PRESENTATION ON STAINLESS STEEL AND SPECIAL STEELS.

INTRODUCTIONIn metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is a steel alloy with a minimum of 10.5% chromium content by mass.Stainless steel does not readily corrode, rust or stain with water as ordinary steel does. However, it is not fully stain-proof in low-oxygen, high-salinity, or poor air-circulation environments.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 and corrosion resistance are required.

HISTORYA few corrosion-resistant iron artifacts survive from antiquity. A famous example is the Iron Pillar of Delhi, erected by order of Kumara Gupta I around AD 400. Unlike stainless steel, however, these artifacts owe their durability not to chromium but to their high phosphorus content, which, together with favorable local weather conditions, promotes the formation of a solid protective passivation layer of iron oxides and phosphates, rather than the non-protective cracked rust layer that develops on most ironwork.

PROPERTIES OF STAINLESS STEEL

OXIDATIONHigh oxidation resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments.Thechromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous and smooth. The layer is impervious to water and air, protecting the metal beneath, and this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium.

ACID AND BASESAcidsStainless steel is generally highly resistant to attack from acids, but this quality depends on the kind and concentration of the acid, the surrounding temperature, and the type of steel. BasesThe 300 series of stainless steel grades is unaffected by any of the weak bases such as ammonium hydroxide, even in high concentrations and at high temperatures. The same grades of stainless exposed to stronger bases such as sodium hydroxide at high concentrations and high temperatures will likely experience some etching and cracking, especially with solutions containing chlorides.

ELECTRICITY AND MAGNETISM

Similarly to steel, stainless steel is a relatively poor conductor of electricity, with a lower electrical conductivity than that of copper.

Ferritic and martensitic stainless steels are magnetic. Annealed Austenitic stainless steels are non-magnetic. Work hardening can make austenitic stainless steels slightly magnetic.

Types Of Stainless Steel

AUSTENITICAustenitic, or 200 and 300 series, stainless steels have an austenitic crystalline structure, which is a face-centered cubic crystal structure. Austenite steels make up over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy.

FERRITICFerritic stainless steels generally have better engineering properties than austenitic grades, but have reduced corrosion resistance, because of the lower chromium and nickel content. They are also usually less expensive. They contain between 10.5% and 27% chromium and very little nickel, if any, but some types can contain lead. Most compositions include molybdenum; some, aluminium or titanium.

MARTENSITICMartensitic stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly machinable, and can be hardened by heat treatment. Martensitic stainless steel contains chromium (12–14%), molybdenum (0.2–1%), nickel (less than 2%), and carbon (about 0.1–1%) (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic.

DUPLEX STAINLESS STEELSDuplex stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels.

SPECIAL STEELS

FREE CUTTING STEELFree-Cutting Steel a steel with a higher than usual content of sulphur and phosphorus intended for the fabrication of parts for high-speed automatic and semiautomatic machine tools. Free-cutting steel is produced in the form of rods, and it contains 0.08–0.45 percent carbon, 0.15–0.35 percent silicon, 0.6–1.55 percent manganese, 0.08–0.30 percent sulphur, and 0.05–0.16 percent phosphorus.

FREE CUTTING STEELThe high sulfur content leads to the formation of inclusions (for example, manganese sulfide) disposed along the grain. These inclusions facilitate shearing and promote grinding and easy chip formation. For these purposes, free-cutting steel is sometimes alloyed with lead and tellurium.

HIGH-STRENGTH LOW-ALLOY STEEL (HSLA)

High-strength low-alloy steel (HSLA) is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. HSLA steels vary from other steels in that they are not made to meet a specific chemical composition but rather to specific mechanical properties. They have a carbon content between 0.05–0.25% to retain formability and weldability.

HIGH-STRENGTH LOW-ALLOY STEEL (HSLA)Other alloying elements include up to 2.0% manganese and small quantities of copper, nickel, niobium, nitrogen, vanadium, chromium, molybdenum, titanium, calcium, rare earth elements, or zirconium. Copper, titanium, vanadium, and niobium are added for strengthening purposes.Their yield strengths can be anywhere between 250–590 megapascals . Because of their higher strength and toughness HSLA steels usually require 25 to 30% more power to form, as compared to carbon steels.

MARAGING STEELSMaraging steels (a portmanteau of "martensitic" and "aging") are steels (iron alloys) that are known for possessing superior strength and toughness without losing malleability, although they cannot hold a good cutting edge. Aging refers to the extended heat-treatment process. These steels are a special class of low-carbon ultra-high-strength steels that derive their strength not from carbon, but from precipitation of inter-metallic compounds.

MARAGING STEELSThe common, non-stainless grades contain 17–19 wt.% nickel, 8–12 wt.% cobalt, 3–5 wt.% molybdenum, and 0.2–1.6 wt.% titanium. Addition of chromium produces stainless grades resistant to corrosion. Due to the low carbon content maragingsteels have good machinability. Maraging steels offer good weldability.

SUPER ALLOYA superalloy, or high-performance alloy, is an alloy that exhibits several key characteristics: excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion or oxidation. The crystal structure is typically face-centeredcubic austenitic. Examples of such alloys are Hastelloy, Inconel, Waspaloy, Rene alloys, Haynes alloys, Incoloy, MP98T, TMS alloys, and CMSX single crystal alloys.

SUPER ALLOYSuperalloy development has relied heavily on both chemical and process innovations. Superalloys develop high temperature strength through solid solution strengthening. An important strengthening mechanism is precipitation strengthening which forms secondary phase precipitates such as gamma prime and carbides. Oxidation or corrosion resistance is provided by elements such as aluminium and chromium.

APPLICATIONS OF STAINLESS STEEL

ARCHITECTURAL USESStainless steel is used for buildings for both practical and aesthetic reasons. Stainless steel was in vogue during the art deco period. The most famous example of this is the upper portion of the Chrysler Building (pictured). Some diners and fast-food restaurants use large ornamental panels and stainless fixtures and furniture. Because of the durability of the material, many of these buildings retain their original appearance.

Type 316 stainless is used on the exterior of both the Petronas Twin Towers and the Jin Mao Building, two of the world's tallest skyscrapers. Type 316 is an austenitic chromium nickel stainless steel containing molybdenum. This addition increases general corrosion resistance, improves resistance to pitting from chloride ion solutions, and provides increased strength at elevated temperatures.

ARCHITECTURAL USES

ARCHITECTURAL USESCala Galdana Bridge in Minorca (Spain) was the first stainless steel road bridge.Duplexstainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels.

AUTOMOTIVE BODIESThe aft body panel of the Porsche Cayman model (2-door coupe hatchback) is made of stainless steel. It was discovered during early body prototyping that conventional steel could not be formed without cracking (due to the many curves and angles in that automobile). Thus, Porsche was forced to use stainless steel on the Cayman.

PASSENGER RAIL CARS

Rail cars have commonly been manufactured using corrugated stainless steel panels (for additional structural strength). Many railcars in the United States are still manufactured with stainless steel, unlike other countries who have shifted away.

AIRCRAFTThe American FleetwingsSea Bird amphibious aircraftof 1936 was also built using a spot-welded stainless steel hull.

APPLICATION OF HIGH-STRENGTH LOW-ALLOY STEEL

(HSLA)

HIGH-STRENGTH LOW-ALLOY STEEL (HSLA)

High-strength low-alloy steel (HSLA) is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. One of the disadvantages of this steel is that it is 30 to 40% less ductile. Examples of uses include door-intrusion beams, chassis members, reinforcing and mounting brackets, steering and suspension parts, bumpers, and wheels.

MARAGING STEEL

MARAGING STEELMaraging steel's strength and malleability in the pre-aged stage allows it to be formed into thinner rocket and missile skins than other steels, reducing weight for a given strength.They are suitable for engine components, such as crankshafts and gears, and the firing pins of automatic weapons that cycle from hot to cool repeatedly while under substantial load.

SUPER ALLOY

SUPER ALLOYSuper Alloy characteristics include Excellent mechanical strength and creep resistance at high temperatures, Good surface stability and Corrosion and oxidation resistant .Application include Aerospace, Turbine blades and jet/rocket engines, Marine industry Submarines Chemical processing industries Nuclear reactors Heat exchanger tubing Industrial gas turbine

Presented By :

Manan Kothari

Chinmay Kule

Prathemesh Mahade

Aniket Lambature

Presentation Made By :

Manan Kothari

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