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Metals, Cu and it's alloys, Ferritic steels/Alloy steels(C<0.1%),…

- - - - Cr, Zr
        
        Strengthening ++
      - Pb, Se
        
        improves machinability
      - Ag
        
        improves heat resistance
- - - - Gamma double prime
        
        Gamma prime
        
        Gamma
        
        Gamma is ordered bcc
        
        weaker than gamma prime, formed due to overaging
        
        hardest phase
        
        partially coherent but can be called coherent
      - coherent and strong strengthening effects
- - - - Good ductility
      - Both cold and hot workable
      - good weldability
    - - Disordered structure
      - Formable at high T
    - - Can't deform plastically
  - - - good ductility
  - - - Strength++
      - Elongation++
    - - Elongation--
    - - Very high Zn
      - Tensile strength -- with increase Zn%
    - - Al
      - Ni
      - Sn
      - Mn
    - - Zn(eq) = (A/B)*100
        A = (sum of equivalency factor*that element%(wt))+zn wt%
        B = A + Cu content ( but wait.. isn't that the total % -.-), No we have multiplied by equivalency factor so NO.... be careful.
- - - - basically completely solubility is observed
    - - strength++
      - oxidation resistance ++
      - corrosion resistance ++
      - electrical resistivity ++
      - good formability due to low work hardenability
- - - - Porosity at grain boundaries
      - Easy fracture/blistering of Cu
      - Spicy name = Hydrogen embrittlement
- - - - lower carbon content to correct this
      - Mn,V and N can be increased to counter the low C
- - - - V adds to major amount of precipitation strengthening
      - VC has the highest solubility therefore it would precipitate at last leading to very fine uniformly distributed precipitates.
      - (not in syllabus): Vanadium first forms VN until N exhausts, then VC from the C in ferrite. VN precipitation effects> VC precipitation effects. and after Carbon is exhausted. No more influence of V
    - - Cut through the precipitate - which is hard
      - loop around the precipitate
  - - - AlN precipitates
        
        Pin the grain boundaries of austenite
        
        Leads to even finer ferrite grains
    - - HSLA specific
      - induces solution drag effects
      - induces strain induce precipitation
- - - - to achieve martensite "particles" at air cooling
      - Si hinders formation of pearlite
- - - - Strain induced martensitic transformation
    - - Low temp tempering(200C)
        
        internal stress goes down but hardness and toughness is constant
      - high temp tempering(200 to 500C)
        
        toughness rises, harness falls
- - - - which results into fine ferrite grains
- - - - has fine flakes of graphite
      - slow cooling
      - only Si is added
    - - has coarser graphite
      - fast cooling
      - can have Cu, Ni, Cr or Mn
- - - - Soft
      - Highly ductile
      - relatively low strength
      - poor wear resistance
      - good thermal conductivity
      - very good machinability
    - - relatively hard
      - moderate ductility
      - high strength
      - good wear resistance
      - reduced thermal conductivity
      - good machinability
      - More Si , more hardness
        
        Si lowers the eutectic carbon %
        
        Si increases the eutectic temperature
- - - - The carbides are retained in martensite and during the tempering phase, we get fine dispersed metal carbide in tempered martensite
      - These carbides are harder than Fe3C
      - contribute to wear resistance of tools
  - - - improves red hardness
- - - - not alloyed much therefore need faster quench than air
  - - - Mo based
    - - TiC
- - - - low material wastage
        
        therefore low cost
  - - - II)Annealed
        1) spheroidites
        2)homogenous distribution of carbides
        3)ferritic matrix
        4)directional properties removed
        a)choice of temp critical ( controls distribution of elements and carbides)
        b) to high of a temp can dissolve carbides and push carbides to grain boundaries giving a naked soft matrix.
        
        III)Hardening(simillar to alloy steels)
        
        IV) Stress relief
        Heat treated around 650C recovery and recrystallization of ferrite
        Carbides are unaffected
        
        V) Tempering
        Secondary hardening occur due to alloy carbide precipitation
        diffusion of the carbides in tempered martensite
        Diffusivity is sluggish but present therefore less distance between the carbide particles.
        2nd or 3rd tempering step is also sometimes provided to get rid of retained austenite. (tough to get rid of them when alloying elements are high)
- - - - Fcc structure and becasue of Ni it can be there in the matrix for a long time as a stable precipitate.
      - starts as spheres(very small precipitate)
        
        forms cubes later to minimize interfacial energy
  - - - coherent BCT Ni3Nb phase
  - - - TiC TaC toe, HfC, NbC
      - major source of C during heat treatment
      - They decompose to M23C6 or M6C at high T or service
      - all of'em are fcc so matches with parent crystal structure
      - beneficial for poly crystal structures. They have an affinity to go to grain boundaries.
        They increase rupture strength
      - M7C3 and M23C6
        
        Secondary carbides
        
        formed during heat treatment
        
        mainly on grain boundaries
        
        irregular and discontinuous
        
        most beneficial
      - M6C
        
        precipitate on grain boundaries and can form widmanstatten structures
        
        rich in refractory elements (W and Mo)
        
        forms at a slightly higher temp than M23C6
      - heterogenous solidification
      - grain boundary carbides
        
        continuous carbide provides easy pathway for crack to propogate
        
        lack of carbide means grains are free to slide against each other
        
        therefore balance of both the above point is required.
      - IN general CARBIDES benefit to rupture strength at high T if right composition, is situated at the desirable spots with the required morphology
- - - - Their atomic radii are 3-13% different only
        Therefore, group V, VI and VII elements.
      - max effect near 10% increase in atomic size
  - - - these particles block dislocation movement
      - always incoherent
      - provides strengthening upto 1300C
    - - Look into the carbides
- - - - oxidation and sulphidation resistance
      - solid solution strengthening
      - grain boundary carbides
    - - raises solvus temp of gamma prime
      - lowers stacking fault energy.
        
        prevents cross-slip of screw dislocations
    - - Al = forms gamma prime (Ni3(AlTi)) and improves oxidation resistance.
      - Ti = forms gamma prime (Ni3(AlTi)) and titie carbides
    - - B and Zr = stress rupture properties ++
      - retards Ti to form Ni3Ti at grain boundary by rather going by itself to the boundaries. oooooOOoooooOOO!! ahhahhahhhahh, ahhahahhhah
      - C = helps in formation of different types of carbide
    - - N and Ta = formation of gamma dubel prime (Ni3Nb) and MC type carbides
      - Mo , Ta and W = Madarchod type carbides
        solid solution strengthening
- - - - low% beneficial
      - high % formation of Al6Mn precipitates
      - solid sol not important commercially
    - - low% beneficial
      - high% forms Al-Cu-Fe(insoluble)
      - solid sol not important commercially
    - - Most effective solid sol hardening
      - high solubility
    - - High solubility
      - very less solid solution strengthening effect
    - - less solid solution strengthening than pure element addition
  - - - Solution treatment
        heated to a temp within single solid phase region
        
        Quenching
        preserve the solid solution
        kinematically impossibleto form precipitates while quench
        
        formation of SSS
        (supersaturated solid solution)
        
        Aging
        SSS is metastable
        Natural aging - kept at room temp
        Artificial aging - kept at elevated temp (100-190C)
        dispersed precipitates are formed(fine dispersion)
        
        If we quench above GP solvus line and age - theta" (nucleation is hard and separated precipitates) ( solutes pile up to wherever nucleation starts)
        
        If we quench below gp solvus and age above gp solvus - some gp zones are nucleated on quench, age and form other phases heterogenously on them.
        
        Most used process:
        Duplex aging treatment(not in syllabus)
        
        I) Quench to below gp sol line.
        
        Age 1
        lower than gp solvus (to create a lot of gp zones in the structure)
        
        1 more item...
    - - upto 5% Cu addition
      - precipitation sequence
        (Valid for other systems too)
        
        SSS
        
        GP(disc)
        
        theta"(disc)
        
        Theta'(plate)
        
        Theta (Al2Cu)
        
        partially coherent
        
        the wanted phase for precipitate ++
        
        Gp zone is ordered.
        fully coherent with matrix
      - It forms precipitation hardeining because the solubility of Cu in aluminum varies signifincantly with changing tempertature
    - - Vacancies diffuse to grain boundaries
      - Precipitates migrate to grain boundaries
        
        easier to make precipitate(higher surface energy)
      - Parallel precipitate free zones to grain boundaries
      - Very weak properties ( matrix properties)
      - Fast quench - narrow PFZ zone
        Slower quench - wide PFZ zone
      - can be drastically reduced by raising the GP solvus line ( adding small amounts of Ag(0.3%)( can therefore age at higher temp > more supercooling > less dependence on diffusion for nucleation) (not in syllabus)
      - introducing elements Cd,In and Sn which hold the vacancies and make their diffusion tough ( not in syllabus)
- - - - Martensitic grades
        
        Ms temp > Room temp
        
        Flow: Austeniztion+quenching+ageing
      - Semi - Austenitic grades
        
        more % of alloys
        
        fcc austenite- so ductile
        
        Flow: forming + cryocooling(form martensite)+ageing(precipitates)
      - Austenitic grades
        
        more% of alloys ++ than semi
        
        Flow: Austenisation+cooling+ageing
  - - - need to balance the austenite and ferrite ratio so therefore accordingly fcc or bcc stabilizers are added
    - - Very high strength
      - Useful ductility and toughness
      - good combination of strength, general corrosion and stress corrosion cracking resistance.
        
        generally teice the yield strength of common austenitic steels
    - - This steel was researched for this particular purpose to make moderate costing steels with good properties.
  - - - martensite+age hardening
    - - TiC
      - Ni3Mo
      - Ni3(Mo,Ti)
- - - - Martensitic > Precipitation hardened > Duplex > Ferritic > Austenitic
    - - Duplex > Austenitic > Ferritic > Precipitation hardened > Martensitic
- - - - supercooling promotes dendrites
- - - - reduced temperature slows the kinetics
    - - 3 regions in graph
        Immunity
        corrosion
        passivation
        
        Very acidic and basic both lead to corrosion
  - - - passive layer is easy to be attacked because it can't be regenerated because of lack of oxygen
      - presence of chlorine ions aggrevate the situation ( applicable to marine application) breaks down the passive film
    - - area near the grain boundaries have depleted Cr content act as anode and the grain are with the passive coating of Cr oxide acts as cathode. This will eat up the metal at the chromium deficit places. - steels(with Cr 11%)
      - to prevent this:
        1: add Ti and Nb, these will form preferential carbides and prevent Cr from making it
        2: lower C content to reduce formation of chromium carbide
        3: Heat treat to equalize chromium content in the solution
    - - caused by a flow of corrosive fluid
      - both corrosion and erosion
      - Conditions
        
        Velocity and turbulence of fluid
        pH and water alkalinity
        deposits
    - - extremely localized
      - creation of small holes and pits
      - Driving force
        
        depassivation of a local area
        
        this area acts like an anode
      - usually happens to passive metals and stainless steels
        
        the passive layer isn't fast to form in some cases like
        
        presence of corrosive environment, Cl- ions
        
        near water droplets, below water Oxy deprived zone
        
        lack of passive shield formation
        
        inside material
        
        presence of MnS
      - preventer
        
        Addition of Mo
        
        lower, P andd S
        
        higher Cr, Ni and Mo
    - - happens in the presence of
        
        corrosive environment
        
        tensile stresses
        
        only tensile or shear loads, not in compression
        
        can be internal or external
      - accelerates with temp typically above 150C
      - more Zn in Brass more susceptibility to this
      - medium level of Ni 7-10% make steels susceptible to this
      - how to prevent
        
        lowering stress below threshold value
        
        eliminating environmental degrading factors
        
        changing alloying elements to less sensitive elements
        
        compressive surface streses ( shot peening etc)