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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=

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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