David Jarreta Material Characteristics and Performance of High-Strength Niobium Micro-Alloyed Steel
David Jarreta
Material Characteristicsand Performance of High-StrengthNiobium Micro-Alloyed Steel
AGENDA
High Strength Steels
Materials Science Essentials
Strengthening Mechanisms
TMCP & Niobium Microalloyed Steels
Optimized Steel & Its Advantages
Examples: Real Cases
For construction, steels with Yield Strength (YS) > 355 MPa (above S355) are
commonly called high strength steels.
What is higher strength steel?
Higher Strength Lower Weight=
Why use higher strength Niobium steels ?
Lower Weight
Higher Strength
Reduced Thickness
Reduced Welds
Reduced Thickness
Reduced Material
Lower Transportation
Easier Handling
Reduced Thickness
Reduced Welds
Reduced Time
Reduced Costs
Reduced Material
Reduced Costs
Reduced Emissions
& Use of Resources
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Materials Science Essentials
P e r f o r m a n c e
M e c h a n i c a l P r o p e r t i e s
M i c r o s t r u c t u r e
G r a i n s t r u c t u r e
P h a s e s
P r e c i p i t a t e s
C h e m i s t r y + P r o c e s s i n g
Materials Science Essentials
Alloy Content (wt%)
Incr
ease
in S
tren
gth
(M
Pa)
Interstitials:
- C & N
- Negative effect to Ductility, Toughness and Weldability.
Solid Solution Strengthening
Graville Weldability Diagram
Source: Pickering, Physical Metallurgy of steel,s 1978, p.11
Orowan-Asby
Modified Orowan Ashby to ferrite in steels (Mater Sci Tech, Sept. 1997, vol 13, p.736):
).10x63.1ln(10x23.1
)( 9
5
DD
fMPa
descarbonitri offraction volume
diameter particle avarage
f
D
Increase Strength
Decrease Ductility
Decrease Toughness
Reduce Weldability
Precipitation Hardening
1010 Steel (10%perlite)
1020 Steel (23%perlite)
1045 Steel (56%perlite)
1070 Steel (90%perlite)
C %
Example: Perlite in Steels
Dispersion Hardening
Increase Carbon: Toughness & Weldability
1010 Steel (10%perlite)
1020 Steel (23%perlite)
1045 Steel (56%perlite)
1070 Steel (90%perlite)
Dispersion Hardening
Example: Perlite in Steels
o and k=constant
= dislocation density
f = final flow stress
2
1
0 kf
Example: Cold Rolling / Cold Forming
Increases dislocation density: from 105 / cm2 to 1011/cm2
Work Hardening
Source: Pickering, Physical Metallurgy of steel,s 1978, p.33
Phase Transformation
i and k=constant
D = grain size
o = flow stress
Hall-Petch Relation
2
1
0
kDi
+ Nb
7 to 12 ASTM: increase in
strength by 200 MPa
Grain Refining
7 to 12 ASTM: increase in strength by 200 MPa
Grain Refining is the only
strengthening mechanism that
also increases toughness!
Finer Grains and Higher Resistance to Cracking
Grain Refining
2
1
dkydispptssiy
Grain Refining
Grain Refining
Niobium Microalloyed Steels vs Mild Steels
TRUMP
Main Strengthening Mechanisms
Steel Strengthening Strategy
Main Strengthening Mechanisms
C,
TRUMP
Steel Strengthening Strategy
TRUMP
Main Strengthening Mechanisms
C,
Steel Strengthening Strategy
TRUMP
Main Strengthening Mechanisms
C,
Steel Strengthening Strategy
TRUMP
Main Strengthening Mechanisms
C,
Steel Strengthening Strategy
C,
Main Strengthening Mechanisms
TRUMP
Steel Strengthening Strategy
Thermo-Mechanical Controlled Processing
• Zone I: carbon < 0.11%, lattice
distortion and hardness is relatively
low, minimal precautions needed.
• Zone II: higher hardenability, need
to control the welding procedure
(preheats and heat input) to ensure
HV<350. If [H] < 5 ppm, we may
tolerate up to HV <450.
• Zone III: Strict procedure control
and post-weld heat treatment
needed. Try to diffuse the [H] away,
stress relieve the weld, and temper
the phases.
Graville Weldability Diagram
Relationship of Carbon & CE on Weldability
Yield Strength (MPa)
27
J T
ran
sitio
n T
em
p. (º
C)
Steels typically contain Niobium
Commercially Available Steels
Grades
Offshore EN 10255 API 2H Gr 42 - 60
API 2W Gr 42 - 60
API 2Y Gr 60
2MT1
Weldable Fine Grain Structural Steels EN 10025-2,3,4 S355 to S960QL
A572 to A633 [M] Gr E
Steels with Improved Atmospheric
Corrosion ResistanceEN 10025-5:2004
S355J2W, J2G1W, K2G1W,
CORTEN-B etc
Examples of Niobium Microalloyed Steel Grades
Steel grade S355 S355 S460 S460 S460
Processing N TM N QT TM + ACC
C 0.15 0.07 0.15 0.10 0.07
Si 0.40 0.30 0.40 0.35 0.25
Mn 1.50 1.50 1.50 1.45 1.55
P 0.012 0.012 0.012 0.012 0.012
S 0.004 0.004 0.004 0.004 0.004
Al 0.03 0.03 0.03 0.03 0.03
N 0.005 0.005 0.005 0.005 0.005
Ti 0.015 0.015 0.015 0.015 0.015
V none none 0.12 none 0.04
Nb 0.04 0.04 0.04 0.04 0.04
Cu none none 0.60 0.30 none
Ni none none 0.60 0.60 0.25
Mo none none none 0.25 none
CEq 0.40 0.31 0.50 0.45 0.36
(N = normalised, TM = thermomechanically rolled, QT = quenched plus tempered,
TM + ACC = thermomechanically rolled plus accelerated cooled)
Steel grade S355 S355 S460 S460 S460
Processing N TM N QT TM + ACC
C 0.15 0.07 0.15 0.10 0.07
Si 0.40 0.30 0.40 0.35 0.25
Mn 1.50 1.50 1.50 1.45 1.55
P 0.012 0.012 0.012 0.012 0.012
S 0.004 0.004 0.004 0.004 0.004
Al 0.03 0.03 0.03 0.03 0.03
N 0.005 0.005 0.005 0.005 0.005
Ti 0.015 0.015 0.015 0.015 0.015
V none none 0.12 none 0.04
Nb 0.04 0.04 0.04 0.04 0.04
Cu none none 0.60 0.30 none
Ni none none 0.60 0.60 0.25
Mo none none none 0.25 none
CEq 0.40 0.31 0.50 0.45 0.36
(N = normalised, TM = thermomechanically rolled, QT = quenched plus tempered,
TM + ACC = thermomechanically rolled plus accelerated cooled)
CET
Pcm
0.30
0.24
0.35
0.29
0.30
0.23
0.22
0.16
0.23
0.16 BVMoCrNiCuSiMn
CPCM 510152060203020
Different Type of 50 mm HSS Plates
Steel Grade S780 S780
Processing QT TM + QT
C 0.15 0.09
Si 0.30 0.30
Mn 1.40 1.40
P 0.01 0.008
S 0.005 0.003
Al 0.035 0.025
N 0.005 0.005
Ti 0.015 0.020
V 0.03 none
Nb 0.030 0.030
Cu none none
Cr 0.40 0.30
Ni none none
Mo 0.15 0.20
B 0.0020 0.0020
CE 0.50 0.42
CET 0.33 0.27
Pcm 0.27 0.21
Grade YS (MPa) TS (MPa) A50 (%)CVN Transverse
FSE @ -40°C (J)
690 MPA 799 828.00 25.00 236
Different Type of 40 mm S780 Plates
550
500
400
350
300
250
0.20
Carbon equivalent CEq (%)
Yiel
d S
tren
gth
(M
Pa)
450
600NormalisedTM-rolled
0.25 0.30 0.35 0.40 0.45
Lower CEq is better !
Relationship of Yield Strength & CE
Source: Dillinger
Advantages of TMCP: Nb-S355TM vs Normalized
Source: Dillinger
Advantages of Higher Strength: S460NL vs S355NL
Source: Dillinger
Advantages of TMCP: Nb-S460ML vs S460NL & S355NL
Benefits of HSS:
Material cost: lower by up to 35%
Welding cost: lower by up to 35%
Material and welding cost of HSS relative to S355
Source: Dillinger
Weight and Cost Reduction
YS (N/mm2) TS (N/mm2) YR VE0*1 (J) PCM
*2 (%)
TS780 P-630T 630-880 780-930 ≤ 95% ≥ 47 ≤ 0.30
Mechanical PropertiesSteel Pipe
Grade PCM Thickness (mm)
75°C 0%
50°C 0%
50°C 0%
25°C 0%
60
40
GMAW (CO2)
Welding consumable:
MG-80, Ø 1.2
Heat Input: 1.1 kJ/mm
Welding
Conditions
Preheating
Temperature
Crack
Ratio
Y-groove weld cracking tests
Steel Plate
780 N/mm2
0.27
0.24
Examples: JFE TS780 Steel
Examples: Tokyo Sky Tree H-SA700 Steel
Sources: Steel Construction No. 31, Nov 2010; NSSMC webpage.
Examples: Tokyo Sky Tree H-SA700 Steel
LSAW
Great weldability
Plate Thickness
t (mm) YS (N/mm2) TS (N/mm2) YR El (%) VE0*1 (J)
H-SA700A Non-welding ≥ 47 (0°C)
H-SA700B Welding ≥ 47 (-20°C)
Specifications of H-SA700 steel for CFT Columns (concrete-filled steel tube)
6 to 50
Mechanical PropertiesGrade Application
630-880 780-930 ≤ 98%≥ 16
JIS No.4
630 N/mm2 ≥ 630
500 N/mm2 ≥ 500
400 N/mm2 ≥ 400
JIS G 3475
STKN490B325 - 475
GradeYield Strength
(N/mm2)
Large-diameter, thick high-strength steel pipes for Tokyo Sky Tree
Nb-TMCP high strength steels used
Sources: Steel Construction No. 31, Nov 2010; NSSMC webpage.
Source: RIST Steel Structural Research Division
- Produced by POSCO
- TMCP + Accelerated Cooling & Transformation Control
- Nb content: 0.020% to 0.040 wt%
Examples: Lotte World Tower HSA800 Steel
SM400
(150x150x10x10)
SM490
(110x110x10x10)
SM570
(80x80x10x10)
HSA800
(60x60x10x10)
Area is reduced by appx. 50% compared to
SM400
Source: RIST Steel Structural Research Division
Examples: Lotte World Tower HSA800 Steel
Comparison of member sizes between HSA800 and SM570TMC for Lotte World Tower
Notation: W000x000
Depth (mm)
Weight per unit length (Kgf/m)Wide Frange (H-shape)
HSA800 (W760x173) SM570TMC (W760x257)
Source: RIST Steel Structural Research Division
Examples: Lotte World Tower HSA800 Steel
Conc Conc
SM570TMC HSA800 SM570TMC HSA800
36,826 9,379 50,730 -
294681 294681 Total steel qty: 10% savings
Steel Steel
294681
Total: 46,205 (91%) Total: 50,730 (100%)
Building
weigth
(ton)
294681Gravity member steel qty:
30% savings (9,379 vs 13,904 ton)
Corner W360x179 (37%↓) W360x287
Face W360x314 (38%↓) W360x509
Top/Bot. chord W360x421 (29%↓) W360x592
Vert W360x551 (13%↓) W360x634
Diagonal W360x509 (25%↓) W360x677
Perimeter
column
Component LocationModel E1
HSA800
Model E2
SM570TMC
Spandrel
girders
Belt truss
- W760x173 (33%↓) W760x257
Niobium Containing Grain Refined High Strength Steels:
Increased strength with ductility and improved toughness and weldability
Reduced variation in mechanical properties
Improved weldability by permitting a reduction in carbon (lower CE)
Allow for reduction of weight, overall cost, CO2 emissions and use of resources
Allow for optimized building performance
Niobium will create added value to the product.
It is an enabling technology, supporting innovation and benefiting the value chain.
Conclusion
Acknowledgements