Chapter 2: Materials and experiments

2-1. Specimen No. 1

Austenitic stainless steel tube was welded to 9Cr-1Mo heat resisting steel tube by
GTAW. Since 9Cr-1Mo heat resisting steel needs preheat and post weld heat treatment a
buffer layer of nickel base electrode of the type ER Ni Cr-3 .Figure 2.1 shows the pipes
after welding.

Figure 2.1 specimen No. 1

2-1.1 Welding procedure:

1. The 9Cr-1Mo specimen was grooved as shown in figure2.2 as a preparation for
buttering.

9Cr 1Mo

Steel

Figure2.2 grooved martensitic 9 Cr -1 Mo St.St.

64
2. The 9Cr-1Mo steel was preheated to 150 °C and this temperature was kept during
welding. Eight buttering layers of the welding electrode ER Ni Cr-3 were deposited on
the prepared edge of the 9Cr-1Mo St. St. part as shown in figure2.3.
The characteristics of the ER Ni Cr-3 are as shown in tables (2.1 a,b and c)
 Chemical composition:

Table 2.1 a the chemical composition of ER NI Cr-3

C% Mn% Cr% Nb + Ta% Ni%

0.05 max 3 20 2.5 balance

 Mechanical properties

Table 2.1 b the Mechanical properties of ER NI Cr-3

Yield stress, MPa Tensile strength, MPa Elongation %

360 700 44

 Charpy V

Table 2.1 c the impact values of ER NI Cr-3

Test temperatures C Impact values

+20 120J

-196 116J

ER NI Cr-3 is used for welding GTAW of high alloyed steel, heat resistant steel,
corrosion resistant steel, 9%Ni steels and for joining dissimilar metals of the types
mentioned.
The welding is usually done with pure Ar as shielding gas using DC current (-)

65
Figure 2.3 deposition of eight buttering layers of the welding electrode ER Ni
Cr-3
3. The buttered layers were flattened by grinding to have 8 mm minimum thickness of the
buttered layers as shown in figure 2.4.

Figure 2.4 The buttered part after flattening

4. The buttered tube was then subjected to post weld heat treatment at 720°C to temper
any untempered martensite in the heat affected zone.
5. The austenitic stainless steel 316 part was grooved to be ready for welding with the
buttered part as shown in figure 2.5.

66
Figure 2.5
6. The austenitic 316 St. St. was welded to the buttered part with the same welding
electrode ER Ni Cr-3 by three passes as shown in figure 2.6.
In this case the heat affected zone will be concentrated in the buttering layer without any
effect on the 9Cr 1Mo steel.

Figure 2.6 Welding austenitic St. St. to the buttered martensitic 9 Cr- 1 Mo St.
St.
7. The WPS and PQR are given in the following tables

67
68
69
70
71
72
73
74
75
2-1.2 Experiments
2-1.2.1. Microstructure for the as received specimen
Specimens for microstructure were subjected to grinding using grades
80,180,320,400,600and 800 and then polished using alumina.
After polishing the specimens were etched using the following solutions:
 3 parts glycerol, 2-5 parts HCl, and 1 part Nitric Acid (for Austenitic st.st.).
 Nitric Acid 10ml Hydrochloric Acid 40ml (for 9Cr-1Mo steel).
 3g molybdic acid, 100mL H2O, 100mL HCL, 100mL HNO3(for Ni buttering
layer).
 Then the microstructure was examined using the optical microscope as shown in
Figure 2.7.

Figure 2.7 the optical microscope

76
2-1.2.2 Hardness
In the weld metal, HAZ and base metal was measured using Vickers hardness (HV-
10).Using hardness testing equipment as shown in figure 2.8.

Figure 2.8 hadness testing equipment

2-1.2.3. Ferrite content

The ferrite number (FN) was measured using feritscope (fischer-MP30) as shown in
figure 2.9

Figure 2.9 Feritscope (fischer-MP30)

77
2-1.2.4. Simulation for HAZ
Three specimens were heated at 950°C in an electric furnace. As shown in figure 2.10.
One of the three specimens was followed by cooling in water, the second specimen was
air-cooled and the third one was furnace cooled.
Hardness values and ferrite content were then measured.

Figure 2.10 heating of specimens using electric furnace.

78
2-2. Specimen No 2
Low carbon and austenitic stainless steel 316 tube were welded by E309 electrode using
gas tungsten arc welding GTAW as shown in figure 2.11.

Figure 2.11 specimen 2

2-2.1 Experiments
2-2.1.1 Microstructure for as received specimen
Specimens for microstructure were subjected to grinding using grades
80,180,320,400,600and 800 and then polished using alumina.
After polishing the specimens were etched using the following solutions:
 It is 3 parts glycerol, 2-5 parts HCl, and 1 part Nitric Acid (for Austenitic st.st.).
 It is 90% alcohol and 10% nitric acid (for Low carbon steel).

2-2.1.2 Hardness
Hardness in the weld metal, HAZ and base metal was measured using Vickers hardness
(HV-10)

2-2.1.3 Ferrite content

The ferrite number (FN) was measured using Feritscope (fischer-MP30).

79
2-2.1.4 Simulation for HAZ
Three specimens were heated at 950 °C one of them followed by cooling in water the
second specimen is air-cooled and the third specimen is furnace cooled, Hardness values
and ferrite content were then measured. As shown in figure 2.12

figure 2.12 the timer of the electric furnace at 900°C

80
2-3. Specimen No. 3
It is similar welding of tube 310 to 310 tube welded using electrode E310 by GTAW
As shown in figure 2.13

Figure 2.13 specimen 3

2-3.1 Experiments
2-3.1.1 Microstructure for as received specimen
Specimens for microstructure were subjected to grinding using grades
80,180,320,400,600and 800 and then polished using alumina.
After polishing the specimens were etched using the following solutions:
 It is 3 parts glycerol, 2-5 parts HCl, and 1 part Nitric Acid (for Austenitic st.st.).

2-3.1.2 Hardness
Hardness in the weld metal, HAZ and base metal was measured using Vickers
hardness (HV-10).

2-3.1.3 Ferrite content

The ferrite number (FN) was measured using Feritscope (fischer-MP30).

81
2-3.1.4. Simulation for HAZ
Three specimens were heated at 950 °C one of them followed by cooling in water the
second specimen is air-cooled and the third is furnace cooled. Hardness values were
then measured and 16 specimens from the base metal heat treated as shown in figure
2.14 below.

16 SPECIMENS

15 specimens
1 specimen is as
are heated as
received
follows

Three Three Three Three Three

specimens at specimens at specimens at specimens at specimens at
1025 °C 960°C 875°C 775°C 710°C

One specimen One specimen One specimen One specimen One specimen
is followed by is followed by is followed by is followed by is followed by
cooling in cooling in cooling in cooling in cooling in
water, the water, the water, the water, the water, the
second second second second second
specimen is air- specimen is air- specimen is air- specimen is air- specimen is air-
cooled and the cooled and the cooled and the cooled and the cooled and the
third specimen third specimen third specimen third specimen third specimen
furnace cooled. furnace cooled. furnace cooled furnace cooled. furnace cooled.

Figure 2.14 Illustration for the simulation of the HAZ.

82