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    Question & Answer Set-11

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    shashi
    This document discusses metal working processes like cold working and annealing. It provides details about advantages and limitations of hot and cold working. It also gives examples of calculating strain, force required for extrusion and number of passes for wire drawing. The document discusses factors like reduction per pass and deformation zone for rolling processes. It analyzes a microstructure to determine grain size and verifies topological relationships. Finally, it describes how to develop different microstructures using cold work and annealing and lists methods to detect preferred orientation in steel sheets.

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    Question & Answer Set-11

    Uploaded by

    shashi
    75 views3 pages
    This document discusses metal working processes like cold working and annealing. It provides details about advantages and limitations of hot and cold working. It also gives examples of calculating strain, force required for extrusion and number of passes for wire drawing. The document discusses factors like reduction per pass and deformation zone for rolling processes. It analyzes a microstructure to determine grain size and verifies topological relationships. Finally, it describes how to develop different microstructures using cold work and annealing and lists methods to detect preferred orientation in steel sheets.

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    This document discusses metal working processes like cold working and annealing. It provides details about advantages and limitations of hot and cold working. It also gives examples of calculating strain, force required for extrusion and number of passes for wire drawing. The document discusses factors like reduction per pass and deformation zone for rolling processes. It analyzes a microstructure to determine grain size and verifies topological relationships. Finally, it describes how to develop different microstructures using cold work and annealing and lists methods to detect preferred orientation in steel sheets.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    75 views3 pages

    Question & Answer Set-11

    Uploaded by

    shashi
    This document discusses metal working processes like cold working and annealing. It provides details about advantages and limitations of hot and cold working. It also gives examples of calculating strain, force required for extrusion and number of passes for wire drawing. The document discusses factors like reduction per pass and deformation zone for rolling processes. It analyzes a microstructure to determine grain size and verifies topological relationships. Finally, it describes how to develop different microstructures using cold work and annealing and lists methods to detect preferred orientation in steel sheets.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 3

    Lecture 27-28:

    Metal working: deformation processing: Cold working & annealing: recovery, re-crystallization & grain
    growth, phenomenological & mechanistic approaches

    Questions:

    1. List a few advantages & limitation of hot working.


    2. List a few advantages and limitations of cold working.
    3. Estimate energy required to extrude 250mm diameter billet of aluminium to 25mm diameter
    rod. Given flow stress of aluminium = 10MPa and therefore find out the amount of force
    needed. Process efficency = 70%. Neglet work hardening.
    4. If the maximum strain per pass in a wire drwing operation is 0.65 how many drawing passes will
    be rquired to draw wire of 0.25mm dia from 5mm wire rod?
    5. While designing rolling process discuss whether large reduction in a single pass is prefrerable to
    smaller reductions in successive passes?
    6. The following figure gives a typical microstructure of a pure metal. Magnification is 100X. Find
    out its grain size in terms of ASTM number (N) which is given by:   2 . Where n represents
    number of grains
    4 cm

    4 cm

    7. Count the number of grains (F), number of edges (E) and number of points (P) in the
    microstructure given above. State the type of relationship these must follow.
    8. Describe how by cold work & annealing the following microstuctures can be developed in a
    single phase alloy (a) fine grain structure (b) coarse grain structure
    9. Suggest at least two methods to know if steel sheet has preferred orientation.

    Answers:

    1. Advatages: Hotworking is done above recrystallisation temperature where flow stress is very
    low therefore it is possible to give large deformation with minimum effort ( energy rquired is
    less). No futher heat treatment is required. Product is in annealed / normalised state. Limitation:
    Metal tends to oxidise. Scaling leads to loss of material. Tool life is shortened because of
    abrasive scale, high temperature and lack of lubrication. Poor surface finish & difficulty in
    precise guage control. It is quite common to pickle hot rolled sheets before cold rolling.
    2. Advantages: Good surface finish & precise guage control. Gives higher strength. Limitation:
    needs intermediate annealing because of work hardening, deformation / pass is limited by flow
    stress which increases with deformation, more energy intensive, needs more powerful
    equipment, Makes the material anisotropic.

        
    3. Work done per unit volume =
          2     2    66/!"
         .
     
    $
    where is efficiency. Stress required = 66MPa. Force = stress x area = 66 # % # 0.25 
    3.24 *
     
    4. Strain in a single pass is =       2   . Using this it can be shown that diameter after
     
    +0    
    nth pass is given by +   ,-. / 
    . Therefore number of pass = 0      .2  . 
    1
    9.3. This means successive dies sholud be so chosen that in 10 passes the wire could be drawn.

    5. During rolling contact length with roll surface is a function of reduction per pass. Let this be l
    and plate thichness be t. The ratio = l/t gives an idea about the deformation zone. If >> 1
    deformation will be inhomogeneous. This would result in residual stresses and may lead to
    cracking. On the other hand if D << 1 there will be too much of friction between work piece and
    the roll. For a given plate thickness the former represents large deformation where as the latter
    represents small deformation. The optimum rolling schedule is some where in between.

    6. Note that a large number indicates fine grain structure where as a small number denotes coarse
    grain structure. The above stucture appears to be coarse. Measurement shows following result.

    Count the number of grains assuming contribution of corner grain as


    & grains at edge as . Thus n= (6+3/4+9/2)/A = 11.25/A

    A = 16/2.54/2.54 = 2.48 in2

    n = 2 = 11.25/2.48 = 4.54

    N = 3.2

    7. Number of grains F = 18, E = 39 & P = 22: It follows the relation P+F = E+1. This is a 2-D form of
    Euler rule in Topology (There is a striking similarity with phase rule). If you count the number of
    corners, faces & edges of the following 3D shapes you get the Eulers rule (a) Tetrahedron (b)
    Cube (c) Octahedron

    P = 4, F = 4, E=6 P = 8, F =6, E=12 P =6, F =8, E=12

    P+F = E + 2 P+F = E + 2 P+F = E + 2


    8. Critical neuclus is inversely proportional to amount of cold work. If before annealing if the metal
    is given small amount of cold wok and then annealed at a relatively higher temperature it is
    likely to have coarse grain structure. On the other hand high amount of cold followed by
    annealing just above its recrystallisation temperature would give fine grain structure.

    9. Preferred orientation would give different properties along different direction. Measurement of
    elastic modulus along diffent direction is a common method to determine anisotropy. It can also
    be established by direct measurement of crystal orientation by X-Ray diffraction technique or
    SEM using EBSD (Electron Back Scattered Diffraction) .

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