Heat Treatment Of Steel

Heat Treatment Of Steel

MOI UNIVERSITY
DEPARTMENT OF MECHANICAL AND PRODUCTION ENGINEERING
CHP 316 - MATERIALS SCIENCE CAT 1 DATE: 10th March. 2011
ATTEMPT ALL QUESTIONS
1. Sketch the electronic structures for the elements shown in table Q1 below, hence Compare
their electronegativities
Element X Y Z
Atomic No. 20 28 35
2. Compare and contrast the following crystal systems
(i) Tetragonal
(ii) Monoclinic
(iii) Hexagonal
3. (a) Explain the following terms:-
(iv) Packing fraction
(v) Coordination number
(vi) Theoretical density
(b) Given that one of the allotropic forms of iron has the following properties:-
Structure - BCC
Lattice constant ao= 0.2866 nm
Atomic mass 55.847 g/mol
Avogadro number Na= 6.02 x 1023 atoms/mol
Determine its theoretical density.
4. Draw the following in a cubic unit cell:-
[121] direction
(210) plane
MOI UNIVERSITY
DEPARTMENT OF MECHANICAL AND PRODUCTION ENGINEERING
CHP 316 - MATERIALS SCIENCE CAT 2 DATE: 16th March. 2011
ATTEMPT ALL QUESTIONS
1. (a) List five characteristic features of martensite transformation in steels
(b) Explain giving reasons, the nature of transformation of austenite during
isothermal cooling at lower temperatures.
(c) Explain the mechanism of Austenite-Pearlite transformation during
isothermal cooling stating the variant microstructures possible during and
after transformation.
(d) Explain the effect of annealing on the following material properties:-
(i) Elongation
(ii) Ultimate tensile strength
(iii) Impact resistance.
2. (a) What factors affect hardenability of components during quenching?
(b) Besides improving hardenability of components, what other purposes do
alloying elements serve?
3. Explain the structures obtained when samples of steel containing 1%C are heated to
austenizing temp (i.e 780°C) for 10 minutes and quenched in a salt bath at the
following temperatures:-
1. Quenching in a liquid bath at 700°C; holding time 4 min.
2. Quenching to 575°C, holding time 4 s.
3. Quenching to...