Steel Casting Plasticity And Toughness
In general, low-carbon steel ZG15 has a high melting point, poor casting performance, used only in the manufacture of motor parts or carburizing parts; medium carbon steel ZG25 ~ ZG45, with higher than all kinds of cast iron comprehensive performance, that is, high strength, excellent Of the plastic and toughness, it is suitable for the manufacture of complex shapes, strength and toughness requirements of high parts, such as train wheels, forging hammers and anvils, rollers and high pressure valves, carbon steel is the most widely used class; High-carbon steel ZG55 low melting point, the casting performance is better than the carbon steel, but its plasticity and toughness is poor, only for the manufacture of a small number of wear parts.
According to the total amount of alloy elements, alloy cast steel can be divided into two low-alloy steel and high alloy steel category.
(1) low alloy cast steel, China's main application of manganese, manganese and chromium system. Such as ZG40Mn, ZG30MnSi1, ZG30Cr1MnSi1 and so on. Used to manufacture gears, Steel Casting hydraulic presses and turbine rotor and other parts, and ZG40Cr1 commonly used to manufacture high-strength gears and high-strength shaft and other important force parts.
(2) high alloy cast steel, with wear, heat or corrosion resistance and other special properties. Such as high manganese steel ZGMn13, is an anti-wear steel, mainly used in the manufacture of dry friction in the working conditions of the use of parts, such as the excavator grab the front wall and grazing teeth, Steel Casting tractors and tanks, etc .; chrome nickel stainless steel ZG1Cr18Ni9 and chromium stainless steel ZG1Cr13 and ZGCr28, nitric acid corrosion resistance is very high, mainly used in the manufacture of chemical, petroleum, chemical fiber and food equipment on the parts.
Cast steel has higher mechanical properties than cast iron, but its casting performance is worse than cast iron. Because the melting point of cast steel is high, the molten steel is easy to oxidize, the fluidity of molten steel is poor, the shrinkage is big, the shrinkage rate is 10% ~ 14%, Steel Casting and the line shrinkage is 1.8% ~ 2.5% .To prevent the cast steel, 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 cast steel produced cold and pouring, cast steel 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, Steel Casting 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 cast steel much more than cast iron, in order to prevent castings shrinkage, shrink loose defects in the casting process mostly use riser, Steel Casting cold iron and subsidies and other measures to achieve the order of solidification.
In addition, in order to prevent shrinkage, shrinkage, stomata and crack defects in the cast steel, make the wall thickness uniform, avoid sharp and right angle structures, Steel Casting add sawdust in mold sand, add coke to the core, and Using hollow core and oil core, etc. to improve the sand or the core of the concession and permeability.
Cast steel has a high melting point and a corresponding pouring temperature is also high. High temperature molten steel and mold material interaction, Steel Casting easy to produce sticky sand defects. Therefore, the use of refractory high artificial quartz sand to do the mold, and in the casting surface brush by the quartz powder or zirconia powder made of paint. In order to reduce the gas source, improve the flow of molten steel and casting strength, most of the cast steel with dry or quick-drying type to cast, such as the use of CO2 hardened water glass sand.