Carbon Content???????

[verisharp]

Is it true that a higher carbon content equals less corrosion resistance, and a higher chromium content equals better edge retention?

 

[HoosierQ]

It is the opposite. The content of either is by no means the last word on edge retention or rust resistance but carbon is there to create stress or tension within the iron at the molecular level which toughens it up. Chromium inhibits the formation of iron oxide by preventing iron from bonding with oxygen somehow.

There are metalurgists who participate on this forum who really understand this very well...I am not such a person.

 

[Russ Andrews]

Verisharp,
It's not that simple.
Carbon contributes to hardenability, and carbide formation. Both
have strong effects on edge retention, but little or none on
corrosion resistance.

Chrome, in small amounts, contributes to hardening depth, and
carbide formation (thus grain refinement), and in larger amounts
it contributes to corrosion resistance.

BUT...there are other elements to consider..like manganese, tungsten,
vanadium, etc....all of which can alter the effects of carbon and chrome.

 

[RubiconSS]

Is it true that a higher carbon content equals less corrosion resistance, and a higher chromium content equals better edge retention?

It's a good question especially if you have a ZDP-189 blade which has ONLY those two elements ( Carbon 3.0 / Chromium 20.0 )

 

[thegeek574]

I have heard from some knifemakers that after about 1% carbon, you start to loose it's benefits unless you know how to make it work. generally, it takes about 15% chromium to make a steel stainless. that is a rule of thumb, and only something to use if you do not want to get too deep into metallurgy.

 

[ROBB]

it takes about 15% chromium to make a steel stainless

I believe it around 12% chromium to make stainless. Kershaw uses some steel with 13% and 14%.

 

[kreole]

It's a good question especially if you have a ZDP-189 blade which has ONLY those two elements ( Carbon 3.0 / Chromium 20.0 )

According to zknives.com, ZDP189 also has molybdenum, vanadium, and tungsten.

 

[EricV]

According to zknives.com, ZDP189 also has molybdenum, vanadium, and tungsten.

Spyderco and A.G. Russell both list it with only Carbon and Chromium.

http://www.agrussell.com/Steel_Guide/a/73/

http://spyderco.com/edge-u-cation/index.php?item=3

But there have been rumors about there being more to it than that for a while back now. I read one about the difference being due to a powdered steel vs ingots. Probably all just rumors but interesting just the same.

 

[verisharp]

It's a good question especially if you have a ZDP-189 blade which has ONLY those two elements ( Carbon 3.0 / Chromium 20.0 )

Thats actually the reason i posted this question... i wasn't sure if zdp 189 would rust ridiculously because of it's 3.0 carbon content

 

[EricV]

The zpd delica I had (sister now has) hasn't rusted even a little, after being used on and around the CT river for 3 years, don't think I ever oiled it or intentionally wiped it down. The tenacious I had did rust up quite quickly from similar use.

 

[me2]

Is it true that a higher carbon content equals less corrosion resistance, and a higher chromium content equals better edge retention?

Neither statement is always true, but both can be true. It all depends on where the chromium and carbon are in relation to each other, and the rest of the elements in the steel.

 

[Noctis3880]

For carbon steels, I don't think 1095 would be more vulnerable to rust than 1060 because of the higher carbon content.

However, for stainless steels like ZDP-189 and even CTS-XHP(for me at least) are vulnerable to corrosion. The reason being that in order for the Chromium to protect against rust, they have to be free within the matrix and not formed into Chromium carbides. So in stainless steels, the more carbon there is, the more chromium carbides, and the less resistance against corrosion.

The addition of vanadium, niobium, and other strong carbide formers will create volumes of vanadium or niobium carbides in place of Chromium, which is why S30V has significantly higher corrosion resistance than 440C despite not having more chromium.

But that's just laymen's terms, I'm not a metallurgist.

 

[knarfeng]

Is it true that a higher carbon content equals less corrosion resistance, and a higher chromium content equals better edge retention?

Partly correct. It's actually rather complex.

In a stainless steel, the higher the carbon content, the less corrosion resistant the alloy is. For those who doubt this, one need only consider the relative corrosion resistances of the 440 family, the alloys of which all vary in composition only in Carbon content. In corrosion resistance, 440A > 440B > 440C.

In a stainless steel, a higher chromium content contributes to corrosion resistance.

All other things being equal, increased carbon content produces increased edge retention.

Carbon reacts with metals to form carbides. Carbides are harder than the parent steel. A good simile is to say steel that has a high carbide content is like concrete. The rocks on concrete are harder than the concrete itself. The rocks make the concrete stronger, but make it harder to make a fine edge.

Alloys with more than 0.77% Carbon can form significant amounts of carbides if there are elements in the alloy to react with the Carbon. This will increase the abrasion resistance of the alloy. If you increase the Carbon content and the Chromium content, you do get more carbides which can improve the edge retention of the alloy.

 

[DennisStrickland]

frank is pretty accurate, in general the harder carbides such as vanadium , tungsten, & some chromiun tend to increase edge abrasion durability. new intros of nitrogen & niobium are being used to give steels good abrasion resistance & reduce corrosion. it remains to be seen if these steels will become mainstream in high performance cutters.--dennis

 

[guitarSteve]

This is part of the fascination of knives to me: all the magic steel and chemistry.

I appreciate it, but don't have the background to understand it. I like the concrete analogy: that helps!

 

[RubiconSS]

Thats actually the reason i posted this question... i wasn't sure if zdp 189 would rust ridiculously because of it's 3.0 carbon content

I use mine on a variety of "things" some would cause rust (salt bags for my drive way on a drizzley winter day) no problems.
The charts I have access to list the 3.0/20.0 carbon/chromium ratio. Not sure if that has changed.
I have enjoyed the knives I own with the ZDP-189.