The Use and Importance of Ferroalloys
Published: 25th April 2019
In the Analytical Services laboratory here at Sheffield Assay Office, we have great experience working with ferroalloys. But what exactly are they and what are they used for?
Ferroalloys - an overview
Ferroalloys is a term used to identify various alloys of iron with a high proportion of one or more other elements; e.g. Cr, Al, Mn, Mo, etc. Used in the production of different steels and alloys and closely associated with the iron and steel industries, ferroalloys are produced generally by two methods: in a blast furnace or in an electric arc furnace:
a) A BLAST FURNACE produces liquid metals by the reaction of a flow of air (oxygen) introduced under pressure into the bottom of the furnace with a mixture of metallic ore, coke (reducing agent), and flux (generally limestone) fed into the top. Coke is ignited at the bottom and burned rapidly with the forced air. The iron oxides in the ore are chemically reduced to molten iron by carbon and carbon monoxide from the coke. The slag formed consists of the limestone flux, ash from the coke, and substances formed by the reaction of impurities in the ore with the flux; it floats in a molten state on the top of the molten iron. Hot gases rise from the combustion zone, heating fresh material in the stack and then passing out through ducts near the top of the furnace. The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron. Modern furnaces are highly efficient, to pre-heat the blast air and employ recovery systems to extract the heat from the hot gases exiting the furnace.
b) An ELECTRIC ARC FURNACE consists of a refractory-lined vessel, usually water-cooled in larger sizes, covered with a retractable roof, and through which one or more graphite electrodes enter the furnace. The furnace is primarily split into three sections:
- the shell, which consists of the sidewalls and lower steel "bowl";
- the hearth, which consists of the refractory that lines the lower bowl;
- the roof, which may be refractory-lined or water-cooled, and can be shaped as a section of a sphere, or as a frustum (conical section). The roof also supports the refractory delta in its centre, through which one or more graphite electrodes enter.
A typical alternating current furnace is powered by a three-phase electrical supply and therefore has three electrodes. The arc forms between the charged material and the electrode, the charge is heated both by current passing through the charge and by the radiant energy evolved by the arc. The electric arc temperature reaches around 3000C. The regulating system maintains approximately constant current and power input during the melting of the charge, even though scrap may move under the electrodes as it melts.
AC furnaces usually exhibit a pattern of hot and cold-spots around the hearth perimeter, with the cold-spots located between the electrodes. Modern furnaces mount oxygen-fuel burners in the sidewall and use them to provide chemical energy to the cold-spots, making the heating of the steel more uniform. Additional chemical energy is provided by injecting oxygen and carbon into the furnace;
In a modern shop such a furnace would be expected to produce a quantity of 80 metric tonnes of liquid steel in approximately 50 minutes from charging with cold scrap to tapping the furnace.
Blast furnace production continuously decreased during the 20th century, whereas the electric arc production is still increasing.
Examples of ferroalloys, their composition and applications
|
Alloy Type |
Main elements |
Main Use |
|
FeCr – ferrochromium |
Fe, Cr |
Stainless |
|
FeMo – ferromolybdenum |
Mo 65 - 75 Fe 22.75 - 32.75 Silicon, Si ? 1.5 Copper, Cu ? 0.50 Carbon, C ? 0.10 Sulfur, S ? 0.10 Phosphorous, P ? 0.050 |
High strength low alloyed |
|
FeNb – ferroniobium |
50-80%Nb |
High temperature application and steel |
|
FeNi – ferronickel |
Ni 30%-90% |
Widely used for stainless, steel and 3D printing |
|
FeSi – ferrosilicon |
15–90% Si
|
Corrosion-resistant, high-temperature-resistant, electromotors and transformer cores |
|
FeTi – ferrotitanium |
Ti 30%75% Ti, max. 5–6.5% Al, max. 1–4% Si
|
Low carbon steel, high temperature and superalloys |
|
FeB – ferroboron |
12–20% of boron, max. 3% of silicon, max. 2% aluminium, max. 1% of carbon |
quenching degree and mechanical behaviour of steel and in high-quality alloy steel |
Determining the chemicial composition of ferroalloys
Our Analytical Services team has a great deal of expertise in determining the elemental composition of any ferroalloys. A highly-skilled approach is required for the elemental analysis of these alloys - a combination of precision instrumentation, analyst expertise and methodology which has been developed at Sheffield Assay Office over many years.
Analytical Service laboratory methods are accredited to the international standard IS0 17025, and we work with our customers to ensure the most appropriate methods of analysis are used to meet the challenges faced by this industry.
Analytical Services expertise enables us to detect elemental contents of impurities in parts per billion (ppb) up to pure metals with 100% contents. We utilize a range of up-to-date instrumentation including Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). We have a great deal of experience in dealing with any sample types and matrices requiring trace and major elemental analysis using appropriate sample preparation, which assures accurate readings.
Elemental analysis is competitively priced and can be used:
• To support mandatory Chemical Safety Assessment (CSA) for REACH.
• For the identification of unknowns - our teams are able to draw on 30 years of experience and awareness of different sample techniques to identify the elemental composition.
• To offer rapid response troubleshooting, where our scientists provide a fast turnaround to solve manufacturing issues
• For Quality Control
Click here to find out more about the services provided by our Analytical Services department here at Sheffield Assay Office, call us direct on 0114 231 2121, or email info@assayoffice.co.uk.
The Sheffield Assay Office was established in 1773, under an Act of Parliament and today the company assays and hallmarks the precious metals - silver, gold, platinum and palladium. Sheffield Assay Office is one of only four UK assay offices who all work to uphold the Hallmarking Act of 1973 and continue to ensure consumer protection for customers purchasing precious metals.
To find out more about the whole range of services offered by Sheffield Assay Office, such as our hallmarking and analytical services, please email us at info@assayoffice.co.uk or complete the contact form on our website at http://www.assayoffice.co.uk/contact-us ,
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