Question (1 Viewer)

[Dreamerish*~]

Q: how does adding Chronium to steel (steel is iron with 1.5% carbon right?) make it more resistant to corrosion? also what does molybdemum do when added to steel?

Thank you.

 

[LostAuzzie]

Firstly: Steel is an iron alloy containing no more than 2% carbon. Adding chromium increases resistance to corrosion because chromium is one of those passivating metals producing the inert layer resistant to corrosion.

Secondly: Molybdenum increases resistance to corrosion as well as strength and hardness.

Hope that helps

 

[dead]

is adding chromium to steel, the same process as galvanising right?

 

[serge]

chromium makes it stainless, right

 

[LostAuzzie]

is adding chromium to steel, the same process as galvanising right?

Not quite, galvanising is cathodic protection involving zinc however they both increase resistance to corrosion

chromium makes it stainless, right

Yep chromium (and Nickel) make steel stainless.

 

[serge]

thanks, thought so

 

[rama_v]

Do we need to know how, say, carbon actually hardens steel? In the Success One book they have this massive description of the crystal lattice of metals and how carbon atoms can fit in and slide or some rubbish, lol, do we need to know it in that much depth?

 

[LostAuzzie]

There are a lot of things in the success one books that I dont agree with in regards to detail.
I'm pretty sure knowledge that carbon increases hardness and decreases maleability is suficient

 

[rama_v]

There are a lot of things in the success one books that I dont agree with in regards to detail.
I'm pretty sure knowledge that carbon increases hardness and decreases maleability is suficient

hehe yeah
phew
but if you think success one is overboard for chem, wait till you read the answers for ipt - a whole page typed for 2 marks! lol

 

[Casmira]

but if they put "just enough" suffecient answers and you remembered most of it you may only get 3/4 marks, where as in a big ass answer youll remember most of it and probably nail down that 4 marks

doesnt adding carbon also increase brittleness?

and when you add chromium to steel and a passivating layer forms, is that because of the actual metal property ? or does the chromium ions oxidise form on the steel (like layers)

 

[LostAuzzie]

doesnt adding carbon also increase brittleness?

Yes it does but malleability and brittleness are opposites.
Thus an increase in malleability is a decrease in brittleness

and when you add chromium to steel and a passivating layer forms, is that because of the actual metal property ? or does the chromium ions oxidise form on the steel (like layers)

I dont quite get what you are asking but...
If your asking whether the passivating layer is formed by chromium, not involving its mixing with steel then the answer is yes.

 

[Haku]

other metals like nickel and molybdnum also increase tensile strength and increase resistance to corrosion. Adding of chronium, molybdnum and nickel also increase the heat resistance of the metal, alowing the metal suitable for work in heat environment. While tool steels have 0.6-1.5% carbon added to further increase tensile strength...

just wondering how much we need to know, cause it can go on and on and on.
there was a 5 marker on the addition of other elements to iron to make different types and purpose of steel. just wondering just how many example metals or alloys we need to actually talk about