HTP Process for Linepipe and Structural Steels The Royal Society of - - PowerPoint PPT Presentation

HTP Process for Linepipe and Structural Steels

The Royal Society of Chemistry 16th July 2014

Charles Hatchett Award

• Creation 1977
• First Award 1979

14 out of 35 Medals involve Austenite Processing* * A major interest of CBMM since 1975

HTP Concept

C 0.02 – 0.06 Percent Mn 1.50 – 1.85 Percent Nb 0.07 – 0.11 Percent (or Higher) Other Cr, Mo, Ni, Cu Produces high toughness plate obviating the need for powerful plate mills, controlled rolling and water cooling (accelerated cooling).

Application Precedes Understanding

Concept Low carbon allows greater solubility of niobium – basis of J. M. Gray PhD Studies circa 1962-1965 (0.02%C 0.50%Mn 0.10%Nb) Proof of Concept BOFORS Heat 1971-1972 (0.06%C 1.60%Mn 0.10%Nb) First Applications Algoma Steel – TCPL 1974 (0.14%Nb) USINOR – Gazprom 1974 Hoesch – Czech Projects 1978

Fundamental Research

DEFORMATION PROCESSING: RECOVERY, RECRYSTALLIZATION, PRECIPITATION & FERRITE FORMATION**

• M. J. Luton, R. Dorvel, R. A. Petkovic, Columbia University, New York, NY

&

• J. M. Gray, Molycorp, White Plains, NY

The results obtained in this way indicate that the presence of dissolved columbium causes a moderate reduction in the rate of static recovery, and a two fold decrease in the recrystallization rate. In the presence

• f finely dispersed columbium carbonitride precipitates, however, the

rate of recrystallization is reduced by almost two orders of magnitude.

**Presented at AIME Seminar on “Precipitation Processes in Structural Steels” Denver, Colorado, February 27 to 28, 1978.

Big Picture

Sequential Contributions (Effects) of Niobium

• Retards austenite grain growth during reheating.
• Reduces austenite grain growth in the transfer bar.
• Retards austenite recovery and recrystallization.

during low temperature finishing (i.e. below Tnr).

• Lowers austenite to ferrite transformation

temperature.

• Precipitation hardens ferrite.

Effect of niobium content on austenite grain size at a soaking temperature of 1175°C for three hours.

Retardation of recrystallization by microalloying elements.

Continuous cooling transformation diagram for a 0.02%C 0.49%Mn 0.10%Nb steel.

Influence of niobium in solid solution at the finish rolling temperature on the volume fraction of bainite in air cooled and accelerated cooled HTP plate.

Effect of niobium (columbium) content and finish rolling temperature on yield strength and notch toughness.

Progress of development showing simultaneous increase in toughness with strength and passage of time.

350 400 450 500 550 200 400 600 800 1000

Finish Cooling Temperature, C

Yield Strength, MPa

• Conv. Nb-V

HTP

X-70 Min

100 200 300 400 200 400 600 800 1000

Finish Cooling Temperature, C CVN Energy at -40C, J

• Conv. Nb-V

HTP

Wide processing window for yield strength of 0.03%C 1.6%Mn 0.095%Nb 0.27%Cr 22 mm plates cooled at 6°C/s

Microalloying Systems used for Linepipe

C Mn Nb V Cr Mo Grade Nb only 0.06 1.60 0.05

• X-65

Nb – V 0.09 1.60 0.04 0.08

• X-70

Nb – Mo 0.04 1.70 0.09

• 0.30

X-70/X-80 Nb – Cr 0.03 1.70 0.10

• 0.28
• X-70/X-80

Nb – Cr – Cu – Ni – Mo 0.03 1.60 0.05

• 0.28

0.30 X-80/X-100

Typical chemical composition of Chinese 18.4 mm X80 Hot Rolled Coil & Plate

Elements wt, % C Mn Nb Ti Nb+Ti +V Cr Mo Ni N CEPcm CNPC Spec. max. 0.09 1.95 0.11 0.025 0.15 0.45 0.35 0.50 0.008 0.23 Coil Actual 0.05 1.74 0.10 0.018 0.12 0.28 Added 0.004 0.19 Plate Actual 0.05 1.92 0.10 0.012 0.12 0.24 0.10 0.24 0.006 0.18

1993--X60 1998--X65 2000--X70 2003—X80 2005—X100 2007—X120 Rapid rate of adoption of API Grade X-80 linepipe in China.

PROGRESS IN ADOPTING X-80 STEEL

CONCLUSIONS

• In 50 years we have moved from simple semi

killed 0.24 percent carbon ingot cast steels to very sophisticated low carbon killed concast steels.

• Fundamental metallurgy is much better known.
• The rolling mill has become a sophisticated

metallurgical tool.

• X-80 has become the workhorse of high pressure
• nshore pipelines.
• 65-70 percent is based on variants of the HTP

concept on both old and new mills.