With advances in both materials and manufacturing methods, cast irons and steels are becoming ever more attractive solutions to a range of engineering problems and requirements. These versatile materials can be formed into increasingly complex shapes, offering the advantage of high strength coupled components the meet the customer's requirement.
Of the many irons and steels available for the casting process, one of the most flexible is the Spheroid Graphite (SG) cast irons. As their name implies, SG cast irons have graphite present as small spheres, rather than flakes as in grey cast irons, and this offers huge mechanical advantages. Because of this fundamental metallurgical difference, SG irons tend to have enhanced mechanical properties, greater ductility, and increased shock resistance. This makes it a desirable from a number of reasons, and gives it positive advantages over many other metallic or even non-metallic materials.
SG Irons were developed in the 1940's as part of an investigation into the manufacture of stronger, yet tougher cast irons. While cast iron materials had been known and used since the previous century, they didn't differ much from those first manufactured and, while they were easy to make and use, they lacked quite a lot in strength and ductility. This reduced the flexibility of them material, and precluded it from many of the increasing high-stress applications that was being demanded of metals as technology - much of it fuelled by war - required. This lead to a glut of research into the mechanical properties of cast irons, and how they might be enhanced, and SG Irons came out of these investigations, and international standards on the manufacture of them formalised
While the materials have been enhanced, there can still be many problems and defects manufactured in as a consequence of the casting process itself. For this reason, many foundries now sign up the ISO/TS 16949 standard which is aimed squarely at ensuring the manufacturing process for parts destined for Automotive and related industries conform. It is this standard - which is akin to the ISO9000 Quality Management System - that ensures continuity of product passing through the foundry.
This standard is so far reaching, and complete, that it is seen as a necessity for any foundry supplying automotive, aircraft, and petro-chemical industries. Key to the adoption of this standard is the requirement to document and control the whole system throughout the foundry, resulting in control not only of the chemistry and manufacture of the resulting materials, but also the sources of raw ingredients that go to make the alloys in the first place and are key to its final properties. By a combination of supplier audit and periodic assaying, a company can be assured of producing the same material again and again and giving the foundry's customers the confidence in the purchased products.
Once gained, the standard gives the Original Equipment Manufacturer (OEM) the strength do demonstrate that they are competent and able to produce components that are acceptable to some of the biggest manufacturing companies in the world. SG cast irons are becoming a material of choice for many components as they can be cast to complex and almost near net shape, and with a standard such as ISO/TS16949 behind them, they can also be a material of high confidence.
While once seen as a cheap and inferior materials, cast irons now have now been subjected to sufficient research and test to demonstrate that they are capable of competing with many other materials, but having the added attractions of ease of manufacture, they have been boosted to a position of material of choice in many metal castings application.
