0

Microstructure of Microalloyed Linepipe Steels FREE

[+] Author Affiliations
Udit Sharma, Douglas G. Ivey

University of Alberta, Edmonton, AB, Canada

Paper No. IPC2000-125, pp. V001T02A015; 9 pages
doi:10.1115/IPC2000-125
From:
  • 2000 3rd International Pipeline Conference
  • Volume 1: Codes, Standards and Regulations; Design and Constructions; Environmental; GIS/Database Development; Innovative Projects and Emerging Issues
  • Calgary, Alberta, Canada, October 1–5, 2000
  • Conference Sponsors: Pipeline Division
  • ISBN: 978-0-7918-4024-5
  • Copyright © 2000 by ASME

abstract

The aim of this study was to characterize the microstructure of microalloyed linepipe steels. The steels investigated were X70 (0.04 wt% C - 0.02 wt% Ti - 0.07 wt% Nb) and X80 (0.04 wt% C - 0.025 wt% Ti - 0.09 wt% Nb) steels, where the numbers refer to their specified minimum yield strength (SMYS) in ksi. This class of steels has the advantage of high strength and good toughness combined with minimal wall thickness (15.5 mm for X70 steel). These attributes result in considerable cost savings when installation of several hundreds of kilometers of pipeline is required for oil and natural gas recovery and transport.

The present study focused on phase identification and quantification, distribution of alloying elements and inclusions and segregation effects. Both steels were primarily composed of a mixed ferrite structure, i.e., polygonal ferrite and acicular ferrite/bainite, with characteristic low angle grain boundaries and high dislocation densities. The proportion of acicular grains was higher for the X80 steel. Pockets of retained austenite, exhibiting a Kurdjumov-Sachs orientation relationship (KS-OR) with the adjoining ferrite, were found in both steels.

Five general classes of precipitates were identified in both steels: 1) Very large (2–10 μm) cuboidal TiN particles nucleated on inclusions; 2) large (0.1–1.0 μm) cuboidal TiN particles; 3) medium sized (30–50nm), irregular shaped Nb-Ti carbonitrides; 4) fine (<20nm), rounded precipitates of Nb carbonitrides with traces of Mo; 5) very fine dispersed precipitates (<5 nm in size). For X80 steels many of the large TiN precipitates were observed with Nb-rich carbonitrides precipitated epitaxially on them.

Inclusion content and morphology were analyzed in both steels. The inclusions in X70 steels were found to be primarily CaS with significant amounts of Al, O, Ti, Fe and Mn. They were essentially spherical in shape with small elliptical distortions along the rolling direction and across the width of the plate. The morphology of the inclusions in the X80 steel was very similar, however, they showed higher Mn levels.

Copyright © 2000 by ASME
Topics: Steel
This article is only available in the PDF format.

Figures

Tables

Interactive Graphics

Video

Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature

Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

NOTE:
Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In