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Low Carbon HTP Structural Steel : A Paradigm Shift
by
J. Malcolm Gray and P. R. Kirkwood
Presented at the Charles Hatchett Seminar, London, UK
Perspective & Summary The technology and application of microalloyed steels has
developed rapidly over the past half century. Metallurgical
developments have been very rapid in linepipe steels and
automotive grades and much slower for structural steels.
Yield strengths above 100-120 ksi are available for
automotive and linepipe applications, but until recently
structural steels rarely exceeded 60 ksi. There are signs,
particularly in China, where linepipe technology and related
specifications are being utilized in impressive construction
projects, (airports, stadiums and very tall buildings).
What is HTP* Steel? (* High Temperature Processed)
• Conventional Steel 0.04%Nb FRT 710-830°C
• HTP Steel 0.10%Nb FRT 840-910°C
RETARDATION OF RECRYSTALLIZATION BY MICROALLOYING ELEMENTS
1993--X60
1998--X65
2000--X70
2003—X80
2005—X100
2007—X120
Huoerguosi
Lunnan
Guangzhou
Shanghai
Beijing
Hongkong
1st West-east
1016mm,10MPa,
3856km X70
2nd Shanxi— Beijing
1016mm,10MPa,
851km X70
2nd West-east
1219mm,12MPa,
4913km X80
1st Shanxi— Beijing
660mm,6.4MPa,
918km X60
Ji-ning
1016mm,10MPa,
912km X70 (7.9km X80)
PROGRESS OF LINEPIPE DEVELOPMENT SHOWING SIMULTANEOUS INCREASE IN TOUGHNESS WITH STRENGTH
AND PASSAGE OF TIME
Changes in maximum niobium and carbon contents with time (and strength increase) for linepipe steel.
Change in Niobium Level in the Production of C-Si-Mn-Nb-Al Steels
Austenite Grain Coarsening Behaviour for steels reheated to 1200°C for 1 hr and water quenched.
Carbon & Niobium Restrictions for TMCP Welded X70 PIPE
Specification C% Nb% Nb+V+Ti %
API PSL2/ISO 3183/GB/T 9711 0.12 - ≤ 0.15
API PSL2 Annex G (pipe resistant to ductile fracture)
0.10 0.08 ≤ 0.15
API PSL2 Annex H (Pipe for sour service)
0.10 0.08 ≤ 0.15
API PSL2 Annex J (Pipe for offshore service)
0.12 0.08 ≤ 0.15
DNV-OS-F101 (Pipe for offshore service)
0.12 0.08 ≤ 0.15
CSA Z 245 0.26 0.11 -
CNPC 0.09 0.11 ≤ 0.15
Carbon & Niobium Restrictions in Structural Steel Specifications
Specification C% Nb% Nb+V+Ti %
ISO 10025-3 355/460 N/R 0.20 0.06
ISO 10025-4 355/460 TMCP 0.16 0.06
ISO 10025-6 ≥ 460 Q&T 0.20 0.07
ISO 4950-2 (E) 355/460 0.18 0.06
ASTM/SA 841- Type F G7 0.10 0.11
CSA G40.21-04 350/480 0.20 Nb+V ≤ 0.1 or 0.12
GB/T 5191 -2004 345 to 690 0.20 0.06 ≤ 0.15
GB/T 5191- 2008 345/420 0.18/0.20 0.07 ≤0.22
GB/T 5191-2008 460/690 0.18/0.20 0.11 ≤0.22
Carbon & Niobium Restrictions in Offshore Structural Steel Specifications (≈ 40mm plates)
Specification C% Nb%
ISO 10025 - S355 G2+ N 0.18 0.06
ISO 10025 - S355 G6+M (TMCP) 0.14 0.06
ISO 10025- S355 G9+M (TMCP) 0.12 0.03
API 2H & 2Y 0.18 0.05
API 2W (50T) TMCP 0.16 0.03
Mobile structures E36/EH36 0.18 0.05
CLEARLY INTERNATIONAL SPECIFICATIONS MUST BE
RATIONALISED AND BROUGHT INTO THE 21ST CENTURY.
Conclusions There are exciting possibilities for rapidly constructing huge
structures with novel designs. Linepipe metallurgy, using low
carbon, low sulfur, calcium treated steel, transferred to the
structural steel arena results in steels with strengths up to
690 MPa, excellent weldability and remarkable Z direction
properties. Opportunities exist to utilize hot rolled steels in
industries and applications which traditionally use normalized
or Q&T grades of steel.