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Posted on Aug 11, 2020
Ductile Cast Iron is also referred to as SG Iron, ductile cast iron, or spheroidal graphite. This type of iron was developed in the USA almost 70 years ago. Ductile cast iron is a type of cast iron that is melted with elements such as magnesium or cerium to cause the formation of free graphite nodules or spherulites. The name of ductile iron means that this form of cast iron has a certain degree of ductility. The key characteristic of this substance is the graphite structure.
In ductile cast iron, graphite is in the shape of small spherical spheres, as opposed to gray cast iron sizes. The spherical graphite structure suppresses the generation of linear cracks, so it can resist deformation. Like gray cast iron, many grades of ductile iron can be specified to provide engineers with varying degrees of tensile strength and elongation. Various grades can be achieved by adding alloys and heat treatment. We will talk about some different grades of ductile cast iron further down in this article to help you pick the right type for your requirements. But first, let us talk about the characteristics and applications of ductile cast iron.
:: Read more : The Many Advantages of Gray Cast Iron
• Cost:compared with steel castings, ductile iron has lower manufacturing costs.
• Castability:ductile cast iron has a lower casting temperature than steel, so it can provide excellent surface finish and can cast complex shapes in conjunction with changes in cross-section
• Elongation:the elongation rate of some grades of ductile cast iron is higher than 20%/p>
• Machining:ductile cast iron is very easy to process, and the machining allowance can be kept to a minimum
• Tensile strength:with ductile cast iron you get a tensile strength of up to 900N/mm2
• Reduced weight:due to density, machining allowance, and mold capacity, the weight of ductile iron castings will be much lighter than equivalent steel castings.
Now, let's take a closer look at some properties and applications of ductile cast iron.
Compared with the weakened plane of graphite flakes in gray iron, the discrete form of graphite nodules means that the properties of ductile cast iron are more determined by the matrix of the material than the form of graphite. Hence ductile iron has higher strength, higher elongation, and greater resistance to impact than gray cast iron. In the casting state, a series of properties can be generated by regulating the composition and production process, from high ductility to high strength. This performance range can be extended by adjusting the alloy and subsequent heat treatment (including surface hardening) and hardening by quenching and tempering. Although the production of ductile cast iron is much more complicated than gray iron, it is still possible to produce complex shapes that are easier to machine than steel. The wide range of properties means that various grades of ductile iron can be used in various applications, such as automotive crankshafts and camshafts, gear rings and drive rings, replacement of manufactured products, castings and forgings, mechanically driven spindles and rotors, gears, and pelletizing machines Rollers, molds for aluminum ingots, etc.
Ductile cast iron has higher production and processing cost advantages than steel structures, forgings, and castings in terms of ductility and impact performance limitations, and has a weight advantage over gray cast iron with cracking problems.
Ductile cast iron (SG Iron) material grades vary according to different regional standards. In the USA for example, the common material standard for ductile cast iron is ASTM A536. Here you could find mechanical properties such as 60-40-18 (tensile strength 414 Mpa, yield strength 276 Mpa, elongation 18%). Therefore, you need to communicate the required mechanical properties to the foundry of your choice with a certain standard so that they can manufacture your castings according to your requirements. Choosing the correct grade of ductile iron material is not easy, at least a certain engineering background is required. However, if you contact a professional foundry, they should be able to guide you through this process. The following are some pointers, these pointers will give you a general understanding of the factors that determine the grade of ductile iron.
Check your 2D engineering drawings and technical requirements. These should indicate the appropriate materials, and the completed drawings should also contain material grade information. If you only now that you need ductile cast iron and have no special requirements for its mechanical properties, you can choose 60-40-18 (GGG40, 400-12, 400-18, AS38, QT400-18). If you have higher requirements for strength, toughness, and stiffness, you may need to consider 65-45-12 or even 70-50-05. If you need the material to have very high strength, very high-pressure load capability, then you could go for 80-60-03. However, you need to know that its elongation rate is only 3%, so its ductility is not ideal which will also affect its impact resistance. Here you need to weigh the pros and cons and decide what is best for you.
For 60-40-18 grade ductile cast iron, you will notice that it may bend under higher pressure loads (over 400Mpa), but it will not break like 80-60-03 grade ductile cast iron. This type of ductile cast iron can withstand high-pressure loads up to 600 Mpa. If you do not have a very specific reason, it is recommended not to choose a level higher than 600-3. Higher material grades have higher tensile strength, but this comes at the expense of lower and lower elongation. The higher the strength of the ductile cast iron type, the more brittle the material, and therefore the impact resistance is reduced. Besides, these high material grades will require higher production levels and further heat treatment, which will result in higher overall casting costs.
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