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Austenite 304: ordinary people in stainless steel

  • Author:E-BON
  • Source:E-BON
  • Release on :2018-07-17
Austenite, a microstructure of steel, is usually a non-magnetic solid solution in which a small amount of carbon is dissolved in Fe. The name of austenite is from the British metallurgist Robert Austin. Austenitic stainless steel was introduced in Germany in 1913 and has always played the most important role in stainless steel. Its production and usage account for about 70% of total stainless steel production and consumption. The steel number is also the most, so in fact, most of the stainless steel you often find on the day is austenitic stainless steel.

Lei Jun did not say anything wrong, strong anti-rust, corrosion resistance, and excellent plasticity and toughness, convenient stamping... These are indeed the characteristics of austenitic stainless steel, but it is almost the basic characteristics of all stainless steel. 304 stainless steel is a very common stainless steel, also known as 18/8 stainless steel. This 18/8 is by composition, 18% chromium, 8% nickel.

This kind of steel has better corrosion resistance, heat resistance, low temperature strength and mechanical properties; good hot workability such as stamping and bending, and no heat treatment hardening phenomenon. Corrosion resistance in the atmosphere is also good, of course, the most important thing is that the price is cheap. We use ordinary spoons, kitchen stainless steel countertops, water basins, mop poles, drying racks... all of this material.

However, this material will rust in places where acid and alkali corrosion is severe, so a little more important places (such as Western cutlery and spoons used in our homes) will use more expensive 316 stainless steel, which is 18/10 stainless steel. More than 10%. I don't know if the next generation of millet phones will use 316 stainless steel.

Although this type of stainless steel is very common in China, the name "304 stainless steel" comes from the United States. The official name for 304 stainless steel in Japan is "SUS304". Among the common marking methods on the market are 06Cr19Ni10, S30408 ??and SUS304. Among them, 06Cr19Ni10 generally represents the national standard production, S30408 ??generally represents the ASTM standard production, and SUS 304 indicates the Japanese standard production.

As far as the metal materials of mobile phones are concerned, aluminum-magnesium alloys and stainless steels are common. Apple used stainless steel early, and later changed aluminum-magnesium alloy. HTC has also been using aluminum-magnesium alloys. The advantages of aluminum-magnesium alloy are light, high specific strength (strength to weight ratio), and good heat dissipation. The disadvantage is that the processing is more troublesome, the surface treatment is troublesome, and the price is expensive. For the first time, Xiaomi made a metal body, and chose 304 stainless steel, which is cheaper and has lower processing cost, is a more pragmatic decision.

Meizu CEO Huang Zhang also retaliated against Lei Jun in Weibo, indicating that Meizu used 304 stainless steel as early as the Meizu M6 in 2007. The middle frame of MX, MX2 and MX3 mobile phones also used 304 stainless steel as the skeleton. However, Meizu also recognizes that 304 stainless steel is not wear-resistant, and the surface is easy to leave scratches, so most of them are made into a matte surface during use.

In general, stainless steel can be divided into four categories, ferritic stainless steel, austenitic stainless steel, austenitic-ferritic stainless steel and martensitic stainless steel, of which martensite has the highest strength.

In austenitic stainless steel, carbon dissolves into a face-centered cubic structure (iron crystals, iron atoms are distributed at the center of the eight vertices and six faces of the cube, and iron atoms in the iron crystals of stainless steel are replaced by some other metal atoms) The solid solution formed in iron is called austenite. The carbon content in austenite can reach 2%, soft and tough, and plastic.

Austenite is a kind of solid solution with good plasticity and low strength and has certain toughness. Does not have ferromagnetism. Therefore, one of the ways to distinguish austenitic stainless steel tools (common 18-8 stainless steel) is to use a magnet to see if the tool is magnetic. The iron that burned red when the ancient blacksmith hit the iron was in the austenitic state.

As a metal material, the thermal conductivity of austenitic stainless steel is far less than that of plastic. If it is used as a mobile phone back shell, its hot hand capacity will far exceed that of plastic back shell. If the mobile phone manufacturer does not control the heat, then the austenitic 304 stainless steel will Have the opportunity to be the hottest mobile phone ever. However, one side is performance, the other side is heat dissipation, how to choose?

How to get austenitic steel? Austenite is the structure of ordinary steel at high temperatures, and its existence has a certain temperature and composition range. In addition to carbon in alloy steel, other alloying elements are also soluble in austenite and expand or reduce the temperature and composition range of the austenite stabilizing zone. For example, the addition of manganese and nickel lowers the austenite critical transition temperature below room temperature, allowing the steel to maintain an austenitic structure at room temperature, the so-called austenitic steel.

Austenitic 304 stainless steel, in which "austenite" is said to be metallographic, metallographic is the structural structure of various elements inside the metal, the metallographic phase is different, the physical and chemical properties of the metal will be different, the austenite is removed, and the horse is removed. Different metallographic phases, such as austenite, 304 are just grades, indicating the composition and content of non-ferrous elements in the stainless steel.

As for the price of austenitic 304 stainless steel, the current market price is 18,000 yuan a ton. 18 dollars 1 kg, 9 dollars 1 kg. At present, if scrap is collected, scrap iron (not iron) is 8 yuan and 1 kg. To put it this way... not counting post-processing, the cost of this stainless steel is slightly higher than the cost of selling scrap iron.

It should be noted that although it is "stainless steel", the corrosion resistance of austenitic 304 stainless steel(Stainless Steel Housewares supplier) in chloride ion solution is not strong enough, and the chloride ion solution will destroy the oxide film on the surface of 304 stainless steel. The principle of stainless steel stainless steel is actually similar to the principle of aluminum stainless steel. It is protected by a layer of oxide film on the surface, and the film is naturally rusted.