Definition of stainless steel
Stainless steel is a kind of high-alloy steel that can resist corrosion. It has a beautiful surface and does not need to undergo surface treatment such as plating or painting. Therefore, many machinery factories often do not do any paint treatment in order to show that they are stainless steel. The so-called black material is the name of general steel), it must be treated with rust prevention.
Simple classification of stainless steel
Stainless steel can be roughly divided into three categories: 200 series, 300 series and 400 series, among which 300 series is the most commonly used, 200 series and 400 series are substitutes for 300 series to a certain extent, and 400 series is not called stainless steel strictly speaking. Called stainless iron, because it does not contain nickel, it can be attracted by a magnet. The 200 series and 300 series have nickel, so they are not magnetic and cannot be absorbed by iron.
304 is the most common variety in the 300 series, so generally the price trend of the entire stainless steel can be judged from the price change of 304. The 200 series contains less nickel, the 400 series does not contain nickel, and the 300 series contains the most nickel. Therefore, the 300 series is most affected by the nickel price.
The 300 series can be simply divided into 304, 304L, 316, 316L, 321, 309S, 310S, etc. The distinction is based on the content of various metal elements, and the characteristics of stainless steel with different content are different. The difference between 304 and 304L is the carbon (C) content is different. The one with L means low carbon content, which is also called low carbon. The difference between 316 and 316L is the same.
Type classification of stainless steel
Stainless steel can be divided into five categories: coils, plates, profiles, steel pipes and parts, the most important being coils and plates. Profiles are materials of various shapes made of plates, including angle steel, flat steel, I-beam, and channel steel. Steel pipe mainly refers to seamless steel pipe, and the opposite of seamless steel pipe is welded pipe. The difference is whether it is formed at one time. Parts mainly refer to elbows and flanges and other small things.
The coil and the plate are actually the same, and the factory form is different. The coil is rolled one by one, and the plate is one by one. If the plate is shipped from the factory, it is also called the original plate. It is generally a thick plate because it is very thick. If it is, it cannot be rolled, generally it cannot be rolled if it is more than 16 mm.
There are coils and plates. In many cases they are plates. The prices of coils and plates are also different. If it is a purchased coil, it is calculated according to the actual weight. Therefore, the price is high. The plate is calculated according to the theory, and the price is low. The reason is that there is a drop, such as 10 mm thick may actually be 9.6mm, there will be a price difference in the middle.
Stainless steel plates are divided into hot rolling and cold rolling according to the different rolling processes of the rolling mill (the rolling mill is the machine name of the rolled plate). The hot rolling is usually marked as NO.1, and the cold rolling is marked as 2B or BA (BA is better than 2B. To be bright, close to the mirror, the best is the mirror surface, the mirror surface is not in stock, all need to be processed), for example, 304 is often a purchased board, which means that the roll must be flattened by a machine in the form of a flattening machine. This kind of machine is a flattening machine. It can be opened to different lengths through the flattening machine. If it is not a regular length, it is called a fixed opening, which means a fixed opening size, because customers often propose different length requirements according to actual needs. At this time, the roll becomes important. The conventional board cannot meet the requirements.
Domestic cold rolling is generally below 3 mm, and hot rolling is generally above 3 mm. The thickness of 3 mm is both hot rolled and cold rolled, but the thickness of imported cold rolled plates can reach 4 mm or even 6 mm. Hot-rolled plates of 3 mm to 12 mm are called medium plates, and those of 12 mm or more are called thick plates, which can be thicker than 120 mm, and are called hot-rolled medium-thick plates, while cold-rolled plates are cold-rolled sheets.
Characteristics and uses of main stainless steel types
As a widely used steel, 304 has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, good hot workability such as stamping and bending, no heat treatment hardening phenomenon, non-magnetic, and the use temperature is minus 193 degrees to positive 800 degrees.
Uses: tableware, kitchen utensils, water heaters, boilers, auto parts, medical equipment, food machinery, wine storage, pressure vessels (chemical machinery, chemical equipment).
As a low-carbon 304 steel, 304L has the same corrosion resistance as 304 under normal conditions, but after welding and stress relief, it has good intergranular corrosion resistance and can maintain good intergranular corrosion without heat treatment. Corrosion resistance, generally used at 400 degrees.
Uses: petrochemical industry, building materials.
321 adds Ti element to 304 steel to prevent intergranular corrosion. It is suitable for plus 430 to 900 degrees below, non-magnetic.
Application: For products that do not undergo heat treatment after welding, such as automobile exhaust, heat exchangers, containers, etc., due to the addition of Ti element, they are not suitable for making food processing equipment.
316 has low carbon and added Mo element, so its corrosion resistance, atmospheric corrosion resistance and high temperature strength performance are particularly good. It can be used under harsh conditions and is suitable for use below 900 degrees. It is non-magnetic.
Uses: equipment used in seawater, chemical, dye, paper, acetic acid, fertilizer and other production equipment, food industry and coastal facilities, products with special requirements for resisting intracrystalline corrosion.
The two materials of 309S/310S have relatively high content of nickel and chromium. At the same time, the content of Si is increased to make it have high temperature resistance and corrosion resistance. Among them, 309S can withstand repeated heating below 980, and the use temperature of 310S reaches 1200 degrees, continuous use The temperature can be 1150 degrees, non-magnetic.
Uses: Suitable for key parts such as high temperature electric furnace equipment, drying equipment, furnace materials, aviation, petrochemical, electric power, etc.
The 200 series is similar to 304, which is cheap and economical.
Uses: food processing utensils, kitchen equipment, food processing equipment, filters, milk tanks, durable consumer goods, washing machine parts, water heaters, steel furniture, building decoration, decoration. In terms of fatigue resistance, 201 has a higher hardness and not as tough as 304, but 304 has better fatigue resistance.
