Effect of Niobium Additions on

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Effect of Niobium Additions on Heat Affected Zone
Toughness of 0.2 Wt C Ferrite-Pearlite Steels
Chirag Shah
shahchi4_at_iit.edu 312-567-5814 Advisor
Prof. Philip Nash nash_at_iit.edu
312-567-3056
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Objectives

• Investigate the relationship between niobium
  content up to 0.05 wt Nb with heat affected
  zone (HAZ) microstructure and toughness for
• 0.2 wt C ferrite-pearlite plate steels
• Establish relationship between results obtained
  from Gleeble simulations of HAZ with commercially
  produced SAW steel plates

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Strategy

• Conduct a literature survey in order to
  identify and analyze
• various effects of Nb on the welding HAZ
  toughness
• Obtain lab heats with similar base chemistry as
  TC 128
• and with varying Nb levels
• (1) lt 0.005, (2) 0.015, (3) 0.032, (4) 0.054
  wt Nb
• Obtain commercial plate materials comprising TC
  128
• with Nb,TC 128 without Nb and ASTM A 945
  steels
• Develop a representative thermal cycle for
  simulating
• the actual welding HAZ

4
Strategy

• Get familiarized with Gleeble 3500 and the
  welding
• simulation techniques
• Perform Gleeble simulation testing and PWHT
• Notch the simulated PWHT as welded samples
  conduct
• Charpy testing at specified temperatures
• Perform the real weldment test followed by
  Charpy testing
• Compare the real weldment and simulated results
• Hardness measurements metallography study

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Experimentation-
 
Schematic Illustration of Various Sub Zones of
Weld HAZ
6
 
Lab Heats Chemical Composition
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Experimentation- 1
Mill Heats Chemical Composition
 
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Experimentation
Schematic Project Planning
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Experimentation-
Why Gleeble Simulation ?

• Fundamental investigation for studying Nb
  effects on
• HAZ toughness in specific microstructure
  generated
• by thermal cycle
• Simple,powerful and rapid test method
• CVN impact testing is a valid identification of
  impact
• toughness in simulated specimens due to
  larger
• homogeneous HAZ microstructure obtained
• Give reproducible results with high accuracy
• Programmed thermal cycle is used as input
• Real time monitoring and data analysis

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Experimentation-
Thermal Profile Calculation
The Uwer-Degenkolbe Formula for calculating the t
8/5 (cooling time between 800 C and 500C) is
given by Where, t Time (seconds) To
Preheat Temp (25C) N Efficiency of the SMA
welding (1) E Heat Input (3 KJ/mm and 5
KJ/mm) F2 Constant for SMA welding (0.9) D
Plate Thickness (1.5875 cm)
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Experimentation-
Calculated Thermal Profiles
3 kJ/mm (76.2 kJ/inch)
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Experimentation-
Calculated Thermal Profiles
5 kJ/mm (127 kJ/inch)
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Experimentation-
Simulation Test
Dynamic Thermo mechanical Simulator Gleeble 3500
_at_ TPTC
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Experimentatio
Experimentation-
Simulation Test
10mm x 10mm x 55mm Specimen Extraction
Spot Welder
Tugg Test
Thermocouple Location
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Experimentation-
Simulation Test
Thermocouple Channel
Thermocouples
Copper Jaws
Test Specimen
Gleeble Specimen Chamber
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Experimentation-
Simulation Test
3 kJ/mm (76.2 kJ/inch)
5 kJ/mm (127 kJ/inch)
Comparison of Programmed and Experimental Thermal
Profiles
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Experimentation-
Real Weldment Tests
Heat Input Achieved 69 kJ/inch
Real Weldment Test Joint Configuration and
Parameters
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Experimentation-
Charpy Test Set Up
Specimen Bath
Thermocouple Reader
Refrigerated Constant Temperature Circulator
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Experimentation
Microstructure Characterization
Schematic Profile for Microstructure
Characterization
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Results
As Received Microstructures Lab Heats-I
lt0.005Nb, 1000 X
lt0.005Nb, 3000 X
0.015Nb, 3000 X
0.015Nb, 1000 X
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Results
As Received Microstructures Lab Heats-II
0.032Nb, 3000 X
0.032Nb, 1000 X
0.054Nb, 1000 X
0.054Nb, 3000 X
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Results
Absorbed Energy v/s Peak Temperature for lt0.005
Nb
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for 0.015 Nb
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for 0.032 Nb
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for 0.054 Nb
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Results
Lateral Expansion v/s Peak Temperature for Lab
Heats-I
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Results
Lateral Expansion v/s Peak Temperature for Lab
Heats-II
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for CVN Test
Temp 32F
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for CVN Test
Temp 0F
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for CVN Test
Temp 30F
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for TC 128
without Nb
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for TC 128
with Nb
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for ASTM A
945
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Results
Lateral Expansion v/s Peak Temperature for ASTM
A 945
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Results
Charpy Test Results
Lateral Expansion v/s Peak Temperature for ASTM
A 945
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for CVN Test
Temp 32 F
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for CVN Test
Temp 0F
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Results
Charpy Test Results
Absorbed Energy v/s Peak Temperature for CVN Test
Temp 30F
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Results
Charpy Test Results
Absorbed Energy v/s Niobium Content for Simulated
As Welded Test
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Results
Charpy Test Results
Absorbed Energy v/s Niobium Content for Real
Weldment PWHT Test
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Results
Charpy Test Results
Absorbed Energy v/s Niobium Content for Real
Weldment As Weld. Test
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Results
Macro photography
Charpy Macrographs for 0.054Nb and CVN Test Temp
of 30F
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Results
Hardness Results
Hardness v/s Niobium Content for Real Weldment
PWHT Test
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Results
Hardness Results
Hardness v/s Niobium Content for Real Weldment
PWHT Test
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Results
Hardness Results
Hardness v/s Niobium Content for Simulated PWHT
Test
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Results
Hardness Results
Hardness v/s Niobium Content for Simulated As
Welded Test
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Results
Metallography Results
lt0.005Nb
0.015Nb
0.054Nb
0.032Nb
Microstructure after 1050C Austenization
Temper Magnification 100 X
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Results
Metallography Results
lt0.005Nb
0.015Nb
0.032Nb
0.054Nb
Microstructure after 1100C Austenization
Temper Magnification 100 X
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Results
Metallography Results
lt0.005Nb
0.032Nb
0.015Nb
0.054Nb
Microstructure after 1150C Austenization
Temper Magnification 100 X
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Results
Metallography Results
lt0.005Nb
0.032Nb
0.015Nb
0.054Nb
Microstructure after 1200C Austenization
Temper Magnification 100 X
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Discussion
Hardness v/s Absorbed Energy for Real Weldment
PWHT Test
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Discussion
Hardness v/s Absorbed Energy for Real Weldment As
Welded Test
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Discussion
Solubility of NbC at High Temperature
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Discussion
Published CCT Diagram for Medium Carbon Nb-V Steel
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Discussion
Garland Kirkwood Model Showing Possible
Metallurgical Effects of Nb
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conclusions

•    Nb bearing carbon-manganese steel are
  embrittled by the unintentional heat treatment
  taking place in the zone next to the bond during
  welding. The embrittlement is higher the higher
  the Nb content of the base metal.
• Under the conditions tested, acceptable weld
  metal toughness in the stress relieved condition
  was obtained only with the lt 0.005 Nb containing
  steel at lower heat input of 76.2 kJ/inch at
  -30F.
•    The adverse influence of Nb on HAZ toughness
  at high heat inputs is also confirmed.
• As the heat input increases the time at
  maximum temperature increases and the cooling
  rate decreases which have a detrimental effect on
  final microstructure achieved.
•   Gleeble simulation results and real weldment
  results shows a reasonably good agreement, which
  validate the data obtained with the simulation.

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conclusions

•   The as welded toughness is higher in both real
  weldment and simulation test than PWHT
  toughness.
• This indicate the deleterious effect of PWHT on
  the heat affected zone toughness for the steel
  under Study. More Pronounce precipitation
  hardening and Precipitate coarsening can be cited
  as the reason.
• A combination of precipitation hardening and
  formation of brittle microstructural constituent
  assumed for explaining the embrittling effect of
  Nb.
  1) Hall-petch
  relationship for DBTT 2) Embrittlement Vector
  Diagram
• Light optical microscopy have a limitation in
  revealing the microstructural constituents tested
• TEM Study Recommended      

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ACKNOWLEDGEMENTS
THERMAL PROCESSING TECHNOLOGY CENTER Dr. Philip
Nash Dr. Robert Foley Dr. Calvin Tszeng
Mr.Carl Hybinette Dr. Sheldon Mostovoy
Learning and experimental resources TPTC Friends
Russ Janota Family Roommates
Friends MMAE DEPARTMENT - IIT