Introduction of stainless steel

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  Group of stainless steel (Inox) formed from alloy steel them, was originated in 1913 in Sheffield, England; Harry Brearley was trying a number of alloys to steel-barreled gun, and he noticed some rust sample cut not see reality and real seasoned difficult

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  Group of stainless steel (Inox) formed from alloy steel them, was originated in 1913 in Sheffield, England; Harry Brearley was trying a number of alloys to steel-barreled gun, and he noticed some rust sample cut not see reality and real seasoned difficult. When Mr. learn the depth of this amazing material, that contains 13% Cr steel. This result led to the development of stainless steel cutlery and also from here, Sheffield became famous. Random development works have also been performed in France at that time had made the summit of their development austenitic stainless steel first.

Stainless steel consumption in the world is increasing. It is the growth in demand for building and construction industry - where stainless steel is used to make decorative and rust, low maintenance requirements and durability. Many other industries are adopting stainless steel for the above reasons as well as it does not have many demands on the handling of the product, coating being brought to use, except that its price is higher than steel Carbon generally. Demonstrated the broad application that manufactures home appliances, they are growing provider of products, traditionally known as "white-whitegoods goods", are manufactured from stainless steel

 They stainless steel

  Stainless steels are iron base alloys that contain a minimum of 10.5% chromium; Cr oxide layer creates passive protection, which is why this steel group characteristics "stainless" or corrosion resistance. The ability of the oxide layer is self "healing - self healing", ie steel resistant to corrosion, even though the surface part continued worn. This is not true for carbon steel and low alloy often when they are protected from erosion by coating metals such as zinc or cadmium Cd Zn or inorganic coating such as paint.

Although all stainless steels depend on the presence of chromium, other metals are added to enhance their properties. The classification of stainless steel metal not by name but on the metallurgical structure (metallurgical structure) of them - the concept used to denote the arrangement of the atoms forming the grains, and they are concerned close to the magnification of the optical microscope through the polished form. Depending on the chemical composition of steel fixed, the structure may be austenitic or ferritic stable phases, mixed "duplex" of both, martenxit phase is formed when steel is cooled rapidly from high temperature, or chemical structure more efficient by the micro phase.

  Relationship between differences of stainless steel they are divided according to Figure 1. A number of other comparable properties in their various steel are listed in Table 1.

1-cac-ho-thep-khong-gi1
Figure 1. stainless steel.

Stainless steel austenitic steel group containing at least 16% Cr and 6% Ni (base steel grade 304 is specified as 18/8) and range depend on the high alloy or "super austenitic" as labels 904L with 6% Mo.

Additional elements such as Mo, Ti or Cu to change or improve their properties, making stainless steel adapted to specific applications in high temperature and corrosion resistance. Steel Group is also suitable for low temperature applications due to the influence of Ni content makes steel duochien avoid cold object at low temperature brittleness, Ni is the prime characteristic of this steel.

Relations between the various austenitic steels are shown in Figure 2. 

2-quan-he-giua-cac-mac-thep-austenit1

Figure 2. Stainless steel austenitic

Ferrite stainless steel These are only Cr steels is the main element in a proportion from 10.5 to 18%, as the steel grade 430 and 409. They are relatively corrosion resistance and poor fabrication, so to improve the quality of high-grade alloys are used as the 434 and 444 marks, and marks their Predominantly this is 3CR12.

Relations between the ferritic stainless steel grades is shown in Figure 3. 

3-thep-khong-gi-ferit1

Figure 3. They ferritic steels.

 

 

Stainless steel martensite

   Stainless steel is also macstenxit on the addition of chromium as the major alloying element but with a higher carbon content and lower chromium content (eg. 12% Cr in 410 and 416 grade) compared to ferritic steel type; Grade 431 has a chromium content of 16%, but its structure is still martensite despite this high chromium level and because this grade also contains 2% Ni.

Relations between the martensitic stainless steel is shown in Figure 4. 
4-ho-thep-khong-gi-mactenxit1

Figure 4. The martensitic stainless steel.

 

Duplex stainless steel

  Duplex stainless steels such as 2304 and 2205 (these regulations, said composition Bi 4% and 22% Cr, Ni is 5% but both grades contain added the other alloying elements) have profiles constituted by a mixture autenite and ferrite. Duplex ferritic - austenitic steels combine some of the characteristics of each group: they are resistant to stress corrosion, albeit not quite as high as the ferritic steels; with toughness (toughness) outperformed the ferritic stainless steel and inferior to austenitic steels, and austenitic steels greater reliability the (annealed), with levels of about 2 times. In addition, duplex stainless steel with corrosion resistance equivalent to or better than 304 and 316, and generally hole corrosion (pitting corrosion resistance) than 316. They were reduced toughness at temperature -50 ° C and lower than after to heat (exposure) on the 300C, so we only used within the temperature limits of this.

Relations between them duplex stainless steel grade is shown in Figure 5. 

5-thep-khong-gi-song-pha1

Figure 5. The duplex stainless steel.

 

Stainless Steel Hardening

  The steel contains chromium and nickel to obtain high tensile strength. The most common grade is 630 marks in the "17-4 PH", with a 17% Cr, 4% Ni, 4% Cu and 0.3% Nb. The biggest advantage of this steel they can "handle" it. That is the process. Following processing, forming, ... steel can be hardened by heat treatment "aging" one step at a relatively low temperature, without causing fluctuations in the size of the product.

 

Characteristics of Stainless Steel

  Features stainless steel groups can be seen in view of their comparable steel C "software" often. In terms of the most common, stainless steel:

Forged hardened high speed (hgher work hardening rate)

Higher viscosity (hgher ductility)

Hardness and higher reliability (Higher strength and hardness)

Reliability hot higher (Higher hot strength)

Higher corrosion resistant (corrosion resistance Higher)

Toughness at low temperatures better (Higher cryogenic toughness)

Reaction from inferior (only with austenitic steel) (Lower magnetic response (austenitic only))

Must retain corrosion resistant surface in the finished product.

  These properties that are actually correct to austenitic steel and can change quite a lot for their steel and other steel.

  These properties that are related to the field of application of stainless steel, but also influenced by the device and method of fabrication.

 

Table 1 (Part A). Comparative Properties of stainless steel families. 


Alloy Group
 
 
Magnetism1
 
 

Forged hardening speed

 
 

Corrosion resistance 2

 
 

Hardening ability

Austenit
Không
Rất cao
Cao
Rèn nguội
Duplex
Trung bình
Rất cao
Không
Ferrit
Trung bình
Trung bình
Không
Martensit
Trung bình
Trung bình
Tôi & Ram
Hóa bền tiết pha
Trung bình
Trung bình
Hóa già
1 = Attraction of magnets to steel. Note, some grades are magnet when Cold worked.
2 = significant fluctuation between grades within each group, for example, the marks are not part with lower corrosion resistance, and when there is a higher Mo will have higher resistance.

Table 1 (Part B). Comparative Properties of stainless steel families.
Nhóm hợp kim
 
 
Tính dẻo
 
 
Làm việc ở nhiệt độ cao
 
 
Làm việc ở nhiệt độ thấp 3
 
 
Tính hàn
Austenit
Rất cao
Rất cao
Rất tốt
Rất cao
Duplex
Trung bình
Thấp
Trung bình
Cao
Ferrit
Trung bình
Cao
Thấp
Thấp
Martensit
Thấp
Thấp
Thấp
Thấp
Hóa bền tiết pha
Trung bình
Thấp
Thấp
Cáo
3 = Measured by toughness or ductility near 0C. Austenitic stainless steel keep the viscosity at low temperatures.
 
Classification Standard
  There are many variations of stainless steel and the American Iron and Steel Institute (AISI) previously defined a standard ingredient labels, and still tieps widely used procedure today. Today, SAE and ASTM standard of AISI according to provisions of its steel grade, is indexed as 1 character UNS + 5 digits for the new steel grade. The scope of the most complete indexing of the stainless steel used in the Iron and Steel Society (ISS), and manual SEA / ASTM index of system consolidation. The other grades do not have standard indicators, which are used in other countries or international regulations or regulations for specialized manufacturers as the standard steel welding wire.

 

719    11-01-2016 09:21:29