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Frequently Asked Questions about Steel for Wire Products

triangle What makes stainless steel "stainless"
triangle What are the common types of stainless steel?
triangle What is the chemical composition of 304 and 316 stainless steels?
triangle What is the main difference between 304 and 316 for the application engineer?
triangle Why would 316 be worth the extra cost over 304?
triangle What does quarter-hard mean?
triangle What is 18-8 stainless steel?
triangle What do the designations 304L and 316L mean?
triangle What is 304H stainless, and what is it recommended for?
triangle What is 321 stainless, and what is it recommended for?
triangle What is 330 stainless, and what is it recommended for?
triangle What fabrication tips should the fabricator keep in mind?
triangle What cleaning tips should the user keep in mind?
triangle Are the less-common grades (not 304 and 316) used in wire form?
triangle Do special finishes make sense for stainless steel?
triangle What finishes do you provide?
triangle What is the right finish for an ultrasonic cleaning basket that can not scratch delicate parts?
triangle What is Passivation?
triangle What is the difference between Electropolishing Stainless Steel and Passivating Stainless Steel?
triangle Is Kynar better than Teflon?
triangle Wire Gauge Chart
triangle Chemical Compatibility
triangle Do Marlin Steel Wire products meet JCAHCO compliance guidelines?
triangle Is MSRA the kind of threat that the Antimicrobial Coating resists? Is "resists" the correct word?
   Is "sloughs off" or "neutralizes" a better word? Is there a whole family of items which Antimicrobial
   Coating resists, of which MSRA is a subset? What is the larger set?

triangle Is the Antimicrobial coating applied like any other powder coating? Do the coaters have to take
   any special precautions in the powder-coating process?

triangle Is the Antimicrobial Coating an aromatic urethane? If yes, aromatic means a ring structure, which is
   tighter, and thus would imply a more-permanent bond to the substrate. Correct?

triangle Is the coating "passive" like Teflon, in that it goes on and stays on, without the need for re-application
   after a few years? Or is it "active", in that it is consumed over time and must be re-applied occasionally?

triangle Related to the previous question, how is the antimicrobial feature "released" to the microbes which
   attach to the substrate?

triangle Are there any restrictions on the color of the Antimicrobial Coatings? Does the price vary with the color?
triangle What is the price difference for Antimicrobial Coatings vs. other powder coatings?
triangle Is there a feel due to Anitmicrobial Coatings which differs in texture from other powder coatings?
   I refer to "hand", in the textile industry sense.

2/18/10       Marlin Steel is proud to supply the U.S. Military with steel wire forms. The document shown here outlines the Military Standard Fusion Welding for Aerospace Applications: mil-std-2219.   US Military Specifications for Welding: mil-std-2219.

Q: What makes stainless steel "stainless"?
A: Compared to plain carbon steel, stainless steels (there are more than 300 grades) contain at least 12% Chromium - a metal that is intrinsically corrosion resistant. Because of this alloying, stainless steels form a tightly-adherent and protective oxide layer which is so thin that the metallic coloration of the underlying steel is visible. The oxide layer that forms in ambient environments on plain carbon steels (i.e. "rust") is a different oxide, which is nearly opaque, orange, thick, loose and porous.

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Q: What are the common types of stainless steel?
A1: Most common are austenitic stainless steels, grades 304, 316, and 317. These have the highest corrosion resistance. These are non-magnetic and can by hardened only by cold work. (Annealed 300-series stainless steels are not magnetic, but they may become magnetic after cold working.)
A2: Next-most common are ferritic stainless steels, grades 430 and 434. These are magnetic and can be hardened by cold work. The price is lower than that of 304SS due to the lower amount of Nickel.
A3: Least common are martensitic stainless steels, grades 410 and 420. These have the highest hardness. These are magnetic and can be hardened by a combination of cold work and heat treatment. The price is lower than that of 304SS due to the lower amount of Nickel.


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Q: What is the chemical composition of 304 and 316 stainless steels?
A:

Nickel Chromium Molybdenum Manganese
304 8 - 10.5% 18 - 20% None Specified 2% maximum
316 10 - 14% 16 - 18% 2 - 3% 2% maximum

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Q: What is the main difference between 304 and 316 for the application engineer?
A: 316 stainless is more expensive (about 20% more) due to the higher Nickel and Molybdenum content and has higher corrosion resistance, higher tensile strength, and a slightly grayer finish.



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Q: Why would 316 be worth the extra cost over 304?
A: For most applications, 304 has the best combination of corrosion resistance, mechanical properties, and cost. For high corrosion resistance in food, biomedical, marine, and heat exchanger applications, 316 can be worth the price difference. The resistance to solvents, chlorides, acetic acid, and especially to salt water can make 316 the preferred choice. The quality of the surface finish and the amount of cold-work (most often referred to as the hardness, as in quarter-hard or half-hard) influences the corrosion resistance greatly.

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Q: What does quarter-hard mean?
A: This refers to higher tensile strength grades. Solution-annealed 304SS typically has ultimate tensile strength of 75 ksi (515 MPa), Brinnell hardness 201, and Rockwell B Hardness 92. Quarter-hard steel has tensile strength of 115 - 135 ksi. It is harder to form than solution-annealed 304SS. Solution-annealed steel has undergone thermal treatment beyond stress relieving to give the higher tensile strength and hardness.

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Q: What is 18-8 stainless steel?
A: 18-8 is another way of referring to 304 stainless and similar alloys (301, 302, etc.). The 18-8 refers to the 18% Chromium and 8% Nickel content of 304 (see the table above), with no more than 0.08% Carbon.

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Q: What do the designations 304L and 316L mean?
A: The "L" in the designations for these grades refers to "low carbon." This low carbon makes it easier to produce corrosion-resistant welds than in standard 304 and 316, respectively, but their higher cost (2% to 10%) and lower strength (by 5 ksi) limit their use. Most fabricators of stainless steel wire products can work well enough with 304 and 316. The maximum Carbon content is 0.03% in an L grade, while the standard 304 and 316 grades can contain up to 0.08% carbon.

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Q: What is 304H stainless, and what is it recommended for?
A: 304H has higher Carbon content (0.04-0.10%) than 304 and is used for high-strength applications.

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Q: What is 321 stainless, and what is it recommended for?
A: 321 stainless has 9-12% Nickel, 17-19% Chromium, and some Titanium. This grade has superior resistance to intergranular corrosion and is recommended for high-temperature and welded applications (but type 347 with Niobium in place of Titanium is preferred for weld filler). 321SS might be suitable for hooks and wire forms in especially difficult environments. Its price is significantly higher than that of 304SS.

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Q: What is 330 stainless, and what is it recommended for?
A: 330 stainless has 35% Nickel and 17% Chromium. This grade is used in very high-temperature applications, to 1,900 degrees F (940 degrees C), such as for heat-treating baskets. 330's cost is much less than that of Inconel 600 and higher than that of 316SS.

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Q: What fabrication tips should the fabricator keep in mind?
A: Design can aid clean-ability, so well-designed parts with rounded corners, fillets and absence of crevices facilitate cleaning, as do smooth ground welds and polished surfaces. Post-fabrication handling is also important. Scale or slag that forms from welding processes is often removed by the fabricator with a stainless steel wire brush. It is important that the wire brushes used for plain steel cleaning NOT be used for stainless steel cleaning, as those brushes will leave carbon steel particles in the surface, which will eventually lead to surface rusting of the stainless. For more severe applications, welded areas should be treated with a de-scaling solution such as a mixture of nitric and hydrofluoric acids, which should be subsequently washed off. For cleaning of small areas, commercially available pickling pastes may be used.

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Q: What cleaning tips should the user keep in mind?
A: Despite their corrosion resistance, stainless steels need care during use to maintain their surface appearance even under normal conditions of service. Many of the routine uses of stainless steel products involve cleaning or sterilizing on a regular basis. Equipment can be cleaned with specially-designed caustic soda, organic solvent, or acid solutions such as phosphoric, oxalic, citric or nitric acid. Some contain special ingredients such as oxalic acid that are particularly effective in removing rust stains. Examples of suitable commercial cleansers are Barkeepers Friend and Bon Ami. Strongly reducing acids such as hydrofluoric or hydrochloric may be harmful to stainless steels.

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Q: Are the less-common grades (not 304 and 316) used in wire form?
A: Yes. However, many wire fabricators stock only 304 and, less so, 316. Thus, specifying the odd grades may entail longer delivery times from the fabricator. The wire mills, including one of Marlin Steel Wire's main vendors, have more than 300 grades readily available, so the user has a cornucopia of options for all applications.

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Q: Do special finishes make sense for stainless steel?
A: Yes - Electropolishing of stainless steel is commonly used for food, drug, medical, and semi-conductor applications and for those where high fatigue strength is needed. Electropolishing is the reverse of plating in that metal is removed from the surface rather than deposited, in order to obtain a bright, clean, and appealing surface, enhancing its appeal in consumer applications. It also removes burrs and sharp edges, and removes stress by removing microscopic nicks and scratches from the surface. Electropolishing is also used to bring overweight or oversized parts into specification, since tolerances can be held to 0.0001 inch. Electropolishing will also remove heat discoloration from spot welds.

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Q: What finishes do you provide?
A: Chemical Finishes

  • Electropolishing
  • Nitric Acid Passivation
  • Citric Acid Passivation
  • Pickling
  • Chem Film (Iridite)
  • Zinc Phosphate
  • Manganese Phosphate
  • Ultra-Tech 500 (Endrion)
  • Black Dye
  • Sandblasting
  • Salt Spray Testing
Spray Finishes
Powder Coatings
Fluidized Bed & Elctrostatic Spray
  • Nylon
  • urethane
  • polyester
  • polyolefin
  • Vinyl
  • Polyethylene
  • Epoxy
  • Polyester
  • Hybrids
  • Urethane
  • PFA
  • HALAR
  • TEFZEL®
Nickel Plating
Chrome Plating

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Q: What is the right finish for an ultrasonic cleaning basket that can not scratch delicate parts?
A: Either Kynar or Nylon coated baskets are designed for ultrasonic cleaning applications that hold delicate - "no scratch" parts.


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Q: What is Passivation?
A: Passivation is the treatment of stainless steel in an acid solution (typically dilute nitric or citric acids) to remove iron contamination on the surface. The contamination might come from fabrication steps such as stamping, drilling, machining, welding, cutting, forming, or wire brushing. Passivation does not change the appearance of the stainless. Passivation is not necessary to form the protective oxide coating; re-forms immediately upon exposure of the stainless steel to air, water, etc. However, specific passivation treatments can thicken and change the composition of the protective oxide layer, increasing the corrosion resistance of the passivated material.


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Q: What is the difference between Electropolishing Stainless Steel and Passivating Stainless Steel?
A: Passivation is the treatment of stainless steel in a nitric acid or citric acid solution to remove iron contamination on the surface. The contamination is from fabrication such as stamping, drilling, machining, welding, cutting, forming or wire brushing.

Passivation does not change the appearance of the stainless. If the stainless has been heat treated or welded, the resultant scale or discoloration must be removed by either abrasive methods or by pickling.

The processor must know the alloy of stainless steel before passivation is attempted so that the proper solution will be used.

Electropolishing is the reverse of plating in that metal is removed from the surface rather than deposited. Electropolishing is primarily used to obtain a bright, clean, appealing surface.

Electropolishing also removes burrs and sharp edges; eliminates hydrogen embrittlement and removes stress from springs and stampings by removing microscopic nicks and scratches from the surface.

Because high points on the surface are removed first, a lower micro inch surface is achieved. Thus the surface is smoother, has good anti-stick properties and is easier to clean. This is required in the food, pharmaceutical and semi-conductor industries. Electropolishing also passivates the surface as mentioned in the ASTM A-967 specification; it is used as an inspection tool to detect surface cracks or imperfections in castings and forgings. It is used for sizing to bring overweight or oversized parts into specifications and tolerances can be held to .0001"

Electropolishing can smooth threads to prevent galling and seizing.

Electropolishing will also remove heat discoloration from spot welds. On your behalf, Marlin can electropolish the ID of tubing and pipe, fittings and a variety of fabrications. We have electropolished vessels 16' diameter and 56' long.

Two important advantages of electropolishing are the speed and uniformity of the process, readily translated into important savings, particularly when treating complicated shapes.


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Q: Is Kynar better than Teflon?
A: Kynar has better chemical resistance and is applied much heavier (with a 5 coat system) which will achieve a coating thickness of .015" - .040". Along with this extra coating, comes better abrasion resistance and a higher price tag. Teflon has good chemical resistance and is applied in a 2 coat system, which will achieve a coating thickness of .002" - .005". The abrasion resistance is not as good as the Kynar coating.

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Q: Is MSRA the kind of threat that the Antimicrobial Coating resists? Is "resists" the correct word? Is "sloughs off" or "neutralizes" a better word? Is there a whole family of items which Antimicrobial Coating resists, of which MSRA is a subset? What is the larger set?
A: The active ingredient attaches to the microbes DNA and prevents if from spreading. MARLIN STEEL WIRE has not tested for every microbe that the silver compound will attack, but the makers of the antimicrobial additive have done many tests. Their data show activity and reduction of the MSRA. We do not make any claims, we can just present the data. Our information from the vendor indicates the following organisms are controlled by the silver additive:
Bacteria

  • Bacillus cereus
  • Bacillus thuringiensis
  • Mycobacterium tuberculosis
  • Legionella pneumophila
  • Escherichia coli
  • Klebsiella Pneumoniae
  • Salmonella gallinarum
  • Salmonella typhimurium
  • P. gingivalis
  • Staphylococcus aureus
  • Staphylococcis epidermidis
  • Streptococcus faecalis
  • Streptococcus agalactiae
  • Streptococcus mutans
  • Pseudomonas aeruginosa
  • Proteus mirabilis
  • Proteus vulgaris
  • Vibrio parahaemolyticus
  • Saccharomyces cerevisiae
  • Enterobacter aerogines
  • Trycophyton malmsten
  • Chaetomium globosum
  • Aureobasidium pullulans
  • Gliocladtum virens Yeast & Mold
  • Stachybotrys
  • Aspergillus niger
  • Candida albicans
  • Penicillium funiculosum

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Q: Is the Antimicrobial coating applied like any other powder coating? Do the coaters have to take any special precautions in the powder-coating process?
A: It is applied like any thermoset, electrostatic grade powder coating.

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Q: Is the Antimicrobial Coating an aromatic urethane? If yes, aromatic means a ring structure, which is tighter, and thus would imply a more-permanent bond to the substrate. Correct?
A: The Antimicrobial products are formulated in most powder chemistries such as TGIC-Polyester, Urethane-Polyester, Hybrid and Epoxy. We do not have any in aromatic urethanes currently, but they could be developed. Our weatherable Urethane-Polyesters are Aliphatic. There are many variables that affect adhesion. Generally speaking the adhesion of the various chemistries is very similar.

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Q: Is the coating "passive" like Teflon, in that it goes on and stays on, without the need for re-application after a few years? Or is it "active", in that it is consumed over time and must be re-applied occasionally?
A: Silver is the active ion that imparts the antimicrobials properties. It is NOT passive and it will be consumed over time. The coating will last a long time depending on end use. The antimicrobial can be used up over time, again depending on end use.

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Q: Related to the previous question, how is the antimicrobial feature "released" to the microbes which attach to the substrate?
A: The silver ion is activated by moisture and migrates to the surface.

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Q: Are there any restrictions on the color of the Antimicrobial Coatings? Does the price vary with the color?
A: We have not run into any color restrictions so far. As with regular powders, cost does vary with color.

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Q: What is the price difference for Antimicrobial Coatings vs. other powder coatings?
A: Approximately 100% more due to the cost of the active ingredient and the specialized method of incorporation, for which we hold a patent.

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Q: Is there a feel due to Anitmicrobial Coatings which differs in texture from other powder coatings? I refer to "hand", in the textile industry sense.
A: Generally, there is nothing in the feel or appearance of the coating that will indicate an antimicrobial product, but the incorporation process can lead to more orange peel.

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We are happy to acknowledge the assistance of Professor Roger Wright, Rensselaer Polytechnic Institute, Dr. Jack Grubb, Allegheny Ludlum, Dr. William H. Cullen, Jr., Nuclear Regulatory Commission, and Dr. Shui Lee, Central Wire Industries, for providing much of this information. The web sites of AK Steel, Allegheny Technologies, Carpenter Technology, Sandmeyer Steel and Haward Corporation were also helpful. Any errors are the sole responsibility of Marlin Steel Wire Products, Baltimore, MD USA. Please contact us with any errors or omissions or comments for improvement.

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