Ductile Iron Is Widely Used In All Kinds Of Mechanical Parts

- Oct 20, 2017 -

In the way of improving the performance of cast iron, improving the morphology of graphite is the fundamental way to improve the mechanical properties of cast iron greatly. Spherical graphite is the most ideal form of graphite. For this purpose, a spherical agent (such as magnesium metal, magnesium alloy, etc.) is added to the molten iron before pouring. The nodular cast iron, called Ductile Iron, Ductile Iron Casting that has a large part or all of the graphite is spherical.

1. Microstructure and properties of ductile iron

At room temperature, ductile iron is characterized by the spherical form of graphite on the base of the steel. But with the different chemical composition and cooling speed of ductile iron, Ductile Iron Casting ductile iron can get different metal substrates. The common tissues are ferrite ductile iron, ferrite + pearlite ductile iron and pearlite ductile iron.

Because the shape of graphite in nodular cast iron is spherical, the fragmentation of the matrix is greatly reduced, and the performance of the metal matrix can be fully brought into play, and because there is no sharp angle of flake graphite, the tendency of stress concentration is reduced, Ductile Iron Casting so the mechanical properties of nodular cast iron are greatly improved than gray iron. The smaller the diameter of graphite ball, the more uniform the distribution, the more rounded the shape, the better the mechanical properties of cast iron. For example, the mechanical properties such as tensile strength, yield point and fatigue limit of ductile iron with pearlite as matrix are even higher than that of 45 steel. Because ductile iron is close to cast steel in strength and plasticity, Ductile Iron Casting and has the good machinability of cast iron performance, casting performance, vibration and wear resistance, therefore, in the actual production, will often use ductile iron instead of cast steel and forged, to create some of the force of the complex, mechanical properties of the higher requirements of the parts, such as crankshaft, connecting rods, camshaft, Gears and so on. Hydraulic Universal Testing Machine

2. Grade of ductile Iron

The grade of Nodular cast iron is composed of the first letter "QT" and two sets of digits of "ductile iron", Ductile Iron Casting which represent the minimum tensile strength and elongation. For example, the QT400 sings 18 that the minimum tensile strength σb is 400MPa, the elongation rate is 18% ductile iron.

Properties and applications The graphite in Nodular cast iron is spherical, the ratio of surface area and volume is the smallest, the stress concentration is not obvious, so the strength and toughness of the metal matrix in ductile iron can be fully played. According to the degree of graphitization and the structure of the matrix, the tensile strength is generally in 400~1200 MPA, and the elongation is between 1~17%. Nodular cast iron has good antioxidant growth and corrosion resistance and machinability. Ductile Iron Casting Its casting performance is characterized by good fluidity, low line shrinkage and small thermal cracking tendency. However, the manufacturing process of ductile iron is more complicated, if the control is improper, it is possible to produce the defects of spheroidal graphite, Ductile Iron Casting inoculation and degeneration, black-spot inclusions, subcutaneous pores and porosity. Large section castings often appear black spots, reduce the mechanical properties of castings, leading to early failure of parts.

Ductile iron because of its high comprehensive mechanical properties, has been widely used in various types of mechanical parts, such as internal combustion engine crankshaft, camshaft, automotive clutch and chassis parts, some machine tool spindle, agricultural machinery in the plough, general machinery in the body, hydraulic components. It is also widely used in the production of cast pipes, rollers and ingot molds.

In order to reduce the casting defects and improve the mechanical properties of nodular cast iron, it is studied to improve molten iron smelting process, reduce sulphur content in molten iron, Ductile Iron Casting develop new inoculant, and carry out research work on various mechanical properties such as high, low temperature, fatigue strength, fracture toughness and testing. Ductile Iron Casting It is also an important development direction to manufacture ductile iron which can make the desired performance of ductile iron and to obtain higher tensile strength and elongation by adding a small number of alloying elements without heat treatment.