%) and high (> 10%). Low alloy cast irons have a pearlite or bainite matrix structure, srednelegirovannye - usually martensitic, high-alloy - in most cases, austenitic or ferritic.
Cast with 5-7% Si is used as a heat-resistant material. Cast with 12-18% Si (ferrosilid) has high corrosion resistance in solutions of salts, acids (except hydrochloric acid) and alkalis. Such iron-doped molybdenum (antichlor), is characterized by high resistance in hydrochloric acid. Cast with 19-25% Al has the highest compared with the known cast iron, heat-resistant in the air and media containing sulfur. As wear most widely irons alloyed with Cr (2.5%) and Ni (6%) - nihard. Austenitic nickel cast irons, alloyed Mn, Cu, Cr (Ni-Resist), used as a corrosion-resistant and heat-resistant.
Marking cast iron. According to the USSR adopted labeling designation marks pig iron contain letters and numbers. The letters indicate the main purpose of iron: P - pig for the oxygen-converter and open-hearth production and R - foundry for cast iron industry. Foundry coke iron stand for LK, unlike iron smelted on charcoal (LD). With increasing numbers in the designation of the brand silicon content decreases (e.g., iron LK5 contain less silicon than iron LK4). Each brand of iron depending on the content of Mn, P, S, respectively, divided into groups, classes and categories. Stamps iron foundry, usually denoted by the letters, showing the main character or the appointment of iron: MF - Charles Gray, HF - high, CN - malleable; antifriction cast iron to mark the beginning by letter A (SYD, AVCH, AKCH). The figures in the designation marks an undoped iron indicate its mechanical properties. For gray chugunaov regulated lead indicators of the tensile strength and bending strength (in the kgf/mm 2 ), for example SCH21-40. For ductile and malleable iron numbers define the ultimate tensile strength (in the kgf/mm 2 ) and elongation (in%), for example VCH60-2. The designation marks alloy cast consists of the letters indicating the alloying elements which are part of the cast, and standing directly behind each letter of numbers that characterize the average content of alloying element; when the content of the alloying element is less than 1.0% figure for the corresponding letter should be put. Symbol chemical elements is the same as in the marking of steels. Example identification alloy cast .: CHN19HZ – iron containing ~ 19% Ni and Cr ~ 3%. If doped iron regulated spherical graphite end brand added the letter W (CHN19HZSH).