Stainless Steel FAQ
FREQUENTLY ASKED QUESTIONS
- What makes stainless steel stainless?
- What is the difference between 18/8, 18/10 and 18/0 stainless steel?
- Can stainless steel rust? Why? (I thought stainless did not rust!)
- What is the difference between 304 and 316 stainless steel?
- Is stainless steel magnetic?
- What is "passivation"?
- Can stainless steel be "welded"?
- Can stainless steel be "hardened"?
- What does the "L" designation mean?
- What is the recycle content of stainless steel?
- The stainless steel on my refrigerator door, dishwasher, and/or countertop is scratched. How can I remove the scratches?
- What is the "annealed" condition?
- What does the term "CRES" mean?
- Can stainless steel be used at very low and very high temperatures?
- What are AISI Specification for stainless steel?
- Can stainless steel be machined?
- I have a stainless steel kitchen with a tile floor and when the tile grout was cleaned with muratic acid the stainless discolored. How can I repair this problem?
- I have a stainless steel refrigerator and since some stainless steels are non-magnetic I cannot attach items to the surface magnetically. What is the best way to attach something to stainless steel?
- Who invented stainless steel?
- What is the best way to clean my stainless steel BBQ grill?
- What are the standard finishes for stainless steel like 2B and #4?
- What is the difference between the “annealed” condition and the “dead soft” condition for stainless steel?
- Do you need to “preheat” stainless steel before welding?
- What is the inch dimension for the various “gauges” that are sometime used?
- What is the “recycle” rate for stainless steel?
1. What makes stainless steel stainless?
Answer: Stainless steel must contain at least 10.5 % chromium.
It is this element that reacts with the oxygen in the air to form a complex
chrome-oxide surface layer that is invisible but strong enough to prevent
further oxygen from "staining" (rusting) the surface. Higher levels
of chromium and the addition of other alloying elements such as nickel and
molybdenum enhance this surface layer and improve the corrosion resistance
of the stainless material. See the "Stainless
Steel Primer" for more information.
2. What is the difference between 18/8 and 18/10 stainless steel?
Answer: The first number is the amount of chromium that
is contained in the stainless, i.e., 18 is 18% chromium. The second number
is the amount of nickel, i.e., 8 stands for 8% nickel. So 18/8 means that
this stainless steel contains 18% chromium and 8% nickel. 18/10 is 18% chromium
and 10% nickel. The higher the numbers the more corrosion resistant the material.
18/0 is a misleading designation. Both 18/8 and 18/10 contain nickel and are
part of the grade family "300 series" stainless. 18/0 means that
there is 18% chromium but zero nickel. When there is no nickel the stainless
grade family is the "400 series". 400 series are not as corrosion
resistant as the 300 series and are magnetic, where the 300 series are non-magnetic.
3. Can stainless steel rust? Why? (I thought stainless did not rust!)
Answer: Stainless does not "rust" as you think
of regular steel rusting with a red oxide on the surface that flakes off.
If you see red rust it is probably due to some iron particles that have contaminated
the surface of the stainless steel and it is these iron particles that are
rusting. Look at the source of the rusting and see if you can remove it from
the surface. If the iron is embedded in the surface, you can try a solution
of 10% nitric and 2% hydrofluoric acid at room temperature or slightly heated.
Wash area well with lots and lots of water after use. Commercially available
"pickling paste" can also be used. See "The
Care and Cleaning of Stainless Steel" for more information.
4. What is the difference between 304 and 316 stainless steel?
Answer: 304 contains 18% chromium and 8% nickel. 316 contains
16% chromium, 10% nickel and 2% molybdenum. The "moly" is added
to help resist corrosion to chlorides (like sea water and de-icing salts)
See "Stainless Steel for
Coastal and Salt Corrosion Applications" for more information.
5. Is stainless steel magnetic?
Answer: There are several "types" of stainless steel. The
300 series (which contains nickel) is NOT magnetic. The 400 series (which
just contains chromium
and no nickel) ARE magnetic.
Answer: When the amount of chromium (in an iron matrix)
exceeds 10 1/2%, a complex chrome
oxide forms instantaneously that prevents the further diffusion of
oxygen into the surface and results in the "passive" nature of stainless steel
and its resistance to oxidation (or corrosion). A chemical "dip" into 10% nitric
acid plus 2% hydrofluoric acid bath will enhance the development of this "passive" oxide.
7. Can stainless steel be "welded"?
Answer: YES. Stainless steel is easily welded, but the
welding procedure is different than that used with carbon steel. The "filler"
rod or electrode must be stainless steel. (Contact the American
Welding Society for more information)
8. Can Stainless steel be "hardened"?
Answer: YES. The 300 series stainless steel can be "hardened"
BUT only by "work hardening." That is by cold working the material,
either by cold rolling down to lighter and lighter gauges, or by "drawing"
through a die or other size altering operation. "Annealing" stainless
steel will REMOVE the work hardening effect. YES and NO. The 400 series have
two different stainless steel structures. One is called "ferritic"
(409, 430, 434. 439) which cannot be hardened by heat treatment. The other
is called "martensitic" (403, 410, 416, 420, & 440 A,B,C) which
CAN be hardened by heat treatment. See "Design
Guidelines for The Selection and Use of Stainless Steel" for more
9. What does the "L" designation mean?
Answer: The use of the letter L after the grade number,
i.e., 304L, means that the carbon content is restricted to a MAXIMUM of 0.03%
0.08% max. and in some grades can be as high as 0.15% max.). This lower level
usually used where "welding" will be performed. The lower level of
carbon helps to prevent the chromium from being depleted (by forming
the weld site)
and therefore allow it to remain over 10 1/2% so it can form the
"passive" oxide layer that gives stainless its corrosion resistance.
10. What is the recycle content of stainless steel?
Answer: Stainless steel can be recycled 100%. That is all stainless steel can be re-melted to made a new stainless steel. The typical amount of recycled stainless steel "scrap" that is used to make new stainless steel is between 65 & 80%.
11. The stainless steel on my refrigerator door, dishwasher, and/or countertop is scratched. How can I remove the scratches?
Answer: Scratches are difficult to remove. Most kitchen
appliances, sinks, and counters have a polished finish with short directional
Restoring a polished finish to its original appearance requires a professional
such as a company that specializes in fabricating or polishing stainless
steel. If the refrigerator or dishwasher door panel is replaceable, purchasing
a new panel is normally more cost effective than professional refinishing.
The homeowner may want to consider obtaining replacement panels with angel
hair, distressed, swirl, or embossed finish. These finishes help to hide
light scratching and can be obtained from companies that specialize in stainless
steel finishes. Counters and appliance doors that are not easily removable
must be refinished in place. When the counter is refinished, it may have
long rather than short polishing lines. If a slightly different finish is
acceptable and cost is a consideration, a homeowner can refinish the counter
or appliance using a non-metallic abrasive pad such as a Scotch Brite® pad.
This can be done by rubbing the surface with the pad using long uniform strokes
in the same direction as the current polishing lines. This will not eliminate
deep scratches. A professional may offer this finish as a less expensive
option. The resulting finish is normally referred to as a hairline or long
grain finish. Some appliance companies are starting to offer this finish.
12. What is the "annealed" condition?
Answer: Stainless steel is usually sold in the "annealed" condition.
It just means that the material is in the "soft" or annealed
condition. The 300 series of stainless steels can not be hardened by heat
treatment (like carbon steels) but can be hardened by cold working. This
cold work can be eliminated by a heating treatment (annealing) that will
restore the original soft condition.
13. What does the term "CRES" mean?
Answer: CRES is something used to designate stainless steel.
It stands for Corrosion RESistant steel. It does not necessarily mean that
in fact stainless
steel as there are other materials that are corrosion resistant but not stainless
14. Can stainless steel be used at very low and very high temperatures?
Answer: Yes. Stainless steel has excellent properties
at both extremes of the temperature scale. Stainless steel can be used down
to liquid nitrogen
temperatures and up to about 1800° F.
15. What are AISI Specifications for stainless steel?
Answer: The AISI (American Iron and Steel Institute) was
the originator of the 300 and 400 series numbering system (i.e., Type 304
stainless steel). They also published a Stainless Steel products manual that
listed these designations and the chemical analysis as well as most mechanical
and physical properties of each individual grade. They are NOT specifications
as such, just definitions of the individual grades. Most specifications that
are used with stainless steel are from the ASTM (American Society for Testing
Material). See "Specifications for
Stainless Steel" for more information. The Iron & Steel Society
took over from the AISI in publishing the Stainless Steel Products Manual
a number of years ago.
16. Can stainless steel be machined?
Answer: Yes. However the standard grades of stainless steel
are usually "gummy" and will not produce a clean chip when machined or turned.
To solve this problem,
many companies produce "free-machining" grades of stainless where
they add a "chip-breaker" to the matrix. Grade 303 is the free-machining
equivalent to grade 304.
17. I have a stainless steel kitchen with a tile floor and when the tile grout was cleaned with muratic acid the stainless discolored. How can I repair this problem?
Answer: The stainless steel that is used on kitchen appliances and vent hood etc. is usually type 304. This is a very good grade of stainless steel, but IT IS NOT RESISTANT TO MURATIC ACID. Cleaners that are used with grout around title and stone etc. SHOULD NOT BE USED IF STAINLESS STEEL IS PRESENT. It is not even necessary that the acid touch the stainless steel, just the “fumes” from it will cause a discoloration of the stainless.
The chances of repairing this discoloration depend on the extent of the
discoloration and the depth of the attack. If possible the entire panel of
stainless steel should be replaced. If that is not possible you can try to
repair the damage by following the procedure for removing scratches.
18. I have a stainless steel refrigerator and since some stainless steels are non-magnetic I cannot attach items to the surface magnetically. What is the best way to attach something to stainless steel?
Answer: We suggest “Remount Spray Adhesive” for
temporary, light weight and repositional bonding. For stronger or more permanent
bonding Super 77 (from 3M) is a good suggestion. Removal using 3M Citrus
Base Adhesive Remover should easily take care of any residual adhesive. For
more info: 3M.com
19. When was stainless steel invented?
Answer:The "discovery" of stainless steel occured in the 1900 to 1915 time period. .
20. What is the best way to clean my stainless steel BBQ grill?
Answer: Check out "The
Care and Cleaning of Stainless Steel” under Information Handbooks
21. What are the standard finishes for stainless steel like 2B and #4?
Answer: Standard, Mill, Polished, and Custom.
22. What is the difference between the “annealed” condition and the “dead soft” condition for stainless steel?
Answer: The usual “condition” that stainless
steel products (sheets, plates, bars, wire etc.) are supplied to is the “annealed”
condition. That means that the last operation is to heat the material up a
temperature where the residual stresses of manufacturing can be relieved,
and the material will be in the “soft” condition. Most flat rolled
products however are made in coils and when a “sheet” is cut from
the coil it is usually “flattened” which does add some small amount
of stress to the material. Bar products are usually straightened and that
adds some small amount of stress as well. The term “dead soft”
usually refers to a product where the even this small amount of stress is
removed, but as a practical matter, this condition is not readily available.
23. Do you need to “preheat” stainless steel before welding?
Answer: NO. Austenitic stainless steel (the 300 series)
do not need to be preheated before welding.
24. What is the inch dimension for the various “gauges” that are sometime used?
Answer: The U.S. Standard Gauges for stainless steel have the following nominal thickness in inches:
However: It is always the best practice to order stainless steel products
by the specific thickness in “inches” and NOT BY GAUGE NUMBERS.
25. What is the “recycle” rate for stainless steel?
Answer: All stainless steel products are 100% recyclable.
Many recycling companies will want the various grade types to be kept separate
(all 300 series together etc.). The typical re-melt rate for stainless steel
is between 60 and 85%.