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Frequently Asked Questions About Stainless Steel

  1. Can I use stainless steel at high temperatures?
    Various stainless steel types are used throughout the entire temperature range from ambient to 1100 ° C. Class selection depends on several factors:
    a) Maximum working temperature

    b) Temperature time, cyclical nature of the process

    c) Atmospheric type, oxidizing, reducing, dehydrogenating, carbonating.

    d) Power requirement In European standards, a distinction is made between stainless steels and heat resistant steels.

    However, this distinction is often cloudy and it is useful to consider them as a series of steel. In the case of artifacts, chromium and silicon give more oxidation resistance. Increasing amount of Nickel gives more carburizing resistance. Stainless steels have good strength and good resistance to corrosion and oxidation at high temperatures. Stainless steels are used at temperatures up to 1700 ° F for 304 and 316 and at temperatures up to 2000 F up to 2100 ° F for stainless steel 309 (S) and 310 (S) at high temperature. Stainless steel is widely used in aircraft and aerospace applications with heat exchangers, superheaters, boilers, feed water heaters, valves and main steam lines. Figure 1 (below) shows a broad concept of stainless steel hot strength advantages over low carbon unalloyed steel It offers. Table 1 (below) shows the temperature against short-time tensile and yield strength. Table 2 (below) shows generally accepted temperatures for both intermittent and continuous service. Changes in metallurgical structure at time and temperature can be expected with any metal. In stainless steel, the changes may be emollient, carbide precipitate or brittle. 300 series (304, 316, etc.) Stainless steels suffer from loss of softening or strength, and the 800 ° F for non-hardening 400 (410, 420, 440) series and the 800 ° F- See Table 1). Coagulation sedimentation can occur at temperatures ranging from 800 to 1600 ° F in the 300 series. It can be deterred by choosing a grade designed to prevent carbide precipitation, i.e. 347 (Cb added) or 321 (Ti added). If carbide precipitation occurs, it can be removed by heating above 1900 ° and cooling rapidly.

    In addition to the 400 hardenable series, the hardenable 400 series and duplex stainless steels containing more than 12% chromium are exposed to brittleness when exposed to 700 – 950 ° F for a long period of time. This sometimes calls for the embrittlement of the 885F because it is the fastest temperature for embrittlement. The 885F results in increased hardness and tensile strength at room temperature, low ductility and low ductility, but maintains the desired mechanical properties at operating temperatures.

  2. Can I use stainless steel at low temperatures?

    Austenitic stainless steels are widely used for servicing as low as liquid helium temperature (-269 ° C). This is largely due to a lack of transition clearly defined from ductility to brittle fracture in the impact strength test. Hardness is measured by impacting a small sample with a rocking hammer. The distance that the darbenin passes after the darbenin is a measure of the distance. The shorter the distance, the harder the steel is to absorb the hammer energy by the sample. The hardness is measured in Joules (J). Minimum durability values ​​are specified for different applications. For most service conditions, a value of 40 J is considered reasonable. Steels with ferritic or martensitic structure exhibit a sudden change without ductile (safe) to brittle (unsafe) cracking over a small temperature difference. Even the best of these steels show this behavior at temperatures higher than -100 degrees C and in most cases only below zero. On the other hand, austenitic steels only show a gradual decline in impact strength and are still above 100 J at -196 ° C Another factor that affects steel selection at low temperatures is the ability to resist austenite to martensite transformation.
  3. Is stainless steel rusty?

    Although stainless steel is more resistant to corrosion than normal carbon or alloy steels, it may undergo corrosion in some cases. ‘Spotless’ spot is not impossible’. In normal atmospheric or water-based environments, stainless steel will not corrode as shown by household wash basin units, cutlery, pots, and work surfaces. On more aggressive conditions, basic stainless steel types can undergo corrosion and higher alloyed stainless steels can be used.
  4. How do I choose which stainless steel to use?
     

    Most decisions about which steel to use depend on a combination of the following factors:
    a) What is the corrosive environment? – Atmospheric, water, concentration of certain chemicals, chlorine content, acidity.

    b) What is the working temperature? – High temperatures generally increase the corrosion rates and therefore show a higher note. Low temperatures will require tough austenitic steel.

    c) Which power is required? – Strengths higher than austenitic, duplex, martensitic and PH steels can be obtained. Other operations such as source and formatting often affect which one is most appropriate. For example, high strength austenitic steels produced as the process hardens will not be suitable when welding is required due to the softness of the process steel.

    d) Which source to be welded? – Austenitic steels are often more susceptible than other types. Ferritic steels can be welded in thin sections. Duplex steels require more care than austenitic steels, but are now considered fully weldable. Martensitic and PH classes may be less common.

    e) How much formatting is required to make the compound? – Austenitic steels are the most formable of all types that can be subjected to high-grade deep drawing or stretching. In general, ferritic steels are not formable, but they can still produce very complex shapes. Duplex, martensite and PH grades can not be specially shaped.

    f) Which product form is required? – Not all qualifications are available in all product forms and sizes, eg, sheet, rod, tube. In general, austenitic steels are available in a wide variety of sizes in all product forms. It is likely that the ferritics are more than the plate-shaped bar. For martensitic steels, the opposite is true.

    g) What are the expectations of the customer regarding the performance of the material? – This is an important issue that is often missed in the electoral process. In particular, what are the aesthetic requirements according to the structural requirements? Design life is sometimes determined, but it is very difficult to guarantee.

    h) There may also be special requirements such as non-magnetic properties to be considered.

    i) It should not be forgotten that steel type is not the only factor in material selection. Surface coating is of utmost importance in many applications, especially when it is a strong aesthetic component.

    j) Eligibility. It may be an excellent choice of technical material that can not be applied because it is not available at the time.

    k) Cost. Sometimes the right technical option is ultimately not just chosen for cost reasons. However, it is important to evaluate the cost correctly. Many stainless steel applications have been shown to be advantageous over a cost-effective lifecycle cost from the initial cost.

  5. How many types of stainless steel are available?
    Stainless steel is generally divided into 5 types:

    a) Ferritic – These steels are chromium based, containing a small amount of carbon and generally less than 0.10%. These steels have a microstructure similar to carbon and low alloy steels. They are generally limited for use in relatively thin sections due to lack of strength in the welds. However, if the source is not required, it offers a wide range of applications. They can not be hardened by heat treatment. Molybdenum-added high-chromium steels can be used in highly aggressive conditions such as sea water. Ferritic steels have also been chosen for resistance to stress corrosion cracking. Austenitic stainless steels are not as formable. They are magnetic.

    b) Austenitic – These steels are the most common. Microstructures are obtained by the addition of Nickel, Manganese and Nitrogen. It is the same structure that occurs in normal steels at higher temperatures. This structure characterizes weldability and formable combinations of these steels. Corrosion resistance can be increased by adding Chromium, Molybdenum and Nitrogen. They can not be hardened by heat treatment, but they have working properties that can be hardened to high strength levels while maintaining a useful ductility and toughness level. Standard austenitic steels are susceptible to stress corrosion cracking. Higher nickel austenitic steels have increased resistance to stress corrosion cracking. Nominally they are not magnetic, but they generally exhibit some magnetic response depending on the composition and the hardness of the workpiece.

    c) Martensitic – These steels are similar to chromium-based ferritic steels, but with carbon levels as high as 1%. This allows them to be hardened and tempered like carbon and low alloy steels. They are used where high strength and medium corrosion resistance are required. It is more common in long products than it is in sheet and plate form. They generally have low weldability and formability. They are magnetic.

    d) Duplex – These steels have a microstructure of approximately 50% ferritic and 50% austenitic. This gives them a higher strength than ferritic or austenitic steels. The tension is resistant to corrosion cracking. Steels called “oil-free duplexes” have been formulated to have corrosion resistance similar to that of standard austenitic steels, but with higher strength and resistance to stress corrosion cracking. “Superduplex” steels are resistant to all kinds of corrosion and durability compared to standard austenitic steels. They can be welded, but they must be careful in selecting welding consumables and heat inputs. They have medium format. Magnetites are not ferritic, martensitic and PH grades depending on the 50% austenitic phase.

    e) Precipitation hardening (PH) – These steels can develop very high strength by adding elements such as Copper, Niobium and Aluminum to the steel. With an appropriate “aging” heat treatment, very fine particles form in the steel matrix, which gives strength. These steels can be processed to a highly complex shape requiring good tolerances prior to final aging, since there is minimal degradation from the final treatment. This is in contrast to traditional hardening and tempering processes in martensitic steels, where degradation is more of a problem. Corrosion resistance is comparable to standard austenitic steels such as 1.4301 (304).

  6. Is not stainless steel magnetic?
    It is usually stated that “the stainless steel is not magnetic”. This is absolutely not true and the real situation is quite complicated. The magnetic response or magnetic permeability is derived from the microstructure of the steel grade. A completely non-magnetic material has relative magnetic permeability. The austenitic structure is not completely magnetic and will have a 100% austenitic stainless steel permeability. In practice this can not be achieved. There is always a small amount of ferrite and / or martensite in the steel and therefore the permeability values ​​are always above 1. Typical values ​​for standard austenitic stainless steels may range from 1.05 to 11.11. It is possible that the magnetic permeability of the austenitic steels changes during the process. For example, cold work and welding are obliged to increase the amount of martensite and ferrite, respectively, in steel. A known example is a stainless steel sink where a stainless steel sink has a very low magnetic response and the pressed drum has a higher response due to the formation of martensite, especially at the corners. In principle, for “non-magnetic” applications, austenitic stainless steels are used for imaging (MRI). In these cases, it is generally necessary to accept maximum magnetic permeability between the customer and the supplier. It may be as low as 1.004.
  7. What are the right standards for stainless steel?
     

    The most common European standards for stainless steel are:

    Standard Number Title Relevant Technical Information
    EN 10088-1 List of stainless steels
    EN 10088-2 Technical delivery conditions for sheet/plate and strip for corrosion resisting steels for general purposes Chemical Composition
    Properties of Ferritic Steels
    Properties of Martensitic Steels
    Properties of Austenitic Steels
    Properties of Duplex Steels
    Properties of PH Steels
    EN 10088-3 Technical delivery conditions for semi-finished products, bars, rods, wire, sections and bright products for corrosion resisting steels for general purposes All Products
    Chemical Composition
    Standard Products
    Properties of Ferritic Steels
    Properties of Martensitic Steels
    Properties of Austenitic Steels
    Properties of Duplex Steels
    Properties of PH Steels
    Bright Bars
    Properties of Ferritic Steels
    Properties of Martensitic Steels
    Properties of Austenitic Steels
    Properties of Duplex Steels
    Properties of PH Steels
    EN 10095 Heat resisting steels and nickel alloys Chemical Composition
    Ambient Temperature Properties
    EN 10028-7 Flat products made of steels for pressure purposes – Stainless steels Elevated Temperature Properties
    EN 10296-2 Welded circular steel tubes for mechanical and general engineering purposes – Technical delivery conditions – Stainless steel Chemical Composition
    Mechanical Properties
    Tolerances
    EN 10297-2 Seamless circular steel tubes for mechanical and general engineering purposes – Technical delivery conditions – Stainless steel Chemical Composition
    Mechanical Properties
    Tolerances
    EN 10216-5 Seamless steel tubes for pressure purposes – Technical delivery conditions – Stainless steel tubes  Chemical Composition
    EN 10217-7 Welded steel tubes for pressure purposes – Technical delivery conditions – Stainless steel tubes  Chemical Composition
    Mechanical Properties

    These standards are based on old national standards, and users are encouraged to use them. However, it is clear that the old standards are still in use, as most of the existing drawings and company features refer to them. For this reason, it is possible to encounter the following standards:

    BS 1449 and BS1501 for flat products

    BS 970 for long products

    US standards such as ASTM and ASME are very important and will never be changed. Common standards:

    Standard Number Title Relevant Technical Information
    ASTM A240 Chromium and chromium-nickel stainless steel plate, sheet and strip for pressure vessels Chemical Composition Austenitic Steels
    Chemical Composition Ferritic Steels
    Chemical Composition  Martensitic Steels
    Chemical Composition  Duplex Steels
    Chemical Composition  PH Steels
    ASTM A276 Standard Specification for Stainless Steel Bars and Shapes Chemical Composition Austenitic Steels
    Chemical Composition Ferritic Steels
    Chemical Composition  Martensitic Steels
    Chemical Composition  Duplex Steels
    Chemical Composition  PH Steels
    ASTM A312 Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipes Chemical Composition Austenitic Steels
    Chemical Composition Ferritic Steels
    Chemical Composition  Martensitic Steels
    Chemical Composition  Duplex Steels
    Chemical Composition  PH Steels

     

  8. What kind of corrosion can occur in stainless steels?
    The most common types of corrosion in stainless steel are:

    a) Pitting corrosion – The passive layer of the stainless steel can be attacked by some chemical species. The chloride ion is the most common Cl- and is found in everyday materials such as salt and bleach. Pitting corrosion is avoided if stainless steel does not come into contact with harmful chemicals for a long time or if a more resistant steel grade is chosen for the attack. The pitting corrosion resistance can be evaluated using the Pitting Resistance Equivalent Number calculated from the alloy content.

    b) Range cracking – Stainless steel requires an oxygen supply to ensure that the passive layer is formed on the surface. In very narrow cracks, it is not always possible for oxygen to reach the stainless steel surface, which makes it vulnerable to attack. Crack corrosion is prevented by sealing the cracks with a resilient sealant or with a more corrosion resistant seal.

    c) General corrosion – Normally, stainless steel does not wear homogeneously as ordinary carbon and alloy steels. However, with certain chemicals, especially acids, the passive layer can be attacked homogeneously depending on concentration and temperature, and the metal loss is distributed throughout the entire surface of the steel. In some concentrations, hydrochloric acid and sulfuric acid are particularly aggressive against stainless steel.

    d) Stress corrosion cracking (SCC) – This is a relatively rare type of corrosion that requires a very special combination of tensile strength, temperature and corrosive species, usually chloride ion, to come to the foreground. Typical applications that the SCC might come up with are hot water storage and swimming pools. Another form known as sulfur-stress corrosion cracking (SSCC) is associated with hydrogen sulfide in oil and gas exploration and production.

    e) Intergranular corrosion – This is now a fairly rare form of corrosion. If the level of carbon in the steel is too high, it combines with Chromium Carbon to form Chromium Carbide. This occurs at temperatures of about 450-850 degrees Celsius. This process is also called sensitization and typically occurs during welding. The chromium present to form the passive layer can be effectively reduced and corroded. By choosing a low carbon quality termed ‘L’ qualities or by using a steel with Titanium or Niobium, which preferably combines with carbon.

    f) Galvanic corrosion – If two different metals are in contact with each other and with an electrolyte, water or other solution, it is possible to install a galvanic cell. This is like a battery and can accelerate the corrosion of less ‘noble’ metal. The metal can be prevented by separating it with a non-metallic insulator such as rubber.

  9. What is Stainless Steel?
    Stainless steel is an Iron alloy with a minimum of 10.5% Chrome. Chromium produces a thin oxide layer on the surface of the steel, known as the ‘passive layer’. This prevents further surface wear. Increasing the amount of chrome gives more resistance to corrosion. The stainless steel also contains various amounts of Carbon, Silicone and Manganese. Other elements such as nickel and molybdenum can be added to impart other useful properties such as increased formability and increased corrosion resistance.
  10. What is martensitic stainless steel?
     

    Stainless steel is the name given to a corrosion and heat resistant steel family containing a minimum of 10.5% chromium. There are a range of structural and engineering carbon strands meeting different strength, weldability and toughness requirements, as well as a wide variety of stainless steels with increasingly higher levels of corrosion resistance and strength. This is due to the controlled addition of alloy elements, each offering specific properties in terms of strength and strength to withstand different environments. The existing stainless steel grades can be divided into five basic families: ferritic, martensitic, austenitic, duplex and precipitation hardenable.

    Martensitic Stainless Steels

    Martensitic stainless steels are similar to low alloy or carbon steels. The “trunk-centered tetragonal” (bcT) crystal structure has a structure similar to ferritic. Due to the addition of carbon, they can be hardened and strengthened by heat treatment similar to carbon steels. They are classified as a & quot; hard & quot; ferro magnetic group. The main alloy element is chromium with a typical content of 12-15%. In the attained state, there are tensile yield strengths of approx. 275 MPa and are therefore usually processed, cold-formed or cold-worked in this case. The strength obtained by heat treatment depends on the carbon content of the alloy. Increasing the carbon content increases the strength and hardness potential, but reduces ductility and toughness. Higher carbon qualities can be heat treated up to 60 HRC hardness. The optimum corrosion resistance is achieved in the treated, ie hardened and tempered state. Martensitic qualities have been developed with nitrogen and nickel additives, but with lower carbon levels than conventional qualities. These steels have durability, weldability and corrosion resistance.
    Examples of martensitic qualities (420S45) 1.4028, 431 (1.4057), conventional carbon-hardenable qualities and 248SV (1.4418), one of the lower carbon / nitrogen classes,

  11. What is ‘multiple certification’?
    This is where a steel group meets more than one specification or class. By limiting the number of different types of steel, it is a way of allowing the smelting workshop to produce stainless steel more efficiently. The chemical composition and mechanical properties of steel can meet more than one qualities in the same standard or in a series of standards. This also allows stock holders to reduce their stock levels to the minimum. The 1.4401 and 1.4404 (316 and 316L) doubles as a dual certificate – ie the carbon content is less than 0.030%. Steel approved by both European and US standards is also widely available.
  12. What is 316 stainless steel used for?
    Stainless steel 316 is part of a family of stainless steel alloys (301, 302, 303, 304, 316, 347). The 316 family is a group of austenitic stainless steels with superior corrosion resistance to 304 stainless steel. This alloy is suitable for welding because it has a lower carbon content than alloys 301 to 303 to prevent carbide precipitation in welding applications. Molybdenum addition and slightly higher nickel content make 316 Stainless Steel suitable for architectural applications in severe environments, from dirty marine environments to sub-zero temperature areas. Equipment used in chemical, food, paper, mining, pharmaceutical and petroleum industries generally includes 316 Stainless Steel.
  13. What is used for stainless steel?
    Thousands of applications use various types of stainless steels. The following will give you an idea of ​​exactly how to use it:

    Used at home – cutlery, washbasins, pots, washing machine drums, microwave oven liners, razor blades

    Architectural / Civil Engineering – coatings, balustrades, door and window equipment, street furniture, structural parts, reinforcement bar, lighting columns, lentolars, wall supports Transportation – exhaust systems, car trim / grids, road tankers, ship containers, gem chemical tanks, garbage trucks

    Chemical / Pharmaceutical – pressure vessels, process pipes.

    Oil and Gas – platform accommodation, cable ducts, submarine pipelines.

    Medicine – Surgical instruments, surgical implants, MRI scanners.

    Food and Beverage – Catering equipment, beer preparation, distillation, food processing.

    Water – Water and sewage treatment, water pipes, hot water storage.

    General – springs, fasteners (bolts, nuts and washers), cable.

  14. What is the stainless steel composition?
     

    Stainless steel is available in many different alloys with many different elements, but the basic components are iron, carbon and chromium. Low carbon steel containing at least 12 percent chromium forms an even protective oxide layer on the surface and is therefore non-rusting.

  15. Which surfaces are available on stainless steels?

    There are many different surface options in stainless steel. Some of them originate from the mill, but most of them are applied later, for example polished, brushed, sprayed, carved and colored polishes. The importance of surface finishing to determine the corrosion resistance of the stainless steel surface can not be overemphasized. A rough surface coating can effectively reduce corrosion resistance to a lower quality of stainless steel. European standards for stainless steels have attempted to define the most common surface finishes. However, due to the proprietary nature of many of the suppliers, it is possible that a complete standardization is not possible. This is a summary of the most common types for each product form Common Surface Coatings for Flat Products from 10088-2 (for complete list see Determining the surfaces for stainless steel flat products (plate and plate)

    Surface Finish Code Description
    Mill finishes
    1D Hot rolled, heat treated, pickled. The most common hot rolled finish. A non reflective, rough surface. Not normally used for decorative applications
    2B Cold rolled, heat treated, pickled, pinch passed. The most common cold rolled mill finish. Dull grey slightly reflective finish. Can be used in this condition or frequently is the starting point for a wide range of polished finishes.
    2D Cold rolled, heat treated, pickled.
    2H Work hardened by rolling to give enhanced strength level. Various ranges of tensile or 0.2% proof strength are given in EN 10088-2 up to 1300 MPa and 1100 MPa respectively dependent on grade
    2Q Cold rolled hardened and tempered. Applies to martensitic steels which respond to this kind of heat treatment.
    2R Cold rolled and bright annealed, still commonly known as BA. A bright reflective finish. Can be used in this condition or as the starting point for polishing or other surface treatment processes e.g. colouring

    In the following codes “1” means hot rolled as starting point and “2” as cold rolled.

    Special Finishes
    1G or 2G Ground. Relatively coarse surface. Unidirectional. Grade of polishing grit or surface roughness can be specified
    1J or 2J Brushed or dull polished. Smoother than 1G/2G. Grade of polishing grit or surface roughness can be specified
    1K or 2K Satin polish. Similar to 1J/2J but with maximum specified Ra value of 0.5 micron. Usually achieved with SiC polishing belts. Alumina belts are strongly discouraged for this finish as this will have detrimental effect on corrosion resistance. Recommended for external architectural and coastal environments where bright polish (1P/2P) is not acceptable.
    1P/2P Bright polished. Non-directional, reflective. Can specify maximum surface roughness. The best surface for corrosion resistance.
    2L Coloured by chemical process to thicken the passive layer and produce interference colours. A wide range of colours is possible.
    1M/2M Patterned. One surface flat.
    1S/2S Surface coated e.g. with tin = Terne coating
    2W Corrugated. Similar to patterned but both surfaces are affected
    Bead blasting Not in EN 10088-2. Work being undertaken to more accurately define finishes.

     

  16. When was the stainless steel discovered?
    There is a widespread view that stainless steel was discovered in 1913 by Sheffield metallurgist Harry Brearley. It was said that there were different types of steel for weapons, and after a while he realized that 13% of the chrome steel was not worn.

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