Okay

so this is roughly where we stopped last time.

This is

so essentially we went from raw

from pig iron

from the blast furnace and

started looking how we can make raw steel from that.

And the thing that really sets pig iron apart from raw steel is the carbon content.

So from the blast furnace we come through a via indirect reduction as we call it

out

with about 4%, 4.3% carbon.

Now weight percent, and this is roughly the eutectic.

The exact amount of carbon and also other dissolved elements will depend on the tapping

temperature.

So the higher the temperature is where you tap

you tap at

the more things generally

you will have dissolved in your pig iron.

It's kind of like the reason why you clean with warm water at home, because it dissolves

more stuff.

The same thing with iron

the warmer it gets the more stuff it dissolves.

So this is why tapping temperature plays a pretty big role

but roughly we're at about

4.3% carbon.

And then we go and we want to make the raw steel

and the definition of steel is what

separates steel from cast iron?

Okay

I thought this would come as a...

Carbon content?

Yes.

Not a very specific one.

This is our cutoff.

So steel means we have less than 2.1% carbon

or 2.6% carbon

depends on how old your iron

carbon phase diagram is.

And cast iron means above that.

And the reason why we have this cutoff is because it's the appearance of primary cementite

to lead upper right.

So here we've got primary FH3C.

And as soon as that happens

we call it cast iron.

So the old definition of steel versus cast iron was steel is forgable

cast iron is not

forgable.

The reason why steel is forgable is because steel doesn't contain primary cementite

and

steel doesn't contain primary cementite versus cast iron does.