The hardness of this katana is 58-59HRC, and the impact toughness is 110J+, Vacuum heat treatment. It is polished by hand, and the overall hardness is too high, so it’s difficult to completely polish away the scratches on the surface. Therefore, compared with traditional art sword, its polishing looks not so beautiful. Its hamon is a fake straight hamon made later, in order to increase its beauty.
The impact toughness of LD steel under 60HRC hardness is almost the same with 59HRC. And the cost to make 59 or 60 is also the same. Then why don’t we make it into 60HRC? (I know some of you always pursue hardness, and consider higher hardness is better.) Just because the katana is too long and it’s heat-treated over all, the impact it receives during chopping is too strong, incomparable with a short sword. Therefore the key point is to make it difficult to fracture. And reducing the hardness can greatly increase the fracture toughness, making it not that easy to fracture. (hardness dropped a bit, while fracture toughness increased a lot.) That’s why we make it 59HRC. I think we must get rid of the inherent thinking of short swords. Hardness is not always right. The difference between short sword and the long sword are like the difference between sports car and off-road vehicle. They are completely different.
The advantage of modern high-performance materials is that they are more durable and have better sharpness retention. When test chopping, it is best to cut only bamboo and mats, because bamboo and mats will not let the blade get V-shaped notches.
LD is a high quality and toughness cold work die steel，with high crack-resistance and abrasion. Its bending resistance, toughness and many other indicators exceed CPM-3V, especially the toughness index. Under the same hardness of 60, the impact toughness of LD is about 115J, and CPM-3V is 95J. They also have almost the same wear resistance, but the anti-rust performance is far behind CPM-3V. However its price is much lower than CPM-3V. We have tested CPM-3V making standard katana, after bending resistance , side shot, and finally the blade broke when hitting the back of the blade which without a notch. This didn’t happen with the LD. That’s why we gave up on making the CPM-3V steel katana. Maybe we would use CPM-3V steel making tanto and wakizashi.