Sukenari (佑成) YXR7 HSTS Hairline Sujihiki/Long Petty

Sukenari YXR7

K&S Exclusive! I remember I was so excited when K&S was able to offer the Sukenari SG2 at the same time as other major vendors in the industry, as it was a significant recognition by a major Japanese manufacturer (to be the launch customer).

Well, this time it is even more special, with Sukenari creating an exclusive line for Knives and Stones, featuring the Hitachi YXR7 special tool steel.

So why YXR7?

It was about 2 years ago that I was given a sample of Sukenari’s YXR7 knife. I had no idea at the time what was so special about the YXR7 steel, except reading Hitachi defined it as a “Matrix high speed steel for forging tools, extreme toughness in 62-65HRC”. I was not impressed by this type of wording so when I received the knife, I gave it a destructive testing: hacking a piece of dry maple (WARNING: PLEASE DO NOT TRY THIS AT HOME). To my surprise, the knife came out with absolutely 0 chipping and I didn’t notice any part of the edge was rolled. I even posted an Instagram pic, which pieces of the wood cleanly chopped off.

https://www.instagram.com/p/_WmOa7L4eH/?taken-by=knivesandstones

Another surprise was how easy it is to sharpen the YXR7: With factory edge, I was able to form a burr in 3 strokes on a Shapton Pro 1000. This feels just like a normal carbon steel, I was thoroughly impressed. So I went ahead to place the YXR7 order with Hanki-san, little that I know at the time, it will take me almost 2 years to get my hands on them.

Deeper look at the YXR7

Lets have a detailed look about the YXR7. YXR7 is classified by Hitachi as a YSS Matrix High Speed Tool Steel. With 0.8% Carbon content, the strength / toughness is from the highly percentage of alloy that it has (5% Mo, 1.1% W and 1.1V %). With only 5% Chloronium, it can be classified as a semi-stainless steel similar to the SLD / SKD / A2/ D2 steel, which means it behaves like a carbon steel but you are likely to get away with rust problems (since the cladding is stainless) as long as you wipe the knife dry after use. The chance of the knife developing any rust during normal preparation is unlikely.

(www.zknives.com)

Overview of Hitachi Tool Steel

According to Hitachi, we can see that YXR 7 is a very well balanced steel in terms of its toughness and ware resistance.

• Compared to the popular SLD steel, it is both tougher and keeps its edge longer
• Compared to its sibling HAP40, it is tougher but not as hard (less HRC)

From this chart, we are able to conclude that the YXR7 (HRC 65) while substantially harder than SLD (HRC 60), theoretically sharpens quite similar to the SLD and is much easier to sharpen than HAP40.

Again we can see that, compared to SLD, the YXR 7 significantly tougher than the SLD even at much higher HRC.

• Bending: SLD: HRC 60, 3900 N/mm2; YXR7: HRC 64, 5000 N/mm2 (higher the better)
• Impact: SLD: HRC 60, 28 J/cm2; YXR7: HRC 64, 38 J/cm2 (higher the better).

Here is a chart that I pulled from Rockstead (a famous outdoor, tactical knifemaker), showing where most of the Hitachi cutlery steel is at.

(http://www.rocksteadshop.jp/content/technical-specs)

Compare the YXR7 at the top right corner with all the familiar faces like ZDP189, Ginsan (GIN 3) and SLD, you know where the YXR7 is standing.

The Knife

The YXR7 line is a typical sanmai (3-layer) construction with stainless iron cladding, this further reduces the chance of the knife developing any rust in a busy kitchen. The grind is a typical Sukenari grind that I consider in the middle of the Laser-workhorse scale. Not overly heavy and quite thin behind the edge. The fit and finish of the knife is on a very high standard compared at this price point with the choil and spine eased nicely. At K&S, you are also able to choose the design of our custom handles, we offer some of the best handles amongst any major vendors. A beautiful handcrafted hardwood saya can also be purchased with the knife making it a complete package.

Conclusion

I am super excited to offer the Sukenari YXR7 as a K&S exclusive line, this is a very significant moment in the history of Knives and Stones. The YXR7 is a high hardness and high toughness steel that is very forgiving to use in a busy kitchen, gives carbon-like cutting feedback and sharpens just like a normal carbon steel. Sukenari is a proven choice when it comes to heat treatment and grind, and I have certainly enjoyed mine over the years. If you love your SLD or want to give semi-stainless steel a try, I certainly think is the probably one of the best offerings out there.