Cast Iron and Its Welding

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You might wonder why we are into this topic – welding cast iron; but it is a versatile material which is used in manufacturing various industrial products with implications in our day to day life. With its excellent fluidity, low melting point, the extraordinary response to various designs of the machine etc, it has come to be known as an engineering material and is used in a range of applications such as machines, pipes, motor parts, gearbox and numerous other material for daily use. It is resistant to wear and also deformation, but generally tends to be brittle, although there is malleable iron as well.

I don’t know what cast iron is.

Iron or an alloy of iron which has been liquefied by heating and poured into a cast to solidify and take the shape of the cast is what we call cast iron.

The alloy constituents affect the color of this metal. White cast iron, which has impurities of carbide, gets white color when fractured. However, gray cast iron, which contains the carbon in flakes of graphite, assumes a gray color at the fractured lines.

Gray iron is the one that has the most number of applications. Due to the presence of carbon in the form of graphite flakes, gray iron is easy to machine. It also has high compressive strength and is generally responsive to welding.

If it has such a wide use then it must be easy to weld it

On the contrary, iron is not always weldable. Though it is much like steel in composition, both of which are alloys of carbon and iron, in terms of properties there is quite a difference between them. Welding cast iron may pose problems to the welder, and all cast iron is not weldable.

Welding of cast iron materials

  • Gray cast iron is weldable without any loss of inherent properties. But, you have to preheat the casting before fusion welding. If fusion welding is the only choice then you have to choose arc welding, because in arch welding a lesser degree of preheating of the cast will suffice. However, for repair jobs, where a lesser amount of preheating is required, oxy-acetylene braze welding is ideal. So much so that preheating can sometimes be done with the torch. If this is done by an expert welder, this braze-welded joint will have excellent strength that is almost equal to that of the base metal along with extraordinary machines and their ability.
  • Do not attempt to weld gray iron castings that have chilled white cast iron surfaces, because such an attempt may affect the desirable properties of the white iron surface due to the high temperature of welding.
  • Do not attempt to weld white iron if it is not malleable.
  • Welding malleable iron is as easy as welding gray iron, but malleable iron can lose some of its unique properties if it is fusion welded. This is because during welding you are likely to covert some of the malleable iron casting into gray iron casting.

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