Chilled Iron Castings Easy To Install, Easy To Operate
Chilled Iron Castings has higher mechanical properties than cast iron, but its casting performance is worse than cast iron. Because the melting point of Chilled Iron Castings is higher, the molten steel is easy to oxidize, the flowability of molten steel is poor, the shrinkage is big, its body shrinkage is 10 ~ 14%, line shrinkage is 1.2.5%.
In order to prevent the Chilled Iron Castings produced insufficient pouring, cold separation, shrinkage and shrinkage, cracks and sticky sand and other defects, must take more complex than the cast iron process measures:
1, due to the poor fluidity of molten steel, in order to prevent the Chilled Iron Castings produced cold and pouring, Chilled Iron Castings wall thickness can not be less than 8mm; pouring system structure is simple, and cross-sectional size than cast iron; Or hot cast; appropriate to improve the pouring temperature, generally 1520 ° ~ 1600 ℃, because the pouring temperature is high, the superheat of molten steel, to maintain a long liquid, liquidity can be improved. But the pouring temperature is too high, will cause coarse grain, hot cracking, pores and sticky sand and other defects. So the general small, thin-walled and complex shape of the casting, the pouring temperature is about the melting point of steel temperature + 150 ℃; large, thick castings casting temperature higher than its melting point of about 100 ℃.
2, due to the shrinkage of Chilled Iron Castings much more than cast iron, in order to prevent castings shrinkage, shrink loose defects in the casting process mostly use riser, cold iron and subsidies and other measures to achieve the order of solidification. In addition, in order to prevent the steel castings from shrinkage, shrinkage, pores and cracks, the wall thickness should be uniform, to avoid sharp and right angle structure, in the mold with sand in the sawdust, in the core plus coke, and Using hollow core and oil core, etc. to improve the sand or the core of the concession and permeability.
Casting cooling, the surface and the thin section, often produce white mouth. White mouth tissue hard and brittle, poor processing performance, easy to peel off. Therefore, the use of annealing (or normalizing) method must be used to eliminate white mouth tissue. Annealing process: heating to 550-950 ℃ insulation 2 ~ 5 h, then the furnace cooled to 500-550 ℃ and then baked air-cooled. During the high temperature insulation, the high cementite and eutectic cementite are decomposed into graphite and A, and the secondary cementite and eutectoid cement are decomposed during the subsequent cooling process, and the graphitization process occurs. Due to the decomposition of cementite, resulting in decreased hardness, thereby improving the machinability.
In order to improve the mechanical properties of ductile iron, the general casting heated to Afc1 above 30 ~ 50 ℃ (Afc1 represents the formation of the final temperature when heated), heat quenched into the oil, get martensite. In order to properly reduce the residual stress after quenching, the general quenching should be tempered, low temperature tempering organization for the back of the Martian for the addition of residual bainite plus spherical graphite. This kind of tissue wear resistance is good,Chilled Iron Castings for demanding high wear resistance, high strength parts. The tempering temperature is 350-500 ℃. After tempering, the microstructure is tempered and the spherical graphite is applied. It is suitable for thick parts with good abrasion resistance and elasticity. High temperature tempering temperature of 500-60D ℃, after tempering the organization for the tempered cable for the spherical graphite, with toughness and strength combined with a good overall performance, so widely used in production.
What kind of process measures are used to solve and prevent shrinkage of the nodular cast iron, the current consensus is that the mold must have sufficient rigidity and strength, chemical composition close to the eutectic composition, strengthen the spheroidization and inoculation to produce sufficient Graphite expansion. But the specific process design in principle there is still controversy: equilibrium solidification theory that ductile iron ductile expansion can offset the coagulation shrinkage, the process should take measures to make unit time contraction and expansion, contraction and contraction in proportion,Chilled Iron Castings the use of expansion and Dynamic shrinkage superposition, to achieve the purpose of casting the use of the idea of using the riser is limited, the riser does not have to be later than the casting solidification , the role of cold iron is to balance the wall thickness difference, So that part of the graphitization ahead of time; but also have the literature  expressed dissent, that the ductile iron shrinkage is greater than the expansion, there must be external fill, riser can not be later than the casting solidification, the role of cold iron is the first liquid Ahead of time and faster, more conducive to the earlier timely replenishment, the expansion and contraction has no effect. The focus is on whether the graphitization expands itself or emphasizes external shrinkage.
Easy installation, simple operation, the general staff can be a little training to operate. Welding strength is high, the welding parts without annealing, no cracks, no deformation, no internal stress,Chilled Iron Castings the solder joints will not produce hard work, repair speed relative to the placement machine is relatively fast, the repair accuracy is relatively high, And can be X-ray detection, penetration, stretching and other tests. Has been accepted and used by many foundry manufacturers. In addition, in the mold repair also has some use value.