General characteristics

Stainless steel is a complex alloy that is not only resistant to corrosion under the influence of high humidity, but also in aggressive environments. At the beginning of the twentieth century, Harry Brearley (Brearley), experimenting with different metals, discovered the ability of iron alloys with chromium to resist acid corrosion. The higher the percentage of chromium in the steel, the greater the corrosion resistance. Under normal atmospheric conditions and in mildly aggressive environments, an alloy is stainless if its chromium content is 12%. To be resistant in more aggressive environments, e.g. 50% nitric acid, the alloy must have more than 17% chromium. Together with chromium, steel usually contains elements such as Si, C, Mn, and in thousandths of a percent sulfur and phosphorus. Elements such as Ni, Ti, Mn, Nb, Mo, and Co are also added to give special properties. The reason for corrosion resistance is that a micron film of very resistant oxides is formed on the surface of the steel part. The state of the material surface, absence of internal stresses and crystalline defects is of great importance. In concentrated inorganic acids, alloys with high Ni content and molybdenum, copper and silicon additives are used.

Classification

Stainless steels by chemical composition can be chromium, chromium-nickel and chromium-manganese-nickel (there are more than 100 grades); by structure - martensitic, semi-ferritic and ferritic. Chromium martensitic stainless steels in polished form have the best indices of durability. Chromium stainless steels are used as a construction material for the manufacture of valves for hydraulic presses, turbine blades, fittings for cracking units, cutting tools, springs and household goods. Chromium-nickel and chromium-manganese-nickel stainless steels are subdivided into austenitic, austenitic-ferritic, austenitic-carbide and austenitic-martensitic.

Intergranular corrosion

There are austenitic stainless steels that are prone to intergranular corrosion and stabilized austenitic stainless steels to which Ti and Nb are added. The susceptibility to intergranular corrosion can be reduced by reducing the carbon content to 0.03%. Stabilized austenitic stainless steels are indispensable for fabrication of welded valve parts operating in aggressive environments. No heat treatment is required after welding. As a heat-resistant and high-temperature resistant material, these steels are used for products exposed to temperatures between 550 and 800 °C. Steels that are prone to intergranular corrosion are heat-treated after welding according to existing rules. Heat treatment is not necessary if parts are welded by means of spot or roller welding.

Use

Both chromium-nickel and chromium-manganese-nickel stainless steels have found widespread use in industrial production and in the home. For heavily loaded elements of complex structures operating at high temperatures (up to 550°C) maraging austenitic-martensitic steels are justifiably used which have considerable strength (sb = 120-150 ^kgf/mm2), good weldability and rather high ductility. These steels can be supplied in deformed or cast condition.

Buy, price

Evek GmbH has a wide range of stainless steel products in stock, which will satisfy any customer. We deliver stainless steel products of different classes of standard and non-standard sizes. All products are certified. Quality is guaranteed by full compliance with the technological norms of production. The terms of performance of orders are minimal. In case of bulk purchases the preferential discounts are provided.