page 10
What is steel?
Figure 1.
a) tinplateb) hot metal
c) primary steeld) secondary steel
Making steel to order
The bar chart below shows the specification of a steel that is required by a customer for making tinplate. You can see the percentages of the elements, carbon, silicon, manganese, sulphur and phosphorus that must be present in the steel.
Graphs of steel composition with roll over highlights
Removing sulphur
When the hot metal comes out of the Blast Furnace, the percentages of these elements is very different. You can see from the graph that there is far too much sulphur in the hot metal at this stage.

Treating the hot metal with magnesium before it goes into the BOS furnace reduces the percentage of sulphur. This primary steel has a composition close to the specification. This is called desulphurization.

There are further additions during secondary steelmaking, bringing the steel closer to the customer's specifications.

Question 10

With the help of an equation, explain why treating the hot metal from the Blast Furnace with magnesium reduces its sulphur content.