Influence of Effective Grain Size on Low Temperature Toughness of High-Strength Pipeline Steel

Abstract

In this study, the series temperature Charpy impact and drop-weight tear test (DWTT) were investigated, the misorientation angles among structural boundaries where the cleavage crack propagated were identified, and angles of {100} cleavage planes between adjacent grains along the cleavage crack propagated path were calculated in five directions (0°, 30°, 45°, 60°, and 90° to the rolling direction) of high-grade pipeline steel. Furthermore, the effective grain size (grain with misorientation angles greater than 15°) was redefined, and the quantitative influences of the redefined effective grain size on Charpy impact and DWTT is also discussed synthetically. The results showed that the microstructure presented a typical acicular ferrite characteristic with some polygonal ferrite and M-A islands (composed of martensite and retained austenite), and the distribution of the high-angle grain boundaries were mainly distributed in the range of 45°–65° in different directions. The Charpy impact energy and percent shear area of DWTT in the five directions increased with refinement of the redefined effective grain size, composed of grains with {100} cleavage planes less than 35° between grain boundaries. The ductile-to-brittle transition temperature also decreased with the refining of the redefined effective grain size. The redefined effective grain boundaries can strongly hinder fracture propagation through electron backscattered diffraction analysis of the cleavage crack path, and thus redefined effective grain can act as the effective microstructure unit for cleavage.

Effects of Boron Content on the Microstructure and Impact Toughness of 12Cr1MoVR Low-Alloy Heat-Resistant Steel Weld Metals

“…The coarser grain size in the specimen with 0.0028% B forms the larger cleavage fracture facets, which induces the lower impact toughness (which is consistent with ref. [ 27 ]).…”

The Impact of Isothermal Treatment on the Microstructural Evolution and the Precipitation Behavior in High Strength Linepipe Steel

“…The reliability and safety of oil and gas pipelines under various conditions of use and different mechanical damage need to be evaluated due to the higher requirements for structural integrity and environmental factors for safety assessment [4,8]. High-grade pipeline steels have been used for the practical application [9][10][11][12]. Desired mechanical properties can be obtained by optimizing alloy design and using TMCP process [13].…”

Comparison of segmentation of 2D and 3D EBSD measurements in polycrystalline materials

“…The EBSD method considers a grain to be the set of all points (voxels or pixels, respectively) with a similar orientation, which are surrounded by a boundary of a given misorientation threshold. The typical threshold in the EDAX OIM software is 5 • [9], but other choices are possible as well [10,11]. The obtained segmentation into the grains depends on the chosen misorientation threshold, of course, but even if we use a fixed misorientation threshold, we may get different results of the segmentation in 2D and 3D, as shown in [12].…”