Grey iron is easy to machine as it has high compressive strength, low tensile strength and no ductility. A positive property of grey iron is that free graphite acts as a lubricant in its structure. For this purpose, it is well suited for sections where sliding action is required.
Grey iron castings are commonly used in machine tool cabinets, pipe and pipe fittings, automotive cylinder blocks and farm equipment. In this article you can learn why, as of today, grey iron is still the most popular forging material.
Grey Cast Iron Properties
Grey cast iron can be produced by several different metallurgical and core processes, including sand and pressure casting. The choice of the preferred casting process depends largely on the size of the production run and the preferred characteristics of the final part.
Typical grey iron casting applications in OEM , automotive and aerospace industries include valves, forges, compressors, pumps and more. grey cast iron as commercially available iron usually has the following composition:
Carbon - 3 to 35 percent
Silicon - 1 to 2.75 percent
Manganese - 0.40 to 1 percent
Phosphorus - 0.15 to 1 percent
Sulfur - 0.02 to 0.15percent
And the rest is pure iron
Advantages of Grey Iron
So what are the main reasons that grey iron as a forging material is so popular today, Well, first and foremost, there are its ability to make complex structures and its low cost and its excellent properties, which we want to tell you about in more detail below:
Exceptional compressive strength
This strength is characterized as the capacity of any metal or alloy to withstand compressive forces. Gray cast iron has a high compressive strength and is also commonly used in columns and columns of buildings. Moreover, their compressive strength can be as strong as that of some mild steels.
There are various types of gray cast iron and their tensile strength varies accordingly. Some varieties have a tensile strength of 5 tons per square inch, while others have a tensile strength of 19 tons per square inch on average. However, the addition of vanadium can increase the strength of gray cast iron.
Deformation and resistance to oxidation
Gray cast iron is very resistant to deformation and offers a rigid frame. However, even a gray cast iron structure will break down if there is a design problem. Gray cast iron is very resistant to rust, which is formed by the reaction between oxygen and iron. This is the ideal solution to prevent a corrosion problem.
Grey Iron Applications
Grey iron castings can range in size from a few grams to several tons, the complexity of shapes from simple to complex, from single orders (paper crusher) to mass production. The desired dimensional accuracy and surface finish can be achieved by process selection and control.
Castings allow several components to be incorporated into one product, removing assembly and inventory, and reducing costs by 50 percent or more compared to machined pieces. In comparison to plastics, castings can be recycled easily and fully. Castings are currently used in nearly all fields of life.
Below is a partial list of applications in which the transport and heavy machinery sectors account for more than 50% of the castings produced: automobile, aerospace, railroad, shipbuilding, agriculture , mining, machining, casting, molding, forging, stamping and molding, engines, turbines, pumps and much more.
Class 300 Grey Iron
It can be used in the production of heavy machine tools, bed, presses, high pressure hydraulic parts, frame, gears, bushings, piston rings, cams, crankshaft, cylinder block, cylinder head.
Class 200 and 250 grey iron
It can be used in the manufacture of gears, cylinders, base, bed, flywheel, cylinder liners, cylinder block, pistons, brake wheel, gearboxes, pressure valve, coupling plate, etc.
Grade 100 and 150 grey iron
Suitable for the development of cover body, protective cover, frame, handwheels, hammer, floor, handle, chest, frame, bed, bearing, pulleys, bench, pump body, tubing, valve, and so on.
Differences Between Grey Iron and Ductile Iron
Grey and ductile cast iron are distinguished by the type and structure of the carbon they contain. The question of course is which one is right for your project? Before we look at the possible answers, let's analyze some of the key differences between the two cast irons. For a quick summary, please read the content below.
Ductility is defined by the greater percentage of elongation in tension. The addition of magnesium in nodular cast iron means that the graphite has a spheroidal / spherical shape for higher strength and toughness as opposed to grey cast iron which is flake shaped.
Tensile and Yield Strength
There are definitely variations in the tensile strength and ductility of gray and ductile cast iron. Ductile iron has a minimum tensile strength of 60000 psi and a minimum production strength of 40000 psi. There are several grades of gray cast iron in compliance with ASTM A48. Though gray cast iron does not have a measurable yield point, the tensile strength range is 2000-60000 psi.
Impact strength and thermal conductivity
Ductile iron has greater impact resistance than grey iron and can withstand an impact of at least 7 feet (compared to 2 lb. of grey iron). Ductile iron has a lower thermal conductivity than grey cast iron.
Grey iron is more effective at damping vibrations than nodular cast iron. grey cast iron is very easy to cast and has good machinability. It is typically used in the following non-critical applications where strength is not the main property required. Ductile iron, due to its increased strength and ductility, is used in more advanced applications.