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1 CHAPTER I INTRODUCTION 1.1 BACKGROUND In 1913, English metallurgist Harry Brearly, working on a project to improve rifle barrels, accidentally discovered that adding chromium to low carbon steel gives it stain resistance. In addition to iron, carbon, and chromium, modern stainless steel may also contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel, molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel. It is the add
   1 CHAPTER I INTRODUCTION 1.1 BACKGROUND In 1913, English metallurgist Harry Brearly, working on a project to improve rifle  barrels, accidentally discovered that adding chromium to low carbon steel gives it stain resistance. In addition to iron, carbon, and chromium, modern stainless steel may also contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel, molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel. It is the addition of a minimum of 12% chromium to the steel that makes it resist rust, or stain 'less' than other types of steel. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide, called the  passive film. The sizes of chromium atoms and their oxides are similar, so they pack neatly together on the surface of the metal, forming a stable layer only a few atoms thick. If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly form and recover the exposed surface, protecting it from oxidative corrosion. (Iron, on the other hand, rusts quickly because atomic iron is much smaller than its oxide, so the oxide forms a loose rather than tightly-packed layer and flakes away.) The passive film requires oxygen to self-repair, so stainless steels have poor corrosion resistance in low-oxygen and  poor circulation environments. In seawater, chlorides from the salt will attack and destroy the passive film more quickly than it can be repaired in a low oxygen environment. 1.2 PROBLEM FORMULATION 1.What is stainless steel ? 2.How many types of stainless steel are there? 3.What components are made of stainless steel? 1.3DESTINATION To find out what it is stainless steel and the components are made by stainless steel   2 CHAPTER II DISCUSSION 2 . 1.STAINLESS STEEL In metallurgy,  stainless steel , also known as inox steel  or inox  from French inoxydable , is a steel alloy with a minimum of 10.5% [1]  chromium content by mass. Stainless steel does not readily corrode, rust or stain with water as ordinary steel does; but, despite the name, it is not fully stain-proof, most notably under low-oxygen, high-salinity, or poor-circulation environments. [2]  There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where  both the properties of steel andcorrosion resistance are required. Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide; and, because of the greater volume of the iron oxide, this tends to flake and fall away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure, and, due to the similar size of the steel and oxide ions, they bond very strongly and remain attached to the surface. [3]  Passivation occurs only if the proportion of chromium is high enough and oxygen is  present.. Other alloying elements are added to enhance their structure and properties such as formability, strength and cryogenic toughness. These include metals such as:     Nickel    Molybdenum    Titanium    Copper  Non-metal additions are also made, the main ones being:    Carbon     Nitrogen   3 2.2 TYPE OF STAINLESS STEEL Stainless steel is usually divided into 5 types: a.   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.  b.   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. c.   Martensitic - These steels are similar to ferritic steels in 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. d.   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 c orrosion 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 cracking. “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. e.   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 which 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).   4 2.3 COMPONENT MADE OF STAINLESS STEEL Stainless steel’s resistance to corrosion and staining, low maintenance and familiar  lustre make it an ideal material for many applications. There are over 150 grades of stainless steel, of which fifteen are most commonly used. The alloy is milled into coils, sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, household   hardware, surgical instruments, major appliances, industrial equipment (for example,   in sugar refineries) and as an automotive and aerospace structural alloy and construction   material in large buildings. Storage tanks and tankers used to transport orange juice and   other food are often made of stainless steel, because of its corrosion resistance. This also influences its use in commercial kitchens and food processing plants, as it can be steam-cleaned and sterilized and does not need paint or other surface finishes. Stainless steel is used for jewelry and watches with 316L being the type commonly used for such applications. It can be re-finished by any jeweler and will not oxidize or turn  black. Some firearms incorporate stainless steel components as an alternative to  blued or   parkerized steel. Some handgun models, such as the Smith & Wesson Model   60 and the Colt M1911 pistol, can be made entirely from stainless steel. This gives a high-   luster finish similar in appearance to nickel plating. Unlike plating, the finish is not subject to flaking, peeling, wear-off from rubbing (as when repeatedly removed from a holster), or rust when scratched. Some automotive manufacturers use stainless steel as decorative highlights in their vehicles. Stainless steels of various kinds are used in thousands of applications. The following gives a flavour of the full range: 1.Domestic  –   cutlery, sinks, saucepans, washing machine drums, microwave oven liners, razor blades 2.Architectural/Civil Engineering  –   cladding, handrails, door and window fittings, street furniture, structural sections, reinforcement bar, lighting columns, lintels, masonry supports 3.Transport  –   exhaust systems, car trim/grilles, road tankers, ship containers, ships chemical tankers, refuse vehicles 4.Chemical/Pharmaceutical    –   pressure vessels, process piping. 5.Oil and Gas    –   platform accommodation, cable trays, subsea pipelines. 6.Medical  –   Surgical instruments, surgical implants, MRI scanners. 7.Food and Drink     –   Catering equipment, brewing, distilling, food processing. 8.Water  –   Water and sewage treatment, water tubing, hot water tanks. 9.General  –   springs, fasteners (bolts, nuts and washers), wire
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