The effects of thermo-mechanical control process on microstructures and mechanical properties of a commercial pipeline steel

Zhao, Meixia; Yang, Ke; Shan, Yiyin

doi:10.1016/s0921-5093(01)01904-9

Cited by 208 publications

(96 citation statements)

References 11 publications

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“…It's interesting to note the presence of a small volumetric fraction of bainite / degenerated pearlite and the absence of acicular ferrite in X70 steel. For a pipeline steel, if these constituents can be achieved, it will be with better properties combination [24][25][26][27][28][29][30][31][32][33][34] , such as high mechanical strength, excellent fracture toughness, good H 2 S resistance, reduction of the Bauschinger effect and superior fatigue behavior, than the polygonal ferrite -pearlite microstructure. The distribution of inclusions in the two steels was also analyzed.…”

Section: Resultsmentioning

confidence: 99%

Microstructure and mechanical properties of two Api steels for iron ore pipelines

et al. 2014

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This research compares the mechanical behavior of two API steels (X60 and X70) used in the longest pipeline in the world for the conveyance of iron ore. Tensile tests, Charpy impact tests, CTOD tests and fatigue crack growth tests are performed at ambient temperature. Metallographic examination showed a banded microstructure consisting of polygonal ferrite and pearlite in both steels, with smaller grain size and the presence of a small quantity of bainite in the X70 steel. All the mechanical tests revealed a ductile behavior for the two steels. The X70 steel is preferable for the pipeline project, due its better mechanical resistance, with no significant loss of fracture toughness and fatigue resistance. Its performance could be even better, if an appropriate combination of thermomechanical processing parameters were able to produce a microstructure with minor amount of pearlite, where acicular ferrite/bainite are present.

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Section: Resultsmentioning

confidence: 99%

Microstructure and mechanical properties of two Api steels for iron ore pipelines

et al. 2014

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“…[3][4][5][6][7][8] Several researchers studied the role of vanadium and its precipitates on the mechanical properties and toughness of High Strength Low Alloy (HSLA) steels including linepipe steels. [9][10][11][12][13][14] However, the exact mechanism(s) of vanadium precipitation and their contribution to strength increase are not yet completely understood. For example, while N is highly effective in facilitating the precipitation of V, it is usually kept to a very low level due to toughness concern.…”

Section: Introductionmentioning

confidence: 99%

Impact of Vanadium Addition on API X100 Steel

et al. 2014

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Laboratory heats of an API X100 steel (Mn-Mo-Nb) with two levels of vanadium (0.004% and 0.063%) were melted and control rolled simulating a coiled plate production process. Extensive microstructural analyses were performed, including optical, EBSD and TEM. Texture analyses of the two alloys were also compared. Mechanical properties were determined for various rolling and pipe axis orientations. Only minor differences in microstructure and texture properties were observed between the two alloys. Yet the 0.063% V alloy had from 8 to 14% higher yield and tensile strengths in all directions, while the toughness and ductility measurements were similar for both alloys. Higher strength of the V added pipeline steel was partially due to its smaller grain size and larger fraction of subgrain boundaries. Some, but perhaps not all, of the strength differences could be related to the observed smaller precipitate size of the higher vanadium steel. The vanadium addition was necessary in this alloy to ensure meeting the required strength properties of X100 steel.

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“…On the other hand, bainitic ferrite with M/A interlayers is known to be one of the most desirable microstructures due to its high strength and good toughness and can be obtained by optimization of process parameters, without the need for significant concentrations of alloying elements. Bainitic ferrite, formed by mixed diffusion and shear transformation mode has a high dislocation density [21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Effect of manganese content and microstructure on the susceptibility of X70 pipeline steel to hydrogen cracking

Hejazi

Haq

Yazdipour

et al. 2012

Materials Science and Engineering: A

118

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The influence of composition and microstructure on susceptibility to hydrogen induced cracking (HIC) was investigated in high strength pipeline steels, with Mn contents of 1.2% (standard, X70), and 0.5% (medium, MX70). The HIC resistance of the simulated coarse grained heat affected zone microstructures and normalized X70 transfer bar was also investigated. Notched and fatigue pre-cracked samples were charged with hydrogen prior to three point bend tests. The conditional fracture toughness JQ was determined. The results are discussed in relation to grain size, microstructure, composition and the type and distribution of non-metallic inclusions and precipitates. Published as "Effect of manganese content and microstructure on the susceptibility of X70 pipeline steel to hydrogen cracking" AbstractHydrogen, even in very low concentrations, can diffuse to regions of high stress concentration resulting in a degradation of mechanical properties. However, the transport of hydrogen depends on the interaction between hydrogen atoms and microstructural traps which, in turn, is related to microstructure. The influence of composition and microstructure on susceptibility to hydrogen embrittlement was investigated by selecting pipeline steels with different Mn contents, i.e., standard Mn (X70) and medium Mn (MX70) strips. The HAZ (heat affected zone) microstructures of these strips as well as a normlised transfer bar (TB) were also investigated. HAZ simulations were conducted using Gleeble thermo-mechanical machine to simulate a thermal cycle typical of inservice repairs. Notched and fatigue pre-cracked samples were subjected to electrochemical hydrogen charging using a solution of H 2 SO 4 and NaAsO 2 to achieve 2 and 4 ppm hydrogen content. Three point bend tests were conducted on as-received and hydrogen-charged samples. The X70 strip exhibited a higher J Q than the MX70 strip before and after charging, whereas the TB displayed the lowest J Q . The fracture performance of both steels deteriorated almost linearly with an increase in the hydrogen content. Because of their coarser prior austenite grain sizes and the presence of relatively hard bainitic-ferrite structure with martensite/austenite islands, the simulated HAZ microstructures of the two steels demonstrated significantly lower fracture resistance both with and without hydrogen. The results obtained were compared and discussed in relation to the grain size, microstructure, composition and the type and distribution of precipitates in the samples.

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The effects of thermo-mechanical control process on microstructures and mechanical properties of a commercial pipeline steel

Cited by 208 publications

References 11 publications

Microstructure and mechanical properties of two Api steels for iron ore pipelines

Microstructure and mechanical properties of two Api steels for iron ore pipelines

Impact of Vanadium Addition on API X100 Steel

Effect of manganese content and microstructure on the susceptibility of X70 pipeline steel to hydrogen cracking

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