Choose the Right Alloy for the Right Application
Ferrous base metals are the foundation of buildings, bridges, automobiles, and transportation infrastructure. Ferrous metals include mild steel, carbon steel, stainless steel, cast iron, and wrought iron. (Non-ferrous metals include aluminum, brass, copper, nickel, tin, lead, and zinc, and precious metals.) Many iron alloys are created with differing properties suited for these various applications, so it is important to be able to accurately analyze these materials to confirm that their chemical specifications are correct for their purpose.
There are several kinds of irons which are distinguished by their composition and use. They belong to two main categories, pig irons and cast irons.
Pig and/or Blast Furnace Irons (hot metal)
In an integrated mill, pig iron and/or blast furnace iron forms the basic foundation for the ultimate manufacture of steel that can be generally subdivided into low and high alloy steels.
The low alloy steels category covers steels which are destined for a wide variety of uses, such as the production of:
- Steel castings, rails, axles, boiler and ship plates, automobile bodies
- Girders, all kinds of bridge and structural sections
- Wires, nuts, bolts and forgings of almost any description
- Springs, cutting steels just to name a few.
From a compositional point of view, these steels can be distinguished by the fact that the alloying elements generally total less than 5-7 %.
High alloy steels contain notable quantities of one or more of the following elements: nickel, chromium, manganese, silicon, cobalt, tungsten, molybdenum and vanadium. Included under this heading are:
- Stainless steels of types such as 18/8, austenitic, maraging, martensitic and all types of special stainless steels
- Tool steels
- High speed steels
- High manganese steels.
Cast Irons
Cast irons are used for the production of semi-manufactured products such as pipes, machines, various castings, and cookware. Carbon and silicon are the main alloying elements while other elements are similar in composition normally to most low alloy steels. From a metallographic point of view, a distinction can be made between white cast iron and grey cast iron. White cast iron has a cementite structure and is hard and brittle. Grey cast iron has good machinability, wear and heat resistance. It contains free graphite either in the form of laminae or nodules with the addition of magnesium, which can make grey cast iron inhomogeneous and therefore difficult to analyze if in ‘ascast form’. Alloy cast irons also exist where alloying elements such as nickel, chromium, manganese, copper, etc. are added to improve hardness, corrosion resistance or engineering properties.
Given the variety of ferrous materials produced, process analysis and quality control can be a challenge. Costly incidents can result when incorrect or out-of-specification metal alloys caused by material mix-ups, incorrect weld chemistry and dilution, or even counterfeit materials enter the manufacturing process. Wavelength-Dispersive X-ray Fluorescence (WDXRF) is an ideal technology to analyze ferrous metals during processing to ensure the consistency and quality of the product. XRF is the ideal technique for measuring high concentrations of the alloying elements directly in the solid metal.
See how a WDXRF instrument successfully meets the challenge of ferrous base analysis.
Additional Resources:
- Download our free eBook: A Practical Guide to Improving Steel Manufacturing Processes and Production Methods
- Visit our center for Improving Steel Manufacturing Processes and Production
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