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
2007 — X120 2005 — X100 2003 — X80 2000--X70 1998--X65 1993--X60
1st Shanxi — Beijing 660mm,6.4MPa, 2nd Shanxi — Beijing Huoerguosi 918km X60 1016mm,10MPa, 851km X70 Lunnan Beijing 1st West-east 1016mm,10MPa, 3856km X70 2nd West-east 1219mm,12MPa, 4913km X80 Shanghai Ji-ning 1016mm,10MPa, 912km X70 (7.9km X80) Guangzhou Hongkong
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 0.10 0.08 ≤ 0.15 resistant to ductile fracture) API PSL2 Annex H (Pipe for 0.10 0.08 ≤ 0.15 sour service) API PSL2 Annex J (Pipe for 0.12 0.08 ≤ 0.15 offshore service) DNV-OS-F101 (Pipe for 0.12 0.08 ≤ 0.15 offshore service) 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 21 ST 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.
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