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The 2nd chapter forging prepares with raw material and the semifinished materials 2.1 forging forging to use raw material Forging uses raw material generally for the rods and bars, the plate, the tubing. The people mainly select according to the semifinished materials concrete shape and the geometry size. If the semifinished materials select the circular cylinder, then must consider the semifinished materials Gao Jingbi H/d. When Gao Jingbi H/d2, must prefabricate the semifinished product, prevents in the forming process the curving jitter, or produces curving, forms the fold. When H/d is small, may also use the sheet yummy treats. Regarding the thin steel plate semifinished materials, may use the ordinary blanking to fall the material or the precision blanking yummy treats. If forges ring-like, also available tubing cutting system semifinished product.2.1.1 ferrous metalForging with the ferrous metal is all kinds of steel products, Table 2-1 shows for the partial cold forgings uses the steel.TypeQ195、Q215、Q235Ordinary carbon structural steel10、20、30、40Alloy structural steelChrome steel20Cr、30Cr、40CrChrome-molybdenum steel20CrMo、30CrMo、40CrMoChromated nickel molbdenum steel20CrNiMo、30CrNiMoChrome-manganese steel20CrMn、30CrMnStainless steelAustenite steel0Cr18Ni9、0Cr17Ni1Mo2、00Cr18Ni10Martensite steel1Cr13、2Cr13、3Cr13、1Cr17Ni2Ferrite steel1Cr17、0Cr13The calm steel is generally easy compared to the boiling steel the cold forging forming, specially aluminum calm steel. In the steel the carbon and the silicon contents change not only affects the steel the resistance to deformation, moreover influence cold forging forming size precision. Therefore, when uses the non-standard material, must analyze the determination carbon and the silicon content at least, with approves the material the chemical composition to approach consistently. In order to process the precise cold forging forming, best according to chemical composition grouping processing.In the steel the phosphorus, the sulfur, the copper content must the strict control, because their existence causes the steel the cold forging shaping property to reduce. The Japanese cold forging profession uses in the small screw, the bolt, nuts cold forging taking with the wire rod standard the profession standard. the Germany and Europe have the cold forging to use the steel the general standard. The former Soviet Union to ball bearing steel GCr15, GCr15SiMn and aluminums and so on chromium silicon manganese structural steel 30CrMnSi has carried on the cold forging craft production components.1、 The cold forging uses the materials behaviorThe cold forging sees Table with the materials behavior 2-2.The cold forging uses the materialConditionSteelHot rolling annealed conditionAfter the hot rolling annealing skins the material or the centerless grinding semifinished materialsRods and bars which draws after the small amount of deformity; After the annealing, the condition draws the rods and barsIngot castingHammers the semifinished productNon-ferrous metalThe heat pushes the rods and barsThermo-compression plateAnnealed condition extrusion sheetThe annealed condition draws the semifinished materialsCasting2、 The cold forging uses the steel the size common differenceThe cold draw round steels size common difference sees Table 2-3. ( Unit:mm)Round steel foreign economics and tradeCommon differenceRoundnessd9.00+0-0.030.0159.0d18.0+0-0.040.02d18.0+0-0.050.025Skins the material, the centerless grinding material diameter tolerance is 0.050.1 mm. Rods and bars bending 1%. Tubing wall thickness misses3、Forging uses the steel the gross imperfectionThe forging forming uses the material the superficial quality height immediate influence product rejection rate. The forging forming uses the material do not have the naked eye obvious crack, the scar, the fold and the inclusion besides the request surface, the tiny scratch, the indentation, send the grain and so on also not to surpass certain depth. Cannot have the axial flaw specially.1) FoldThe fold is rolls over the material surface the common flaw, the crease direction is the direction of rolling, the edge curving is uneven, sometimes has some oxide compound inclusion. These inclusion are generally long, in rods and bars lateral symmetry distribution. Folding and table delivering in person certain angle to.2）ScratchThe material longitudinal scratchs production is because in the rolling, the extrusion, draw in the process, the superficial metals flowing receives on the pass or the mold some kind of machinery hindrance (for example burr, mark and accumulates lump) to form. Observes this kind of flaw under the microscope to be possible to discover that the scratch root is the round campylodromous, the both sides is smooth, width basic consistent, is vertical in the surface. Scratch which forms under the low temperature, its root has the slight distortion, the nearby decarbonization and the oxidized phenomenon. The scratch can cause the rods and bars, the plate abandonment, is creates the cold forging forming dehiscence the primary cause.The steel products surface polish, corrodes after 10% ammonium persulfate peroxide solution, the detectable thick crystal grain belt and the scratch region correspond mutually. Under a scratch has a thick crystal zone, several scratch docking recently became a macrograin area. Its reason has produced the scratch metallic material, had the recrystallization when the recrystallization temperature, the scratch place formed the nucleus first to crystallize grows up, along scratch production thick crystal grain belt. Several scratches form several thick crystal grain belt close Lian Cheng a macrograin area. The macrograin areas plasticity shaping property is low, also has the scratch to act as the crack source, specially the scratch is located at the semifinished materials side, this place is at the tensile stress condition in the plastic deformation process, thus extremely easy to crack, forms the waste product. After sometimes regarding the semifinished materials side existence obvious scratchs material, needs to skin, can carry on the forging forming.3） Sends the grainSends the grain mostly to appear in the steel products surface, also has the existence in the steel products interior. After sending the grain often to need the magnetic powder test or the hot acid pickling, can demonstrate. In steel inclusion, air bubble or loose and so on flaws, along hammers, rolls over the direction in the hot procedure to extend forms the tiny grain wisp, this sends the grain. Sends the grain to be suitable generally the steel products fibre direction, the length is varying, thin like sends the silk, the forehead is shallow compares the point. Often in sends in the grain to be possible to discover the inclusion, sends the grain the periphery nonoxidation decarbonization phenomenon. The examination sends when the grain must be good at distinguishing the real wig grain. In passes through the overheated acid pickling on the tower-shaped test specimen, possibly appears many along the direction of rolling stripe. And some sends the grain, but because in steel products streamline some low melting point constituent in hot acid pickling time flakes creates, these stripes approach the steel products center section, observes with the magnifying glass, the stripe is wide, the depth is very shallow. If takes the steel products the crosswise test specimen, after hot acid pickling then discovered that sends the grain to assume the circular hole, is quite smooth, and does not have the furcation. In some holes has the inclusion, also in some holes does not have the foreign matter.The steel products surface sends the grain is the cold forging forming uses the steel a significant flaw. After cold forging forming cracks in components, most, because has this kind of flaw to cause. In the forging forming process, the material must receive the very great degree the compression, the surface has the big circumferential tensile stress. If the material surface exists sends the grain, then in forging forming time, will send the grain place to set up stresses inevitably the centralism, possibly will create cracks.2、 Steel low time of organizationThe steel low time of organization was reflecting the steel products metallurgy quality, it can expose the tapping fully, in smelting, the casting as well as hammer, roll over the gross imperfection which in the process produces, like loose, segregation, shrink hole vestiges and lemon spot and so on. These flaw some permissions achieve the certain extent, some simply do not permit the appearance.1） SegregationThe segregation is also called the fluid to analyze, it is the steel ingot the chemical composition which as well as the impurity non-uniform phenomenon produces in the solidification process. The predominant type has the pattern segregation, the punctual segregation and the coring. The coring must pass through the amount of deformity big hot-working, or the high temperature diffusion annealing, is improved, down to eliminates. The pattern segregation is in the steel products crosswise acid pickling preview, presents the dark color square which the organization not compact, easy to corrode, the square shape is by the steel mold shape decided that as a result of the distortion way and distortion degrees difference, the square possibly slightly has the change. Because in the steel solidification process various part of ingredients change is sometimes big, may present several squares. Pattern segregation including ingredient segregation and impurity segregation two types. If the square region is mainly composed of the dark colored dot does not have the hole, is called the ingredient segregation. If the segregation region easy to corrode, presents the hole, then concentrates by the impurity causes. As a result of the segregation reason, the steel products center spots carbon amount is usually high. Usually easy to have this kind of carbide flaw in the carbon amount high alloy steel. Its reason is in the steel lai the body eutectic carbide and two netted carbides when the cogging and the rolling has not been destroyed with the non-uniform distribution. The carbide segregation will reduce the steel the forging performance, serious the components interior has the big internal stress in the hot procedure, will cause the forging dehiscence. Or causes the forging core degree of hardness to be higher than the product stipulation the request, reduces the product toughness. the serious sulfur segregations existence can create the material strength remarkable reduction, after components processing serves in the use process, easy to have the early time brittle fracture.2） Shrink hole vestigesSteel ingot in solidification process, because various part crystallizes is successively different as well as the volume contraction, will form the shrink hole in the steel ingot foreheads axle center place. If steel ingot in cogging time has not been able to remove the shrink hole completely, the shrink hole remains is hammering afterward rolls over in the good steel products, this is the shrink hole is remaining. Steel products crosswise preview after hot acid pickling, may see obviously in the steel products core has the black anomalous cavity or the crack, its periphery loose serious. Among this kind of cavity or the crack is often surviving the external inclusion. If axial cuts open along the steel products from the central spot, then saw empty (crack) along axial extends in the steel products center, even passes through the entire steel products. The shrink hole vestiges are one kind of serious organization flaw, because it has the massive inclusion the hole or the crack, makes the material production components with it is the waste product inevitably.a) Lemon spotThe lemon spot is hides in hammers the semifinished product interior one kind of flaw, assumes the circular or the ellipse silver-white color spot on billets longitudinal fracture, assumes the tiny crack on the crosswise fracture, obviously reduces the steel toughness. The lemon spot size varies, the length probably is 120 mm, or is longer. Generally thought that the lemon spot is because in after the steel has the ration the hydrogen and each kind of stress (organization stress, temperature stress, plastic deformation residual stress and so on) the combined action produces. When in the steel are many including the hydrogen quantity and the thermal pressure processing after-cooling is too quick, easy to produce the lemon spot. In order to avoid producing the lemon spot, first should improve the smelting quality, reduces the hydrogen as far as possible the content; Next after the hot-working uses slow cooling the method, lets the hydrogen transgress and reduce each kind of internal stress fully.3） Non-metallic inclusionsThe non-metallic inclusions destroyed the metallic matrix continuity in the steel, the cause material plasticity and toughness reduce, when especially the inclusion assumes the chain strip distribution, when or along crystal boundary distribution, to the metal mechanical properties, specially moves under the load the mechanical properties influence to be more serious, causes the components as a result of the stress concentration to break suddenly frequently. Therefore, inclusion quantity and the distribution condition are weigh the steel products quality an important target. Each steel products technical standard explicitly stipulates to the inclusion request.a) In steel common non-metallic inclusionsIn the steel the common non-metallic inclusions have two kinds. One kind is the steel in smelting, the casting process, the physical chemistry responses product, another kind is after smelting, in the casting steel ingot process the slag and fire-proof material erosion flaking enters in the molten steel to form. The common tiny non-metallic inclusions pellet has the sulfide, the oxide compound, the silicate and so on. Because each pellet is very small, therefore usually draws support from the microscope to determine its pollution degree.b)SulfideThe sulfur mainly leads in the steel by the pig iron, and in smelting process sulfidizing mixture. If in the steel quantity is low including manganese the , the sulfur and the hard chemical combination production iron sulfide, the iron sulfide and the iron form the eutectic. Its melting point is low, only then 985, and after is everlasting lies in the crystal boundary place. Generally steel products when 8001 200 rolling or forging, as a result of the eutectic melting, causes the steel products along the crystal boundary dehiscence, this kind of phenomenon is called hot shortness. When in the steel is high including the manganese quantity, may reduce the sulfur the harmful effect. Because the manganese and the sulfur affinity is strong, may first form the manganese sulphide. The manganese sulphide melting point is 1 620, is higher than the steel products the hot-working temperature. The manganese sulphide assumes the granular distribution in the intragranular, and has the enough plasticity, thus may eliminate hot shortness phenomenon. The manganese sulphide belongs to the plastic inclusion, observes under the microscope bright field, assumes the sky grey. Assumes the fusiformate tall and slender strip distribution along the direction of rolling. Inclusion two thin, but point, edge neat smooth. If in the steel has many sulfide, will reduce obviously the material the weary performance, particularly crosswise mechanical properties. For example the sulfide 4 levels of some components, its fatigue life reduces approximately 12 times compared to the sulfide 23 levels.i. silicate inclusionThe silicate inclusion may divide into plastic and the brittle two kinds. The plastic silicates shape and curing the manganese is similar, also extends along the steel products direction of rolling, assumes the long strip. The observation color compares the manganese sulphide under the microscope bright field to be slightly deep, is the perse. May see the silicate inclusion edge under high power not to be uneven, assumes the zigzag. Brittle silicate also along metal flow direction distribution, when flow of metal easy to have the embrittlement. The silicate inclusion has the possibility to cause the product to produce the massive waste products in the production process. Some product has a color deep line in the fracture center, is precisely this product dehiscence position. This line is the shrink hole remaining trace. When shaping distorts assumes strip, this spots silicate inclusion quantity is higher than 4 levels. Because the massive silicate inclusions existence, causes the core the plasticity and toughness obviously worsens, therefore when forging along inclusion dehiscence.ii. oxide compoundIn the steel the oxide compound mainly has FeO, SiO2 and Al2O3 and so on. FeO observes under the microscope bright field, assumes the gray to be spherical, observes when the dark field all around has the shining edge; Its distribution not certain rule, some located at grain boundary, some located at crystal grain. FeO is very crisp, in the hot procedure does not have the distortion nearly, only then only then slightly assumes the ellipse under the very tremendous pressure. SiO2 are very few in the steel exists alone, forms the complex compound frequently with other oxide compounds. Al2O3 observes under microscopes Ming Chang assumes the dark ash belt purple, its contour is anomalous, often in groups distributes by the tiny pellet agglomeration. The Al2O3 degree of hardness is high, brittleness is big, the contour has the edges and corners. Plays the incisive gap role in the steel.For example, hammers the system with the 20CrMnTi steel the gear box gear blank, has the serious oxide compound mixture, when broaching spline hole, components roughness cannot meet the technological process requirements; The broach attrition is serious, and discovered continuously quantity many gear flower key hole endophragm has the tiny transversal crack. Has the bulk deposition shape oxide compound and the compound inclusion nearby the crack.b) Entrapped slagThe entrapped slag is the bulk inclusion which may observe with the naked eye. It usually is because in smelting as well as the casting process, the molten steel surfaces slag, or from the steel spout, the molten steel package and so on endophragms flakes fire-proof material, before the molten steel coagulates has not been able to emerge, preserves in the steel ingot. In the steel products has the bulk naked eye obvious inclusion not to permit. This kind of flaws existence will create when steel products forging cracks, causes the forging forming to be unable to carry on. Cuts in the inclusion place takes the test specimen to carry on the metallography observation, detectable ferrite along inclusion superficial separation. Is distributing the black and the French grey two kinds in the inclusion grays substrate. Some of them assume the polygon, some assume strip, assumes acicular. Inclusion degree of hardness reaches as high as above 65HRC. After electron probe determination knowing, the inclusion pessimistic substrate is mainly elements and so on Ca, Si, O, Mn. The black aluminiferous is high, and includes the few manganese and the magnesium; The light gray appearance includes the abundant titanium, is one kind of intermetallic compound.4） Steel crystal grain sizeThe steel crystal grain size refers to the steel generally the austenite grain size, the austenite crystal grain size including the inherent grain size and the actual crystal grain si
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