Why is the track of the train not stainless steel, but rusty iron?
Rail track is short for railway track, made of steel with high hardness and high toughness, because manganese steel is hard and wear-resistant and has a certain impact toughness to meet the conditions of manufacturing rail.
The density of manganese rail is very high. When the oxidation rust film is formed on the surface, it will form a protective effect on the interior and will not affect the use.
Iron and steel are distinguished by their carbon content. The iron carbon alloy with carbon content less than 2% is steel, and the one with carbon content more than 2% is pig iron.
From a metallurgical point of view, there is no such thing as stainless iron. Stainless steel is also a kind of steel, because steel has toughness, elasticity and rigidity, in terms of rust, rust is not corrosion resistant. The main element determining the corrosion resistance of stainless steel is chromium.
When the chromium content is more than 10.5%, the steel will not rust. At this time, the oxidation of chromium and corrosive medium forms an oxide film on the surface, which can prevent the basic further corrosion.
The cost of making iron is much lower than that of stainless steel. In the design and manufacture of some materials with short service life, and the iron quality can meet the requirements of material use, of course, iron will be used.
Rail is a common saying, it is a rail, in order to improve the compressive and wear resistance strength, manganese is usually added. Chromium and molybdenum are usually added to stainless steel for oxidation resistance. The strength, wear resistance, flexibility, plasticity, corrosion resistance, etc. should be considered comprehensively when using the rail, but the high strength and wear resistance is the first choice, and the stainless steel can not meet the requirements, so it will not be used.
The reason why stainless steel can’t be used is that it is easy to be damaged under thermal expansion and cold contraction due to insufficient resistance. Stainless steel will be easily damaged under the daily wind, rain and exposure. Although the high-speed rail looks rusty, there is only a layer of rust on the surface, and the interior is still intact.
In addition, the density of manganese rail is very high, when the surface of oxidation rust film is formed, it will form a protective effect on the internal, and will not affect the use.
First of all, from the technical point of view: most people think that stainless steel is not rusty, but the actual situation is that stainless steel, like other alloys, is rusty, but after stainless steel rusts, the color of the surface oxide film (rust) is the appearance color of stainless steel, and this layer of oxide film is relatively dense, which can protect the internal structure from further oxidation and rust.
However, the oxide film can still be corroded under certain conditions, especially in humid acid environment.
Therefore, stainless steel can not be used in many cases. There are many kinds of stainless steel, and the hardness of stainless steel (especially austenitic stainless steel) is relatively low. For example, it is difficult to sharpen when it is used to make knives, and even if it sharpens, it is easy to become blunt. People with experience know that bright stainless steel plate is very easy to be scratched because of its soft texture.
Therefore, technically speaking, stainless steel is not rusty, but the color after rust is similar to that before rust; its performance is not suitable for all places, so it can not be generalized to use stainless steel instead of other materials.
In terms of resources, nickel and chromium used in stainless steel are relatively scarce minerals, especially nickel. Useful and easy-to-use things always need to be used in key places, and can not be used and wasted at will.
In terms of cost, we will consider the cost of materials, parts and machines. The price of stainless steel is not only a little bit higher than that of ordinary steel, aluminum, magnesium aluminum alloy, plastic and other materials, but several times higher. As long as cheap materials can meet the requirements, who will use expensive materials?
In addition, even if other materials are rusty and corrosion-resistant, there are many kinds of surface treatment technologies that can protect materials from corrosion, such as painting, powder spraying, electroplating, electrophoresis, surface oxidation, surface chemical treatment (nitriding, cyaniding, etc.) can improve the surface corrosion of materials. So it’s not necessarily that rusty materials can’t be used in places with corrosion.
Generally speaking, stainless steel can not be used to replace all other materials. Only after fully considering the function, material performance, working environment, cost, processing performance and possibility of the parts, can a suitable material be selected for the parts. It can not be said that all stainless steel materials should be used instead. In the major of mechanics and materials, there are special materials courses to introduce how to select materials and material performance.
Train track is the established operation track of the train, and it is an indispensable mode of railway technology at present. We should have noticed that basically all the railway tracks are rusty, even the newly built railway tracks are like this. The life of rusty iron products will be shortened, not to mention, they will become very fragile.
Source: China Flanges Supplier: www.epowermetals.com
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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