8/13/2019 Why is Stainless Steel Stainless

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Frequently Asked Questions:

Below are some of the most frequently asked questions. If you cannot find the answer to your question here,please feel free tocontact us.

Why is stainless steel "stainless"?

Stainless steels are iron alloys with a minimum of 10.5% chromium with other elements (Nickel, Molybdenum,Titanium, Copper, Carbon, Nitrogen) added to enhance properties such as formability and strength. But it is thechromium-rich, oxide film that gives the corrosion resistance of stainless steel. This protective film is strong andchemically stable (i.e. passive) where there is sufficient oxygen on the surface. This strong protective film isextremely thin and will usually self repair if sufficient oxygen available. Under certain conditions the passive statecan be broken down and corrosion can result. Therefore the correct grade must be selected.

Should I buy A2 (304) or A4 (316) stainless steel fastenings?

A2 and A4 are known as Austenitic grade of stainless steel with the A4 grade having a higher corrosion resistancethan A2. They are both non-magnetic.

Grade A2 (AISI 304) has excellent resistance to atmospheric corrosion, except in severe industrial and marineenvironments.

Typical applications include street furniture, food processing, domestic appliances, medical and brewingequipment, fasteners for aluminium alloy, plastics, building fixings and fastenings for oak. Also suitable for mostnon-saltwater marine domestic applications.

Grade A4 (AISI 316) has a higher corrosion resistance than A2 grade in many chemical environments, includingcontact with dilute sulphuric acid, and acetic acid. Suitable for marine conditions, but not recommended forimmersion in sea water.Typical applications include fasteners for boat deck fittings, chemical plants, swimming pools, dye vats, sewagetreatment plants, dairy and medical sterilising equipment, and specialist building fixings.

Is stainless steel environmentally friendly?

Recycled scrap is used to produce over 90% of new stainless steel, and all stainless steel is fully "recyclable" atthe end of its useful life. Great care is taken to minimise fume and dust emissions in the production of stainlesssteel. The steel is melted electrically and in most cases refined by using inert air distilled gases, such as argon.

Life expectancy in stainless steels is usually long because of there corrosion resistant quality. Only minimummaintenance is needed therefore eliminating the environmental problems and costs of painting or galvanizing.Stainless steel is easy to clean and safe, being widely used for catering equipment and food manufacturing.

Why are there rusty marks on my stainless steel?

These rusty marks are unlikely to be the result of corrosion to the stainless steel, but are likely to result fromsmall particles of "ordinary" (non-stainless) steel from wire wool or scouring pads becoming attached orembedded in the surface. In the damp environment these iron particles rust and cause staining. Rust marks maybe removed using non-scratching creams, or an oxalic acid solution, where iron particles have been embedded inthe surface. Special precautions should be taken with oxalic acid, as if ingested is poisonous.

What does the 70 or 80 in a stainless steel bolt head mean?

The 70 or 80 refers to the tensile strength of the bolt; this is the maximum stretching force it can withstandbefore breaking. The class 80 bolt is stronger than the class 70. Class 70 is the most commonly used type offastener.

The tensile strength of class 70 bolts =