The Secrets of Steel - Part 2: High Carbon Steel
March 5, 2013
Steel glorious steel! In my last blog post The Secrets of Steel, we learned a little bit about steel and the various properties that are great for making knife blades and for creating a great edge. Now it’s time to expand our basic knowledge of steel and learn about the two basic classes of knife steel; High Carbon Steel and Stainless Steel.
The big difference between High Carbon Steel and Stainless Steel comes down to the chromium content. Stainless Steel is loosely defined as a type of steel that has over 13% chromium. Chromium adds wear resistance, hardness and more importantly, corrosion resistance. That means that high chromium content in steel make the steel more resistant to oxidation (rusting). That’s fantastic right? Well, like everything in life it’s a give and take. High chromium content reduces the steel’s toughness and makes it likely to break under pressure. This can be offset by adding nickel into the mix, which will help increase toughness, harden-ability and even wear resistance. Even after offsetting the chromium content, Stainless Steel does not produce a very tough, sharp edge compared to High Carbon Steel but will produce a serviceable blade and edge for everyday purposes.
Now, I’ll say High Carbon Steel is my personal preference. High Carbon Steel rusts easily but I don’t mind putting some extra care into my tools and knives. I absolutely love putting an edge on a blade that’s sharp enough to shave with. But, the big reason I tend to lean towards carbon steel blades is the temper. Temper or Tempering, is the last part of the heat treating process for a blade, and is done after the blade is fully profiled and quenched (when the blade is in its hardest state). Tempering is used to increase or decrease a blade’s hardness and flexibility to produce qualities that the knife maker desires. (Tempering is complicated and the scope of techniques, myths and rules are bit too much for this one post.) Now all knife blades have a temper but most High Carbon Steel blades can have a variable (differential) temper. Variable Tempering is the process of tempering different parts of the blade for desirable qualities (a blade with a very hard edge (sharp) but its’ cheeks and spine are softer and more flexible). For example, a filet knife needs to be flexible and sharp. A knife maker would temper the spine and cheek at a high temperature to let the blade be very flexible without breaking, but he would temper the edge at a very low temp to keep the edge hard. A harder and more brittle edge will generally retain an edge better and will be much sharper than a softer edge. Then again, there is a give and take; a harder edge will often be very wear resistant and harder to sharpen.
Now there are plenty of High Carbon Steels used for knife blades on the market today. Some are better than others, but really it comes down a balance of qualities and preference.
High Carbon Steels
- D2- This High Carbon Steel is one of my personal favorite for knife making. D2 steel is an air-hardened tool steel that is considered “semi-stainless” because of its high chromium content (about 12%). This means D2 is more corrosion resistant that other High Carbon Steel but still has great wear resistance and toughness. D2 is a happy medium between stainless and high carbon steels. It’s easy to work and looks nice, but because it’s air-hardened steel you can’t differentially temper the blade like other High Carbon Steels. It can also be difficult to sharpen.
- A2- Is another air-hardened tool steel. A2 is very similar to D2 but a bit tougher and with less wear resistance.
- The 10 Series of Steels- (1095-1050) - The 10 series is another one of my personal favorites: 1095 and 1075 for making knives: 1050 and 1060 for machetes or even swords. The 10 Series are generally considered simple tool steels that have a lot of desirable properties for knife blades. They hold an edge well and are easy to sharpen but they tend to rust easily. The big advantage to the 10 Series of Steels is their ability to take a differential temper and produce different qualities across the parts of the blade.
- O1- A very popular blade steel with blacksmiths, O1 is considered to be“forgiving” steel that is easy to work and takes a differential temper well. O1 is truly great steel, it takes and holds an edge very well and is very tough. Not to be confused with O6 Steel which is very similar to O1 but O6 steel is little tougher and it produces a very sharp edge with greater edge retention.
- L6- Similar to O1, L6 steel is often considered to be one of the best steels available for knife making. L6 steel is often used to make saw blades. Knives made from L6 steel need constant maintenance.
- CPM Series of Steels (CPM 10V, CPM-3V, CPM-M4) – These tool steels are some of the most wear resistant steels you can find, but they differ on toughness. CPM-3V and CPM-M4 have pretty good toughness for tool steel while retaining its wear resistance. CPM 10V is not very tough.
- W-2 - Reasonably tough and holds an edge well, W-2 and W-1 are basic carbon steels with some extra carbon. Most files are made from W-1, which is the same as W-2 except for the vanadium content (W-1 has no vanadium). These steels rust easily.
- 5160- This steel is renowned for its toughness, harden-ability and reasonable toughness. Chromium is added to the steel to add some strength and harden-ability but not enough to produce stainless steel. 5160 is great for making large blades like Bowie’, kukris and swords due to its toughness.
- 52100- This steel is very similar to 5160 but it sacrifices some toughness for better edge holding ability and wear resistance. Also, 52100 has much less chromium than other steels’ and is more likely to rust quickly. This steel is popular for smaller hunting knives used primarily for processing and skinning, but it can be used for some larger knives.
Well, those are the most commonly used High Carbon Steels for knife blades. Hopefully this has helped you understand the different qualities of the High Carbon Steels. I didn’t list all available steels but I encourage questions and comments about this post or the different High Carbon Steels in the comment section. I’ll try to answer any questions you have. Thanks for staying with me; this was a long, but hopefully eduational post. Stay an Edge Above the Rest.
Apr 12th, 2013
Apr 20th, 2014
So what's going on? I have an understanding of hardness and toughness trade offs so you can give it to me straight. Their individual formulas are lost to posterity.
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