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Unit III Ppt

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UNIT III FERROUS AND NON-FERROUS METALS

UNIT III FERROUS AND NON-FERROUS METALSFERROUS METALSEffect of alloying additions on steel and stabilisersStainless steelsTool steelsHSLA, Maraging steels Cast Iron

NON FERROUS METALS Copper and copper alloys Brass, Bronze and Cupronickel Aluminium and Al-Cu Precipitation strengthening treatmentBearing alloys, Mg-alloys, Ni-based super alloys Titanium alloys

One question from Ferrous and one from Non Ferrous for semester Exam

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ALLOY STEELS An alloy steel may be defined as one whose characteristic properties are due to some element other than carbon. Although all plain-carbon steels contain moderate amounts of manganese (up to about 0.90 percent) and silicon (up to about 0.30 percent), they are not considered alloy steels because the principal function of the manganese and silicon is to act as deoxidizers. They combine with oxygen and sulfur to reduce the harmful effect of those elements

Purpose of Alloying (Alloying elements are added to steels for many purposes)

Increase hardenabilityImprove strength at ordinary temperaturesImprove mechanical properties at either high or low temperaturesImprove toughness at any minimum hardness or strengthIncrease wear resistanceIncrease corrosion resistanceImprove magnetic propertiesImprove machiniabilityGeneral Effects of Alloying ElementsWhen selecting a steel for a particular job, plain carbon steels are preferable over alloy steels are expensive.On other hand, an alloy steel can be used to desired properties throughout the heavy section and wherever the service conditions demand the enhanced properties which are unattainable with a plain steel. in some instances, use of alloy steel may intensify the problem rather than reducing them. Designer recognize the situation in which alloy steels are preferable

Classification of alloying ElementsSolid Solution FormationCarbide formationShifting of critical temperature

Solid Solution FormationAlloying elements dissolve in Ferrite and form solid solution when added to steel. Increases the strength and hardness of steel by solid solution strengthening .Small loss in ductility.Ex: Ni, Si, Al, & Mg,Carbide formationSome alloying elements are combined with carbon and form stable carbides.Extensively hard and they increase wear resistance.Increase resistance to softening at elevated temperature and prevent grain coarsening.Ex: Niobium, Titanium, vanadium, molybdenum, tungsten and chromium. Shifting of Critical TemperatureAlloying elements could lower or raise the critical temperature of steel.Some alloying elements like manganese and nickel lower the critical temperature (Enlarges Austentite region and stable at room temperature ) so these elements are called as austenite stabilizers.Chromium, tungsten, Vanadium, Molybdenum, silicon and titanium shift the critical temperature to higher values and these alloys reduce the autentite region and if elements are added more quantity austenite region may not appear. Also it shift of this type tends to merge ferrite and delta iron together to give a continuous ferrite from the room temperature to the melting point. Ferrite Stabilizer

Behavior of the Individual Elements

Effects of Alloying Elements on Steel 12Manganesecontributes to strength and hardness; dependent upon the carbon content. Increasing the manganese content decreases ductility and weldability. Manganese has a significant effect on the hardenability of steel.Phosphorus increases strength and hardness and decreases ductility and notch impact toughness of steel. The adverse effects on ductility and toughness are greater in quenched and tempered higher-carbon steels.Sulfur decreases ductility and notch impact toughness especially in the transverse direction. Weldability decreases with increasing sulfur content. Sulfur is found primarily in the form of sulfide inclusions.Siliconis one of the principal deoxidizers used in steelmaking. Silicon is less effective than manganese in increasing as-rolled strength and hardness. In low-carbon steels, silicon is generally detrimental to surface quality.Copper in significant amounts is detrimental to hot-working steels. Copper can be detrimental to surface quality. Copper is beneficial to atmospheric corrosion resistance when present in amounts exceeding 0.20%. Nickel is a ferrite strengthener. Nickel does not form carbides in steel. It remains in solution in ferrite, strengthening and toughening the ferrite phase. Nickel increases the hardenability and impact strength of steels. Molybdenumincreases the hardenability of steel. It enhances the creep strength of low-alloy steels at elevated temperatures.

Probable hardening effect ot the various elementsStainless SteelsInmetallurgy,stainless steel, also known asinox steelorinox, means"inoxydable", is steelalloywith a minimum of 10.5% or11% chromiumcontent by mass.Stainless steel does not readilycorrode,rustor 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 andcorrosion resistanceapplication.

Contd.Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steelrustsreadily when exposed to air and moisture. Thisiron 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 apassivefilm 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 andoxide ions, they bond very strongly and remain attached to the surface.

Types of SSClassified into 5 types:Ferritic SSMartensitic SSAustenitic SSPrecipitation Hardening (PH) SSDuplex Stainless Steel

Ferritic SSThe steels containing greater amount of chromium (from 10.5 to 27%) and about 0.12% carbon are called ferritic stainless steels.They are Ferro-magnetic, high cold formability usually undergo excessive grain growth during prolonged exposure to elevated temperatures. These stainless steels remain ferritic at all temperatures below solidification become chromium is ferrite stabilizer.These steels cannot be hardened by martensitic transformation because there is no possibility of forming austenite.Annealing is only HT applied to relieve cold working stress and hardened by cold working. These steels have lower strength at elevated temperatures.Corrosion and oxidation resistance and less expensive.Applications: Vessels for chemical and food industries, automotive and architeture and household applicationCommon ferritic grades include 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2NiMartensitic SSMartensitic stainless steel contains chromium (1214%) and molybdenum (0.21%), nickel (less than 2%), and carbon (about 0.11%) - first stainless steels.Since these steels possess martensitic structure, therefore, they are called martensitic stainless steels.These steels are magnetic and cold workedwith low carbon. They may be hardened by suitable heat treatment and the hardness obtainable depends upon the carbon content.These steels can be easily welded and machined. When formability, softness, etc. are required in fabrication, steel having 0.12 per cent maximum carbon is often used in soft condition. With increasing carbon, it is possible by hardening and tempering to obtain tensile strength.

Martensitic SS -1In this condition, these steels find many useful general applications where mild corrosion resistance is required.Also, with the higher carbon range in the hardened and lightly tempered condition, tensile strength may be developed with lowered ductility.These steels may be used where the corrosion conditions are not too severe, such as for hydraulic, steam and oil pumps, valves and other engineering components.However, these steels are not suitable for shafts and parts working in contact with non-ferrous metals (i.e. brass, bronze or gun metal bearings) and with graphite packings, because electrolytic corrosion is likely to occur. After hardening and light tempering, these steels develop good cutting properties. Therefore, they are used for cutlery,springs, surgical and dental instruments.Austenitic SSThey 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 thecryogenicregion to the melting point of the alloy. Here nickel is austenite stabiliser. These steels cannot be hardened by quenching, in fact they are softened by rapid cooling from about 1000C. They are nonmagnetic and possess greatest resistance to corrosion (than ferritic and martensitic) in media except hydrochloric acid and other halide acids and salt.These steels are very tough and can be forged and rolled but offer great difficulty in machining.

Austenitic SS-1They can be easily welded, but after welding, it is susceptible to corrosive attack in an area adjacent to the weld. This susceptibility to corrosion (called intercrystalline corrosion or weld decay) may be removed by softening after welding by heating to about 1100C and cooling rapidly. If Cr is decrease by below 12% there is a sharp decrease in corriosion resistance this is known as sensitising. Carbide formation are to be prevented in this steel thats why the carbon is0.15%. Other elements are also have strong affinity for carbon (titanium, niobium, tantalum or columbium) The most widely used steel contain 18 per cent chromium and 8 per cent nickel with carbon content as low as possible. Such a steel is commonly known as 18/8 steel.Application of austenite SSThese steels areused in the manufacture of pump shafts, rail road car frames and sheathing, screws, nuts and bolts and small springs. Since 18/8 steel provide excellent resistance to attack by many chemicals, therefore, it is extensively used in chemical, food, paper making and dyeing industries.

Grades: 200 Seriesaustenitic chromium-nickel-manganese alloys.300 SeriesThe most widely used austenite steel is the304, also known as18/8for its composition of 18% chromium and 8% nickel.Precipitation Hardening SSPrecipitation-hardening SS have a matrix structure of either austenite or martensite.Austenite PH SS are magnetic and contains atleast 10% Ni in order to reamin austenitic. They strengthening elements are Mo,Nb,Cu, or Ti. These steels are used succesfully upto about 650oC. Martensitic PH SS usually contains 17% Cr and are alloyed with small amounts of Cu, Mo, Al, Ti, or Nb. These steels are more common in use than those with austenitic matrix.PH SS have good corrosion resistance and ductility. They have high strength at elevated temp. These are the most expensive SS.APPLICATION: Aircraft and Aerospace structural ComponentsDuplex SSCarbon content very low (0.03%) with additions of Ti or Mo. They have a microstructure of ferrite grains in austenite or vice-versa. Their yield strength is twice as that of austenitic SS. The other advantages are high corrosion resistance , greater resistance to stress- corrosion cracking and good weldability.Application: Water Treatment plants, heat exchanger components, off shore drilling rigsMicrostructure of SS Austenite PH

Ferrite Martensite