A few questions about carbon steel vs stainless properties

[adrian44]

Curious about a few things and would appreciate it if you'd enlighten me.

1/ Carbon steel is hard, brittle, and keeps a sharp edge longer. These characteristics are related to one another and understandable. But why is it said that it's easier to sharpen? A harder material would have higher resistance to abrasion which is the process of sharpening. Why is it in reality easier to sharpen?

2/ High carbon content is what makes carbon steel harder. Yet when I look at steel composition charts I see that for example carbon steel 1095 has 0.9 - 1.03 % carbon while stainless 440-c has 0.95 - 1.2 % carbon which is higher. Why would stainless not be harder? Does the added chrome in stainless steel reduce it's overall hardness?

3/ If I go with a classic carbon steel like C75 for my hunting knife, what would be the safest product to clean it and protect it from rust? Is WD40 safe and effective? Would mineral oil be a good option? How about synthetic oil? Don't want to use something without asking first then later find that it's not the best protection or that it alters the chemical composition of the carbon steel.

Thank you

 

[PMQ]

1/ Carbon steel is hard, brittle, and keeps a sharp edge longer. These characteristics are related to one another and understandable. But why is it said that it's easier to sharpen? A harder material would have higher resistance to abrasion which is the process of sharpening. Why is it in reality easier to sharpen?

Because stainless steel need chromium. Some chromium will bond with carbon, forming chromium carbide, some chromium will just stay there, we call that "chromium in solution". Chromium carbides are 1. big, 2. hard and 3. brittle.

1. Since they are big, it's hard to get a fine smooth edge. But rather a toothy edge
2. Since they are harder than what whetstones are designed to handle, they sharpen slower. Not impossible, just slower.
3. Since they are brittle, they are... brittle.

Carbon steel, even simple carbon steel is very fine, it's like baby powder or flour fine, compare to chromium carbide gravel. And since you can sharpen it to a finer edge, you'll feel that it's "more keen" (yes, I know the terminology is confusing).

Now... this is where it get interesting:

When you say the knife keeps an edge for longer, I'd have to ask, what are you cutting and how are you cutting it. If you use a knife to cut food, are those food abrading the steel off? heck no, unless you eat abrassives. Here, the edge is acting like a wedge, splitting the food. So a finer edge feels easier to split. But when you're sharpening, you're not trying to wedge/split the whetstone (hope not), but you are abrading the steel, so it's a different story.

 

[David Mary]

A adrian44 , answers to the questions you have asked are not going to lead you to a complete picture. My suggestion is spend some time looking over Larrin's website, Knifesteelnerds.com, and things will start to click.

 

[PMQ]

I totally agree with David Mary ,most of the terminology and science will be extremely confusing for beginners. I'm not a metallurgist but I have background in engineering, when I read articles by Larrin Thomas and Nathan at CPK, it's easy for me to understand "hardness", "toughness", "carbide", "energy", "force",... But when I explain them to my friend, who does not have a background in engineering, they are totally confused, "isn't hardness=toughness" or "isn't energy=force"

 

[David Mary]

Carbon steel is hard, brittle, and keeps a sharp edge longer

This was the blanket statement that made me suggest it. It is a gross oversimplification that is misleading at best, and in many cases outright wrong at worst.

 

[PMQ]

2/ High carbon content is what makes carbon steel harder. Yet when I look at steel composition charts I see that for example carbon steel 1095 has 0.9 - 1.03 % carbon while stainless 440-c has 0.95 - 1.2 % carbon which is higher. Why would stainless not be harder? Does the added chrome in stainless steel reduce it's overall hardness?

Carbon isn't hard, carbon is just carbon, it doesn't do anything, it's the heat treatment process that hardens the steel, the more carbon you have, the higher the hardness you can reach. Hardness depends more on the quality of the heat treatment process as well as what HRC hardness the maker aimed for.

To elaborate on stainless steel sharpening:

One of the reason why stainless steel is hard to sharpen, as I have explained, is large chromium carbides. However, with modern manufacturing processes, we are able to make stainless steel with very fine carbides. AEB-L and 14C28N are stainless but they have very fine and small carbide, so they are extremely easy to sharpen, and toughness rivaling tool steels like 3V.

Also, I highly recommend reading about Magnacut, it's a steel designed by dr Larrin Thomas, it's a steel by knife nuts, for knife nuts. It's a stainless steel, with edge retention that'll put most tool steels and carbon steels to shame, very high toughness and relatively easy to sharpen. The reason why it's easy to sharpen is because the microstructure and carbide is ultra ultra fine.

 

[NapalmCheese]

As for #3: I use a 1075 carbon steel knife in my kitchen every day. After cutting stuff I wipe it dry, or rinse and wipe it dry. I store it dry. It has no rust but has quite the patina at this point. For my outdoor carbon steel knives (1075 or 1095 for the most part) I use Ballistol if anything, but mostly I just wipe them dry. Mineral oil would be fine. I wouldn't use anything you would avoid accidentally ingesting.

 

[knarfeng]

Why have you had an account since 2011 and are only now asking these questions?
Or have we been imbibing a bit of the juice of the grape and are being silly. Since these are questions that do indeed appear over and over again.

Curious about a few things and would appreciate it if you'd enlighten me.

1/ Carbon steel is hard, brittle, and keeps a sharp edge longer. These characteristics are related to one another and understandable. But why is it said that it's easier to sharpen? A harder material would have higher resistance to abrasion which is the process of sharpening. Why is it in reality easier to sharpen?

Because softer steel is more likely to form a wire edge. Wire edges can be difficult to remove.

2/ High carbon content is what makes carbon steel harder. Yet when I look at steel composition charts I see that for example carbon steel 1095 has 0.9 - 1.03 % carbon while stainless 440-c has 0.95 - 1.2 % carbon which is higher. Why would stainless not be harder? Does the added chrome in stainless steel reduce it's overall hardness?

Because if the steel has more than ~0.77% Carbon, the carbon above that percentage is in the form of carbides. Carbon steel forms iron carbides. Also known as cementite. In stainless steel the carbon most often combines with chromium.

3/ If I go with a classic carbon steel like C75 for my hunting knife, what would be the safest product to clean it and protect it from rust? Is WD40 safe and effective? Would mineral oil be a good option? How about synthetic oil? Don't want to use something without asking first then later find that it's not the best protection or that it alters the chemical composition of the carbon steel.

Thank you

Mineral oil. The kind sold in the pharmacy as a laxative.

Closed.