Knowledge of stainless steel
Stainless steel (Stainless Steel) refers to the resistance to air, steam, water and other weak corrosive media and acid, alkali, salt and other chemical corrosion medium corrosion of steel, also known as stainless steel. Practical applications, often weak corrosive medium corrosion of steel known as stainless steel, and corrosion resistance of chemical corrosion of steel known as acid-resistant steel. Due to the difference in the chemical composition of the two, the former is not necessarily resistant to chemical corrosion, while the latter are generally have a stainless. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.
Stainless steel often according to the organizational state is divided into: martensitic steel, ferritic steel, austenitic steel. In addition, according to the composition is divided into: chrome stainless steel, chrome nickel stainless steel and chromium manganese nitrogen stainless steel.
1, ferritic stainless steel: chromium 12% to 30%. Its corrosion resistance, toughness and weldability with the increase in chromium content increased resistance to chloride stress corrosion resistance is better than other types of stainless steel.
Belongs to this category are Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and so on. Ferritic stainless steel because of high chromium content, corrosion resistance and oxidation resistance are better, but the mechanical properties and process performance is poor, and more for the resistance of acid structure and for the use of anti-oxidation steel. This kind of steel can resist the corrosion of atmospheric, nitric acid and brine solution, and has high temperature oxidation resistance, thermal expansion coefficient is small, for nitric acid and food factory equipment, can also be made in high temperature work parts, such as gas turbine parts The
2, austenitic stainless steel: chromium greater than 18%, also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Comprehensive performance is good, can withstand a variety of media corrosion. Austenitic stainless steel commonly used grades are 1Cr18Ni9,0Cr19Ni9 and so on. 0Cr19Ni9 steel wC <0.08%, steel marked as "0". This kind of steel contains a lot of Ni and Cr, so that steel at room temperature was austenitic state. This type of steel has good plasticity, toughness, weldability and corrosion resistance. It is good for corrosion resistance in oxidizing and reducing media. It is used to make acid resistant equipment such as corrosion resistant containers and equipment lining, Nitric acid equipment parts and so on. Austenitic stainless steel is generally treated with solution, that is, the steel heated to 1050 ~ 1150 ℃, and then water-cooled, in order to obtain single-phase austenite.
3, austenitic - ferrite duplex stainless steel: both austenitic and ferritic stainless steel advantages, and has a super plasticity.
Austenitic and ferrite organizations account for about half of the stainless steel. In the case of low C, Cr content of 18% to 28%, Ni content of 3% to 10%. Some steel also contains Mo, Cu, Si, Nb, Ti, N and other alloying elements. The steel has the characteristics of austenitic and ferritic stainless steel, compared with the ferrite, plasticity, higher toughness, no room temperature brittleness, resistance to intergranular corrosion and welding performance are significantly improved, while also maintaining iron Qualified stainless steel 475 ℃ brittleness and high thermal conductivity, with super plasticity and so on. Compared with the austenitic stainless steel, high strength and resistance to intergranular corrosion and resistance to chloride stress corrosion has improved significantly. Duplex stainless steel has excellent resistance to pitting corrosion resistance, but also a section of nickel stainless steel.
4, martensitic stainless steel: high strength, but poor plasticity and weldability.
Martensitic stainless steel commonly used grades are 1Cr13, 3Cr13, etc., because of high carbon content, it has a high strength, hardness and wear resistance, but slightly less corrosion resistance, for high mechanical properties, corrosion resistance Requirements of some general parts, such as springs, steam turbine blades, water pressure valves and so on. This type of steel is used after quenching and tempering.
Stainless steel effect
Stainless steel does not produce corrosion, pitting, corrosion or wear. Stainless steel or building materials are used in the highest strength material. Because stainless steel has good corrosion resistance, it allows the structural parts to permanently maintain the integrity of the engineering design. Chromium-containing stainless steel also combines mechanical strength and high elongation in one, easy to manufacture parts, to meet the needs of architects and structural designers
Most of the use requirements are long-term to maintain the original appearance of the building. In determining the type of stainless steel to be selected, the main consideration is the required aesthetic standards, the corrosiveness of the atmosphere and the clean-up system to be used.
However, other applications are increasingly seeking structural integrity or impermeability. For example, the roof and side walls of industrial buildings. In these applications, the owner of the construction costs may be more important than the aesthetic, the surface is not very clean .
In the dry indoor environment using 304 stainless steel effect is quite good. However, in rural areas and cities in order to keep its appearance outdoors, you need to regularly clean. In heavily polluted industrial areas and coastal areas, the surface will be very dirty, and even rust. But to get the aesthetic effect of outdoor environment, you need to use nickel-containing stainless steel. Therefore, 304 stainless steel is widely used in curtain walls, side walls, roofs and other construction purposes, but in the serious erosion of industrial or marine atmosphere, the best use of 316 stainless steel.
Now, people have fully realized the advantages of using stainless steel in structural applications. Several design guidelines include 304 and 316 stainless steel. Because the "two-phase" stainless steel 2205 has a good resistance to atmospheric corrosion and high tensile strength and elastic strength of the integration, so the European guidelines also include this steel.
In fact, stainless steel is manufactured in a fully standard metal shape and size, and there are many special shapes. The most commonly used products are made of sheet and strip, and are also produced with plates for special products such as hot rolled structural steels and extruded structural steels. But also round, oval, square, rectangular and hexagonal welded pipe or seamless steel pipe and other forms of products, including profiles, bars, wire and castings.
As will be discussed later, in order to meet the aesthetic requirements of architects, has developed a variety of different commercial surface processing. For example, the surface may be highly reflective or dull; it may be glossy, polished or embossed; it may be colored, colored, electroplated or etched on a stainless steel surface, To meet the design of the appearance of the various requirements.
It is easy to keep the surface state. You can remove dust by occasional rinsing. Due to good corrosion resistance, it is also possible to easily remove surface contamination or other similar surface contamination.
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