Stainless steel is steel with a chromium content of at least 10.5% and a maximum carbon content of no more than 1.2%, as specified in GB/T20878-2007.
The corrosion resistance of stainless steel decreases with the increase of carbon content. Therefore, the carbon content of most stainless steel is low, with a maximum of no more than 1.2%. The ωc (carbon content) of some steels is even lower than 0.03% (such as 00Cr12 ). The main alloying element in stainless steel is Cr (chromium). Only when the Cr content reaches a certain value, the steel has corrosion resistance. Therefore, stainless steel generally has a Cr (chromium) content of at least 10.5%. Stainless steel also contains Ni, Ti, Mn, N, Nb, Mo, Si, Cu and other elements.
Stainless steel is a type of steel that is resistant to weak corrosive media such as air, steam, water, etc. or is stainless. Steel types that are resistant to chemical corrosive media (chemical corrosion such as acids, alkali, salts, etc.) are called acid-resistant steel.
Due to the difference in chemical composition between the two, their corrosion resistance is different. Ordinary stainless steel is generally not resistant to corrosion by chemical media, while acid-resistant steel is generally stainless. “Stainless steel” workpieces not only refer to a kind of stainless steel, but represent more than one hundred industrial stainless steels, so the stainless steels developed have good performance in their specific application fields. There are usually only six types of steel relevant to building construction applications. They all contain 17 to 22% chromium, and the better steel types also contain nickel. Adding molybdenum can further improve atmospheric corrosion, especially corrosion resistance in chloride-containing atmospheres.
In terms of hardness, stainless steel is harder than ordinary aluminum alloy, and the cost of stainless steel is higher than that of aluminum alloy.
Main type:
Stainless steel is often divided into martensitic steel, ferritic steel, austenitic steel, austenitic-ferritic (duplex) stainless steel and precipitation hardening stainless steel according to the organizational state. In addition, it can be divided according to its composition: chromium stainless steel, chromium-nickel stainless steel, chromium-manganese-nitrogen stainless steel, etc. There is also special stainless steel for pressure vessels “GB24511_2009_Stainless steel plates and steel strips for pressure-bearing equipment”.
According to the composition, it can be divided into Cr series (400 series), Cr-Ni series (300 series), Cr-Mn-Ni (200 series), heat-resistant chromium alloy steel (500 series) and precipitation hardening series (600 series).
200 Series: Chromium-Manganese-Nickel
201, 202, etc.: Nickel is replaced by manganese, which has poor corrosion resistance and is widely used as a cheap substitute for 300 series in China
300 Series: Chromium-Nickel Austenitic Stainless Steel
304: Universal model; i.e. 18/8 stainless steel. Products such as: corrosion-resistant containers, tableware, furniture, railings, medical equipment. The standard composition is 18% chromium plus 8% nickel. It is a stainless steel that is non-magnetic and cannot change its metallographic structure by heat treatment. The GB grade is 06Cr19Ni10.
304 L: The same characteristics as 304, but low carbon so it is more corrosion resistant, easy to heat treatment, but poor in mechanical properties, suitable for welding and products that are not easy to heat treatment.
309 S: It has a lot of chromium and nickel, so it has good heat resistance and oxidation resistance. Products such as: heat exchangers, boiler components, and jet engines.
310: Excellent high temperature oxidation resistance, maximum use temperature 1200℃.
316: After 304, the second most widely used steel grade is mainly used in the food industry, watch accessories, pharmaceutical industry and surgical equipment. Adding molybdenum element makes it obtain a special corrosion-resistant structure. Because it has better resistance to chloride corrosion than 304, it is also used as “marine steel”. SS316 is usually used in nuclear fuel recovery devices. Grade 18/10 stainless steel is also generally suitable for this application level.
316 L: Low carbon, so it is more corrosion-resistant and easy to heat treatment. Products such as: chemical processing equipment, nuclear power generators, and refrigerant storage tanks.
321: In addition to reducing the risk of material weld corrosion due to the addition of titanium, other properties are similar to 304.
400 series: ferritic and martensitic stainless steel, no manganese, can replace 304 stainless steel to a certain extent.
430: Ferritic stainless steel, for decoration, such as for automotive accessories. Good formability, but poor temperature resistance and corrosion resistance.
500 Series: Heat-resistant chromium alloy steel.
600 Series: Martensitic precipitation hardening stainless steel.
Stainless steel surface processing grade
-Original surface: NO.1 The surface subjected to heat treatment and pickling treatment after hot rolling. Generally used for cold rolled materials.
-Blunt surface: NO.2D, which has been heat treated and pickled after cold rolling. The material is soft and the surface is silvery white. It is used for deep stamping processing.
-Matt surface: NO.2B After cold rolling, it is heat treated, pickled, and then finished rolled to make the surface moderately bright.
-Coarse grit NO.3 is a product ground with No. 100-120 grinding belt. Has better gloss and discontinuous rough lines
-HAIRLINE: HLNO.4 is a product with a grinding pattern produced by continuous grinding with a polishing belt of appropriate particle size. It is mainly used for architectural decoration.
-Bright surface: BA is a product obtained by cold rolling, bright annealing and smoothing. The surface has good gloss and high reflectivity, like a mirror.
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