The document outlines a metallurgical analysis of barrels regarding temper brittleness and fracture toughness, detailing various tempering processes and their results. It categorizes barrels based on trace elements that contribute to temper brittleness and discusses testing methods for evaluating fracture toughness and critical crack lengths. The report also includes evaluations of failures in certain barrels, along with photographic evidence of observed fractures.

1. Temper Brittleness
&
Fracture Toughness

2. Temperature of Tempering

Specified Temp
 1st tempering - 520 - 550ºC
 2nd tempering - 530 - 570ºC

Tempered at (1st & 2nd)
 380 - 460ºC
( most of the barrels were tempered between
this range prior to 1996)

3. METALLURGICAL REPORT SUMMARY
FAILED INVESTIGATED CONCLUSION
IMPORTED 30 19 No remarkable metallurgical
deficiency that could lead to
failure
INDIGENOUS 7 7 No metallurgical deficiency.
(T2 - 500C Overload failure
& above)
INDIGENOUS 13 12 a) Temper brittleness due to
(T2 – 460 C low tempering temperature
& below) -(8 Cases)
b) No metallurgical deficiency
(3cases)
-

4. Salvaging of Low Temperature Tempered
Barrels
 Barrels tempered at temp. 401-430ºC be
grouped based on trace elements contents
(As, Sb, Sn, P) , since they play major role in
development of temper brittleness.
• Grouping of Barrels (Sn + Sb + As + P)
• Category A - > 0.025
• Category B - 0.025 % - 0.02 %
• Category C - < 0.02 %
• Category D - <0.02%, but Impact Value Lower
than specified min
on th Drawing.( 2 )

Proposal of DMRL

5. Effect of Trace Elements

6. Decisions
Category A - Rejected
Category B - • Re-tempered at 500ºC for 4 hrs
• Each barrel Subjected to high pressure proof
•Two barrels subjected to life cycle proof
Category C - • Initially 3 barrels from first batch of
100 be subjected to life cycle proof
• next 1 barrel from every 100 barrels
subjected to life cycle test
Category D - • Not to be considered now
 Barrels tempered below 400ºC not considered

7. Implementation of the Decision

436 Nos of such barrels were identified

435 Nos analysis of trace elements
completed

Barrels were categorised and confirmed by
rechecking at DMRL as under
A B C D
40 42 347+5* 1
* 5 barrels used for LIFE CYCLE firing

8. Life Achieved
Barrel EFC Bore Dia(mm)
L/882 304.25 128.15
L/993 303.63 127.60
L/762 304.125 128.15
L/868 309.00 128.40
L/1610 312.75 128.13

All the Barrels were brought to CQA
(Metals) for further study of fire crack
growth

9. Report on Fire Crack Growth

Barrels were parted longitudinally across its
whole length and examined visually for any
abnormality

Discs from various section were cut and extent
of crack depth was measured
Barrel No Max Depth Of
Crack(mm)
L/762 0.39
L/882 0.70
L/933 0.30
L/868 0.42
L/1610 0.34

10. Evaluation from Fracture
Toughness Point of View

Fracture toughness & critical crack lengths for
failure were calculated

Fracture toughness of few tempered brittle failed
barrels were estimated

Fracture toughness of 4 low temperature
tempered ‘C’ category barrels were estimated

Fracture toughness of Russian barrel was
estimated

Fracture toughness of correctly tempered MSF
barrels were estimated

11. Calculated KIC Values & Critical
Crack Length
KIC acr Expected Life
(mm) Initial Crack (2mm) Initial Crack (3mm)
85.00 2.630 49 -
90.00 3.593 113 38
93.34 5.00 192 117
95.00 10.73 508 433
100.00 13.17 622 547
 Where acr is critical crack length
 Taking into consideration that life of the barrel is 250
FSAPDS rds or 250 EFC, critical value for fracture
toughness with ultrasonic acceptance standard 2mm
hole size works out to be 95 MNm-3/2

12. Tested Value ( KIC )

Russian Failed Barrel - 102

Failed temper brittle (Indian) - 85

MSF (tempered correctly) -
102/113

‘C’ cat barrel - 95/105

This data generally agrees with calculated
values

Data also fairly agree with literature

14. Failure of T-72
Barrels
Photographs

15. Barrel No. L/876 – Blown of region of barrel

16. Barrel No. L / 876 – Small longitudinal crack on inner
surface

17. Barrel No. L / 876 – Point of initiation of fracture from
the region containing longitudinal crack on inner surface

18. Barrel No. L / 876 – propagation of fire crack in inter
crystalline mode

19. Barrel No. L /0199 – Barrel piece in as received condition

20. Barrel No. L / 0199 – Inter crystalline crack

21. Barrel No . L / 0199 – Macro Photograph. Presence
of transverse crack inside the wall

22. Barrel No. L / 0199 – Secondary Inter Crystalline
crack from the main fracture

23. Barrel No L / 014 – Transverse crack on inner surface of
the barrel piece
Bore
Outer Surface

24. Barrel No. L / 014 Fracture surface where inside crack
extended to outer surface

25. Barrel No. L / 014 – Fracture surface away from severed zone

26. Barrel No. L / 014 – Fracture towards inner
surface where crack progresses transversely

27. Barrel No. L / 231 – Failed barrel

28. Barrel No L/231- Some fragments of the barrel

29. Barrel No. L / 753 – Transverse fracture surface of segments

30. Barrel No L / 753 – Fragments of barrel