"Are all mild steels also carbon steels which are further broken down into low carbon, medium carbon, and high carbon steels?"

Yes and no. Controlling carbon content was the great eureka of steel making. Higher carbon steels are not typically referred to as mild steel.


"And the lower the carbon content the less prone to oxidation?"

It seems like the opposite. High carbon steels seem less prone to heavy rust.
For example, a forklift tine.

 

Mild steel is a steel with a low carbon content. Typically, once the carbon content goes above about 0.3%, it is no longer a mild steel. So 1018 or 1020 are mild steel, 1040 is a medium carbon steel, and 1095 is a high carbon steel.

Carbon steel is a steel consisting of almost entirely of iron and carbon, and no real other alloying elements are in there (barring low levels of impurities). In the AISI numbering scheme, carbon steels are the 10xx steels.

See http://en.wikipedia.org/wiki/Carbon_steel

The carbon content of steel does have an effect on the steel's rusting potential. But other alloying elements have a -much- greater effect on a steel's resistance to corrosion. Two elements that greatly increase a steel's corrosion resistance are chromium and nickel, so much so that adding about 13% chromium to a steel alloy generally turns that steel into a stainless steel.

That said, the lower the carbon level in a stainless steel usually makes the steel more resistant to corrosion. It's a sort of complex relationship in that it's not the carbon per say which increases the corrosion potential but the interaction of the carbon, iron, chromium, and other alloying elements and the carbides and their grain boundaries that affect the corrosion potential of the alloy.

 

How do you pronounce mild steel. Does it rhyme with wild? Or does it rhyme with billed?

 

Mild just like wild, long "i" sound like "eye".

Bill and mill have the short "i" sound, as in "it".

Southern drawls, New England mumbles, and other regional speech may make things sound different.

 

Good explanation MoonRise.

 

thank you moonrise

Appreciate the comeback.

 

Someone will probably butt in here to say I am wrong because of "Soandso Steel" but all steel contains carbon. In fact, iron ore contains carbon and cast iron has some of the highest carbon content of all, but are still not considered steel yet. It's how it's mixed with other ingredients that makes it into the alloy. Other ingredients like coke, chromium, nickel, limestone, dolomite, manganese, aluminum and others are also added to make other variations like stainless steel.

Carbon content as moonrise explained is the main thing that separates most steels, as is different methods for hardening or changing the way the atoms crystalize. Two identicle pieces of steel can have completely different properties including tensile strength, how brittle/soft, and as you mentioned oxidization potential just from heat treating/tempering the steel afterwards. Even with the same carbon content.

 

Hey, the OP didn't ask "what is steel?" he asked about mild steel and carbon steel and then about carbon's relationship to corrosion rates/potential.

Steel is an alloy of iron and carbon. It is precisely the addition of (relatively) small amounts of carbon into the iron and the possible later heat treatment(s) that can transform a relatively soft and ductile metal like iron into a hard and strong piece of steel. Or the steel can be alloyed or treated differently to widely change the physical properties of the steel. A steel that is still hard at a red-hot heat? Sure, high-speed tool steel. Steel at cryogenic temperatures? Sure, many stainless steels. Steel that is hard and very fine-grained, say for precision cutting blades or bearings? Sure, several different alloys of steel can meet those needs.

Like many, many recipes, the proportions in the recipe and the processing of the recipe matter to get the desired results (and properties).

Cast iron is cast iron because the large amount of carbon (and cast iron typically contains more carbon in it than high carbon steels!) is not in the molecules of metal or in between the molecules of metal but is more just mixed in the whole blob at a 'big pieces' level and not at the molecular level. The carbon is just there, it's not incorporated into the crystal structure. That's why if you rub against a piece of freshly cut cast iron you get that grey smear coming off, that's the carbon just rubbing off. Rub against a piece of high carbon steel and all you feel or get is steel, because the carbon is -within- the metal crystals and not just mixed in the metal like a bunch of chunks of carbon.

 

Hey, the OP didn't ask "what is steel?" he asked about mild steel and carbon steel and then about carbon's relationship to corrosion rates/potential.

Hehe, sorry. I got sidetracked. But later in my post I tracked back on topic. :cool2:

 

Mild Steel and Carbon Steel are basically the same animal, well at least as far as I have learned. Carbon steel can be broken down into a range of steel types, low medium and high for example. Mild steel falls into one of these catagories. I have always been taught carbon steel classigficaion in this manner.

Low Carbon Steel - 0.05 -0.30% Carbon <- Mild Steel goes here - the 0.15-0.30% range
Medium Carbon Steel - 0.30 - 0.45% Carbon
High Carbon Steel - 0.45 - 0.75% Carbon
Very High Carbon Steel - 0.75 - 1.50% Carbon

Hope that helped.