Carbide-carrying austempered ductile iron and quenching technology thereof

Abstract

The invention relates to a carbide-carrying austempered ductile iron and a quenching technology thereof. Cr and B are added to an Mn-Si alloy, the carbide amount is properly increased, and inoculating deterioration treatment is carried out by using RE-B, so the carbide becomes a fine uniformly-distributed agglomerate to improve the hardness, the abrasion resistance, the hardenability and the toughness; and the addition of Sn and the increase of the Si amount are carried out to improve the potential of a matrix electrode, and the added Sn and the increased Si form a surface passivating film together with Cr to improve the corrosion resistance. The quenching technology of the carbide-carrying austempered ductile iron is step austempering and is characterized in that an austempered workpiece undergoes first-step austempering by using grading quenching oil to avoid the generation of pearlite, and then second-step austempering is carried out at a proper temperature in an air isothermal furnace to obtain a proper amount of fine lower bainite, increase the amount of tempered martensite, and improve the hardness and the abrasion resistance, so the carbide-carrying austempered ductile iron having the advantages of high strength and hardness, appropriate toughness, strong abrasion and corrosion resistances, good processing properties, easy precision guarantee and low cost is obtained.

Description

technical field [0001] The invention relates to the technical field of heat treatment of metal materials, in particular to an austempering ductile iron with carbides and a quenching process thereof. Background technique [0002] In the prior art, many parts and components of fluid machinery have special requirements, such as the impeller of the impurity pump, the pump casing and other flow-passing parts that need to be machined and require high precision, high hardness, high strength and appropriate toughness. Structural parts, this is because such structural parts usually operate in working conditions containing similar hard particles and corrosive media such as quartz sand, so that such structural parts are often scrapped due to wear or corrosion. If stainless steel and high-nickel corrosion-resistant cast iron are used to manufacture such structural parts, although they can meet the requirements of corrosion resistance, the hardness and strength of these materials are low...

AI Technical Summary

Problems solved by technology

If the current austempered ductile iron is used to manufacture such structural parts as the impeller and pump casing of the impurity pump, the hardness, wear resistance and corrosion resistance are still insufficient, and further improvement and improvement are still needed to meet the requirements of the impurity pump. The need for higher performance of such structural parts as the flow parts

[0004] Moreover, the traditional austempering ductile iron needs to add expensive molybdenum (Mo) and nickel (Ni) to greatly increase its price

In the traditional nitrate salt bath isothermal quenching process, not only will a large amount of nitrite harmful substances be produced when nitrate is melted, which will seriously pollute the environment and endanger human health, but also the nitrate will melt during the isothermal quenching process. and austempering for a long time, resulting in low productivity and high production costs

[0005] Chinese invention patent (patent number 200910088451.4) discloses "an austempering nodular iron plowshare with carbides and its production method". The main technical problem is the high hardness and low toughness of traditional white iron, low chromium or high chromium cast iron. The method adopted changes the composition of ductile iron, which includes the following chemical composition in weight percentage: C3.40~3.80, Si2. 20~2.80, Mn0.20~0.50, P≤0.03, S≤0.02, Mg0.03~0.04, Re0.01~0.02, Cr0.25~0.50, the rest is iron; The structure is: the spheroidization rate is above grade 2, the graphite size is above grade 6, and the number of graphite is >100 pieces / MM2; the matrix of the ductile iron is: martensite+lower bainite+retained austenite+carbide; The carbide <20WT%

[0006]However, the corrosion resistance, machinability and hardenability of this kind of ductile iron are still insufficient, and the machining accuracy is difficult to guarantee, so it is still difficult to meet the requirements in the process of manufacturing impurity pumps. Requirements on the material properties of structural parts such as flow parts, and the heat treatment method is isothermal quenching with nitrate salt, which has high cost, heavy pollution, poor performance, and low efficiency

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