Stainless Steels

Stainless steels which represent less than 2% of total world steel production make use of chromium and nickel. They also contain about 1% manganese. There are also manganese-stainless steels, where nickel is replaced partly or entirely by manganese, giving a manganese content of 4 to 16%. These are not yet produced in large quantities, but they could develop in the future depending on the evolution of the nickel price compared with manganese and on the marketing effort devoted to them. Most commonly known as Series 200 stainless, this high Mn content stainless steel uses Manganese metal. China is the largest producer of Mn metal, producing over 560,000 mt, 90% of the world’s production, in 2005. Series 200 was originally created in India, and is still made there as well.


Any overview of high Mn steels must include Hadfield steel, named after its 19th century UK inventor and the first alloy steel ever invented. This steel contains 13% or more manganese. It has unique properties which make it indispensable for applications in which great toughness and wear resistance are required. Among these can be cited gyratory crushers, jaw-crusher plates, railway points and crossover components, teeth for earth-moving equipment, etc. High manganese (10-12%) non-magnetic steels are used for such products as retainer rings for turbo alternators and collars on oil rigs. Grades with a similar chemistry are used as cryogenic steels. A high manganese stainless "memory" steel has been developed.

Other Metallurgical Uses of Manganese

Aluminum

Although ranking far behind steel, the second most important metal in which manganese plays an important alloying role is aluminum. Some 23 million tons of aluminum are produced annually. Small amounts of manganese are found in many of these Al alloys, enhancing corrosion resistance. The explanation for this beneficial effect is simple. Intermetallic compounds, formed with iron and silicon, have an electrolytic potential which is far less negative than that of aluminum. This means that the aluminum surrounding such particles will be attacked under corrosive conditions, with disintegration further spreading as a series of deep pits are formed which spread the process to other particles. Manganese replaces iron-silicon compounds with manganese-iron-silicon compounds which have an electrolytic potential very close to that of aluminum. As a result there is no potential difference and therefore no corrosion.

Manganese is used as an alloying element up to its solubility limit of about 1.5%. Aluminum-manganese alloys and aluminum-manganese-magnesium alloys, which have been sold under different trade names, have found applications in such diversified areas as kitchenware, roofing, car radiators and transportation. By far the most important use of aluminum-manganese alloys is for beverage cans, of which some 100 billion units are produced each year. The market for aluminum-manganese cans has grown steadily, thanks to the fact that such cans can be recycled.

Aluminum alloys containing up to 9% Mn have promising properties, but they cannot as yet be economically produced. Technologies to produce these commercial “amorphous” metals through very fast cooling are of potential interest but the processes used are still very expensive and can only be applied to high value materials used in the aerospace industry