FREQUENTLY ASKED QUESTIONS
What is Stainless Steel?
With the addition of 12% chromium to iron, stainless steel is formed. The chromium protects the iron against most corrosion or red-colored rust; thus the term "stainless" steel. The ability of stainless to form a thin layer of protection on its outside surface, called a "passive film", is its most important characteristic in preventing corrosion. The overriding purpose of stainless steel is to provide corrosion resistance against: (a) atmospheric conditions such as carbon dioxide, moisture, electrical fields, sulfur, salt, and chloride compounds; (b) natural artificially produced chemicals (c) extremes of weather where cold temperatures cause brittleness and hot temperatures reduce strength and increase corrosion.
What is Type 304 grade Stainless Steel?
300 series, also known as 18/8, stainless steel has approximately (not exactly) 18% chromium and 8% nickel. It is the most versatile and most widely used stainless steel, available in a wider range of products, forms and finishes than any other. It has excellent forming and welding characteristics. The term “18-8” is used interchangeably to characterize fasteners made of 303, 303HQ, 303, 304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the 18-8 types, but slight differences in chemical composition do make certain grades more resistant than others against particular chemicals or atmospheres. “18-8” has superior corrosion resistance to 400 series stainless, is generally non-magnetic, and is hardened only by cold forming.
What is Type 316 Marine grade Stainless Steel?
Grade 316 is the standard molybdenum-bearing grade, second in importance to 304 amongst the austenitic stainless steels. The molybdenum gives 316 better overall corrosion resistant properties than Grade 304 and a particularly higher resistance to pitting and crevice corrosion in chloride environments. It has excellent forming and welding characteristics. It is readily brake or roll formed into a variety of parts for applications in the industrial, architectural, and transportation fields.
What is the best screw for Cedar and pressure treated decking lumber?
Without question, Stainless Steel is the best. Current pressure treated lumber sold in the market includes one or more of the following chemicals: ACQ-C (Alkaline Copper Quat Type C), ACQ-D Carbonate (Alkaline Copper Quat Type D, Carbonate formulation), CA-B/ CA-C (Copper Azole Types B and C), µCA-C (Azole biocide), as well as SBX/DOT (Sodium Borate) and Zinc Borate preservatives. These chemicals are highly corrosive to steel and most coated steel compared to the now prohibited CCA treated lumber.
Are coated screws or hot dipped galvanized good for treated decking lumber?
Both coated and hot dipped galvanized screws use Carbon Steel as the base metal in these screws. When these screws are driven into lumber, most all of the coating is sheared off in the process which exposes the bare Carbon Steel against the highly corrosive chemicals found in the treated lumber. Rust attack will prevail within weeks and through corrosion is likely in the first year.
Why is Stainless Steel required for Cedar, Redwood, and exotic woods?
These wood species have high levels of Tannic Acid and will cause black staining when Carbon based metals are in contact. Coated screws, of all varieties, will cause staining within a few days and ultimate through rust as early as 6 months.
To heat metal in order to lower its hardness. The term anneal refers to the heat treatment given all 300 series stainless and most 400 series stainless by steel mill after the raw material has been completed but before fasteners are manufactured. Anneal also refers to the heat treatment given 400 series stainless fasteners after their manufacture (also called hardening and tempering) to lower hardness and increase toughness. For example, fasteners of 410 stainless may score over 200,000 psi after manufacture and be too brittle. By annealing at 1000 degrees F. tensile strength would decrease to 125,000-150,000psi; annealing the same material to 500 degrees F. would bring tensile to 160,000-190,000 psi.
Refers to 300 series stainless, the most popular of the stainless alloys accounting for 85%-90% of stainless fasteners sold. Named for Sir Ropers Williams Austen, and English metallurgist, austenitic stainless is a crystal structure formed by heating steal, chromium, and nickel to a high temperature where it forms the characteristics of 300 series stainless steel. An “AUSTENITE” is a molecular structure where 8 atoms of iron surround on atom of carbon, thus limiting the corrosive effects of the carbon. Austenitic fasteners have the highest level of corrosion resistance in the stainless family, cannot be hardened by heat treatment, and are almost always nonmagnetic. Sometimes heat and friction in cold-forming can causes austenitic stainless to take on slight magnetism, but the corrosion-resistant properties remain the same. The most popular of austenitic grades is know generically as “18-8 stainless” and includes grades 302, 302HQ, 303<304,305, and XM-7. Typical industries using 18-8fastners include: food, dairy, wine, chemical, pulp and paper, pharmaceutical, boating, swimming pool, pollution control, electronic, medical and hospital equipment, computer, textile. Type 316 stainless has added nickel and especially molybdenum. The molybdenum (called moly) sharply increases corrosion resistance to chlorides and sulfates, including sulfurous acids in the pulp industry. It has superior tensile strength at high temperatures compared to 18-8. Besides pulp and paper, typical industries using 316 are: photographic and other chemicals, ink, textile, bleach, rubber.
Adds strength to stainless steel, but also lowers corrosion resistance. The more carbon there is, the more chromium must be added, because carbon offsets 17 times its own weight in chromium to form carbides, thus reducing the chromium available for resisting corrosion.
Ordinary steel with no significant additions besides carbon.
Louis Nicolas Vauquelin, who later was the first to produce it on its own, discovered chromium in 1797. A blue-white metal, chromium is the most important element providing corrosion resistance in stainless steel and occurs in nature only in combination. Stainless Steel is formed when Chromium offsets the corrosive effects of carbon found in steel and is the primary factor in the ability of stainless to form a passive film on its surface providing corrosion resistance. In its pure state, chromium is a steel-silvery grey with bluish tinge luster. It is an extremely hard metal that takes a high polish. The principal ore is chromite (FeO.Cr2O3), from which it is obtained by reduction with aluminum and electrolysis. Chromium metal lacks ductility and is susceptible to nitrogen brittleness and is not used as a structural metal. It is resistant to oxidation and does not react with nitric acid. However, it dissolves in hydrochloric acid and slowly in Sulphuric Acid. It is subject to inter-granular corrosion at temperatures above 816°C (1500°F). When plated on highly polished metal chromium gives a smooth surface that has no capillary attraction to water or oil and chromium-plated bearing surfaces can be run without oil.
Cold Forming or Cold Heading
When fasteners are produced without heating or small heat below crystallization temperature (so the raw material bond of stainless remains unchanged) by pressing metal wire against various dies at high speed to form a fastener’s head or basic shape. Cold working causes an increase in tensile strength and hardness (know as work hardening) and a decrease in ductility.
An accelerated degree of corrosion occurring when two different metals are in contact with moisture, particularly sea water. All metals have what is termed a specific electric potential, so that low level electric current flows from one metal to another. A metal with higher position in the galvanic series will corrode sacrificially rater than one with a low position, meaning stainless, for example, will corrode before gold. The further apart the metals on the chart, the more electro current will flow and the more corrosion will occur. No serious galvanic action will occur by combining the same metals, only dissimilar ones. To prevent galvanic corrosion, use insulation, paint or coatings when separated dissimilar metals; or put the metal to be protected next to a metal which is not important in the assembly so it can corrode sacrificially.
Normally stated in terms of Rockwell or Brinell scale of measurement, hardness shows resistance of a faster to rough marks and abrasions, can indicate yields strength and brittleness., and has a direct relationship to tensile strength in alloy steel fasteners. However, for stainless, brass, and silicon bronze, the correlation between hardness and tensile or yield is tenuous with no definite relationship.
Case hardening uses surface heat treatment on ferrous material to cause a harder outside surface than the center. Through-hardening hardens the entire fastener. Bright hardening calls for heat treatment without oxygen, so no oxides are formed on the material surface.
Hot Dip Galvanizing of screws and nails
The process of dipping steel screws and nails in an 860 °F (460 °C) molten bath of Zinc. After dipping, the fasteners are spun in a cylindrical drum to remove the excess Zinc. When exposed to the atmosphere, the pure Zinc reacts with Oxygen to form Zinc Oxide, which further reacts with Carbon Dioxide to form Zinc Carbonate. Hot dip galvanizing in its original form (as applied to fabricated steelwork) is also a growing industry. That is not true of many industries that are more than 150 years old and still recognisable to someone from that era. The reasons for the process’s continued success are in the intrinsic relationship between iron and zinc, improved organisation of the handling of work in the plant and, most importantly, a better appreciation of the economics of corrosion protection. As these factors are better understood by design engineers, the tonnages of steel galvanized have risen steadily. In Europe the total annual tonnage rose from 3.6 million tonnes in 1983 to 4.6 million tonnes in 1996 and the trend continues.
Also known as Moly, Molybdenum is a metal added to 316 stainless steel which sharply increases its corrosion resistance to chlorides and sulfates and especially various sulfurous acids in the pulp industry. Molybdenum helps reduce hardness and increase tensile strength at higher temperatures. Originally molybdenum was confused with graphite and lead ore, and was not prepared till 1782 by Hjelm in the impure state. Molybdenum does not occur native, and is obtained mainly from Molybdenite (MoS2). Other minor commercial ores of molybdenum are Powellite (Ca(MoW)O4) and Wulfenite (PbMoO4). It may also be recovered from copper and tungsten operations as a by-product. The metal is prepared from the powder made by the hydrogen reduction of purified Molybdic Trioxide or ammonium Molybdate. Molybdenum the metal is silvery-white, and very hard. However, it is softer and more ductile than tungsten and is readily worked or drawn into very fine wire. It cannot be hardened by heat treatment, only by working. It exhibits a high elastic modulus and a very high melting point. Above temperatures of 760°C (1400°F) Molybdenum the metal forms an oxide that evaporates as it is formed and its resistance to corrosion is high. It has a low thermal expansion and its heat conductivity is twice that of iron. It is one of the few metals that has some resistance to hydrofluoric acid.
Nickel was discovered in 1751 in the mineral Nickeline/Niccolite by Axel Crostedt and is obtained commercially from Pentlandite and Pyrrhotite. Nickel is a silvery-white metal and takes on a high polish. It is hard, malleable, ductile and to an extent ferromagnetic (up to 360°C). It has a fair electrical conductivity (25% that of copper) and heat conductivity and belongs to the iron-cobalt group of metals. It's added to 300 series stainless to provide corrosion resistance, increased strength in both high and low temperatures, and increased toughness in low temperatures. Nickel lowers the effects of work hardening, thus reducing traces of magnetism caused by cold forming and making material flow more freely in manufacturing. Nickel is highly resistant to atmospheric corrosion and resists most acids, but is attacked by oxidizing acids such as nitric acid. Natural nickel is a mixture of five stable isotopes, while nine other unstable isotopes are known. Nickel carbonyl is considered very toxic and exposure should be very limited. The fumes and dust of nickel sulphide are recognized as having carcinogenic potential.
To heat material after hardening to a temperature of perhaps 1000 degrees F. and allow to cool naturally in order to soften material and make it less brittle. Or to heat to a lower temperature of possibly 500 degrees F. to relieve stress in metal without affecting the hardness.
A common measure to compare the strength of a fastener. It is the load needed to pull the fastener apart.
Torque or Strength
Torque is the force used in twisting, such as tightening a fastener. Torsion strength is the amount of force needed to twist a fastener apart. Both measures consider the amount of pressure applied to the fastener and the length of the wrench used in the application.
Metallic zinc was produced in the 13th century A.D.
in India by reducing calamine with organic substances such as wool.
It was not until 1746, that it was rediscovered by Marggraf who
showed that it could be obtained by reducing calamine with charcoal.
The principal ores of zinc are sphalerite or blende (ZnS),
smithsonite (ZnCO3), calamine (silicate) and franklinite (zinc,
manganese, iron oxide). Zinc can be obtained by roasting its ores to
form the oxide and by reduction of the oxide with coal or carbon,
with subsequent distillation of the metal. Zinc has five (5)
naturally occurring stable isotopes, there are sixteen (16) other
unstable isotopes recognised, half of which are zinc 64. The stable
isotope zinc 67 occurs to the extent of 4% in natural zinc. Zinc is
a blue-white, lustrous metal. It is brittle at ordinary temperatures
but is malleable at 100°C to 150°C. It conducts electricity
moderately, and burns in air at high red heat with the evolution of
white clouds of the oxide. On exposure to air, zinc becomes coated
with film of carbonate and is then very corrosion-resistant.
HOW NUTS AND BOLTS ARE MADE
HOW NAILS AND STAPLES ARE MADE
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