In classical novels and storytelling, you can often hear the description of cutting iron like mud and finding fault. Everyone is most familiar with the story of Yang Zhi selling knives in Water Margin. Yang Zhi's treasure knife cut twenty coppers, blew his hair on the blade, and it became two pieces in succession. Finally, he killed the villain Niu Er, and there was no blood on the knife.
Then, does the treasure knife in the novel really exist in reality?
Let's talk about cutting iron like mud first.
In fact, Yang Zhi's behavior of cutting copper coins is very cheating. As we all know, the hardness of copper is lower than that of iron, so it is not difficult to cut copper coins. Even the stainless steel broken bone kitchen knife at home can easily cut copper coins.
It is not difficult to cut iron like mud. Because pure iron is actually very soft. The hardness of pure iron is about 185~ 125HV according to Vickers hardness. The hardness of high-quality heat-treated steel knives is generally above 6 10HV. Japan once experimented with ancient Japanese knives. Among a batch of knives tested at that time, the one with the highest hardness was called Shui Xin Purple Zheng Xiu, and the hardness of the riding blade was as high as 700HV. Although this huge hardness difference is exaggerated, it is really not difficult to cut iron.
It should be noted that there are two main reasons for the huge hardness difference between steel knives and pure iron:
The first is the composition. The definition of the word steel in the dictionary is: "Steel is the general name of iron-carbon alloy with carbon content between 0.02%-2. 1 1%." The higher the carbon content of steel, the higher its hardness and, of course, the worse its toughness. At the same time, adding one or more alloying elements to carbon steel can also make steel have various special properties. For example, tungsten steel and manganese steel are famous for their high hardness. In ancient times, it was difficult to add various elements to steel at will as it is now. In ancient legends, there was a treasure knife made of meteorites because meteorites might contain elements such as manganese.
Yanxiadu iron sword
Followed by heat treatment.
The heat treatment of cutting tools is what we commonly call quenching. Quenching of steel is a heat treatment process, in which steel is heated to a critical temperature, kept for a period of time, so that it is completely or partially austenitized, and then rapidly cooled at a cooling rate greater than the critical cooling rate of martensitic transformation. Martensite crystallization in steel will change the hardness of steel several times. Without quenching, even manganese steel and tungsten steel, which are famous for their hardness, are far less hard than ordinary steel after heat treatment.
As early as 770 BC to 222 BC, China people discovered in production practice that the properties of steel would change due to the influence of temperature and pressure deformation. Two swords and a halberd unearthed in Yanxiadu, Yixian County, Hebei Province, China, have martensite in the microstructure, indicating that they have been quenched.
It can be said that quenching is the soul of a knife, and a knife without quenching can only be regarded as an iron bar.
Speaking of which, you can crack the so-called gimmicks of businesses selling kitchen knives near tourist attractions. In fact, whether it's poking iron drums or cutting steel bars, there is no technical content. Steel bars are unquenched steel. Even ordinary people can Bai Wan fine steel bars, but their hardness is actually very low. Simply cutting steel bars, if the blade is thick enough and the cutting angle of the knife is large, can be easily completed.
Another example is the common steel scissors. Anyone who has seen steel scissors will know that the cutting edge of steel scissors is actually very thick and the cutting angle is very large, so it is not laborious to cut steel bars. If we only pursue the ability to cut steel bars, the small steel bars imported from Germany only need 60 yuan even if they are cut online, and the domestic steel bars only need more than ten yuan. ...
Next, let's talk about blow-drying and broken hair.
Generally speaking, for the sharpness of the knife, the knife friend's own judgment standard is generally sharp, at least he can push the paper and cut it open with a piece of paper; Then sharpen it to shave, as sharp as a razor; No matter how sharp it is, you can cut your hair in the air with a knife. Even if you can cut your hair without pressure, it is very sharp. That knife is extremely sharp if it can be broken with one breath.
But in fact, the sharpness of blowing and breaking hair does not need the high hardness of the tool itself, and the steel does not need to be very good, as long as the blade thickness is as thin as possible and the blade is ground well.
Of course, to achieve the degree of hair blowing and hair breakage, the requirements for polishing are very high. This requires that the cutting angle of the blade is very small, and the mesh number of the grindstone (grindstone) to be polished for the last time is also very fine (referring to the particle size or thickness of the material, generally used for sandpaper). However, this sharpness is not of great use value, but it is easy to cut yourself. And because the blade is too thin, it will be fragile, unable to cut hard objects, and more likely to hurt and blunt the blade. Generally, polishing to such a sharp degree is mainly used to show the polishing technology.
Generally speaking, however, knives whose sharpness can reach the degree of hair blowing and hair breaking are mostly short knives, because short knives can be made thinner without worrying about breaking or deformation, while long knives need to be thicker to ensure strength. Nowadays, many knife friends play with kitchen knives, pushing the sharpness of kitchen knives to a high level.
For example, you can peel the tomato slices without holding them in your hands, and the tomatoes will become two halves when they fall on the blade; Spread the grapes cut in half on the table, cross them with a knife and cut the grapes horizontally (using the viscosity of grape juice). These seemingly dazzling sharpness are all because the kitchen knife used for slicing is very thin and can be sharpened to achieve this difficult dazzling technology.
Generally speaking, knives that can cut iron, copper and paper can still exist. After all, the tools are now made and polished at a level where there is no visible damage after iron cutting, and then they can be shaved like razors. The sharpness of the iron cutting part of the blade will inevitably decrease, and basically the other parts of the blade finish shaving.
However, if it can be ground to shave and iron without visible damage, it is enough to show that the toughness and hardness of this knife have reached a perfect balance. A sword of this degree can really be called a treasure knife in ancient times. Even with modern technology, knives that can reach this level are expensive.
But generally speaking, the knives with good quality on the market and affordable by ordinary people can also cut nails and push paper at the same time without hurting the blade. Of course, the premise of doing this is to be able to cut and grind.