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What is the cause of the high chromium cast steel short life

by:BoQiao Machinery     2020-12-04
High chromium cast iron riser size according to carbon steel design, gating system according to the design of gray cast iron. By using gas cutting cutting poured riser, easy to produce hot crack, therefore the design using easy cutting riser or side riser, tapping method is used to purify. High chromium cast iron is the cause of the short life, not a metallographic is unqualified, rather, is present in the casting casting defects such as shrinkage cavity, porosity, inclusions and so must be adequate attention to casting process. High chromium cast iron is easy to crack. Careful not to let the casting shrinkage on casting process design, so as not to cause craze. High chromium cast iron castings in the mold should be fully cooled, and then out of the box. Out too early, out of the temperature is too high, is the main reason for the casting crack. High chromium cast iron using metal mold casting, pouring temperature should be kept at above 150 ℃, so as to avoid the casting cooling fast craze. In high chromium cast iron with high temperature air quenching and low temperature tempering heat treatment, obtain martensitic matrix of high hardness. High chromium cast iron as-cast matrix organization before heat treatment depends on the cooling rate of as-cast high and low. Sand mold cast steel cooling rate is high, usually in the form of austenitic matrix with the decreasing cooling speed gradually began to precipitate some martensite, a mixture of perlite and austenite. Further reduce the cooling rate could obtain the pearlite matrix organization. High chromium cast iron in according to the content of chromium and parts thickness choices quenching temperature. The higher the quenching temperature, the higher hardenability, but the number of retained austenite is formed after quenching the more likely. High chromium cast iron quenching temperature is 940 - 970 ℃, Cr20 quenching temperature 960 - high chromium cast iron 1010℃。 According to the time of heat preservation wall thickness. General 2 - Part 4-4 h, the wall thickness 6h。 Air quenching after the internal stress of high chromium cast iron is obviously, tempering heat treatment shall be implemented as soon as possible. For some complex shape, wall thickness disparity of high chromium cast iron castings should strictly control the heating temperature ( ≤ 50℃/小时) In order to avoid the casting crack. Sometimes adopted cascade heat ( At 200 ℃, 400 ℃, 600 ℃ for 2 - 3h) More security, at above 700 ℃ temperature can accelerate appropriately. But do not exceed 150 ℃ / h. Heat preservation time should be casting wall thickness, furnace charging quantity, status, and heating speed factors such as comprehensive consideration, in order to avoid because some casting or casting core appeared due to lack of heat preservation time quenching. High chromium cast iron out should be killed. Usually add 0 to the furnace. 5% of ferromanganese deoxidization, add 0 to the furnace. Add 0 25% ferrosilicon in early deoxidization, in the package. 05% aluminum for final deoxidization. High chromium cast iron in the process of smelting temperature control at 1450 ℃, fast temperature control at 1480 ℃ deoxidization. In general, high melting point, low carbon steel ZG15 casting performance is poor, only used in the manufacture of machine parts or carburized parts; Medium carbon steel ZG25 ~ ZG45, is higher than that of the comprehensive performance of various types of cast iron, namely, high strength, good plasticity and toughness, therefore is suitable for manufacturing complex shape, high strength and toughness requirement of parts, such as the train wheels, forging hammer frame and the anvil block, roll and high pressure valves, etc. , are used in carbon steel casting much category; The low melting point of high carbon steel ZG55, its casting properties of a medium carbon steel is good, but its low plasticity and toughness, used to make a few wear parts.
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