Structure and mechanical properties of the welded joints of large-diameter pipes

The structure and mechanical properties of the technological welded joints of large-diameter pipes of strength class K60 produced by two companies are studied. Along with standard mechanical properties (σ0.2, σu, δ, ψ), specific work of deformation a (tensile toughness) and true rupture strength Sf are estimated from an analysis of the stress-strain diagrams constructed in true coordinates. The mechanical behavior is found to be different for samples cut from different zones of a welded joint (central weld, heat-affected zone, and base metal). The mutual correlation between parameters a, S f, and impact toughness KCV is considered. © 2013 Pleiades Publishing, Ltd

Evolution of microstructure in stainless martensitic steel for seamless tubing

Scanning electron microscopy with orientation analysis by the electron backscatter diffraction (EBSD) method is used to study microstructures and textures formed in the 0.08C-13Cr-3Ni-Mo-V-Nb steel through seamless tube production route: after hot deformation by extrusion; after quenching from various temperatures and subsequent high tempering. It is shown that the martensitic microstructure formed both after hot deformation and after quenching is characterized by the presence of deformation crystallographic texture, which is predetermined by the texture of austenite. The effect of heat treatment on texture, packet refinement, lath width, precipitation of carbides and Charpy impact energy is analyzed. © 2017 Author(s).The work was done using the equipment of the laboratory of Structural Methods of Analysis and Properties of materials and nanomaterials of the Collective Use Center affiliated to Ural Federal University. The study was supported by the program of increasing the competitiveness of the leading Russian universities, RF Government resolution No. 211, contract No. 02.А03.21.0006. We are grateful to the TMK company for their support and assistance in organizing the study

Features of shear transformation texture in seamless pipes

Microstructure and texture in seamless 0.08C-Cr-Mo-V, 0.25C-Cr-Mo-V-Nb, 0.08-13Cr-3Ni-Mo-V-Nb, and 18Cr-9Ni steel pipes are studied in the as-rolled and heat-treated states using orientation EBSD microscopy. It has been found that all types of microstructure (ferrite, martensite, and bainite) in products, both after hot rolling and after heat treatment, have well-defined axial crystallographic texture, where the direction is predominately perpendicular to the pipe surface. It is demonstrated that texture formation in heat-treated states is inherited due to the following factors important for the rules of orientation selection during the γ→α phase transformation: 1) occurrence of stable orientation of austenite grains resulted from straining; 2) special misorientation (boundaries) of austenite grains where transformation starts; 3) orientation relationships known for phase transformation; 4) thermal stresses in a product, formed during cooling. The latter can be considered as factor determining special texture in seamless steel pipes. © 2018 Author(s)

Crystallographic reconstruction study of the effects of finish rolling temperature on the variant selection during bainite transformation in C-Mn high-strength steels

The effect of finish rolling temperature (FRT) on the austenite- () to-bainite () phase transformation is quantitatively investigated in high-strength C-Mn steels. In particular, the present study aims to clarify the respective contributions of the conditioning during the hot rolling and the variant selection (VS) during the phase transformation to the inherited texture. To this end, an alternative crystallographic reconstruction procedure, which can be directly applied to experimental electron backscatter diffraction (EBSD) mappings, is developed by combining the best features of the existing models: the orientation relationship (OR) refinement, the local pixel-by-pixel analysis and the nuclei identification and spreading strategy. The applicability of this method is demonstrated on both quenching and partitioning (Q&P) and as-quenched lath-martensite steels. The results obtained on the C-Mn steels confirm that the sample finish rolled at the lowest temperature (829{\deg}C) exhibits the sharpest transformation texture. It is shown that this sharp texture is exclusively due to a strong VS from parent brass {110}, S {213} and Goss {110} grains, whereas the VS from the copper {112} grains is insensitive to the FRT. In addition, a statistical VS analysis proves that the habit planes of the selected variants do not systematically correspond to the predicted active slip planes using the Taylor model. In contrast, a correlation between the Bain group to which the selected variants belong and the FRT is clearly revealed, regardless of the parent orientation. These results are discussed in terms of polygranular accommodation mechanisms, especially in view of the observed development in the hot-rolled samples of high-angle grain boundaries with misorientation axes between and

Textural heredity at phase transformations in low-carbon low-alloy pipe steel after controlled thermomechanical processing

The orientation microscopy (EBSD) was used for studying of the structural and textural states of the low-carbon low-alloy pipe steel close to 06G2MB after the thermomechanical controlled processing (TMCP) and subsequent thermal treatments – heating up to 1000 °C followed by: 1) water quenching; 2) isothermal quenching with holding at 300 °C; 3) slow cooling in a furnace. All heat treatments included double phase recrystallization: α → γ → αN (where αN is martensite, ferrite or bainite, respectively). The texture obtained after TMCP, was formed mainly by two strong orientations {112}<110> and two weaker orientations close to {110}<223>. It was shown that despite dual phase recrystallization the main crystallographic orientations of bainite after TMCP and after isothermal quenching are consistent with each other. This indicates some mechanism of structure and texture heredity within the material. The structures obtained through other thermal treatments, martensite and ferrite, were also characterized by complex multi-textures. Part of the basic textural components of martensite and ferrite were the same as in case of bainite. All structures after various thermal treatments have common spectrum of high angle boundaries with the most pronounced boundaries of the coincidence site lattice (CSL): Σ3, Σ11, Σ25b, Σ33с, Σ41c. It has been demonstrated that the orientations inside textures of all obtained structures are associated with the major orientations of the strained austenite grains formed as a result of hot rolling during TMCP and the orientation relationships (ORs) that are intermediate between ORs of Kurdyumov-Sachs and Nishiyama-Wasserman. In all cases, the fact of correspondence between orientation bonds of textures in initial and all resulting states is explained through a selective initiation of phase transformations (both shear and diffusion) on crystallographic (including special) boundaries close to the CSL boundaries Σ3 and Σ11. © 2017, National University of Science and Technology MISIS. All rights reserved

Effect of Structure and Texture on Failure of Pipe Steel Sheets Produced by TMCP

The method of orientation microscopy (EBSD) is used to study the structure and texture of low-carbon, low-alloy pipe steel sheets processed by controlled thermomechanical processing (TMCP). The temperatures of isothermal hot rolling varied. Samples cut from sheets showed a different fracture tendency during mechanical testing. The formation of cleavages (secondary cracks) during failure of steel is related to the presence of ferrite grains with orientation {001} <110> extended in the hot rolling direction. The formation of grains is a consequence of the isothermal hot rolling below the temperature