To successfully weld cast iron it is necessary to consider which type of cast iron you are dealing with and the welding technique required for that particular type. Some types of CI are not weldable such as white aka chilled iron. cast iron. It is also necessary to investigate the reason for the damage and to take into account the requirements of the finished piece.
Types of Cast Iron
Gray cast iron,the most common of cast iron types, is usually identified according to its tensile strength. 30 grade cast iron has a tensile strength of 30,000 psi; 40 grade cast iron has a tensile strength of 40,000 psi; and 60 grade cast iron has a tensile strength of 60,000 psi. The most common grades of cast irons are the 20 and 40 grades. Gray cast iron is a ferrous material containing more than 1.75% of carbon, the greater part of which is present in the structure in the form of graphite. This graphite gives to the fracture a color varying from light to dark gray. Compared with steel, gray cast iron has low malleability or ductility caused by the separation of the major portion of the elementary carbon in the form of graphite, which form a network throughout the metallic matrix and separate from it.
The chemical composition of a common machine casting is as follows:
Carbon 3.0% to 4.2% any higher than this as a carbon content and it get real hard to weld.
Silicon 1.5% to 2.5%
Manganese 0.6% to 1.2%
Phosphorus 0.4% to 0.6%
Sulphur 0.05% to 0.18%
Basically, cast iron is steel with a lot more carbon. Steel contains carbon up to 1.75%. If steel has more than 1.75% carbon, it is called cast iron. Steel can dissolve up to 1.75% carbon. If more carbon is added, it won’t dissolve and remains a free carbon. When you look at cast iron under a microscope the free carbon appears as black flakes, hence the name “gray cast iron.” With the use of proper techniques and the correct filler alloy, most gray cast irons can be successfully welded.Be aware that there is another type of cast iron, called “white” or “chilled” cast iron. It is generally considered not weldable. White cast iron does not have the distinctive gray color of most cast iron and is generally found in equipment where extreme hardness is needed (e.g. rock crushers, steel mill rollers, etc.).
Generally id is usually by its application .It its off a machined part you can usually say its grey cast iron,though the exception is nodular cast iron found in cranks and camshafts. Even preheating is called for especially in castings with thin to thick sections .Braze welding is the easiest, followed by cast iron filler rods with oxy and lastly arc welding with nickel based electrodes. Cast iron does tend to absorb materials that interfere with a sound welding process. Some exhaust manifolds can be difficult to weld as the carbon in the exhaust material mixes with the carbon in compound and raises the overall carbon content too high to do a reasonable job.Diesel oil (a hydracarbon) soaked into a crack ain't a whole lot of fun either.
The Lincoln Electric book "Metals and how to weld them" gives some pretty good info on the types and process .
Personally I like to weld with Oxy acetylene and cast iron filler with borax based flux.Its possible to float the contaminants out on top of the molten weld puddle. Its time consuming but gives the best results ,but the process takes time to learn and is hot and uncomfortable for non welders.
Thats the quick and dirty on it.
Oz
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ASTM A 48 castings are castings that are intended for general use when tensile strength is a key consideration.
Also called grey cast iron, gray iron is a kind of cast iron with a graphitic microstructure. It has high thermal conductivity, good machinability and excellent damping capacity. Unfortunately, because of its low ductility and tensile strength, it has very little impact and shock resistance. It does, however, have good corrosion resistance because of its silicon content, which can occupy up to 6 to 10% of the content of gray iron. Because of its low cost of production and attractive properties, gray iron is one of the most commonly used ferrous alloys.
Pro Tip: That being said, there are a number of instances where ductile iron would be preferred for a given application. To learn more, read “The Differences Between Ductile Iron and Gray Iron.”
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We pour several grades of gray iron including:
Note: For castings that experience temperatures up to 1400 F consider using ASTM A319 Heat Resistant Gray Iron.
Possible Applications for Gray Iron
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