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It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1. See Composition effects on the magnetic permeability of austenitic stainless steels
It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.
In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.
Martensitic, ferritic, duplex and precipitation hardening steels are magnetic.
Friday, March 29, 2013
How many types of stainless steel are there?
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Stainless steel is usually divided into 5 types:
Ferritic – These steels are based on Chromium with small amounts of Carbon usually less than 0.10%. These steels have a similar microstructure to carbon and low alloy steels. They are usually limited in use to relatively thin sections due to lack of toughness in welds. However, where welding is not required they offer a wide range of applications. They cannot be hardened by heat treatment. High Chromium steels with additions of Molybdenum can be used in quite aggressive conditions such as sea water. Ferritic steels are also chosen for their resistance to stress corrosion cracking. They are not as formable as austenitic stainless steels. They are magnetic.
Austenitic - These steels are the most common. Their microstructure is derived from the addition of Nickel, Manganese and Nitrogen. It is the same structure as occurs in ordinary steels at much higher temperatures. This structure gives these steels their characteristic combination of weldability and formability. Corrosion resistance can be enhanced by adding Chromium, Molybdenum and Nitrogen. They cannot be hardened by heat treatment but have the useful property of being able to be work hardened to high strength levels whilst retaining a useful level of ductility and toughness. Standard austenitic steels are vulnerable to stress corrosion cracking. Higher nickel austenitic steels have increased resistance to stress corrosion cracking. They are nominally non-magnetic but usually exhibit some magnetic response depending on the composition and the work hardening of the steel.
Martensitic - These steels are similar to ferritic steels in being based on Chromium but have higher Carbon levels up as high as 1%. This allows them to be hardened and tempered much like carbon and low-alloy steels. They are used where high strength and moderate corrosion resistance is required. They are more common in long products than in sheet and plate form. They have generally low weldability and formability. They are magnetic.
Duplex - These steels have a microstructure which is approximately 50% ferritic and 50% austenitic. This gives them a higher strength than either ferritic or austenitic steels. They are resistant to stress corrosion cracking. So called “lean duplex” steels are formulated to have comparable corrosion resistance to standard austenitic steels but with enhanced strength and resistance to stress corrosion cracking. “Superduplex” steels have enhanced strength and resistance to all forms of corrosion compared to standard austenitic steels. They are weldable but need care in selection of welding consumables and heat input. They have moderate formability. They are magnetic but not so much as the ferritic, martensitic and PH grades due to the 50% austenitic phase.
Precipitation hardening (PH) - These steels can develop very high strength by adding elements such as Copper, Niobium and Aluminium to the steel. With a suitable “aging” heat treatment, very fine particles form in the matrix of the steel which imparts strength. These steels can be machined to quite intricate shapes requiring good tolerances before the final aging treatment as there is minimal distortion from the final treatment. This is in contrast to conventional hardening and tempering in martensitic steels where distortion is more of a problem. Corrosion resistance is comparable to standard austenitic steels like 1.4301 (304).
What is 'multiple certification'?
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This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimize stock levels.
For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.
This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimize stock levels.
For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.
Stainless Steel Surface Finishes
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The surface of Stainless Steel is actually and extremely thin but stable and passive Chromium rich oxide film, on which Stainless Steel relies for its excellent corrosion resistance. The surface finish on Stainless Steel should therefore be developed and maintained to ensure this vital property, and also for the secondary reason of the pleasing aesthetic appearance of Stainless Steel.
STANDARD MILL FINISHED - FLAT ROLLED PRODUCTS
The Standard Mill Surface Finished are laid down in Specifications (BS 1449, Part 4, and the Committee of Stainless Steel Producers, American Iron & Steel Institute).
The finished are designated by a system of numbers, and these are broadly described hereunder relative to the finishing operations employed. It should be remembered that different grades of Stainless Steel can result in a variation of visual appearance for the same finishing operation. The thickness can also have an effect, generally the thinner the material the smoother the surface finish.
The thicker gauge sizes of Stainless Steel are hot rolled. This is done at high temperatures and will always result in a scaled surface.
Stainless Steel Flat Product is supplied in the annealed ie fully softened condition.
This is also a high temperature operation and unless carried out in a very closely controlled inert atmosphere, will result in oxidation (scaling) of the surface.
The scale is usually removed by a pickling process, that is the removal of the scale by use of suitable acids, and the passivated by the use of Nitric Acid.
No. 0 Finish
Also referred to as Hot Rolled Annealed (HRA). The plate is hot rolled to required thickness, and then annealed. No pickling or passivation operations are effected, resulting in a scaled black finish.
This does not develop the fully corrosion resistant film on the Stainless Steel, and except for certain high temperature heat resisting applications, this finish is unsuitable for general end uses.
No 1 Finish
Plate is hot rolled, annealed, pickled and passivated. This results in a dull, slightly rough surface; quite suitable for industrial applications which generally involve the range of plate thicknesses. Grinding marks may be visible in isolated areas.
Some of the thinner thicknesses within the plate range are Cold Rolled; but Sheet, Coil and Strip gauges are produced by Cold Rolling, ie rolled without and heating of the material. Cold Rolling hardens the material, and the thinner sizes may have to be subjected to an intermediate anneal and pickle, or bright annealed, during the reduction of thickness to final gauge.
The starting material for Cold Rolling always has a No. 1 finish. Cold Rolled material is supplied with the following standard mill finishes.
No 2D Finish
A no. 1 Finish after being Cold Rolled, Annealed, Pickled and Passivated. This results in a uniform dull matt finish, superior to a No. 1 Finish.
Suitable for industrial application, and eminently suitable for severe deep drawing as the dull surface, (which may be polished after fabrication) retains the lubricant during the drawing operation.
No 2B Finish
A 2D Finish is given a subsequent light skin pass cold rolling operation between polished rolls.
This is the most common finish produced and called for on sheet material. It is brighter than 2D and is semi-reflective. It is commonly used for most deep drawing operations, and is more easily polished to the final finished required than is a 2D finish.
No 2BA Finish
This is more commonly referred to as a BRIGHT ANNEALED (BA) FINISH. Material with a No. 1 finish is Cold Rolled using highly polished rolls in contact with the steel surface. This smooths and brightens the surface.
The smoothness and reflectiveness of the surface improves as the material is rolled to thinner and thinner sizes. Any annealing which needs to be done in order to effect the required reduction in gauge, and the final anneal, is effected in a very closely controlled inert atmosphere. No oxidation or scaling of the surface therefore occurs and there is no need for additional pickling and passivating.
The final surface developed can have "MIRROR" type finish similar in appearance to the highly polished No. 7 and No. 8 Finishes.
Note
Much of the 2B Finish sheet imported is not a true 2B Finish. Mills which operate bright annealing facilities will often carry out all the annealing operations of Cold Rolled material in such facilities. This leads to a superior "2B" finish as no oxidation or scaling takes place during the annealing operation, even though the actual rolling may be effected on polished rolls as for normal 2B Finish, but not highly polished as would be needed to produce a BA finish.
The following finishes are all mechanically produced polished finishes. As well as being standard mill finishes, they are also applied to stainless steel articles and components to meet the required aesthetic criteria. It should be appreciated that factors such as hand polishing vs. mechanical polishing; polishing a flat product as against a component of complex shape; thickness and composition of material can affect the visual appearance of the final surface.
No. 3 Finish
This is a ground unidirectional uniform finish obtained with 80 - 100 grit abrasive.
It is a good intermediate or starting surface finish for use in such instances where the surface will require further polishing operations to a finer finish after subsequent fabrication or forming.
No. 4 Finish
This is a ground unidirectional finish obtained with 150 grit abrasive. It is not highly reflective, but is a good general purpose finish on components which will suffer from fairly rough handling in service (eg restaurant equipment).
No. 6 Finish
These finishes are produced using rotating cloth mops (Tampico fibre, muslin or linen) which are loaded with abrasive paste.
The finish depends on how fine and abrasive is used, the uniformity and finish of the original surface.
The finish has a non-directional texture of varying reflectiveness. "Satin Blend" is an example of such a finish.
No. 7 Finish
This is a buffed finish having a high degree of reflectiveness.
It is produced by progressively using finer and finer abrasives and finishing with Buffing compounds. Some fine scratches (grit lines) may remain from the original starting surface.
No. 8 Finish
This is produced in an equivalent manner to a No. 7 Finish, the final operations being done with extremely fine buffing compounds.
The final surface is blemish free with a high degree of image clarity, and is the true mirror finish.
Note
The finer polished finishes (No. 4, No. 6, No. 7 and No. 8) are generally only produced one side of the sheet, the reverse side being either a 2B or No. 3 Finish.
The surface of Stainless Steel is actually and extremely thin but stable and passive Chromium rich oxide film, on which Stainless Steel relies for its excellent corrosion resistance. The surface finish on Stainless Steel should therefore be developed and maintained to ensure this vital property, and also for the secondary reason of the pleasing aesthetic appearance of Stainless Steel.
STANDARD MILL FINISHED - FLAT ROLLED PRODUCTS
The Standard Mill Surface Finished are laid down in Specifications (BS 1449, Part 4, and the Committee of Stainless Steel Producers, American Iron & Steel Institute).
The finished are designated by a system of numbers, and these are broadly described hereunder relative to the finishing operations employed. It should be remembered that different grades of Stainless Steel can result in a variation of visual appearance for the same finishing operation. The thickness can also have an effect, generally the thinner the material the smoother the surface finish.
The thicker gauge sizes of Stainless Steel are hot rolled. This is done at high temperatures and will always result in a scaled surface.
Stainless Steel Flat Product is supplied in the annealed ie fully softened condition.
This is also a high temperature operation and unless carried out in a very closely controlled inert atmosphere, will result in oxidation (scaling) of the surface.
The scale is usually removed by a pickling process, that is the removal of the scale by use of suitable acids, and the passivated by the use of Nitric Acid.
No. 0 Finish
Also referred to as Hot Rolled Annealed (HRA). The plate is hot rolled to required thickness, and then annealed. No pickling or passivation operations are effected, resulting in a scaled black finish.
This does not develop the fully corrosion resistant film on the Stainless Steel, and except for certain high temperature heat resisting applications, this finish is unsuitable for general end uses.
No 1 Finish
Plate is hot rolled, annealed, pickled and passivated. This results in a dull, slightly rough surface; quite suitable for industrial applications which generally involve the range of plate thicknesses. Grinding marks may be visible in isolated areas.
Some of the thinner thicknesses within the plate range are Cold Rolled; but Sheet, Coil and Strip gauges are produced by Cold Rolling, ie rolled without and heating of the material. Cold Rolling hardens the material, and the thinner sizes may have to be subjected to an intermediate anneal and pickle, or bright annealed, during the reduction of thickness to final gauge.
The starting material for Cold Rolling always has a No. 1 finish. Cold Rolled material is supplied with the following standard mill finishes.
No 2D Finish
A no. 1 Finish after being Cold Rolled, Annealed, Pickled and Passivated. This results in a uniform dull matt finish, superior to a No. 1 Finish.
Suitable for industrial application, and eminently suitable for severe deep drawing as the dull surface, (which may be polished after fabrication) retains the lubricant during the drawing operation.
No 2B Finish
A 2D Finish is given a subsequent light skin pass cold rolling operation between polished rolls.
This is the most common finish produced and called for on sheet material. It is brighter than 2D and is semi-reflective. It is commonly used for most deep drawing operations, and is more easily polished to the final finished required than is a 2D finish.
No 2BA Finish
This is more commonly referred to as a BRIGHT ANNEALED (BA) FINISH. Material with a No. 1 finish is Cold Rolled using highly polished rolls in contact with the steel surface. This smooths and brightens the surface.
The smoothness and reflectiveness of the surface improves as the material is rolled to thinner and thinner sizes. Any annealing which needs to be done in order to effect the required reduction in gauge, and the final anneal, is effected in a very closely controlled inert atmosphere. No oxidation or scaling of the surface therefore occurs and there is no need for additional pickling and passivating.
The final surface developed can have "MIRROR" type finish similar in appearance to the highly polished No. 7 and No. 8 Finishes.
Note
Much of the 2B Finish sheet imported is not a true 2B Finish. Mills which operate bright annealing facilities will often carry out all the annealing operations of Cold Rolled material in such facilities. This leads to a superior "2B" finish as no oxidation or scaling takes place during the annealing operation, even though the actual rolling may be effected on polished rolls as for normal 2B Finish, but not highly polished as would be needed to produce a BA finish.
The following finishes are all mechanically produced polished finishes. As well as being standard mill finishes, they are also applied to stainless steel articles and components to meet the required aesthetic criteria. It should be appreciated that factors such as hand polishing vs. mechanical polishing; polishing a flat product as against a component of complex shape; thickness and composition of material can affect the visual appearance of the final surface.
No. 3 Finish
This is a ground unidirectional uniform finish obtained with 80 - 100 grit abrasive.
It is a good intermediate or starting surface finish for use in such instances where the surface will require further polishing operations to a finer finish after subsequent fabrication or forming.
No. 4 Finish
This is a ground unidirectional finish obtained with 150 grit abrasive. It is not highly reflective, but is a good general purpose finish on components which will suffer from fairly rough handling in service (eg restaurant equipment).
No. 6 Finish
These finishes are produced using rotating cloth mops (Tampico fibre, muslin or linen) which are loaded with abrasive paste.
The finish depends on how fine and abrasive is used, the uniformity and finish of the original surface.
The finish has a non-directional texture of varying reflectiveness. "Satin Blend" is an example of such a finish.
No. 7 Finish
This is a buffed finish having a high degree of reflectiveness.
It is produced by progressively using finer and finer abrasives and finishing with Buffing compounds. Some fine scratches (grit lines) may remain from the original starting surface.
No. 8 Finish
This is produced in an equivalent manner to a No. 7 Finish, the final operations being done with extremely fine buffing compounds.
The final surface is blemish free with a high degree of image clarity, and is the true mirror finish.
Note
The finer polished finishes (No. 4, No. 6, No. 7 and No. 8) are generally only produced one side of the sheet, the reverse side being either a 2B or No. 3 Finish.
Sunday, March 24, 2013
Extruded Finned Tube
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This fin type is formed from a bi-metallic tube consisting of an aluminium outer tube and an inner tube of almost any material. The fin is formed by rolling material from the outside of the exterior tube to give an integral fin with excellent heat transfer properties and longevity. Extruded fin offers excellent corrosion protection of the base tube.
Maximum working Temperature 285°c
Atmospheric corrosion Resistance Acceptable
Mechanical resistance Poor
Fin materials Aluminium
Tube materials Any
G Embedded Finned Tube
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The fin strip is wound into a machined groove and securely locked into place by back filling with base tube material. This ensures that maximum heat transfer is maintained at high tube metal temperatures.
Maximum working Temperature 400°c
Atmospheric corrosion Resistance Acceptable
Mechanical resistance Poor
Fin materials Aluminium, copper
Tube materials Any
Helical KL finned tube
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'KL' FINNED TUBE
Manufactured exactly as the 'L' finned tube except that the base tube is knurled before application of the fin foot. After application, the fin foot is knurled into the corresponding knurling on the base tube thereby enhancing the bond between the fin and tube, resulting in improved heat transfer characteristics.
Maximum working Temperature 260°c
Atmospheric corrosion Resistance Acceptable
Mechanical resistance Poor
Fin materials Aluminium, copper
Tube materials Any
Helical LL finned tube
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'LL' FINNED TUBE
Manufactured in the same way as the 'L' finned tube type except that the fin foot is overlapped to completely enclose the base tube thereby giving excellent corrosion resistance. This type of finned tube is often used as an alternative to the more expensive extruded type fin in corrosive environments.
Maximum working Temperature 180°c
Atmospheric corrosion Resistance Acceptable
Mechanical resistance Poor
Fin materials Aluminium, copper
Tube materials Any
Helical L Finned tube
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'L' FINNED TUBE
The strip material is subjected to controlled deformation under tension giving the optimum contact pressure of the foot of the fin onto the base tube thus maximising the heat transfer properties.
The foot of the fin considerably enhances the corrosion protection of the base tube.
Maximum working Temperature 150°c
Atmospheric corrosion Resistance Acceptable
Mechanical resistance Poor
Fin materials Aluminium, copper
Tube materials Any
Saturday, March 23, 2013
Heat recovery steam generator
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A heat recovery steam generator or HRSG is an energy recovery heat exchanger that recovers heat from a hot gas stream. It produces steam that can be used in a process (cogeneration) or used to drive a steam turbine (combined cycle).
HRSGs
HRSGs consist of four major components: the economizer, evaporator, superheater and water preheater. The different components are put together to meet the operating requirements of the unit. See the attached illustration of a Modular HRSG General Arrangement.
Modular HRSGs can be categorized by a number of ways such as direction of exhaust gases flow or number of pressure levels. Based on the flow of exhaust gases, HRSGs are categorized into vertical and horizontal types. In horizontal type HRSGs, exhaust gas flows horizontally over vertical tubes whereas in vertical type HRSGs, exhaust gas flow vertically over horizontal tubes. Based on pressure levels, HRSGs can be categorized into single pressure and multi pressure. Single pressure HRSGs have only one steam drum and steam is generated at single pressure level whereas multi pressure HRSGs employ two (double pressure) or three (triple pressure) steam drums. As such triple pressure HRSGs consist of three sections: an LP (low pressure) section, a reheat/IP (intermediate pressure) section, and an HP (high pressure) section. Each section has a steam drum and an evaporator section where water is converted to steam. This steam then passes through superheaters to raise the temperature beyond the one at the saturation point.
Applications
Heat recovery can be used extensively in energy projects.
In the energy-rich Persian Gulf region, the steam from the HRSG is used for desalination plants.
Universities are ideal candidates for HRSG applications. They can use a gas turbine to produce high reliability electricity for campus use. The HRSG can recover the heat from the gas turbine to produce steam/hot water for district heating or cooling.
Large ocean vessels (e.g. Emma Maersk) make use of heat recovery
Manufacturers
Alstom
Ansaldo Caldaie S.p.a.
BHI Co.
Express Integrated Technologies (EIT)
Vogt Power/Babcock Power([4])
IHI Corporation
CMI Energy
Victory Energy
Nooter/Eriksen
NEM
Doosan Heavy Industries & Construction ([10])
BHEL
3DCAD (I) PVT LTD
Thermax Ltd
Innovative Steam Technologies
Larsen & Toubro Ltd
Hamon Deltak, Inc
Greshams Ltd
Rentech Boiler Inc.
AZARAB Industery Co.
DESCON Engineering Limited
Retubeco, Inc.
GREENS POWER EQUIPMENT INDIA PVT.LTD.
MAPNA Boiler
Friday, March 15, 2013
Stainless steel grade 439
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Stainless steel grade 439 is capable of being made into complex shapes such as tubular manifolds and exhaust system components, where temperatures tend to go beyond the oxidation limit of grade 409 steel. It is also preferred where wet corrosion resistance especially to chlorides is needed.
Stainless steel grade 439 has good weldability, brightness, and pitting corrosion resistance. It polishes well, and is good for deep drawing.
The following datasheet provides an overview of stainless steel grade 439.
Chemical Composition
The chemical composition of grade 439 stainless steel is outlined in the following table.
|
Element
|
Content (%)
|
|
Iron, Fe
|
81.35
|
|
Chromium, Cr
|
17.35
|
|
Silicon, Si
|
0.35
|
|
Titanium, Ti
|
0.335
|
|
Manganese, Mn
|
0.25
|
|
Nickel, Ni
|
0.2
|
|
Molybdenum, Mo
|
0.1
|
|
Niobium, Nb
(columbium, Cb)
|
0.02
|
|
Phosphorous, P
|
0.02
|
|
Nitrogen, N
|
0.01
|
|
Carbon, C
|
0.01
|
|
Sulfur, S
|
0.002
|
Mechanical Properties
The mechanical properties of grade 439 stainless steel are displayed in the following table.
|
Properties
|
Metric
|
Imperial
|
|
Tensile strength
(annealed)
|
438 MPa
|
63500 psi
|
|
Yield strength
(annealed/ @strain 0.200 %)
|
263 MPa
|
38100 psi
|
|
Modulus of
elasticity
|
GPa
|
ksi
|
|
Poisson�s ratio
|
0.270 - 0.290
|
0.270 - 0.290
|
|
Elongation at break
(In 2", 50% cold worked)
|
2.80%
|
2.80%
|
|
Hardness, Rockwell B
(annealed)
|
72.9
|
72.9
|
Other Designations
Equivalent material to grade 439 stainless steel is DIN 1.4510.
Applications
Stainless steel grade 439 is applied in areas that require oxidation and corrosion resistance. It is also widely used in catering equipment.
Ferritic stainless steel 430
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430 is a low-carbon plain chromium ferritic stainless steel. The steel has good corrosion resistance in mildly corrosive environments and good resistance to oxidation at elevated temperatures. In the annealed condition the steel is ductile, does not harden excessively during cold work and can be formed using a large variety of roll forming or mild stretch-bending operations, as well as the more common drawing and bending processes. The steel has limited weldability and should not be used in the as welded condition for dynamic or impact loaded structures. Being a ferritic material, 430 is liable to brittle fracture at sub-zero temperatures, and cannot be used in cryogenic applications. As the steel does not contain nickel or molybdenum, it is cheaper than any of the 300 series steels.
Type 430 is ductile, has good forming characteristic and is readily fabricated by such operations as bending, pressing, drawing and heading. Its tendency to work harden is much less than that of the nickel-bearing 300 series stainless steel. Type 430 does not have as good corrosion resisting properties as the chromium nickel steels. However, it is suitable for interior architectural and decorative household appliances trim as well as automotive body molding. Cold rolled Type 430 has an attractive bright finish which can be maintained with reasonable care and periodic cleaning. Type 430 is by far the most popular of all straight chromium stainless steels. It is the general purpose alloy of the ferritic class. This type contains approximately 17 percent chromium and is often referred as 17 chrome stainless. The higher chromium content imparts improved resistance of Type 430 is slightly less than carbon steel, but its thermal conductivity is one half that of carbon steel. Chromium stainless steel is magnetic.
Typical Applications:
Automotive Trim and Molding
Builders Hardware
Fasteners
Furnace Parts
Interior Architectural Trim and Paneling
Kitchen Trim and Equipment
Storage Vessels
Television Cones
Tobacco Machinery
Tubing
Vaults
Zippers
Thursday, March 14, 2013
Stainless Steel - Grade 904L (UNS N08904)
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Stainless Steel - Grade 904L (UNS N08904
904L is a non-stabilised low carbon high alloy austenitic stainless steel. The addition of copper to this grade gives it greatly improved resistance to strong reducing acids, particularly sulphuric acid. It is also highly resistant to chloride attack - both pitting / crevice corrosion and stress corrosion cracking.
This grade is non-magnetic in all conditions and has excellent weldability and formability. The austenitic structure also gives this grade excellent toughness, even down to cryogenic temperatures.
904L does have very substantial contents of the high cost ingredients nickel and molybdenum. Many of the applications in which this grade has previously performed well can now be fulfilled at lower cost by duplex stainless steel 2205 (S31803 or S32205), so it is used less commonly than in the past.
Key Properties
These properties are specified for flat rolled product (plate, sheet and coil) in ASTM B625. Similar but not necessarily identical properties are specified for other products such as pipe, tube and bar in their respective specifications.
Grade Specification Comparison
904L N08904 904S13 1.4539 X1NiCrMoCuN25-20-5 2562
Chemical Formula
Fe, <0.02% C, 19-23% Cr, 23-28% Ni, 4-5% Mo, <2.0% Mn, <1.0% Si, <0.045% P, <0.035% S, 1.0-2.0% Cu
Corrosion Resistance
Although originally developed for its resistance to sulphuric acid it also has a very high resistance to a wide range of environments. A PRE of 35 indicates that the material has good resistance to warm sea water and other high chloride environments. High nickel content results in a much better resistance to stress corrosion cracking than the standard austenitic grades. Copper adds resistance to sulphuric and other reducing acids, particularly in the very aggressive "mid concentration" range.
In most environments 904L has a corrosion performance intermediate between the standard austenitic grade 316L and the very highly alloyed 6% molybdenum and similar "super austenitic" grades.
In aggressive nitric acid 904L has less resistance than molybdenum-free grades such as 304L and 310L.
For maximum stress corrosion cracking resistance in critical environments the steel should be solution treated after cold work.
Heat Resistance
Good resistance to oxidation, but like other highly alloyed grades suffers from structural instability (precipitation of brittle phases such as sigma) at elevated temperatures. 904L should not be used above about 400°C.
Heat Treatment
Solution Treatment (Annealing) - heat to 1090-1175°C and cool rapidly. This grade cannot be hardened by thermal treatment.
Welding
904L can be successfully welded by all standard methods. Care needs to be taken as this grade solidifies fully austenitic, so is susceptible to hot cracking, particularly in constrained weldments. No pre-heat should be used and in most cases post weld heat treatment is also not required. AS 1554.6 pre-qualifies Grade 904L rods and electrodes for welding of 904L.
Fabrication
904L is a high purity, low sulphur grade, and as such will not machine well. Despite this the grade can be machined using standard techniques.
Bending to a small radius is readily carried out. In most cases this is performed cold. Subsequent annealing is generally not required, although it should be considered if the fabrication is to be used in an environment where severe stress corrosion cracking conditions are anticipated.
Applications
Typical applications include:
• Processing plant for sulphuric, phosphoric and acetic acids
• Pulp and paper processing
• Components in gas scrubbing plants
• Seawater cooling equipment
• Oil refinery components
• Wires in electrostatic precipitators
Tuesday, March 12, 2013
Stainless steel & type of stainless steel
Stainless steel is a name given to a group of steel alloys with many differences in properties and behaviour having one property in common - resistance to corrosion.
When an Alloy of Steel contains more than approximately 10.5% Chromium it can be classed as a stainless steel. This is due to the fact that Chromium has a high affinity for oxygen and forms a tenacious, stable oxide film, which is resistant to further chemical or physical change. This film, known as the passive film, forms practically instantaneously in ordinary atmospheres and has the remarkable property of being self-healing and rebuilding when it has been removed.
The large group of stainless steels can be divided into two major groups, namely Austenitic and Ferritic. The Ferritic group can be split again into two groups, Martensitic and Ferritic. If you would like to know more about the different types of steels within these groups, please follow below.
Austenitic
This group of steel alloys contains chromium normally in the range 17-25% and nickel in a range 8-20%, with various additional elements to achieve the desired properties. In the fully annealed condition, the steel alloys exhibit a useful range of physical and mechanical properties. The mechanical properties can be can be increased with cold working. Welding of this group must be carried out with the correct methods but the low carbon content results in fewer problems than the Ferritic or Martensitic grades. Normally these steels are non-magnetic but when a significant amount of cold working is involved, as in centreless grinding, the magnetic permeability may be increased. If this group is included with the Ferritic and Martensitic groups it can be seen that the stainless steel alloys offer a great deal of versatility for applications within modern industry. The numbers listed below represent grades within British Standard 970(bar) and British Standard 1449 (sheet and plate). The figures in brackets after each number are the Euronorms currently being introduced to supersede British Standards.
Ferritic
This group contains a minimum of 17% chrome and carbon in the range of 0.08% - 2.00%. The increase in chromium imparts increased resistance to corrosion at elevated temperatures, but the lack of mechanical properties due to the fact that it cannot be heat treated, limits its applications. Like martensitics they are magnetic and the welding of this group should be carried out with the necessary precautions.
Martensitic
This group contains a minimum of 12% chrome and usually a maximum of 14% with carbon in the range of 0.08% - 2.00%. Due to the high carbon content of the steel, it responds well to heat treatment to give various mechanical strengths, such as hardness. The carbon, however, is detrimental when welding and care should be taken during this operation. In the heat-treated condition this group of steels show a useful combination of corrosion resistance and mechanical properties that qualify them for a wide range of applications. The numbers listed below represent grades within British Standard 970. The figures in brackets after each number are the Euronorms currently being introduced to supersede British Standards.
Monday, March 11, 2013
Effects of Alloying Elements in Steel
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Effects of Alloying Elements in Steel
Steel is basically iron alloyed to carbon with certain additional elements to give the required properties to the finished melt. Listed below is a summary of the effects various alloying elements in steel.
Carbon
The basic metal, iron, is alloyed with carbon to make steel and has the effect of increasing the hardness and strength by heat treatment but the addition of carbon enables a wide range of hardness and strength.
Manganese
Manganese is added to steel to improve hot working properties and increase strength, toughness and hardenability. Manganese, like nickel, is an austenite forming element and has been used as a substitute for nickel in the A.I.S.I 200 Series of Austenitic stainless steels (e.g. A.I.S.I 202 as a substitute for A.I.S.I 304)
Chromium
Chromium is added to the steel to increase resistance to oxidation. This resistance increases as more chromium is added. 'Stainless Steel' has approximately 11% chromium and a very marked degree of general corrosion resistance when compared with steels with a lower percentage of chromium. When added to low alloy steels, chromium can increase the response to heat treatment, thus improving hardenability and strength.
Nickel
Nickel is added in large amounts, over about 8%, to high chromium stainless steel to form the most important class of corrosion and heat resistant steels. These are the austenitic stainless steels, typified by 18-8, where the tendency of nickel to form austenite is responsible for a great toughness and high strength at both high and low temperatures. Nickel also improves resistance to oxidation and corrosion. It increases toughness at low temperatures when added in smaller amounts to alloy steels.
Molybdenum
Molybdenum, when added to chromium-nickel austenitic steels, improves resistance to pitting corrosion especially by chlorides and sulphur chemicals. When added to low alloy steels, molybdenum improves high temperature strengths and hardness. When added to chromium steels it greatly diminishes the tendency of steels to decay in service or in heat treatment.
Titanium
The main use of titanium as an alloying element in steel is for carbide stabilisation. It combines with carbon to for titanium carbides, which are quite stable and hard to dissolve in steel, this tends to minimise the occurrence of inter-granular corrosion, as with A.I.S.I 321, when adding approximately 0.25%/0.60% titanium, the carbon combines with the titanium in preference to chromium, preventing a tie-up of corrosion resisting chromium as inter-granular carbides and the accompanying loss of corrosion resistance at the grain boundaries.
Phosphorus
Phosphorus is usually added with sulphur to improve machinability in low alloy steels, phosphorus, in small amounts, aids strength and corrosion resistance. Experimental work shows that phosphorus present in austenitic stainless steels increases strength. Phosphorus additions are known to increase the tendency to cracking during welding.
Sulphur
When added in small amounts sulphur improves machinability but does not cause hot shortness. Hot shortness is reduced by the addition of manganese, which combines with the sulphur to form manganese sulphide. As manganese sulphide has a higher melting point than iron sulphide, which would form if manganese were not present, the weak spots at the grain boundaries are greatly reduced during hot working.
Selenium
Selenium is added to improve machinability.
Niobium (Columbium)
Niobium is added to steel in order to stabilise carbon, and as such performs in the same way as described for titanium. Niobium also has the effect of strengthening steels and alloys for high temperature service.
Nitrogen
Nitrogen has the effect of increasing the austenitic stability of stainless steels and is, as in the case of nickel, an austenite forming element. Yield strength is greatly improved when nitrogen is added to austenitic stainless steels.
Silicon
Silicon is used as a deoxidising (killing) agent in the melting of steel, as a result, most steels contain a small percentage of silicon. Silicon contributes to hardening of the ferritic phase in steels and for this reason silicon killed steels are somewhat harder and stiffer than aluminium killed steels.
Cobalt
Cobalt becomes highly radioactive when exposed to the intense radiation of nuclear reactors, and as a result, any stainless steel that is in nuclear service will have a cobalt restriction, usually aproximately 0.2% maximum. This problem is emphasised because there is residual cobalt content in the nickel used in producing these steels.
Tantalum
Chemically similar to niobium and has similar effects.
Copper
Copper is normally present in stainless steels as a residual element. However it is added to a few alloys to produce precipitation hardening properties.
Sunday, March 10, 2013
Ferritic Stainless Steels 444 UNS S44400
444 UNS S44400
This alloy is a low carbon and low nitrogen ferritic stainless steel that contains 18% chromium and 2% molybdenum. One advantage of Type 444 over austenitic stainless steels, such as 304 and 316 alloys, is the practical immunity of the Type 444 alloy to chloride stress corrosion cracking (SCC). The alloy’s enhanced resistance to pitting and crevice corrosion combined with its good general corrosion resistance to a multitude of environments makes it an excellent choice for a wide range of applications such as heat exchanger tubing, food processing equipment, hot water tanks, and automotive exhaust.
CHEMICAL COMPOSITION LIMITS (%)
CHEMICAL COMPOSITION LIMITS (%)
Carbon
C |
Manganese
Mn |
Phosphorus
P |
Sulfur
S |
Silicon
Si |
Chromium
Cr |
Nickel
Ni |
Nitrogen
N |
Titanium & Columbium
Ti&Cb | |
0.07
|
1.00
|
0.040
|
0.030
|
1.00
|
17.00-19.00
|
0.50
|
1.75-2.50
|
0.04
|
Ti + Cb 0.20+4
(C+N) min; 0.80 max |
REPRESENTATIVE MECHANICAL PROPERTY
CONDITION
|
TENSILE STRENGTH
|
YIELD STRENGTH
|
ELONGATION
|
ROCKWELL
|
KSI
|
MPA
|
KSI
|
MPA
|
IN 2 INCHES %
| |||
Annealed
|
60
|
(415)
|
40
|
(275)
|
20
|
B-96 max.
| |
*Minimum
Chemical composition is percent maximum unless shown as a range or a minimum. Information presented as a guide for reference purposes only and is not intended for product design or application. | |||||||
Martensitic Stainless Steel 420, 2Cr13
420 stainless steel is a martensitic higher carbon version of types 410 and 416 stainless that can be hardened by heat treatment. It contains a minimum of 12 percent chromium, sufficient to give 420 corrosion resistance properties. It has good ductility in the annealed condition but is capable of being hardened up to 50 RHC. Its best corrosion resistance is achieved when 420 is hardened and surface ground or polished. In the hardened condition, 420 has good corrosion resistance to the atmosphere, foods, fresh water, mild alkalies and acids, steam, sterilizing solutions, crude oil, gasoline, and other similar corrosive media. The higher carbon content employed in 420 gives higher strength and hardness over stainless grades 410 and 416. In the annealed condition, 420 is relatively easy to machine, but if hardened to above 30 HRC, machining becomes more difficult. Fabrication must be by methods allowing for poor weldability and usually allow for a final harden and temper heat treatment. 420 is not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties. The scaling temperature is approximately 650°F.
Applications
420 stainless is widely used in the medical and cutlery industries. It is suitable for applications such as instruments, knives, hand tools, pump shafts and plastic moulds. 420 is not recommended for use in temperatures above the relevant tempering temperature, because of the reduction in mechanical properties.
Corrosion Resistance
Best corrosion resistance of 420 stainless is achieved when 420 is hardened and surface ground or polished. In the hardened condition 420 has good corrosion resistance to atmosphere, foods, fresh water, mild alkalis and acids, steam, crude oil and other similar corrosive media.
Hardening
420 is suitable for heat treatment up to 52 HRc or higher depending on the carbon content and size of the component. European grade 1.2083 is a high carbon type 420 stainless and is ideally suited for application where highest achievable hardness is required.
Form of Supply
main sizes ass hot rolled Thk 4.0--60mm x Width 20--350mm
Cold Rolled Thk 0.3--6.0 x Width 20--350mm
Martensitic Stainless Steel 420, 2Cr13
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420 stainless steel is a martensitic higher carbon version of types 410 and 416 stainless that can be hardened by heat treatment. It contains a minimum of 12 percent chromium, sufficient to give 420 corrosion resistance properties. It has good ductility in the annealed condition but is capable of being hardened up to 50 RHC. Its best corrosion resistance is achieved when 420 is hardened and surface ground or polished. In the hardened condition, 420 has good corrosion resistance to the atmosphere, foods, fresh water, mild alkalies and acids, steam, sterilizing solutions, crude oil, gasoline, and other similar corrosive media. The higher carbon content employed in 420 gives higher strength and hardness over stainless grades 410 and 416. In the annealed condition, 420 is relatively easy to machine, but if hardened to above 30 HRC, machining becomes more difficult. Fabrication must be by methods allowing for poor weldability and usually allow for a final harden and temper heat treatment. 420 is not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties. The scaling temperature is approximately 650°F.
Applications
420 stainless is widely used in the medical and cutlery industries. It is suitable for applications such as instruments, knives, hand tools, pump shafts and plastic moulds. 420 is not recommended for use in temperatures above the relevant tempering temperature, because of the reduction in mechanical properties.
Corrosion Resistance
Best corrosion resistance of 420 stainless is achieved when 420 is hardened and surface ground or polished. In the hardened condition 420 has good corrosion resistance to atmosphere, foods, fresh water, mild alkalis and acids, steam, crude oil and other similar corrosive media.
Hardening
420 is suitable for heat treatment up to 52 HRc or higher depending on the carbon content and size of the component. European grade 1.2083 is a high carbon type 420 stainless and is ideally suited for application where highest achievable hardness is required.
Form of Supply
main sizes ass hot rolled Thk 4.0--60mm x Width 20--350mm
Cold Rolled Thk 0.3--6.0 x Width 20--350mm
Thursday, March 7, 2013
Nickel-copper alloy Monel 400
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Nickel-copper alloy Monel 400 Equivalents: UNS N04400/Alloy 400/Werkstoff 2.4360
Monel 400 is a nickel-copper alloy (about 67% Ni – 23% Cu) that is resistant to sea water and steam at high temperatures as well as to salt and caustic solutions. Alloy 400 is a solid solution alloy that can only be hardened by cold working. This nickel alloy exhibits characteristics like good corrosion resistance, good weldability and high strength. A low corrosion rate in rapidly flowing brackish or seawater combined with excellent resistance to stress-corrosion cracking in most freshwaters, and its resistance to a variety of corrosive conditions led to its wide use in marine applications and other non-oxidizing chloride solutions. This nickel alloy is particularly resistant to hydrochloric and hydrofluoric acids when they are de-aerated. As would be expected from its high copper content, alloy 400 is rapidly attacked by nitric acid and ammonia systems.
Monel 400 has great mechanical properties at subzero temperatures, can be used in temperatures up to 1000° F, and its melting point is 2370-2460° F. However, alloy 400 is low in strength in the annealed condition so, a variety of tempers may be used to increase the strength.
In what forms is Monel 400 Available?
Sheet
Plate
Bar
Pipe & Tube (welded & seamless)
Fittings (i.e. flanges, slip-ons, blinds, weld-necks, lapjoints, long welding necks, socket welds, elbows, tees, stub-ends, returns, caps, crosses, reducers, and pipe nipples)
Wire
What are the characteristics of Monel 400?
Resistant to seawater and steam at high temperatures
Excellent resistance to rapidly flowing brackish water or seawater
Excellent resistance to stress corrosion cracking in most freshwaters
Particularly resistant to hydrochloric and hydrofluoric acids when they are de-aerated
Offers some resistance to hydrochloric and sulfuric acids at modest temperatures and concentrations, but is seldom the material of choice for these acids
Excellent resistance to neutral and alkaline salt
Resistance to chloride induced stress corrosion cracking
Good mechanical properties from sub-zero temperatures up to 1020° F
High resistance to alkalis
Corrosion Resistant Monel 400
Alloy 400 is virtually immune to chloride ion stress corrosion cracking in typical environments. Generally, its corrosion resistance is very good in reducing environments, but poor in oxidizing conditions. It is not useful in oxidizing acids, such as nitric acid and nitrous. Nevertheless, it is resistant to most alkalis, salts, waters, food products, organic substances and atmospheric conditions at normal and elevated temperatures.
This nickel alloy is attacked in sulfur-bearing gases above approximately 700° F and molten sulfur attacks the alloy at temperatures over approximately 500° F.
Monel 400 offers about the same corrosion resistance as nickel but with higher maximum working pressures and temperatures and at a lower cost due to its superior ability to be machined.
In what applications is Monel 400 used?
Marine engineering
Chemical and hydrocarbon processing equipment
Gasoline and freshwater tanks
Crude petroleum stills
De-aerating heaters
Boiler feed water heaters and other heat exchangers
Valves, pumps, shafts, fittings, and fasteners
Industrial heat exchangers
Chlorinated solvents
Crude oil distillation towers
Wednesday, March 6, 2013
Stainless steel 440C
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440C Stainless steel is a type of modern steel and famous for its high corrosion resistant, wear resistance, strength and hardness qualities, among all the stainless alloys, capable of attaining (after heat treatment) the highest hardness (60 HRC). It has good resistance to the atmosphere, fresh water and mild acids. It has best resistance in the hardened, tempered and passivated condition. It allows creating a smooth polished surface and Razor sharp edges. It is being used in cutting instruments, rolling element bearings, valve seats, high quality knife blades, surgical instruments, chisels, ball bearings and valve parts and most commonly used in the production of Cutting tools, including Haircutting Scissors, daggers and swords.
Grades 440A and 440B are identical except for slightly lower carbon contents (0.60 - 0.75% and 0.75 - 0.95% respectively), they attain lower hardness but have slightly higher corrosion resistances. Although all three versions of this grade are standard grades, in practice 440C is more available than the A or B variants.
Another alloy 440F (UNS S44020) also exists, with the same high carbon content as 440C.
440 Steel family, there is a new modern kind of steel, known as 440V steel. Basically, it is the advancement of 440C steel. This steel has same level of hardness like 440C, but it has more corrosion resistant ability and more machine-ability.
Heat Resistance:
Not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties by over-tempering.
Not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties by over-tempering.
Heat Treatment:
Annealing - Full anneal - 850-900C, slow furnace cool to about 600C and then air cool. Sub-critical Annealing - 735-785C and slow furnace cool.
Annealing - Full anneal - 850-900C, slow furnace cool to about 600C and then air cool. Sub-critical Annealing - 735-785C and slow furnace cool.
Hardening - Heat to 1010-1065C, followed by quenching in warm oil or air. Oil quenching is necessary for heavy sections. Immediately temper at 150-370C to obtain a wide variety of hardness values and mechanical properties as indicated in the accompanying table.
Tempering in the range 425-565C is to be avoided because of reduced impact resistance and corrosion resistance. Tempering in the range 590-675C results in lower hardness (the product become machinable) and high impact resistance.
Welding
If welding is necessary pre-heat at 250C and follow welding with a full anneal. Grade 420 filler will give a high hardness weld (not as high as the 440C). Generally welding of 440C is not recommended due to its hardening capability which can lead to the formation cracks within or near the weld.
If welding is necessary pre-heat at 250C and follow welding with a full anneal. Grade 420 filler will give a high hardness weld (not as high as the 440C). Generally welding of 440C is not recommended due to its hardening capability which can lead to the formation cracks within or near the weld.
Machining
In the annealed condition this grade is relatively easily machined; approximately the same as for high speed steel. If this grade is hardened machining becomes very difficult and probably impossible.
Composition
Chemical Composition ranges of 440C stainless steel
Chemical Composition ranges of 440C stainless steel
| Grade440C | ||
| Ingredients | Min. | Max. |
| Carbon | 0.95 | 1.20 |
| Manganese | - | 1.00 |
| Silicon | - | 1.00 |
| Phosphorus | - | 0.040 |
| Sulphur | - | 0.030 |
| Chromium | 16.00 | 18.00 |
| Molybdenum | - | 0.75 |
| Iron | Balance | |
440C Physical Properties
Physical properties for grade 440 stainless steels.
Physical properties for grade 440 stainless steels.
| Grade | Density (kg/m3) | Elastic Modulus (GPa) | Mean Coefficient of Thermal Expansion (mm/m/C) | Thermal Conductivity (W/m.K) | Specific Heat 0-100C (J/kg.K) | Electrical Resistivity (nW.m) | |||
| 0-100C | 0-200C | 0-600C | at 100C | at 500C | |||||
| 440A/B/C | 7650 | 200 | 10.1 | 10.3 | 11.7 | 24.2 | - | 460 | 600 |
440C Related Specifications
| USA | Germany | Japan | Australia |
| ASTM A276-98b 440C SAE 51440C AISI 440C UNS S44004 | W.Nr 1.4125 X105CrMo17 | JIS G4303 SuS 440C | AS 2837-1986 440C |
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