Technology, a driving force throughout ATI, is coordinated from a 139,000 square foot Technical Center. Many of our engineers, technicians and support personnel are located at the Technical Center with the remaining staff members at plant sites. This ensures a rapid and continuous transfer of information between product development, product engineering, customer requirements, process control, metallurgical investigations, process automation and manufacturing.
The Technical Center has an extensive range of sophisticated process and analytical equipment allowing us to pilot operations from melting to final rolling and then conduct detailed analyses on the product.
Helpful Links
Corrosion
-
NACE International provides education and communicates information to protect people, assets, and the environment from the effects of corrosion.
-
Corrosion Doctors The main mission of this popular Web site is to improve the general awareness of corrosion causes and solutions.
-
Corrosion Source The one-stop materials and corrosion information resource.
Metals
Stainless Steel
-
Stainless Steel Industry of North America - The Stainless Steel Information Center.
-
British Stainless Steel Association Promotes and develops the use of stainless steel by UK manufacturers and end users. Online Technical Advice provides technical support and advice on stainless steel and its applications.
-
World Stainless On this site you will find original International Stainless Steel Forum (ISSF) documents as well as links to most significant stainless articles published on the Internet. The site is based on the combined knowledge of the global Stainless Steel Industry (the members of ISSF) and its Raw Material Supplier.
Titanium
FAQs
-
When should an "L-grade" stainless steel be used?
-
What are the differences among "standard", "L", and "H" grade stainless steels?
-
What is an "N" grade?
-
Can stainless steel be magnetized?
-
What influence does deformation-induced martensite have on corrosion resistance?
-
What are PRE and PREN and how do they relate to corrosion resistance?
-
Will a ferritic and an austenitic stainless of the same PRE have the same corrosion resistance?
-
How do I select which stainless steel to use?
-
What do I need to know about "free-iron", surface contamination, cleaning, passivation, and pickling?
-
What are XM alloys?
-
Is there a corrosion problem if I join two stainless steels, such as type 316L and type 304 stainless steel, by welding?
-
What other factors should be considered when welding together different stainless steels?
-
Is there a problem if I join a low-alloy steel to a stainless steel?
-
How is it possible to assess carburization or nitriding of austenitic alloys using magnetic measurements?
-
How can depletion of the ferritizing element chromium increase the ferrite number?
-
Why am I getting carburization of the alloy of my bright annealing furnace when the atmosphere contains no carbon?
-
What does "CRES" mean?
-
How does stainless steel perform in wear-resisting applications?
-
What is 885°F (475°C) embrittlement?
-
Can stainless steel be soldered?
-
What stainless steels are suitable for food contact usage?
-
What is the fire resistance rating of stainless steel?
1. When should an "L-grade" stainless steel be used?
L-grade stainless is not generally more corrosion resistant than standard grades and need not be specified for most applications. Where heavy plate is being welded using multi-pass welds, the use of L-grade stainless steels may prevent sensitization and consequent in-service weld corrosion. Where stress-relief heat treatments are anticipated, L-grade stainless steels are generally preferred.
2. What are the differences among "standard", "L", and "H" grade stainless steels?
(This answer is specific to the 300 series alloys.) L-grades have 0.03% carbon maximum and are resistant to sensitization in short-term exposures or heat treatments. L-grade often have slightly lower (typically 5,000 psi less) minimum strengths than standard stainless steels. Most standard grades of stainless steel have 0.08% maximum carbon (note - there is no minimum carbon for these) and are suitable for use in non-welded parts and equipment or for as-welded applications in light-gauge applications. H-grade stainless steels contain 0.04%-0.10% carbon. This increased carbon provides these alloys with higher design allowable stresses under ASME Boiler and Pressure Vessel Code rules for uses in the creep temperature (above 800°F) range.
3. What is an "N" grade?
N-grade alloys contain a deliberate addition of nitrogen, typically 0.10-0.16%. This nitrogen increases strength and may slightly improve corrosion resistance. LN alloys contain low (0.030% max) carbon with increased nitrogen and so combine the sensitization resistance of the L-grade material with the higher strength of the standard alloy.
4. Can stainless steel be magnetized?
Many stainless steels can be magnetized. In general, annealed 200 and 300 series stainless steels are nonmagnetic and cannot be magnetized. Many of these alloys become magnetic after severe cold working. All of the 400 series alloys are ferromagnetic and can easily become magnetized. The strength of the residual magnetism is controlled by many factors, including composition and heat treatment. In general, the harder the alloy, the stronger will be its remnant magnetism. All of the precipitation hardenable stainless steels are magnetic in the hardened condition, with the exception of the fully-austenitic ATI A 286™ alloy, which retains its low magnetic permeability in the heat treated condition. Consult the individual alloy Technical Data Sheets for information on the various alloys.
5. What influence does deformation-induced martensite have on corrosion resistance?
Generally very little. Susceptibility to hydrogen embrittlement will, however, increase.
6. What are PRE and PREN and how do they relate to corrosion resistance?
PRE stands for Pitting Resistance Equivalent and is usually calculated as PRE=%Cr + 3.3x%Mo. PREN is usually used to mean Pitting Resistance Equivalent (with Nitrogen). Many PREN formulae have been proposed. The most widely used are PREN=%Cr + 3.3x%Mo + 16x%N and PREN=%Cr + 3.3x%Mo + 30x%N. (The magnitude of the benefit conferred upon austenitic stainless steels by the addition of nitrogen is a point of some dispute, although the highly beneficial influence of nitrogen upon these alloys is universally agreed upon.)
7. Will a ferritic and an austenitic stainless of the same PRE have the same corrosion resistance?
Generally not. A ferritic stainless steel of a given PRE will typically show greater localized corrosion resistance than an austenitic alloy of the same PRE. (Remember that nitrogen is not beneficial in superferritic stainless steels and PREN calculations for such alloys are not valid.)
8. How do I select which stainless steel to use?
This is a tough question and many entire books have been written on this subject. The most important factors to consider are the environment and what is desired that the material do and/or not do. The chloride content of the environment is a key variable. Resistance to chloride-induced pitting and crevice corrosion typically increase in the sequence 304 - 316 - 317 - 6% Mo (AL-6XN® alloy) - alloy 276 (or alloy 22).
9. What do I need to know about "free-iron", surface contamination, cleaning, passivation, and pickling?
Again, this is a complex question with many issues to be considered. Briefly, stainless steels obtain their corrosion resistance from the existence of a thin passive film of chromium oxides or chromium hydroxides on the surface. Anything which inhibits the formation of this film is detrimental to the corrosion resistance of a stainless alloy. One such condition is the presence of "free-iron" on the surface. Embedded non-stainless steels (from tooling, handling equipment, etc.) on the surface can rust, causing surface staining. If the stainless steel is being used under corrosion conditions (chloride concentration, temperature, pH, etc.) near the limits for the alloy, such surface free-iron contamination may promote corrosion attack. Removal of the free iron by "passivation" in dilute nitric acid is frequently used to prevent such problems. Other forms of surface contamination may require more aggressive treatment by pickling, typically with nitric plus hydrofluoric acid mixtures.
10. What are XM alloys?
See
this document
11. Is there a corrosion problem if I join two stainless steels, such as type 316L and type 304 stainless steel, by welding?
Unless steps are taken to prevent it, galvanic corrosion of the non-stainless steel in such a joint will be a problem. Protective coatings and/or cathodic protection are generally employed in such situations. Use of weld filler is recommended. If joining common steel to an austenitic stainless such as type 304, overmatching filler such as type 309L should be used to avoid martensite formation in the fusion zone. Alternatively, a high-nickel filler metal such as ENiCrFe-1 may be used, especially if thermal expansion matching is necessary. Because stress relief annealing of welds involving common steel is frequently required, use of low carbon (such as 304L) or stabilized (such as 321 or 347) stainless steel is often advisable.
12. What other factors should be considered when welding together different stainless steels?
The properties (strength, thermal expansion, temperature limits, etc.) of each base metal must be suitable and compatible. You must ensure that each of the stainless alloys is itself weldable. If autogenous (i.e. without filler metal) welding is contemplated, the character of the composite fusion zone must be considered, especially if different classes of stainless steel, such as austenitic and ferritic, are being joined. If weld filler metal is used, it should be selected for compatibility with each base metal, with suitability for use in the intended environment, and for its potential for minimizing potentially deleterious interactions between the base metals. Compatibility with post-weld heat treatment (PWHT) and elevated temperature service, if anticipated, should also be considered. A high ferrite number (FN) filler metal could become embrittled in such situations, due to sigma formation.
13. Is there a problem if I join a low alloy steel to a stainless steel?
Unless steps are taken to prevent it, galvanic corrosion of the non-stainless steel in such a joint will be a problem. Protective coatings and/or cathodic protection are generally employed in such situations. Use of weld filler is recommended. If joining common steel to an austenitic stainless such as type 304, overmatching filler such as type 309L should be used to avoid martensite formation in the fusion zone. Alternatively, a high-nickel filler metal such as ENiCrFe-1 may be used, especially if thermal expansion matching is necessary. Because stress relief annealing of welds involving common steel is frequently required, use of low carbon (such as 304L) or stabilized (such as 321 or 347) stainless steel is often advisable.
14. How is it possible to assess carburization or nitriding of austenitic alloys using magnetic measurements?
As carburization or nitriding reduces the amount of chromium in solid solution, the magnetically-determined ferrite number, FN, increases.
15. How can depletion of the ferritizing element chromium increase the ferrite number?
For “lean” alloys, such as 18-8 stainless steels, the austenite is metastable, but the Martensite start temperature (Ms) is far below room temperature due to the influence of the alloying elements Cr, Ni, Mn, C, etc. As carbide or nitride precipitation decreases the Cr content of the solid solution, the Ms increases. When the Ms exceeds the ambient temperature, the ferromagnetic martensite phase will form, and the measured FN will increase. For high-nickel alloys, such as alloy 600, the austenite is stable even without chromium, so Martensite will not form. As carbide or nitride precipitation decreases the Cr content of the solid solution, the Curie (magnetic transformation) temperature increases from its normal cryogenic value. When the Curie temperature exceeds the ambient temperature, the ferromagnetic austenitic Ni-Fe phase will exhibit its ferromagnetic character and again the measured FN will increase.
16. Why am I getting carburization of the alloy of my bright annealing furnace when the atmosphere contains no carbon?
Parts being bright annealed frequently contain residues of lubricants. Although each part may contribute only a miniscule amount of carbonaceous material, the cumulative amount of carbon carried by thousands of parts will eventually cause severe carburization of furnace muffles or other components.
17. What does "CRES" mean?
CRES mean Corrosion Resistant Steel. This designation includes stainless steels and related alloys.
18. How does stainless steel perform in wear-resisting applications?
There have been many cases where a softer stainless steel has out-performed a much harder carbon steel in wear resistance. The most notable of these cases are in coal handling, where stainless steel bins and chutes are preferred both for better life and for ease of sliding of the coal. Mechanistically, the wet coal (it is wetted to control dust) rusts the steel and the sliding coals strips off the rust layer. Similar behavior has been reported in wet cyclones, where 201 stainless far outlasts hardened AR (Abrasion-resisting) steel. Phosphate hauling railcars are another example where the use of stainless steel (ATI 201LN™ or ATI 412™ alloys) provides enhanced resistance to the effects of corrosive wear.
19. What is 885°F (475°C) embrittlement?
885°F (475°C) embrittlement is a loss of toughness that affects most ferritic and duplex stainless steels after exposure to temperatures in the 600 to 1000°F (315-540°C) range. This embrittlement is most rapid at 885°F (475°C), hence its name. Embrittlement rates become negligible below 600°F (315°C) or above 1000°F (540°C). Low (10.5-12%) Cr stainless steels, like Type 409 stainless steel, are essentially immune to 475°C embrittlement. The susceptibility to 885°F (475°C) embrittlement increases with increasing Cr content. The ferrite phase in duplex stainless steels is also subject to 885°F (475°C) embrittlement.
It is important to remember the following about 885°F (475°C) embrittlement:
- 885°F (475°C) embrittlement is usually only detrimental if the embrittled part is impact loaded at near-ambient or lower temperature.
- 885°F (475°C) embrittlement can be rapidly reversed by brief exposures at temperature above ~1050°F (565°C).
- 885°F (475°C) embrittlement is not a rapid process, and short-term excursions into the embrittlement temperature range are unlikely to have any discernible effect, but extended use in the embrittlement temperature range should be avoided unless a careful evaluation determines that it is safe.
- 885°F (475°C) embrittlement slightly increases strength and reduces tensile ductility, but only after substantial reduction in impact resistance has occurred.
20. Can stainless steel be soldered?
Yes, stainless steel can be soldered. To obtain a good bond, removal of surface oxides to obtain proper wetting is necessary. Special fluxes are available for soldering stainless steels. These are usually based on zinc chloride plus hydrochloric acid solutions. Silver solders (such as 6% Ag, 94% Sn) are typically used. It is important that all flux residues be removed promptly to prevent corrosion of the stainless later. The user should evaluate the solder for compatibility with the intended service environment and usage.
21. What stainless steels are suitable for food contact usage?
The USA FDA has classified stainless steel among "Generally Recognized As Safe" (GRAS) materials irrespective of the grade. ANSI Standard NSF 51 specifies that series 200 and 300 stainless steels, and the cutlery grades, are accepted without further testing. For other stainless grades (400 series), resistance to a standardized salt spray test is required.
22. What is the fire resistance rating of stainless steel?
Stainless steels inherently exhibit high resistance to oxidation at elevated temperature and also exhibit significant elevated temperature strength. This makes them useful in building structures where fire resistance is important. Austenitic stainless steels are typically considered for these applications, but because fires are short-term events, embrittlement should not be a practical concern and so the ferritic and duplex alloys can also be considered for use. However, tests to assess fire resistance are done on specific fabrications under precise conditions, and are design-specific. As materials, stainless steels do not have an intrinsic "fire rating".
