nucor steel astm a709 plate rolling process
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Agenda
Overview of Process
Discussion of Caster in detail
Defects and preventative measures Discussion of inspection
procedures
UT ASTM A578
Questions
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Steelmaking Process
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Melt Shop: Scrap
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Melt Shop: EAF
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Tapping EAF
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Melt Shop: Twin LMF
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Melt Shop: LMF
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Meltshop: Casting
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Slab
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Roll Mill: Reheat Furnace
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Roll Mill: Rolling Mill
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Roll Mill: Hot Shear
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Roll Mill: Leveler
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Cooling Bed
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Roll Mill: Cold Shear
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Mechanical Testing Lab
Impact Testing Tensile Testing
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Product Traceability
Die Stamping Paint Marking
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On-Site MetallurgicalFacilities
Scanning ElectronMicroscope Electrolytic Macro-etch
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Shipping
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Discussion of Internalimperfections
Segregation
Voids
Streaks Laminations
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Slab Defects
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Segregation
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Solidification
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Solidification
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Grain Structure
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Ways to minimizesegregation
Lower carbon
Control superheat
Control bulging Lower cast speed to be able to do
more soft reduction
Lower Hydrogen Minimize Chemistry
Higher reduction ratios
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What is Soft Reduction?
Final point ofsolidificationmoves down
withincreasingcasting speed
Squeeze atfinal point ofsolidification
Localized Linear
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Superheat Monitoring
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Voids and Laminations
Caused by similar factors assegregation
Superheat
Dissolved gases
Misalignment in machine
Steel shrinks as it solidifies.
Voids considered normal
Laminations not considerednormal.
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Radial Streaks
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W i i i
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Ways to minimizestreaking
Excellent roll alignment
Control bulging
Lower Hydrogen Minimize Chemistry
Higher reduction ratios to heal any
streaks Uniform cooling
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Rolling process
Elongated Grains
Very high strength
and low ductility
Equiaxed Grains
Rolling Direction
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Nucor-Hertford Inspection of Bridge Grades
All weathering grades > 1.25, each end for 24
All grade 50 > 1.50, each end for 24
All grade 36 > 1.50, each end for 24
Nucor In-House Quality Checks
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Industry Standard ASTM A578 or A435, only when ordered
Flaw size permitted, up to 3 diameter with total loss of back
reflection
Nucor Standard Rejection criteria is more stringent than ASTM
Nucor vs Industry Standard for InternalSoundness
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Level Criteria Bridge Other Structural
Level 1 Less than 10% Screen Height Pass Pass
Level 2 10%-30% Screen Height Pass Pass
Level 3 30%-50% Screen Height Pass Pass
Level 4 50% Screen HeightIndication Less than 1
Fail Pass
Level 5 50% Screen Height
Indication Greater than 1
Fail Fail
Nucor-Hertford UT Acceptance Criteria
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Typical UT Indication on a 2 plate
0
20
40
60
80
100
0 0.5 1 1.5 2
ScreenHeight(%)
Distance (in.)
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ASTM UT Reject at Mid-Thickness of 2 Plate
0
20
40
60
80
100
0 0.5 1 1.5 2
ScreenHeight(%)
Distance (in.)
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Nucor Hertford UT Rejection
0
20
40
60
80
100
0 0.5 1 1.5 2
ScreenHeight(%)
Distance (in.)
M Cl
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Mannesman Class 1
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Class 2
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Class 5
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Short and Long term plans
Short term
Machine alignment
Increased inspection when a problem
is found Reduced cast speed
Degassing
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Speed Restrictions
Since 2008, Nucor has 62 gradesthat have speed restrictions to helpwith centerline and porosity(35% of
our grades and mix). Speed restriction cause solidification
higher in the machine and allows for
more time to perform soft reduction 60% of all greater than 1 material has
speed restrictions.
95% of all greater than 2 material has
speed restrictions.
Work done on improving
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Work done on improvingsurface quality
2010 revised our soft reduction tables
2011 set up routine macro sampling
Added personnel to do this
Helps identify problems in machinesooner
2011 Improved superheat control
2012 Installed Degasser Started up July of 2012
Now degassing 20-25% of our product
Results of Quality
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Results of QualityImprovements
YearInternal
Soundness Porosity Total
2008 0.21% 0.04% 0.25%
2009 0.31% 0.01% 0.32%
2010 0.42% 0.12% 0.55%
2011 0.24% 0.04% 0.28%
2012 0.17% 0.02% 0.18%
* Results are summary across all gauges/grades and includenon degassed material.
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Long term plans
Long term
Replace segments to improve coolingpatterns
Current segments leave non-uniformsoldification patterns
Danieli new anti-bulging program
Investigating on-line UT
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