Stainless steel density depends on the chemical composition in general: chromium stainless steel 7.75, chromium-nickel stainless steel: 7.93, common stainless steel: for example, 304, 316 belong to chromium-nickel stainless steel. 　　
The density of carbon steel is slightly higher than ferritic and martensitic stainless steels, and slightly lower than austenitic stainless steels.
304 stainless steel is a common material in stainless steel with a density of 7.93 g/cm3, also known in the industry as 18/8 stainless steel. 304 is a general purpose stainless steel that is widely used to make equipment and machine parts that require good overall performance. In order to maintain the inherent corrosion resistance of stainless steel, the steel must contain more than 18% chromium, more than 8% nickel content. 304 stainless steel is a grade of stainless steel produced in accordance with ASTM standards.
There is a wide range of stainless steel, which can be divided into several categories according to the tissue structure at room temperature: 1.
1. austenitic (300 series, chromium-nickel): such as 304, 321, 316, 310, etc., 200 is a cheap and economical stainless steel with low nickel, also austenitic.
2. Martensitic or ferritic type (400 series): such as 430, 420, 410, etc.; austenitic is non-magnetic or weakly magnetic, martensitic or ferritic is magnetic.
Hardware products to consider his rust, hardness, processing performance, etc., 201 202 301 304 316 in the rust and heat resistance toughness are in order to enhance.
202 304 316 corresponds to the density: 7.74 7.93 7.98 ;. 316 stainless steel plate is the grade under the American standard, belongs to the stainless, heat-resistant, corrosion-resistant steel, is austenitic stainless steel, is better than 304 stainless steel, for the national standard (GB) is 0Cr17Ni12Mo2.
Commonly used stainless steel sheet is divided into two types of 201 and 304, the actual is is a different composition.
Among them, 304 stainless steel plate as stainless steel heat-resistant steel used most widely, is austenitic stainless steel. 400 series is martensitic stainless steel. 304 stainless steel is not magnetic, 400 series has magnetic. But some 304 why the sucker can suck up, because the sucker can feel the micro-magnetic is no problem (austenitic in cold processing or smelting improper may also have micro-magnetic). Relative to the 400 series, 304 nickel content is high, about 8-10%.
400 series stainless steel, this type of stainless steel internal organisation is tempered martensite, has a magnetic conductivity, can be attracted by magnets.
Austenitic stainless steel with non-absorbing magnetism, its typical representative is 304 # stainless steel, but such stainless steel can not be heat-treated with a variation to get a higher strength, non-magnetic austenitic stainless steel can not be heat-treated with a variation to get a higher strength, non-magnetic austenitic stainless steel will not be used in the manufacture of knife body, only applied to the knife handle, knife seat, etc.. So can not simply use whether magnetic to explain whether stainless steel.
The 400 series stainless steel has a lower chromium content than the 300 series stainless steel, but does not have the problem of carbon deposits as the 300 series does, and can be heat treated for use in high temperatures up to 1200F (about 393 degrees C). Increasing its hardness.
400 series of ferritic and martensitic stainless steels. Such as 410 belongs to the 400 series of stainless steel, generally speaking 304 will be better rust and corrosion resistance some special places 410 rather than 304 to be better such as some need higher hardness but do not need good rust resistance nor corrosion resistance then 410 will be much better 400 series of stainless steel can be heat-treated to increase hardness now do tableware generally 400 series for 304 is used for higher end products.
300 series – chromium-nickel austenitic stainless steel.
Type 301 – good ductility, used for forming products. Can also be rapidly hardened by mechanical processing. Good weldability. Wear resistance and fatigue strength are better than 304 stainless steel.
Type 302 – Same corrosion resistance as 304, better strength due to relatively high carbon content.
Type 303 – easier to machine than 304 by the addition of small amounts of sulphur and phosphorus.
Type 304 – common type; i.e. 18/8 stainless steel, GB grade 0Cr18Ni9.
Type 309 – has better temperature resistance than 304.
Type 316 – After 304, the second most widely used steel grade, mainly in the food industry and surgical equipment, with the addition of molybdenum to give it a special structure that resists corrosion. It is also used as a “marine steel” due to its better resistance to chloride corrosion than 304, while SS316 is commonly used in nuclear fuel recovery installations. 18/10 grade stainless steel is also usually qualified for this application.
Type 321 – similar properties to 304 except that the addition of titanium reduces the risk of corrosion in the material welds.
400 series – ferritic and martensitic stainless steels.
Type 408 – good heat resistance, weak corrosion resistance, 11% Cr, 8% Ni.
Type 409 – the cheapest type (British and American), usually used for automotive exhausts, is a ferritic stainless steel (chromium steel).
Type 410 – Martensitic (high strength chromium steel), good wear resistance, poor corrosion resistance.
Type 416 – Sulphur is added to improve the machinability of the material.
Type 420 – “Cutting tool grade” martensitic steel, similar to Brinell high chromium steel, the earliest stainless steel. Also used for surgical knives and can be made very bright.
Type 430 – Ferritic stainless steel, used for decorative purposes, e.g. for car accessories. Good formability, but less resistant to temperature and corrosion.
Type 440 – High-strength cutting tool steel with a slightly higher carbon content, high yield strength after appropriate heat treatment and hardness up to 58 HRC, among the hardest stainless steels. The most common application is in “razor blades”. There are three common types: 440A, 440B, 440C and also 440F (easy to machine type).
When the surface of the stainless steel tube brown rust spots (points), people are surprised: that “stainless steel is not rust, rust is not stainless steel, may be a problem with the quality of steel”. In fact, this is a one-sided misconception of 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 steel, but also in the medium containing acid, alkali, salt corrosion resistance – that is, corrosion resistance. But the size of its corrosion resistance is with its steel itself chemical composition, plus mutual state, the use of conditions and environmental media type and change. Such as 304 steel pipe, in a dry and clean atmosphere, there is absolutely excellent corrosion resistance, but it will be moved to the seaside area, in the sea spray containing a large amount of salt, will soon rust; and 316 steel pipe is good performance. Therefore, not any kind of stainless steel, in any environment can be resistant to corrosion, not rust.
Stainless steel is formed on its surface by a layer of very thin and strong and fine stable chromium-rich oxide film (protective film), to prevent the continued penetration of oxygen atoms, continued oxidation, and the ability to obtain the resistance to rust and corrosion. Once this film has been continuously damaged for some reason, oxygen atoms in the air or liquid will continue to infiltrate or iron atoms in the metal will continue to precipitate out, forming loose iron oxide, and the metal surface will be subject to continuous rusting. This surface film is damaged in many forms, the following are common in daily life.
1. stainless steel surface containing other metal elements of the dust or foreign metal particles of adhesion, in the humid air, adhesion and stainless steel between the condensation, the two will be connected into a microcell, triggering an electrochemical reaction, the protective film is damaged, called electrochemical corrosion.
2. Stainless steel surface adhesion of organic matter juice (such as squash, noodle soup, spit, etc.), in the case of water oxygen, constitute organic acids, a long time then organic acid corrosion of the metal surface.
3. Stainless steel surface adhesion containing acid, alkali, salt substances (such as decorative walls of alkaline water, lime water spray), causing local corrosion.
4. In the polluted air (such as containing a large number of sulfides, carbon dioxide, nitrogen oxide atmosphere), encountering condensation, the formation of sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.
All of the above can cause the destruction of stainless steel surface protective film caused by rust corrosion. Therefore, to ensure that the metal surface is permanently bright and not rusted, we recommend that
1. The decorative stainless steel surface must be cleaned and scrubbed frequently to remove adherents and eliminate external factors that trigger retouching.
2. Beach areas to use 316 stainless steel, 316 material can resist seawater corrosion.
3. Some stainless steel tubes on the market chemical composition can not meet the corresponding national standards, not up to 304 material requirements. Therefore, it will also cause rust, which requires users to carefully select the products of reputable manufacturers.
