Steel questions

[rayback]

I've been doing some research on the internet about different kind of steels.
I couldn't understand the following points.
1. What's the difference between Tool Steel and Very High Carbon Steel? aren't they the same because they both contain high amounts of carbon?

2. It's said that when steel contains 13%+ Chromium it becomes stainless. If we add A-2 tool steel for example 13% Chromium wouldn't it impart the steel stainless ability?
as far as I know tool steel cannot be stainless, why?

3. I saw properities of A-2 steel, it contained about 13% and it was still not stainless, why?

Thanks
Ray

 

[Cliff Stamp]

1. What's the difference between Tool Steel and Very High Carbon Steel? aren't they the same because they both contain high amounts of carbon?

There are many naming conventions for steels, one of them is the AISI tool steels which are steels like S7, A2, D2, some of them are high carbon and some of them are not. The tool steels are held to tighter standards on composition than the alloy steels of the same composition which is the basic difference between them. There are in fact many alloy steels like 1095 which have pretty much direct tool steel counterparts like W1.

2. It's said that when steel contains 13%+ Chromium it becomes stainless. If we add A-2 tool steel for example 13% Chromium wouldn't it impart the steel stainless ability?

Yes, the composition would be similar to VG-1. However you would also reduce the maximum hardness, lower the toughness, make the grain much more coarse and increase the size of the carbides. Generally these are the reasons why you simply don't make everything stainless because the other properties would suffer too much.

3. I saw properities of A-2 steel, it contained about 13% and it was still not stainless, why?

That isn't A2. However you can have a lot of chromium and still not be stainless if the carbon content is high such as in D2. Chromium makes steel stainless because it protects the iron by forming a passive layer on the steel, like varnish on wood. However as the carbon content is raised the chromium combines with this carbon which locks it in the form of little hard chunks in the steel and it is no longer able to protect the iron, the varnish is essentially locked inside the wood and thus can't coat the surface. This is why 440A is much more corrosion resistant than 440C even though the chromium contents are the same. There is more chromium in 440A which is free to form a protective layer on the surface of the steel.

-Cliff

 

[sog]

1. What's the difference between Tool Steel and Very High Carbon Steel? aren't they the same because they both contain high amounts of carbon?

Tool steel contains chromium and Very High Carbon Steel contains none.

 

[Cliff Stamp]

There are many tool steels which don't contain chromium (several of the W, S, and O series) and there are many high carbon non-tool steels which do such as 52100. The difference is in the tolerances put on the steels.

-Cliff