SEMINAR ONEFFECT OF DUCTILE TO BRITTILE TRANSITION

TEMPeRATURE ON SHIP

SANJAYA KUMAR SAHOO

METALLURGICAL AND MATERIALs ENG.

ROLLNO…… 25628

REGD NO….0601105153

Presented ByGuided by Mr. p. k. mallick

SUBJET OF INTEREST

• Objective • Introduction• What is DBTT• Problem on ship due to DBTT• Factors affecting DBTT• Remedy of upcoming problem• Conclusion

OBJECTIVES

• The awareness of brittle fracture under service conditions will be made by the use of ductile to brittle transition temperature curve.

• This chapter provides an understanding of characteristics and causes that effect on ship.

Introduction• Big failure of Titanic in 10th April 1912• Failure of different material due to DBTT• Commitment to safety pervades all deep sea

shipping operations• An alternative to increasing the component

reliability is to provide redundancy in a part of the system

WHAT IS DBTTDuctile to brittle transitiontemperature curve• The absorbed energy (Joule) is plotted again testing temperature, giving a ductile to brittle transition temperature curve (DBTT curve).• The curve represents a change in fracture behavior from ductile at high temperature to brittle at lower temperature

Lower shelf

Transition – mixed mode

Upper shelf

DBTT curve

Upper shelf

Transition

Lower shelf

contd….1. As temperature decreases a ductile material can

become behave brittle - ductile-to-brittle transition2. FCC metals remain ductile down to very low

temperatures.3. For ceramics, this type of transition occurs at much

higher temperatures than for metals.4. The ductile-to-brittle transition can be measured by

impact testing: the impact energy needed for fracture drops suddenly over a relatively narrow temperature range – temperature of the ductile-to-brittle transition.

Charpy impact testThe energy absorption is ameasure of the impact energyThe results are qualitative innature and are useful inmaking comparisons

Determine whether or not amaterial experiences a ductile brittle transition with decreasing temperature and, if so, the range of temperatures over which occur

Transition temperatureDifferent criteria are used to determinethe transition temperature, dependingon the purpose of the application

Various criteria of transition temperatureobtained from Charpy test

1) T1 transition temp is theTemp at which fracture is100% ductile (fibrous).2) T2 transition temp is theTemp at which fracture is50% cleavage and 50%ductile.3) T3 transition temp is theTemp at the average energyabsorption of upper andlower shelves.4) T4 transition temp is theTemp defined at Cv = 20J.5) T5 transition temp is theTemp at which fracture is100% cleavage

Note: FTP is fracture transition plastic

The brittle-fracture problems

Failure of Liberty Ships during services inWorld War II.

The cause of failure was due to crack of materials to brittle behavior.initiated from defects in the welded areaand subjected to subzero temperature

Material failures

• When the Titanic collided with the iceberg, the hull steel and the wrought iron rivets failed.

• Brittle facture is a failure of a metal by rapid crack propagation and without any significant deformation.

• The steel and the wrought iron rivets failed by brittle fracture.

What caused the brittle fracture• What caused the brittle fracture?• What was the effect of the impact with the

iceberg?• Did the sulphur content play a role in the failure?• Temperature for the steel used to construct the

hull of Titanic?• Did the water temperature experienced by the

Titanic ( -20degreeC ) play a role?

Metallurgical factors affectingDBTT curves

• The shape and position of the DBTT curve is important because it determines the transition temperature, which indicates where it is safe to use for the required application.

• There are several factors affecting the DBTT curve

• Crystal structure• Interstitial atom• Grain size• Heat treatment• Specimen orientation• Specimen thickness

Effect of crystal structure

Relationship between energy absorptionand test temperature

• Only BCC structure materials experience ductile to brittle transitiontemperature. be careful to select the service temperature.• This is due to limited active slip systems operating at lowtemperature. very low plastic deformation.• Increasing temperature allowsmore slip systems to operate more plastic deformation.• FCC and HCP metals do notexperience ductile to brittletransition, therefore they give thesame energy absorption at anytemperatur

Effect of interstitial atom

Ex: in steel• Mn: C ratio should be at least3:1 to satisfy notch toughness.• P, Si, Mo, O raise the transitiontemperature while Ni is beneficialto notch toughness.

• Carbon and manganese contents have been observed to change the DBTT curve

Carboncontent

Smoother curve

Higher Transition tempBecome ductile athigher temperature

Effect of grain size• Grain size has a strong effect on transition

temperature• Grain size

Transition tempt• Reducing grain size shifts the DBTT curve to the left

has a wider range of service temperatures.• Heat treatments that provide grain refinement

such as air cooling, recrystallisation during hot working help to lower transition temperature.

Effect of heat treatment

• Tempered martensiticstructure steel produces the best combination of strength and impact toughness

Tempering temperature

Energy absorption

Effect of specimen orientationFor impact test, anisotropic properties are also observed in rolled or forged products, giving different energy absorption according to specimen orientations

• Longitudinal (B) shows thebest energy absorption becausethe crack propagation is acrossthe fiber alignment.• Transverse (C) gives the worstenergy absorption because thecrack propagates parallel to therolling direction.

Effect of specimen thickness• Larger specimen size (in-service components) provides higher constraint more brittle

If large size specimens areused, the transitiontemperature will increase

Large scale testsEffect of section thickness ontransition temperature

Effect of sulfur

http://db1.wdc-jp.com/isij/pdf/199107/is310712.pdf

The presence of relatively high amounts of P and S embrittles the steel at low temperatures

Composition comparison

Titanic steel Modern steel

c 0.21 0.20

Mn 0.47 0.55

p 0.045 0.012

S 0.069 0.01 to0.04

Si 0.017 0.007

Cu 0.024 0.01

O 0.013 -

N 0.0035 0.032

Mn:S ratio 7:1 15:1(typical)

Ductile-brittle transition temperatureTitanic Steel Modern Steel

LongitudinalDirection

TraverseDirection

LongitudinalDirection

TraverseDirection

Impact energyat –2 °C

4 J 4 J 325 J 100 J

Ductile-brittleTransitionTemperature

30 °C -42 °C -42 °C -42 °C

The steel used for the Titanic hull was not suited for service atlow temperaturesH. P. Leighly, B. L. Bramfit, and S. J. Lawrence. Practical Failure Analysis

Remedy of upcoming problem• Analysis of titanic failure• Effect of grain size• How does the grain size affect strength?• Hall-Petch equation: YS= a + bd-1/2 • Yield strength of a steel with 26 micrometer grain

is higher• redundant ship navigational radar system is

performed• prototype tool has been implemented that allows

selective failure of system resources on the fly during testing.

conclusion• By analysis of the factor affecting the DBTT we

can take the approach• Finally, a quantitative comparative reliability

analysis of the two-component standby redundant ship navigational radar system is performed

• Both directly through safer construction designs and indirectly through intelligence and surveillance

• The enhanced characteristics of materials will allow us to create new and innovative devices to protect all of us from failure of ship

reference1.Dieter, G.E., Mechanical metallurgy, 1988, SI metric

edition ,McGraw-Hill, ISBN 0-07-100406-82. a b c Rich, Jack C. (1988), The Materials and Methods of

Sculpture, Courier Dover Publications, p. 129, ISBN 0486257428

3.John, Vernon. Introduction to Engineering Materials, 3rd ed.(?) New York: Industrial Press, 1992. ISBN 0831130431

4.Standard Methods for Notched Bar Impact Testing of Metallic Materials, E 23, Annual Bookof ASTM Standards, v. 03.01, ASTM, Philadelphia, 1984, pp. 210-233

Thank you