What are malleable iron and ductile iron?

Malleable Iron, referred to as malleable iron, is the main material of JIANZHI pipe fitting products.

Malleable cast iron is made from molten iron with a certain chemical composition poured into a white blank and then annealed. It has high strength, plasticity, and impact toughness and can partially replace carbon steel.

High-strength cast iron made from white cast iron after heat treatment.

● White cast iron: Cast iron that does not contain graphite. Almost all carbon forms cementite with iron. Has great hardness and brittleness. It cannot withstand cold working or hot working, and can only be used directly in the casting state. Gray iron: Most or all of the carbon exists in the form of flake graphite, and the cross-section is dark in color. This cast iron has good casting performance, cutting performance, shock absorption, and wear resistance. The smelting process is Simple and low cost. The disadvantages are poor mechanical properties, low strength, plasticity, and toughness.

● Ductile iron: Most or all of the carbon exists in the form of spherical graphite, so the splitting effect on the cast iron matrix is much smaller than that of graphite in other forms. This improves its strength, plasticity, and toughness.

Classification of malleable cast iron

From 1720 to 1722 AD, the Frenchman Reaumur invented the production method of white-core malleable iron that was later commonly referred to as the "European method" (Procede Europe). In 1982, American Seth Boyden decomposed Fe3C in white cast iron through accidental heat treatment, precipitating flocculent graphite + metal matrix (ironite or pearlite). The malleable iron he obtained at that time was in a ferrite matrix. This method is often called the "American Method," black heart malleable iron.

● White heart malleable cast iron: The outer layer is ferrite, and the microstructure of a small amount of pearlite and flocculent graphite remains in the center. Its core port is white, so it is called white-core malleable iron. Since its outer layer is composed of ferrite, its weldability is good. Due to the complexity of the process, there currently need to be more applications. It is limited to the manufacture of thin-walled castings and castings that do not require heat treatment after welding.

● Black-core malleable cast iron: developed based on the process of white-core malleable iron. The matrix is ferrite + flocculent graphite structure. At present, 90% of the malleable iron produced in China is black-core malleable iron. Because carbon exists in the form of flocculated graphite, it has good strength, high plasticity, and toughness. The malleable steel pipe fittings currently being built are all made of black-core malleable iron.

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