Thermo-mechanical processing of Elgiloy:
Introduction:
Elgiloy is an austenitic cobalt base alloy (40%Co, 20%Cr, 16%Ni, 7%Mo) strengthened by cold
work and capable of additional hardening by aging. In soft annealed tempered condition its UTS
is only approximately 900N/mm2 but its mechanical strength increases with cold rolling and its
UTS can reach more than 1900N/mm 2. The influence of aging is negligible in annealed
condition, but increases significantly.
Experimental procedure:
The first experiment was conducted to formulate the proper annealing cycle. Eight samples were
subjected to various treatments i.e they were heated in an electrical resistance furnace in an open
atmosphere at the temperatures of 1100oC, 1075oC, 1050oC, 1025oC, 1000oC, 975oC, 950oC,
925oC. All samples were heated for two hours and then cooled in furnace. Then these samples
were tested for Vicker’s Hardness test. It is worth noting that all these samples were obtained
from a plate which was hot forged in a temperature range of 1100 oC to 1000oC and the cold
rolled to approximately 40/50% reduction.
Eight more samples were obtained from the same plate and then they were subjected to various
temperatures in the range of 900o to 1100oC and then they were water quenched and air cooled.
Results:
And their result is represented graphically in Fig-I
500
450
400
350
300
250
Hv
200 Hardness
original
150
100
50
0
1100 1075 1050 1025 1000 975 950 925 900
temperature
Fig-I (Hardness vs. annealing temperature furnace cool)
As can be seen from the graph the maximum drop in the hardness occurs in the temperature
range of 1050oC to 1100oC i.e. from about 450Hv to just below 250Hv.
500
450
400
350
300
250
Hv
original
200
annealed
150
100
50
0
1100 1050 1000 950
Annealing temp.
Fig-II (Hardness vs. annealing temperature Air cool)
500
450
400
350
300
250
Hv
original
200
annealed
150
100
50
0
1100 1050 1000 950
Annealing Temp.
Fig-III (Hardness vs. annealing temperature Water Cool)
Sample-01 Sample-02
Sample03 Sample-04
Sample-05 Sample-06
Sample-07 Sample-08
Table-1
Annealing Grain Size
Sample
temp. (µm)
01 1100 37
02 1075 33
03 1050 27
04 1025 9
05 1000 4
06 975 5
07 950 3
08 925 4
40
35
30
25
20
15
10
0
1100 1075 1050 1025 1000 975 950 925
Figure-IV (Grain Size µm vs. annealing temp. °C)
As can be seen that the maximum increase in the grain size is achieved when annealing
temperature is increased from 1025°C to 1050°C. This indicates that most of the effects of cold
working have been eliminated above 1025°C. This fact has also been proven by maximum drop
in hardness for samples heated above 1025°C.
Effect of cold reduction on mechanical properties:
Three sets of samples were made in the form of strips, and after subjecting to different
Heat treatments they were subjected to various degrees of cold reductions (cold rolling) and
subsequently tensile samples were obtained the results are summarized as under:
Set-I:
Heat treatment cycle: 1075°C+ 45mins+ Air Cool
Table-II
%age Cold Yield UTS %age
Reduction Strength (MPa) Elongation.
(MPa)
10 789 1037 29.60
20 1003 1156 14.23
30 1147 1379 6.96
40 1303 1544 3.90
50 1543 1714 2.40
1800
1600
1400
1200
1000
800
600
400
200
0
10 20 30 40 50
Fig-VA (%age cold reduction vs. ‘Y.S. & UTS’)
35
30
25
20
15
10
0
10 20 30 40 50
Fig-IB (%age cold reduction vs. %age elongation)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.01 0.02 0.02 0.03 0.03
Stress vs. Strain (50% Cold reduction)
1400
1200
1000
800
600
400
200
0
-0.01 0 0 0.01 0.01 0.02 0.02 0.03
Stress vs. Strain (40% Cold reduction)
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.01 0.02 0.02 0.03 0.03
Stress vs. Strain (30% Cold reduction)
12
10
0
0 0.01 0.01 0.02 0.02 0.03 0.03
Stress vs. Strain (20% Cold reduction)
12
10
0
0 0.05 0.1 0.15 0.2 0.25 0.3
Stress vs. Strain (10% Cold reduction)
Set-2
1075°C + 45mins+ W.Q.
Table-III
%age UTS
Yield
Cold %age
Strength
Reductio (MPa) Elongation.
(MPa)
n
10 1082 1182 24.8
20 1182 1356 12.2
30 1246 1565 6.72
40 1440 1653 4
30
25
20
15
10
0
10 20 30 40 50
Figure-VIB (%age cold reduction vs. %age elongation)
1800
1600
1400
1200
1000
800
600
400
200
0
10 20 30 40
Figure-VIA (%age cold reduction vs. Y.S. & UTS)
1800
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04
Stress vs. Strain 40% Cold reduction
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04
Stress vs. Strain 30% Cold reduction
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stress vs. Strain (20% Cold reduction)
1400
1200
1000
800
600
400
200
0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stress vs. Strain (10% Cold reduction)
Set-3
Table- III
1050°C + 45mins+ A.C.
%age UTS
Yield
Cold %age
Strength
Reductio (MPa) Elongation.
(MPa)
n
10 812 1041 34.0
20 1000 1234 15.8
30 1192 1436 7.44
40 1360 1550 6.8
50 1565 1736 4.16
40
35
30
25
20
15
10
0
10 20 30 40 50
Fig-VIIB (%age cold reduction vs. %age elongation)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
10 20 30 40 50
Fig-VIIA (%age cold reduction vs. Y.S. & UTS)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.01 0.02 0.02 0.03 0.03
Stress vs. Strain (50% Cold reduction)
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Stress vs. Strain (40% Cold reduction)
1600
1400
1200
1000
800
600
400
200
0
0 0.01 0.01 0.02 0.02 0.03 0.03
Stress vs. Strain (30% Cold reduction)
1400
1200
1000
800
600
400
200
0
0 0.01 0.01 0.02 0.02 0.03 0.03
Stress vs. Strain (20% Cold reduction)
1200
Stress vs. Strain (10% Cold
1000
reduction)
800
600 Comparison of ductility behavior of
400 these three sets is shown by plotting
200 the elongation curves together, vs.
0 the %age reduction.
0 0.05 0.1 0.15 0.2 0.25
%age Elongation vs. %age cold
reduction
Set-I: 1075°C+ 45mins+ A.C.
Set-II: 1075°C + 45mins+ W.Q.
Set-III: 1050°C + 45mins+ A.C.
