Ferroalloys can be divided into high quantity low value bulk alloys, and low quantity high value noble alloys. Ferroalloys are important to steel production as alloys of addition and refinement. Refinement is usually used to desulpherise, deoxidise. Alloys of addition as their name implies, are used to alter the chemical analysis of the resultant steel and the skill in their use is to get as much of the desired element into the steel as possible, while limiting as far as possible the inclusion of undesirable elements. Their application may comprise small additions to ordinary mild steel for structural applications, the high strength low alloy steels, or it may involve larger additions such as 12-18% of chrome added to various grades of stainlesss steel. Alloys of refinement on the other hand have a specific job to do in removing undesirable elements from the steel during manufacture and are therefore expected to be almost completely eliminated from the finished steel analysis by ending up in the slag, along with the elements which they have eliminated from the melt.
High Carbon Ferro Manganese is by far the biggest in tonnage and the more versatile, being an alloy of both addition and refinement. World resources of manganese ore are vast on land and under the ocean. Containing mainly Mn and C, the balance is always Fe and traditionally produced in Blast or Electric Arc Furnaces. FeMn is a universal desulphuriser in all steel production in the ratio of 10-14 lb of Mn per tonne of steel produced.
Refined Ferro Manganese is always used as an alloy of addition in high grade engineering steels where the controlled addition of manganese is required in the ladle without upsetting the finely balanced C content that has already been achieved.
Mn 75% min 80% min
Si 1.5% max 1.5% max
C 6-8% 1.5%, 2.0% max
S 0.03% max 0.03% max
P 0.20% max 0.20% max.
Ferro Silicon has a lower density than FeMn and much lower than FeCr and lies in second place by tonnage. It can be used for both refinement and addition. The raw material used to produce FeSi is high grade quartz very common throughout the world, however the biggest cost of producing FeSi is power. Large and cheap sources are usually hydro-electric and unfortunately not a stable source as it is dependant on rainfall, snowfall and thawing. Ferro Silicon is the workhorse deoxidiser in steel production and iron foundries, its consumption is in a more or less fixed ratio to steel production at about 5lb per tonne.
Si 75%, 65%, 45%
C 0.10% max
Al 1.5% max
S 0.03% max
P 0.03% max
Ferro Chrome is the smallest by tonnage of the big 3 bulk alloys and the most expensive due the higher cost of its raw material, chrome ore, and its higher conversion cost. FeCr is wholly an alloy of addition used in the AOD (argon-oxygen decarburisation) process for making alloy steels – particularly stainless steel. High quantities of High Carbon FeCr are consumed and the rule of thumb is the more modern the steel industry, the greater dependance on lower cost, High Carbon FeCr. Demand for more expensice Low Carbon FeCr has dropped steadily over the years. Producers however use Low Carbon FeCr as an additive in the last stages of alloying to make precise additions of chrome without affecting the carbon content. Carbon content in chrome containing steels is important due to the fact that welding of such steel with any but the lowest C content is followed by carbide precipitation around the weld and intergranular cracking. Apart from stainless steel, some high performance engineering steels such as aircraft alloys also contain chrome
Cr 65-70% 65-70% 65-70% 50-55%
Si 1.5% max 1.5% max 1.5% max 5% max
C 7%, 8%, 9% 1%, 2% 0.10%, 0.15%, 0.25% 5-8%
N 0.1% max 0.1% max 0.10% max 0.1% max
S 0.01-0.04% 0.01-0.04% 0.01-0.04% 0.04% max
P 0.03% max 0.03% max 0.015% max 0.03% max
Ferro Phosphorus is used as a furnace charge and ladle trimming addition to control phosphorus levels in iron and steel
P 25% min
Si 1% max, 2% max