Let’s continue our discovery of CTS™-XHP. Possibly the best knife steel ever.

CTS™-XHP is one of the most fantastic steels on the market. I don’t just say that because I use it. I say that because it is possibly the best. It is in high demand. The thought that went into the formula is dumbfounding. The quality of the manufacturing is top notch. And most importantly the performance of the steel is unbelievable. I have a hard time saying something is the best ever, but this steel might just be the best knife steel ever. Let’s keep describing it. Hope you enjoy!

Carpenter’s XHP is Air Hardening:

Recall the last post when we talked about how CTS™-XHP was formed using powder metallurgy? Ok. So you also recall that there are three phases to making an alloy using powder metallurgy? Powder blending, die compaction, and sintering are the three basic steps to forming an alloy from powder. In the die compaction step, the metal is at room temperature. During sintering, however, the temperature is elevated but not to the point of liquefaction. So, it stands to reason that it will need to cool down.

When cooling steel, traditionally, the best way to do this is to quench the steel using some kind of cool liquid. The reason to cool the steel quickly is to prevent the carbon atoms from diffusing out of the steel. Basically, you want to freeze the crystalline structure of the metal without letting the carbon out. If you let it cool naturally in the air the carbon atoms will have time to migrate out of the steel and escape the crystalline structure. Making a much weaker steel. There is always a downside. That downside for rapid quenching is that there is a lot more dislocations (scientific term) in the steel. This increase makes for a very hard steel but makes the steel much more brittle.

Unless you use powder metallurgy. When you use powder metallurgy the metal never liquifies. The crystalline structure forms due to the sintering. That means the carbon atoms are stuck inside the crystalline structure of the steel from the beginning. Incidentally, adding chromium, nickel, molybdenum and manganese aid the air hardening greatly. Very cool.

Oh, a quick bit of trivia… Air hardening has been around since 1868 when Robert Forester Mushet invented the first tool steel. Which was also the first air hardening steel.

Bottom Line: Air hardening is awesome.

Carpenter’s XHP is High Carbon Steel:

We throw this term around a lot. But what does it mean? For a steel to be able to undergo heat treatment the percentage of carbon in the steel must be between .3 – 1.7%.

CTS™-XHP contains 1.6% by weight. That places this steel toward the upper end of the spectrum. Any higher and heat treatment becomes infeasible. By most accounts to be considered high carbon steel the percentage of carbon is between .6 – 1% by weight. What is above “high carbon”? “Ultra High Carbon” of course! CTS is being modest about CTS™-XHP by saying that this alloy is just some kind of pedestrian ‘high carbon’ when really it is clearly in the category of ‘Ultra High Carbon’!

The next logical question you may be asking is what benefits does having more carbon in the steel produce? Glad you asked. The more carbon the steel has the harder and stronger it becomes through heat treating.

As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. and more brittle. You have to give something to get something. To make a steel that is very hard and able to hold a sharp edge for a really long time we need to give away its ductility.

The higher the percentage of carbon in the steel the harder it becomes to weld. The types of steel that we use to make tools (like knives) are not the same types of steels that we make structures. Make sense?

Carpenter’s XHP is High Chromium Steel:

Ever wondered what made stainless steel… stainless? The answer is in Chromium. To be considered a stainless steel the percentage of chromium needs to be above at least 10.5 percent. When you add chromium to steel it helps to form a chromium oxide film on the outside (where it is exposed to oxygen). This film forms a protective layer on the outside of the metal and is very resistant to further corrosion. The thickness of this chromium oxide layer is directly related to the percentage of chromium added to the stainless steel. If follows that the thicker that chromium oxide layer is the more corrosion-resistant the stainless steel will be.

When you add chromium to low carbon steel you get ferritic stainless steels. When you add chromium to high carbon steel you get martensitic stainless steels. When you add chromium and nickel to high carbon steel you get austenitic stainless steels.

So you would think that CTS™-XHP is an austenitic stainless steel. Right? Almost.

Carpenter’s XHP is Corrosion Resistant:

Austenitic stainless steels aren’t as hard as martensitic stainless steels but they are more corrosion resistant. To hold an edge on your knife that is beyond razor sharp for as long as possible you need a metal that is very very hard.

CTS™-XHP is kind of a mix between martensitic and austenitic. It has some special properties of both. It has superior corrosion resistance of austenitic stainless steels and superior hardness of martensitic stainless steels. This is because it adds in a few extra elements to the alloy. Specifically, molybdenum, manganese, and vanadium.

The CTS™-XHP Bottom Line:

Carpenter CTS™ XHP alloy is powder metallurgy, air-hardening, high carbon, high chromium, corrosion-resistant alloy.

CTS™-XHP is a very carefully constructed alloy. It is a stainless steel with very hard and very corrosion resistant. A unique combination. Very hard to achieve. It is just as corrosion resistant as 440C and just as hard as D2 tool steel. It is a truly special metal. Well done Carpenter! You guys are seriously full metal alchemists!

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