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Starting from 1942 NII STALI has been dealing with
welding of high-strength armor and high-carbon steels, aluminum
and titanium alloys. During the time welding methods for different
components and units of armored vehicles have been developed, unique
welding equipment constructed, new welding materials implemented,
new techniques of weld quality control and analysis created.
Some of the techniques developed by NII STALI and
widely used in R&D projects are described below.
Hydrogen test in built-up metal in the concentration
range of 0.2 to 50cm3/100g
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The method is based on suction of molten metal
from the melting zone into a quartz tube and detention of
hydrogen by the sample water hardening.
Hydrogen loss is no more that 10% in the concentration
range of 1 to 8cm3 per100g of the metal.
The hydrogen content in the weld metal is evaluated
to check the quality of the wire, electrodes, welding compounds,
shielding gases as well as for evaluation of cold cracking
probability in welds.
The hydrogen content in the metal is characterized
by the amount of hydrogen escaped from the sample and related
to 100g of the metal.
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Apparatus diagram
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1. Compensating chamber
2. Compensation sample of the same size as the analyzed sample
3. Sealing nut
4. Insert
5. Rubber gasket
6. Gas-distribution unit
7. Extraction chamber
8. Analyzed sample
9. Vacuum rubber tube
10. Clamp
11. Manometer
12. Dibutyl phthalate
13. Rubber tube
14. Oil container
15. Electric furnace
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Simulation of thermal strain cycle of high-strength
steel welding on thermal microscopy equipment
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1. Sample
2. Processing chamber
3. Fixed clamp
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4. Movable clamp
5. Current power supply
6. Optical microscope
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7. TV camera
8. TV set
9. Videotape recorder |
Main specifications
- Heating of simulating samples:
- heating temperature: 1400°C;
- heating rate: (50-150) °C/s.
- Cooling of simulating samples:
- cooling rate in the temperature range of 400 to
600°C (Vc): (0.5-5.0)°C/s;
- cooling rate in the temperature ranges of 1400 to
600°C and 400°C to room temperature is not monitored.
- Straining of simulating samples in the temperature
range of 400 to 600°C:
- straining rate Vstrain: (0.02-0.05) mm/s;
- maximum tensile stress Smax: 10-30 kgf/mm2.
- Determining of thermomechanical characteristics;
- Examination of specific features of structure formation.
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Acoustic emission investigation of delayed weld fracture
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The acoustic emission (AE) behavior
at delayed weld fracture is characterized by the AE
pulse rate.
AE is recorded in the frequency range
of 300-3000 kHz, which is typical for cold crack formation
and propagation.
P-5 apparatus is used for acoustic emission.
Main specifications of P-5 apparatus
- force control step: 10 dB
- pulse counter capacity: 102, 103, 104
- pulse acquisition interval: 3, 10, 30 s
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Diagram of the installation
for delayed weld fracture investigation
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1. Sample
2. Plate welded to the sample
3. Knife-edge
4. Cramp
5. Screw
6. Locknut
7. Piezosensor
8. P-5 apparatus
9. (13) Self-recorder
10. Digital recorder
11. Inductive movement pickup
12. Strain gage
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Quantitative assessment of weld resistance
to cold cracks at metal-arc welding of special steels
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The method allows estimation of the effect of the
following factors on the fracture criterion:
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chemical composition, production
method and thermal treatment modes of steel;
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chemical composition and quality
of welding materials;
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welding process.
The critical stress in the sample insert from outer
loading at which a microcrack is formed in the sample
is taken as the fracture criterion Scr.
1. Tested material
2. Plate
3. Burner
4. Weld
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