The review presents analysis of literature sources on the problem of predicting mechanical properties of large-diameter pipes based on the properties of the original hot-rolled sheet. It is shown that methods of physical and simulation modeling make it possible to obtain reliable data on the behavior of pipe steels and their properties without manufacturing pipes and to develop models for calculating and predicting mechanical properties of finished pipes, taking into account the conditions of their production. Models that take into account the Bauschinger effect, which occurs during alternating deformation during pipe processing, have been considered.

Abstract—The results of studying the influence of pipe forming on the mechanical properties (ultimate tensile strength, yield strength) of the base metal of large diameter pipes of strength classes K52–K65 (X56–X80) are analyzed. The differences in the properties determined by testing longitudinal and transverse standard cylindrical and full-thickness specimens cut from both a sheet and the finished pipe and plate specimens cut at various distances from the pipe surface (from different layers) are analyzed. The relation between the state of stress in pipe steel at various stages of pipe forming and its mechanical properties is considered.

The influence of heat treatment, simulating thermal cycles and welding in the process of manufacturing joint fittings on microstructure, strengthening phase precipitation, and mechanical properties of base metal and near-weld zone of fittings, made of low-carbon copper-containing steel, is studied. Rolled product specimens are produced under laboratory and industrial conditions. Heat treatment regimes are developed, and mechanical properties of pipeline fittings of strength class K60 (X70) after normalizing with tempering and strength class K65 (X80) after additional quenching before tempering combined with satisfactory impact strength and weldability are provided.

The Bauschinger effect is a phenomenon of a decrease in material resistance to small plastic deformations after preliminary plastic deformation of the opposite direction, discovered in 1881. This effect is of great importance and is used, in particular, in studying the fatigue strength of materials under alternating loads. The Bauschinger effect is inherent in all metals and alloys, although it is most pronounced in steels. Therefore, it is one of the factors affecting the quality of finished metal products subjected to alternating loading during manufacture. This review analyzes the literature data on the problem of the Bauschinger effect in the case of alternating deformation of metals. Various mechanisms explaining the Bauschinger effect are briefly considered. The factors that qualitatively and quantitatively affect the Bauschinger effect are described in detail, namely the degree of preliminary deformation, composition, structure and properties of the material, deformation conditions, the phenomenon of dynamic deformation aging, and temperature. The problem of the Bauschinger effect in the case of alternating deformation of steel products is considered, in particular, in the production of oil and gas pipes of large diameter. Various methods and approaches to the evaluation and quantitative measurement of the Bauschinger effect are described; the dependence of the Bauschinger parameter on the value for residual deformation is shown. It is concluded that the Bauschinger effect plays both a positive and a negative role in the production of metal products, in particular oil and gas pipes. On the one hand, the Bauschinger effect has a negative effect, reducing the level of mechanical properties of the final product below the required one. On the other hand, it creates a certain margin of plasticity of the deformable material in the process of forming and laying pipes.

Новые технологии, Химическая промышленность, Химическая технология, Научные журналы, Защита от коррозии, Технология металлов, Свойства материалов, Технические журналы, Наука и технологии, Справочная литература, Научные разработки

In this research effect of the pipe forming on strength properties of rolled metal was investigated. Deformed state of metal during pipe processing was analyzed and tests with specimens from plate were performed. Analysis of the experimental data was exploited to evaluate effect of the strain on yield stress in each stage of the pipe forming and specimen flattening. The model for estimation of mechanical properties of the rolling mill product based on the required mechanical properties of the pipe was created.

A method is described for experimentally determining the parameters of a model of the kinetics of static recrystallization. Use of the method ensures a close correlation between calculated and experimental values of the percentage of recrystallized metal (R = 0.97). It is shown that the probability of the occurrence of partial recrystallization between roughing passes must be accounted for in order to evaluate the completeness with which static recrystallization takes place during multipass rolling. It was found that the kinetics of static recrystallization of niobium-microalloyed pipe steels depends on their chemical composition. A convenient software tool, HRRM (Hot Rolling Recrystallization Model), has been created to develop new rough-rolling regimes and correct existing such regimes for the controlled rolling of high-strength microalloyed steels.

The effect of heating temperature and holding duration for slabs in a furnace soaking zone on the structure of microalloyed steel austenite with a different strength category is studied. It is revealed that after heating and soaking in all cases there is possible formation of one of three types of austenitic structure: fine-grained, varying grain size, and coarse-grained. The reason for forming different types of structure is irregular growth of individual grains as a result of dissolution of fine niobium carbonitride particles. It is shown that the start of irregular grain growth depends on steel heating temperature, soaking time, and chemical composition. An effective method is proposed for calculating slab heating temperature and time in a furnace soaking zone providing maximum dissolution of niobium carbonitride inclusions without forming an inhomogeneous structure before the start of the rough rolling stage.

The effect of temperature and soaking time during slab heating for rolling on austenite structure size and uniformity, and dissolution of microalloying element precipitates, is considered. It is shown that the heating regime has a strong effect on austenite structure uniformity. With an increase in heating temperature, there is anomalous growth of individual grains, and this is a consequence of gradual microalloying element dissolution. As a result of this, boundaries acquire mobility, thus leading to generation of secondary recrystallization and significant inhomogeneity, and embrittlement of the structure. It is also shown that austenite grain size and distribution after heating is inherited during roughing rolling.

The effect of welded joint heat-affected zone (HAZ) cooling rate on structure, mechanical properties and brittle failure resistance of pipe steels of strength class X100 is studied by simulating welding thermal cycles in a Gleeble-3180 test unit. These properties are compared with results obtained with pipe welding, and good correlation of data obtained in a laboratory and for an actual pipe is demonstrated. It is also shown that the method for simulating thermal cycles makes it possible to evaluate properties of the heataffected zone without associated processing factors during actual pipe welding. Research results make it possible to establish the range of HAZ cooling rates providing preparation of the required values of longitudinal weld properties for pipe of considerable diameter made from steel of strength class X100.

Mechanical behavior of structural nitrogen-containing steels with various structures and compositions, including the same steels with different summary C+N content and C/N ratio were studied using pressing tests in a wide temperature range, tensile tests, impact bending tests, hardness measurements and shock-wave loading resistance. The tempering and aging under load processes after quenching or thermomechanical treatment with various regimes have been investigated using optical and electron microscopies, X-ray diffraction analysis, calorimetric and dilatometric analyses. Hot strain resistance of the austenite is determined essentially by the steel composition, while the final structure and mechanical properties of hot-deformed austenite are determine mainly by hot deformation conditions. The higher the nitrogen content and C/N ratio, the higher hot strain resistance was and earlier the softening processes start, especially recrystallization process. The nitrogen microalloying of low-alloyed structural steels changes kinetics of the martensite tempering. Application of the high temperature thermomechanical treatment or combined thermomechanical strengthening with following tempering under load allows the use of these steels in a high-strength state after low-temperature tempering.

The influence of nitrogen and the joint action of carbon and nitrogen on diagrams of the hot and warm deformation and strain aging of austenitic steels is studied.

The effects of slab reheat temperature and soaking time are studied to characterize austenite grain growth, microstructure homogeneity and dissolution of precipitates in linepipe X80 grade steel. It is shown that the uniformity of austenite microstructure strongly depends on the slab reheat temperature and soaking time. With increasing reheat temperature an abnormal growth of individual grains is observed that stems from gradual dissolution of microalloy carbonitrides. As the result, individual grain boundaries become unpinned and mobile thus "nucleating" secondary recrystallization. The highest reheat temperature at which the dissolution kinetics of precipitates is still slow enough to prevent the onset of secondary recrystallization within long soaking times is 1160°C. The as reheated austenite microstructure and the character of austenite grain size distribution are inherited throughout the entire roughing rolling sequence and even further downstream to the finishing rolling entry.

The effects of slab reheat temperature and soaking time are studied to characterize austenite grain growth, microstructure homogeneity and dissolution of precipitates in linepipe X80 grade steel. It is shown that the uniformity of austenite microstructure strongly depends on the slab reheat temperature and soaking time. With increasing reheat temperature an abnormal growth of individual grains is observed that stems from gradual dissolution of microalloy carbonitrides. As the result, individual grain boundaries become unpinned and mobile thus "nucleating" secondary recrystallization. The highest reheat temperature at which the dissolution kinetics of precipitates is still slow enough to prevent the onset of secondary recrystallization within long soaking times is 1160°C. The as reheated austenite microstructure and the character of austenite grain size distribution are inherited throughout the entire roughing rolling sequence and even further downstream to the finishing rolling entry. The effects of reheat soaking time on shear fracture area and impact toughness are also described.

The effect of thermomechanical treatment with different hot deformation on the structure and mechanical properties of structural steels (20 – 50)KhNMAF, microalloyed with nitrogen, is studied and analyzed. On the basis of analyzing tensile test results, hardness measurement, and a study of steel grain structure temperature regimes and stress–strain state, schemes are selected making it possible to use the test steels as high-strength materials, especially for components where high strength and ductility are important in a specific direction.

The effect of thermomechanical treatment on the structure and mechanical properties of the constructional steels (35 – 50)KhNMAF micro-alloyed with nitrogen is studied. Tensile and impact tests are conducted, the HV hardness is measured, and the structure of the steel is investigated by means of light microscopy and X-diffraction analysis. The regimes of thermal and thermomechanical treatment that make it possible to use this type of steel as a high-strength steel are determined.