Technical parameters of stainless steel

Steel symbol and representation
① chemical element with the international symbols and symbols to represent the country’s chemical composition, using the Arabic alphabet to represent the content:
Such as: China, Russia 12CrNi3
② with a fixed number of digits to represent the steel type series or digital; such as: USA, Japan, 300 series, 400 series, 200 series;
③ composition of the Latin alphabet and the order number, saying only that purpose.
China’s numbering rules
① using element symbols
② use Hanyu Pinyin, open-hearth steel: P, boiling steel: F, killed steel: B, Group A steel: A, T8: Special 8, GCr15: Ball
◆ alloy steel, spring steel, such as: 20CrMnTi 60SiMn, (with a very few that C content)
stainless steel, alloy tool steel (with a few thousandths C content), such as: 1Cr18Ni9 thousandth (ie, 0.1% C), stainless C≤0.08% as 0Cr18Ni9, ultra-low carbon C≤0.03% as 00Cr17Ni13Mo
International Stainless Steel labeling method
American Iron and Steel Institute with three digits to indicate a variety of standard grade stainless steel malleable. Among them:
① austenitic stainless steel 200 and 300 series of numerals, for example, some of the more common austenitic stainless steel is 201, 304, 316 and 310 marks.
② ferritic and martensitic stainless steel 400 series is represented by a number.
③ ferritic stainless steel is marked 430 and 446, 410, 420, and 440C martensitic stainless steel is marked.
④ duplex (austenitic – ferritic), stainless steel, precipitation hardening stainless steel and high alloy iron content of less than 50% usually uses proprietary name or trademark name.
4). Standard classification and grading
4-1 of Classification:
National Standard GB ② ① industry standards YB ③ ④ local standards enterprise standard Q / CB
4-2 Categories:
① ② Packaging Standard Products Standard Method Standard ③ ④ basic standards
4-3 standard level (three points):
Y levels: international advanced level class I: Class H common international level: the advanced level
4-4 GB
GB1220-84 stainless steel rods (I grade) GB4241-84 stainless steel plate welded Park (H level)
GB4356-84 stainless steel plate welded Park (I-level) GB1270-80 stainless steel tubing (I Class)
GB12771-91 stainless steel pipe (Y class) GB3280-84 stainless steel cold (I Class)
GB4237-84 stainless steel hot plate (I grade) GB4239-91 stainless steel cold strip (I Class)

History of the development of high speed steel

In 1898, the American Society of Mechanical Engineers and management Taylor (TaylorF.W.) And metallurgists White (WhiteM.) Developed the invention of high speed steel, and made a cutting test system. When they determine high speed steel components for C-0.67%, W-18.91%, Cr-5.47%, Mn-0.11%, V-0.29%, F- margin, and later W18Cr4V composition is very close. High-speed steel cutting tools available 30m / min cutting speed steel, which is several times more efficient than carbon tool steel and alloy tool steel used in the past, for the United States at the time of the machinery industry won a huge economic benefits.

W18Cr4V speed steel thermoplastic bad, because the twist need hot rolling process, and later the successful development of high-speed steel W6Mo5Cr4V2 addition, there W9Mo3Cr4V. Cutting and mechanical properties of these three high-speed steel approximation, called universal.
After the mid-20th century, the rapid development of science and technology, a variety of difficult materials continue to emerge, the performance of general-purpose high-speed steel no longer use, so high speed steel and high speed steel powder metallurgy have appeared, so the performance of high-speed steel cutting tool material has been greatly improved.

Typical uses of stainless steel

Most of the long-term requirements of maintaining the original appearance of the building. In determining to choose the type of stainless steel, the main consideration is the aesthetic standards required by the system to be used to clean the corrosion and the location of the atmosphere. However, a growing number of other applications, or just looking for the integrity of the structure is not permeable. For example, industrial building roof and side walls. In these applications, the construction cost of ownership may be more important than the aesthetic, the surface is not very clean and can be. Effect of using 304 stainless steel in dry indoor environment is quite good.

However, in rural and urban outdoors in order to maintain their appearance, they need regular cleaning. In heavily polluted industrial areas and coastal areas, the surface will be very dirty, and even rust. But to get the aesthetic effect of the outdoor environment, it requires the use of nickel-containing stainless steel. So, 304 stainless steel is widely used in curtain wall, side walls, roofs and other construction purposes, but in severe erosion of industrial or marine atmosphere, the best use of 316 stainless steel. There are several design criteria are included in the 304 and 316 stainless steel.

Because “duplex” 2205 has already good resistance to atmospheric corrosion and high tensile strength and elastic limit of integration, so that the European criteria also included the steel. Product shape, in fact, stainless steel is the whole shape and size of the standard metal manufacturing, and there are many special shapes. The most commonly used products are made with sheet and strip, and plate production with special products, for example, the production of hot-rolled structural steel and structural steel extrusion. And there are round, oval, square, rectangular and hexagonal welded or seamless steel tubes and other forms of products, including profiles, rods, wire and castings. In order to meet the aesthetic requirements of architects, has developed a wide variety of commercial surface processing.

Stainless steel products production materials

Because of the different uses of each product, its process and materials quality requirements are also different. Generally different stainless steel products, which require raw materials thickness tolerances vary, like second-class cutlery and mug, etc., generally require a higher thickness tolerances, -3 to 5%, and a thickness tolerance tableware General requirements – 5% -10% steel such requests, hotels with a freezer timber thickness tolerance requirements for 8%, dealers thickness tolerance requirements generally between 4% to 6%. At the same time export products will lead to different customers in different thickness tolerance requirements for raw materials. Generally higher exports of customers thickness tolerance requirements, while domestic enterprises thickness tolerance requirements are relatively low (mostly because of cost considerations), some customers even require -15%.

①DDQ (deep drawing quality) material: refers to the material used for deep drawing (punching) use, that is, we called a soft material, the main characteristics of this material is higher elongation (≧ 53%), compared with the hardness low (≦ 170%), internal grain grading between 7.0 to 8.0, excellent deep drawing properties. Many production thermos pot class enterprises, processing their products generally have higher than (BLANKING SIZE / products in diameter), which processed more than 3.0,1.96,2.13,1.98 respectively. SUS304DDQ timber is mainly used for processing these requests higher than that of the product, of course, the processing ratio of more than 2.0 products are generally subject to stretch a few times to complete. If the extension of terms of raw materials reach it, in the processing of deep drawing products product cracks easily, pull wear phenomenon, affecting the rate of qualified products, of course, will increase the cost of manufacturers;

② General Material: mainly used for purposes outside except DDQ material characteristics of this material is relatively low elongation (≧ 45%), while the hardness is relatively high (≦ 180HB), internal grain grade of 8.0 to 9.0 Rooms, compared with DDQ timber, its performance relative somewhat less deep drawing, it is mainly used in the products can be obtained without thrust, like a class tableware spoon, spoon, fork, electrical appliances, steel uses. But it is compared with DDQ material has an advantage that BQ relatively good, mainly because of its hardness slightly higher reason.
Stainless steel sheet is an inexpensive material, but customers of its very high surface quality requirements. Stainless steel sheet in the production process inevitably there will be a variety of defects, such as scratches, pits, sand hole, dark lines, creases, pollution, etc., so that its surface quality, such as scratches, creases, etc. These defects are advanced materials allowed, and pitting, sand holes this defect in the spoon, spoon, fork, the production is never allowed because it is difficult to throw away when polishing. Required depending on the degree and frequency of surface defects of various kinds, to determine its quality level table, thereby to determine the product level.

Stainless steel structural components

Increase the corrosion resistance of stainless steel with the carbon content decreases, and therefore, most of the lower carbon stainless steel volume, to a maximum of 1.2%, and some steel ωc (carbon content), and even less than 0.03% (e.g. 00Cr12 ). Stainless steel is the main alloying elements Cr (chromium), only when the Cr content reaches a certain value, there is corrosion resistance of steel. Therefore, stainless steel is generally Cr (chromium) content of at least 10.5%. Stainless steel also contains Ni, Ti, Mn, N, Nb, Mo, Si, Cu and other elements.

What are the main characteristics of stainless steel?

What are the main characteristics of stainless steel?
Weldability

Usage of different welding performance requirements also vary. A class of cutlery on the welding performance in general is not required, even including some pot enterprises. But the vast majority of products are required welding materials properties, like second-class cutlery, mug, steel pipes, water heaters, drinking fountains.

Corrosion
The vast majority of stainless steel products require good corrosion resistance, like a second class tableware, kitchen utensils, water heaters, drinking fountains, and some foreign businessmen corrosion products also do test: NACL solution heated to boiling, pour some time after out of solution, wash and drying, said weight loss, to determine the degree of corrosion (Note: When polishing products, emery cloth or sandpaper because the ingredients contained Fe, will lead to the surface rust test)

Polished performance

Today’s society is generally in the production of stainless steel products are polished this process, only a few products such as water heaters, drinking fountains, interior, etc. do not need polishing. Therefore, the performance of which requires a good polishing materials. Factors affecting the performance of polishing the following main points:
① material surface defects. Such as scratches, pitting, excessive pickling.
② raw material problem. Hardness is too low, it is not easy to throw light (BQ bad) when polished, and the hardness is too low, in the deep drawing surface prone to orange peel, thus affecting BQ sex. BQ relatively high hardness like.
③ after deep drawing products, deformation of the surface area will be a great little black spots and RIDGING, thus affecting BQ sex.

Heat resistance

Refers to a high temperature heat resistance stainless steel can maintain its excellent physical and mechanical properties.
The impact of carbon: carbon in austenitic stainless steel is strong and stable formation. Given austenite and the austenite region of the expansion element. Carbon formation of austenite capacity of about 30 times that of nickel, carbon is an interstitial element, solid solution strengthening can significantly improve the strength of austenitic stainless steel. Austenitic stainless steel carbon can also improve performance in high concentration of chloride (eg boiling 42% MgCl2 solution) resistance to stress corrosion.

However, in austenitic stainless steels, carbon is often regarded as harmful elements, mainly due to the corrosion of the stainless steel under some conditions of use (such as by welding or by 450 ~ 850 ℃ heating), the carbon steel may Cr23C6 type carbon chromium compounds leading to the formation of a local high chromium chromium depleted, especially the corrosion resistance of the steel is decreased resistance to intergranular corrosion. As such. Chromium-nickel austenitic stainless steel is mostly carbon content of new developments since the 1960s, less than 0.03% or 0.02% ultra-low carbon type, you can know with lower carbon content, intergranular corrosion susceptibility of steel decreases, when the carbon content of less than 0.02% that has the most significant effect, some experimental pearl also noted that carbon will increase the tendency of pitting points chromium austenitic stainless steel. Due to the harmful effects of carbon, not only in austenitic stainless steel smelting control over, and in accordance with the requirements as low carbon content, and in the subsequent heat, cold and heat treatment process also prevents the stainless steel surface by carbon and chromium-free carbide precipitation.

Corrosion

When the number of atoms of chromium content in the steel of not less than 12.5%, the electrode potential of steel can be mutated by the negative potential to rise to the positive electrode potential. Prevent galvanic corrosion.

Physical properties of stainless steel

Compared with steel

1. Density
Slightly higher than the density of steel ferritic and martensitic stainless steel, while slightly lower than austenitic stainless steel;

2, the resistivity
Resistivity by carbon steel, ferritic, martensitic and austenitic stainless steel Sort Ascending;

3, the size of the linear expansion coefficient of the sort similar, austenitic stainless steel and carbon steel up to minimum;

4, carbon steel, ferritic and martensitic stainless steel magnetic, non-magnetic austenitic stainless steel, but it will have to generate a magnetic work hardening, heat treatment method available martensitic transformation to eliminate this martensite organization and restore its non-magnetic.

Compared with austenitic stainless steel, has the following characteristics:
1) high resistivity, carbon steel is about 5 times.
2) a large linear expansion coefficient, 40% larger than that of carbon steel, and as the temperature rises, the value of the linear expansion coefficient is also increased accordingly.
3) low thermal conductivity, about 1/3 of carbon steel.

Austenitic stainless steel

More than 18% chromium, it also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Good overall performance, corrosion resistant variety of media. Common austenitic stainless steel grades are 1Cr18Ni9,0Cr19Ni9 like. Wc 0Cr19Ni9 steel <0.08%, steel labeled “0.” This kind of steel contains large amounts of Ni and Cr, the steel at room temperature was austenitic state. Such steel has good ductility, toughness, weldability, corrosion resistance and non-magnetic or weakly magnetic, corrosion resistance are good in oxidizing and reducing medium, used to produce acid and equipment, such as corrosion resistant containers and equipment linings, pipelines, nitric acid resistant parts and other equipment, and also can be used as the main material of stainless steel jewelry watches.

Austenitic stainless steels commonly used solution treatment, is about steel heated to 1050 ~ 1150 ℃, and then air-cooled or water-cooled, in order to obtain a single phase austenite.

Ferritic stainless steel

Chromium 15% to 30%. Its corrosion resistance, toughness and weldability with the increase of chromium content increased resistance to chloride stress corrosion better than other types of stainless steel, fall into this category have Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and so on.

Ferritic stainless steel because of high chromium content, corrosion and oxidation resistance are relatively good, but poor mechanical properties and process performance, and more for large discontinuity acid structure and antioxidant for steel. Such stainless steel is resistant to corrosive atmosphere, nitric acid and saline solution, and has good oxidation resistance, thermal expansion coefficient, etc., for the nitric acid plant equipment and food, can also be produced parts at high temperatures, such as gas turbine parts, etc. .

What are the main types of stainless steel?

Stainless steel” is not merely the word refers to a stainless steel, but said that more than one hundred kinds of industrial stainless steel developed for each specific application in their fields with good performance. The key to success is to understand the use of the first, and then determine the correct steel. Building construction and steel-related applications usually only six of them. They contain 17 to 22% chromium, preferably steel further contains nickel. Adding molybdenum can be further improved atmospheric corrosion, especially corrosion resistance to chloride-containing atmosphere.

Stainless steel is often divided by organizational status: martensitic steels, ferritic steels, austenitic steels, austenitic – ferritic (duplex) stainless steel and precipitation hardening stainless steel. In addition, according to the ingredients into: chrome stainless steel, chrome-nickel stainless steel and chrome manganese nitrogen stainless steel.