There are many types of stainless steel, which are usually divided into several categories according to their structure:
1. Austenitic type (300 series, chrome-nickel): such as 304, 321, 316, 310, etc., 200 is a low-nickel cheap economic stainless steel, also austenite;
2. Martensite or ferrite type (400 series): such as 430, 420, 410, etc.; austenite type is non-magnetic or weak magnetic, martensite or ferrite is magnetic.
Hardware products should consider his rust, hardness, processing properties, etc., 201, 202, 301, 304, 316 in rust and heat resistance toughness are increased.
202 304 316 corresponds to a density of 7.74 7.93 7.98. 316 stainless steel plate is the grade under the American standard. It belongs to stainless steel, heat-resistant and corrosion-resistant steel. It is austenitic stainless steel, which is better than 304 stainless steel. For the national standard (GB), it is 0Cr17Ni12Mo2.
Commonly used stainless steel sheets are available in 201 and 304 models. Among them, 304 stainless steel plate is the most widely used as stainless steel heat-resistant steel, and is austenitic stainless steel. The 400 series is martensitic stainless steel. 304 stainless steel is not magnetic, and the 400 series is magnetic. But some 304 why the magnet can be sucked up, because the magnet can feel the micro-magnetic is no problem (the austenite may have micro-magnetic in cold processing or improper smelting). Compared with the 400 series, 304 nickel content is high, about 8-10%.
400 series stainless steel, this kind of stainless steel internal structure is tempered martensite, with magnetic permeability, can be attracted by magnets. Austenitic stainless steel has non-magnetic properties, and its typical representative is 304# stainless steel, but such stainless steel can not obtain high strength by heat treatment, non-magnetic austenitic stainless steel can not be improved by heat treatment. The strength, non-magnetic austenitic stainless steel will not be used to make the body, only for the shank, knife seat and so on. Therefore, it is not easy to use whether or not there is magnetism to indicate whether it is stainless steel.
The 400 series stainless steel has a lower chromium content than the 300 series stainless steel, but does not have carbon deposition problems like the 300 series, and can be heat treated for use in high temperature environments up to 1200F (about 393 degrees Celsius). Increase its hardness.
400 series of ferritic and martensitic stainless steel. For example, 410 is a kind of 400 series stainless steel. Generally speaking, 304 will be better, and some special places of rust and corrosion resistance are better than 304. For example, some need higher hardness but do not need good anti-rust ability, and do not need corrosion resistance, then 410 will be much better. The 400 series of stainless steel can be hardened by heat treatment. Now the tableware is generally used for the lower end of the 400 series, and the 304 is used for the higher end products.
300 Series - Chromium - Nickel Austenitic Stainless Steel
Model 301—Good ductility for molded products. Can also be processed by machining
Speed hardening. Good weldability. Wear resistance and fatigue strength are better than 304 stainless steel.
Model 302—Corrosion resistance is the same as 304, because the carbon content is relatively high and the strength is better.
Model 303—It is easier to cut than 304 by adding a small amount of sulfur and phosphorus.
Model 304—Universal model; ie 18/8 stainless steel. The GB grade is 0Cr18Ni9.
Model 309 - Better temperature resistance than 304.
Model 316—After 304, the second most widely used steel grade is used primarily in the food industry and surgical equipment, adding molybdenum to give it a special structure that resists corrosion. It is also used as "ship steel" because it has better resistance to chloride corrosion than 304. SS316 is commonly used in nuclear fuel recovery units. 18/10 grade stainless steel also generally meets this application level.
Model 321—Besides the addition of titanium, which reduces the risk of weld corrosion of the material, other properties are similar to 304.
400 Series - Ferritic and Martensitic Stainless Steel
Model 408—Good heat resistance, weak corrosion resistance, 11% Cr, 8% Ni.
Model 409—The cheapest model (British and American), usually used as a car exhaust pipe, is a ferritic stainless steel (chrome steel).
Model 410—Martensite (high-strength chrome steel) with good wear resistance and poor corrosion resistance.
Model 416—Addition of sulfur improves the processing properties of the material.
Model 420—“cutting grade” martensitic steel, similar to Brinell high-chromium steel. This earliest stainless steel is also used in surgical knives and can be very bright.
Model 430 - Ferritic stainless steel, for decoration, for example for automotive accessories. Good formability, but poor temperature resistance and corrosion resistance.
Model 440—High-strength cutting tool steel with slightly higher carbon content. After proper heat treatment, it can obtain higher yield strength and hardness can reach HRC58, which is among the hardest stainless steel. The most common application example is the "razor blade." There are three commonly used models: 440A, 440B, 440C, and 440F (easy processing type).
When brown rust spots (dot) appeared on the surface of the stainless steel tube, people were amazed: "Stainless steel is not rusted, rust is not stainless steel, and there may be problems with steel." In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel will also rust under certain conditions.
Stainless steel has the ability to resist atmospheric oxidation - that is, stainless, and also has the ability to resist corrosion in medium containing acid, alkali, and salt - that is, corrosion resistance. However, the degree of corrosion resistance varies with the chemical composition of the steel itself, the state of addition, the conditions of use, and the type of environmental medium. For example, 304 steel pipe has absolutely excellent rust resistance in a dry and clean atmosphere, but it is moved to the coastal area, and it will soon rust in sea fog containing a lot of salt; while 316 steel pipe will perform. good. Therefore, it is not any kind of stainless steel, it can resist corrosion and rust in any environment.
Stainless steel is a very thin and strong and stable chromium-rich oxide film (protective film) formed on the surface to prevent the oxygen atoms from continuing to infiltrate and continue to oxidize, thereby obtaining the ability to resist rust. Once for some reason, the film is continually destroyed, oxygen atoms in the air or liquid will continue to infiltrate or iron atoms in the metal will continue to separate out, forming loose iron oxide, and the metal surface will be continuously rusted. There are many forms of such surface film damage, and the following are common in daily life:
1. The surface of the stainless steel contains dust or other metal particles attached to other metal elements. In humid air, the condensed water between the attached material and the stainless steel connects the two into a micro battery, triggering an electrochemical reaction. The protective film is destroyed, which is called electrochemical corrosion.
2. The surface of the stainless steel adheres to the organic juice (such as melon, noodle soup, glutinous rice, etc.), and in the case of water and oxygen, constitutes an organic acid, and the organic acid corrodes the metal surface for a long time.
3. The surface of the stainless steel adheres to acid, alkali and salt substances (such as alkali water and lime water splashing on the wall), causing local corrosion.
4. In polluted air (such as the atmosphere containing a large amount of sulfide, carbon oxide, nitrogen oxide), in the case of condensed water, sulfuric acid, nitric acid, acetic acid liquid point is formed, causing chemical corrosion.
All of the above can cause the corrosion of the stainless steel surface protective film to cause rust.
To ensure that the metal surface is permanently bright and not rusted, we recommend:
1. The surface of the decorative stainless steel must be cleaned and scrubbed frequently to remove the deposits and eliminate external factors that cause modification.
2. The 316 material should be used in the coastal area, and the 316 material can resist seawater corrosion.
3. Some stainless steel chemical components on the market cannot meet the corresponding national standards and cannot meet the requirements of 304 materials. Therefore, it will also cause rust, which requires the user to carefully select the products of reputable manufacturers.
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