1. Silicon Content Defines the Grade
Ferrosilicon is traded and specified by its silicon content, expressed as a grade number such as 65#, 72# or 75#. The silicon percentage determines the deoxidation and alloying contribution of the material, and it is the first item checked on the certificate of analysis. Understanding how the grades are defined helps buyers compare offers and match the material to their steelmaking or foundry process.
2. Common Grades
65# ferrosilicon: silicon content higher than 65%, used where moderate silicon addition is required.
72# ferrosilicon: silicon content close to or slightly higher than 72%, a widely traded general-purpose grade.
75# ferrosilicon (national standard): actual silicon content reaches or exceeds 72%, although the grade is called 75#.
75# ferrosilicon (hard grade): actual silicon content reaches or exceeds 75%.
The naming convention means the grade label alone is not enough; the certificate of analysis should state the actual silicon content per batch.
3. Low-Aluminum Ferrosilicon
Low-aluminum ferrosilicon is a special grade in which the aluminum content is controlled below 1.0%. According to customer needs, the aluminum content can be further reduced to 0.5%, 0.2% or even below 0.1%. The low aluminum limit is important for clean steel production, because residual aluminum forms oxide inclusions and can interfere with the final steel chemistry.
4. Why Silicon Content Matters in Use
Silicon is a strong deoxidizer and a ferrite strengthener in steel. The grade determines how much material must be added to reach the target silicon level in the bath, which affects both cost and the impurity load on the steel. A stable silicon content across batches makes melting behavior and alloy recovery predictable.
5. Choosing the Right Grade
The choice among 65#, 72#, 75# and low-aluminum grades depends on the target silicon level, the impurity budget of the steel grade, and the addition method. For standard deoxidation, 72# or 75# is typical; for clean steel and aluminum-sensitive grades, the low-aluminum version is specified.
6. FAQ
Q1: What do the numbers in ferrosilicon grades mean? They indicate the nominal silicon content: 65#, 72# and 75# refer to grades with silicon levels around those percentages.
Q2: What is the actual silicon content of national-standard 75# ferrosilicon? In practice it reaches or exceeds 72%; the hard 75# grade reaches or exceeds 75%.
Q3: What is low-aluminum ferrosilicon? A grade with aluminum content controlled below 1.0%, and optionally reduced to 0.5%, 0.2% or below 0.1%.
Q4: Why does aluminum need to be controlled? Residual aluminum forms hard oxide inclusions and can affect steel cleanliness, fatigue life and the final alloy chemistry.
Q5: How is silicon content verified? By chemical analysis of each batch, reported on the certificate of analysis against the agreed grade.
Q6: Which grade should I choose? 65# for moderate additions, 72# or 75# for standard deoxidation, and the low-aluminum version for clean or aluminum-sensitive steel grades.
