For the ancients, there was really no better way to solve this annoying problem than to wipe it with oil graciously. To solve this problem once and for all, we must rely on the rapid development of modern material science in the last two hundred years.
The stainless steel we are familiar with is actually an alloy steel with a high proportion of chromium. Once the stainless steel comes into contact with the air, the doped chromium will indicate the formation of a passivation film 1-2 nanometers thick, thus isolating the further oxidation of the steel by the air; even if there is bump wear on the surface, a new oxide film will be quickly formed on the cross section. Therefore, it is not surprising that stainless steel is widely used in engineering, medical treatment and life.
In addition to stainless steel, there are many alloy steels in our lives. For example, manganese steel has achieved all-round development in terms of hardness, strength and toughness. Except for the small defects that are not convenient for secondary processing after primary casting, it almost satisfies all the ancients' fantasies about steel, which is comparable to the legendary "metaphysical iron". Manganese steel can be seen on tank armor, crawlers, excavator buckets and other parts that require long-term "hard work". Tungsten steel with high hardness can be used as high-quality high-speed cutting steel. even in the high temperature of high-speed friction, tungsten steel can still be hard and sharp, and can even be used to make armor-piercing projectiles that can kill tanks with one blow.
With the further development of science and technology. People's research on steel has also gone deep into the level of micro-crystal structure, and great progress has been made in smelting technology. there is a "powdered steel" which melts the molten steel into powder and then re-forms it through high temperature and high pressure. The internal structure of this expensive steel is highly uniform, and its amazing mechanical properties are unthinkable by the ancients.
However, no matter how "hyperevolved" steel is, it still can not get rid of the problem of excessive density. Tough steel is obviously too heavy for emerging high-speed vehicles, airplanes and even spaceships.
Titanium is a magical metal, although its chemical properties are very active, but the surface can form a passivation film similar to stainless steel, thus showing excellent stability. The titanium commonly used now is basically titanium alloy containing aluminum and other metals. Interestingly, two light metals, titanium and aluminum, were more expensive than gold because they were difficult to prepare when they were first discovered. In the modern European court, aluminum tableware was once the supreme specification beyond gold and silver, making us laugh or cry in modern times.