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Stainless Steel & Corrosion

The very name of stainless steel implies virtual metallurgical immortality. Since the accidental discovery of stainless steel nearly a hundred years ago, it has become a fixture in almost everything, from skyscraper trim and turbine blades to automobile and household appliance manufacturing. It is also very well know to the recreational boat builders, boatyards and owners. Most cruising vessels today are riddled with a variety of stainless steel alloys, of which there are many, that are used to support everything from headliners (stainless steel staples) to propellers (stainless alloy propeller shafts).

It may come as a surprise to many professional as well as casual users, that the primary alloy contained within stainless steel is humble and familiar iron. After all, there is a reason for the name, stainless steel. To this ordinary and plentiful element, there are other more exotic alloys such as nickel and chromium added to it, which gives stainless steel its corrosion resistant properties. The chrome allows the stainless steel to form the tough oxide film as soon as and for as long as it is exposed to oxygen, even when it is submerged, provided that the water contains oxygen, while the nickel increases its resistance to acid. Depending on the role that it will be filling, architectural trim, bow rail or cutlery for example, differing amounts of elements are then added, along with trace amounts of the still more exotic materials like tantalum and columbium.

Essentially, there’s three sub groups of stainless steel, namely: martensitic, which is very often used for many fasteners, cutlery and turbine blades. Then there is Ferritic, which is very often used for automotive trim applications. And lastly Austenitic, which is generally used in the marine environment. Of the three groups, high nickel content is exclusive to marine or austenitic grade. Therefore, contrary to its appearance which is silvery, not all stainless steel is created equal. The marine grade stainless steel is then further distilled into 2 popular alloys, which is designated by the American Iron and Steel Institute as 300 series. 304 and 316 are the most commonly used for recreational marine applications. The alloy ratio used in 304 stainless steel consists of 8-12% nickel and 18-20% chromium, which is added to the conventional carbon steel.

At Kwal Kraft we specialise in the manipulation of stainless steel pipes, components and bars, for more information on our products and services visit our website on www.kwalkraft.co.za.

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