STAINLESS STEELS
Stainless steels are alloys of iron with a minimum of 10.5% chromium. Chromium produces a thin layer of oxide on the surface of the surface of the steel which prevents any further corrosion of the surface. Increasing the amount of chromium gives an increased resistance to corrosion.
Stainless steels also contain varying amounts of Carbon,, Silicon nd Manganese. Other elements such as Nickel and Molybdenum may be added to impart other useful properties such as enhanced formability and increased corrosion resistance.
Stainless steels are usually divided into 5 types:
Ferritic - These steels are based on Chromium with small amounts of Carbon usually less than 0.10%. These steels have a similar microstructure to carbon and low alloy steels. They are usually limited in use to relatively thin sections due to lack of toughness in welds. However, where welding is not required they offer a wide range of applications. They cannot be hardened by heat treatment. High Chromium steels with additions of Molybdenum can be used in quite aggressive conditions such as sea water. Ferritic steels are also chosen for their resistance to stress corrosion cracking. They are not as formable as austenitic stainless steels. They are magnetic.
Austenitic - These steels are the most common. Their microstructure is derived from the addition of Nickel, Manganese and Nitrogen. It is the same structure as occurs in ordinary steels at much higher temperatures. This structure gives these steels their characteristic combination of weldability and formability. Corrosion resistance can be enhanced by adding Chromium, Molybdenum and Nitrogen. They cannot be hardened by heat treatment but have the useful property of being able to be work hardened to high strength levels whilst retaining a useful level of ductility and toughness. Standard austenitic steels are vulnerable to stress corrosion cracking. Higher nickel austenitic steels have increased resistance to stress corrosion cracking. They are nominally non-magnetic but usually exhibit some magnetic response depending on the composition and the work hardening of the steel.
Martensitic - These steels are similar to ferritic steels in being based on Chromium but have higher Carbon levels up as high as 1%. This allow them to be hardened and tempered much like carbon and low-alloy steels. They are used where high strength and moderate corrosion resistance is required. They are more common in long products than in sheet and plate form. They have generally low weldability and formability. They are magnetic.
Duplex - These steels are similar to ferritic steels is being based on Chromium but have higher Carbon levels up as high as 1%. This allows them to be hardened and tempered much like carbon and low-alloy steels. They are used where high strength and moderate corrosion resistance is required. They are more common in long products than in sheet and plate form. They have generally low weldability and formability. They are magnetic.
Duplex - These steels have a microstructure which is approximately 50% ferritic and 50% austenitic. This gives them a higher strength than either ferritic or austenitic steels. They are resistant to stress corrosion cracking. So called ''lean duplex'' steels are formulated to have comparable corrosion resistance to standard austenitic steels but with enhanced strength and resistance to stress corrosion craking. ''Superduplex'' steels have enhanced strength and resistance to all forms of corrosion compared to standard austenitic steels. They are weldable but need care in selection of welding consumables and heat input. They have moderate formability. They are magnetic but not so much as the ferritic, martensitic and PH grades due to the 50% austenitic phase.
Precipitation hardening (PH) - These steels can develop very high strength by adding elements such as Copper, Niobium and Aluminium to the steel. With a suitable ''aging'' heat treatment, very fine particles form in the matrix of the steel whiich imparts strength. These steels can be machined to quite intricate shapes requiring good tolerances before the final aging treatment as there is minimal distortion from the final treatment. This is in contrast to conventional hardening and tempering in martensitic steels where distortion is more of a problem. Corrosion resistance is comparable to standard austenitic steels like 1.4301(304).
Stainless steels are used in many areas in our Daily life and industry;
Domestic Use : Cutlery, sinks, saucepans, washing machine drums, microwave oven liners, razor blades
Architectural / Civil Engineering : cladding, handrails, door and window fittings, street furniture, structural sections, reinforcement bar, lighting colummns, lintels, masonry supports
Transport : Exhaust systems, car trim / grilles , road tankers , ship containers , ships chemical tankers , refuse vehicles
Chemical / Pharmaceutical Industry : Pressure vessels , process piping.
Oil and Gas Industry : Platform accommodation , cable trays , subsea pipelines
Medical Industry : Surgical instruments , surgical implants , MRI scanners.
Food and Drink Industry : Catering equipment , brewing , distilling , food processing
Water Systems : Water and sewage treatment , water tubing , hot water tanks
General Use : Springs , fasteners ( bolts , nuts and washers ) , wire
In CEL-MER we are specialized especially on the hot rolling / cold drawing / peeling and grinding of stainless steels in different grade / size combinations. For detailed information please contact us: export@celmercelik.com