Types Of Malleable Steel

White Heart Malleable Iron

White-hearted malleable cast iron was successfully developed in 1722 by the French R.A.F. de Romaud. The white cast iron with low carbon and silicon content is sealed in an oxidizing medium, and the decarburization annealing is carried out at a temperature of 950 to 1050 ° C for dozens of hours, and the outer layer is ferrite, and a small amount of pearlite remains in the center. and microstructure of flocculent graphite. The fracture of its heart is white, so it is called white-heart malleable cast iron.

black heart malleable iron

Black-heart malleable iron was developed by American S. Boyden in 1826 on the basis of the introduction of white-heart malleable iron technology. After the white cast iron with low carbon and silicon content is placed in a neutral medium for graphitization, it is kept at a temperature of 850 to 950 ° C for dozens of hours, and then cooled to 720 to 740 ° C in the furnace for more than ten hours. Ferritic black-core malleable cast iron with ferritic matrix and flocculent graphite is obtained; or after being kept at 850-950 ° C for more than ten hours, it is released from the furnace and cooled in air to obtain pearlitic black-core malleable cast iron with pearlite matrix and flocculent graphite. Properties and uses The graphite in malleable cast iron is flocculent, with less content and less significant stress concentration. The effective load area of cast iron is not reduced much, the tensile strength can reach 300-700 MPa, and the elongation can reach 2- 12%, good machinability, oxidative growth resistance and corrosion resistance. Malleable cast iron as-cast structure is white, the molten iron has poor fluidity, is prone to shrinkage cavities, and has a large tendency to thermal cracking, so it is generally only suitable for castings with less complex shapes. In addition, since the annealing time increases with the increase of wall thickness, and it is difficult to achieve complete annealing of the central part of the overly thick casting, the wall thickness of white-heart malleable iron castings generally does not exceed 12 mm, and the wall thickness of black-heart malleable iron castings does not exceed 25 mm. Ferritic malleable cast iron is widely used in rims, differential housings and chassis parts of automobiles and tractors, wrenches in machine tool accessories, porcelain bottle iron caps, wire clips, bowl head plates in power transmission lines, and roving machines in textile machinery. And printing machine pan head and elbows, tees, joints, medium pressure valves, etc. in water and oil pipelines. Pearlitic malleable iron is used in gas valve rocker, stoker parts, high pressure joint valve body and automobile industry fork, differential gearbox, etc. Whiteheart malleable cast iron is used in hangers for auto parts, steering column fork shoulders, textile machine parts, etc. The research on the development of malleable iron mainly focuses on the stable carbides in the as-cast state, the absence of free graphite flakes in the casting, and the shortening of the annealing time to improve the mechanical properties and service performance. In addition, the thickness and weight limits of castings have been expanded, and malleable iron castings with wall thicknesses of 2 to 80 mm or weighing up to 150 kg have been produced in modern times.