• MATERIALS

    Steels with bainite structure for railway wheels

    Machines. Technologies. Materials., Vol. 14 (2020), Issue 5, pg(s) 215-218

    Some wheel steels inclined for the self-quenching on bainite structure were produced and investigated after hot deformation and heat strengthening. Steels contained 0,12…0,45% of carbon, and also Si, Mn, Mo, Cr, Ni, V, Ti, Al. Steels with bainite structure after hot deformation and tempering were investigated. It was shown the possibility of the railway wheels production with bainite structure and hardness of 400HB without heat strengthening treatment. The results of investigation shown the possibility of railway wheels production with bainite structure, hardness of 400 HB and high complex of the mechanical and operating properties without heat strengthening treatment. These tasks solved owning to application of new wheel steels and up-to-date technology.

  • Transformation of non-metallic inclusions “eutectics” in steels under laser action

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 5 (2019), Issue 4, pg(s) 130-134

    Melting and crystallization of heterophase non-metallic inclusions ―eutectics‖ was investigated. Mechanism of melting of the eutectic inclusions and inclusion-matrix boundaries under contact laser melting with steel matrix in the conditions of abnormal mass transfer connecting with formation of zones with high dislocation density and also with electron and electro-magnetic interaction between inclusion and steel matrix was proposed. That allows to create the possibilities for the influence on the inclusion-matrix boundaries and also on the chemical and phase composition of surface layer of non-metallic inclusions. Peculiarities of structure of non-metallic inclusions after speed crystallization were investigated. It was shown that under laser action the initial composite colonial structure of inclusions transits into abnormal eutectic structure. Also it was shown that under laser action the initial structure of inclusion-steel matrix boundaries transits into unstable equilibrium high-energy condition that cause development of the dissipation processes connecting with aspiration of system inclusion-matrix to the state with minimum of the free energy. In the result of the system eutectic inclusion-matrix transits to the state of unstable equilibrium which determines structure and properties of laser-quenched interphase boundary. Processes of melting, fusion and dissolution of non-metallic inclusions ―eutectics‖ and also of the melting of steel matrix play the great role in transformation of interphase inclusion-matrix boundaries under laser action.

  • Computer modeling of influence of previous deformation degree and strain rate on carbonitrides precipitation kinetics in low-carbon micro-alloyed steel

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 5 (2019), Issue 3, pg(s) 81-83

    Using computer modelling with originally developed semi empirical physical grounded models a study was carried out to investigate influence of previous hot deformation on carbonitrides formation from austenite in low-carbon micro-alloyed steel. Studied in the article is an influence of degree and rate of the deformation on processes of nucleation and growth of Nb and Ti carbonitride particles. The model helps to predict not only process of changing in number and average size of the particles but also to estimate their final size distribution. One of additional peculiarities of the developed model is its ability to predict composition of the cabinetries formed in certain conditions. The model takes into account process of recrystallization and returning, which affect carbonitrides precipitation and are influenced by it. Acceleration was shown of both nucleation and growth rates of the particles due to increasing of deformation degree and strain rate. Another result is that previous deformation significantly affects size distribution function of the particles precipitated with rather lesser effect on their average size. Kinetic curves and final size distribution plots are given.

  • Modelling and finite element analysis of tensile testing for the coated specimens

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 4 (2018), Issue 4, pg(s) 122-125

    In this study, the stress state of metal coating on a steel substrate under tensile straining was investigated by with finite element modelling with the aim of better understanding the mechanism of delamination for the coating. The investigations showed cracking and delamination of the coating by the application of uniaxial tensile strain to the substrate. Due to interfacial stress crack appeared in the coating-substrate interface. The stress measurements in coated substrate, using FEA, indicated interfacial shear and peeling stresses at the interface near the edges of the coating under tensile load. When tensile stress is applied externally on the coated substrate, the coating exhibits multiple cracking perpendiculars to the tensile direction, and then interfacial debonding occurs. A good agreement is found between the modelling approach and the corresponding experimental tensile tests of the coated specimens. The effect of coating thickness on the evolution of the stress distribution was also studied. The cracking and delamination of the coatings with a thickness ranging from 90 to 160 m was studied by tensile test experiments. The estimation of the stress distribution and concentration at the interface during these experiments allows the failure stress of the coating in the interface coating–substrate to be evaluated.

  • Effect of thermal-cyclic deformation and heat treatment on the structure and electrical properties of Ст3

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 4 (2018), Issue 3, pg(s) 102-104

    The results of the effect of preliminary thermal-cyclic deformation on the microstructure of hot-rolled low-carbon steel Ст3пс are presented. It is shown that the regime of thermal-cyclic rolling leads to a decrease in the average grain size of ferrite from 8 to 6 microns in comparison with the structure of steel after industrial production. There is a decrease in the size of pearlite colonies and their volume fraction in the structure of steel after using thermal-cyclic deformation. The results of the effect of heat treatment: normalization and tempering on the electrical resistivity of the hot-rolled carbon steel sheet Ст3пс produced using thermal-cyclic mode of deformation processing (DTCT). DTCT preliminary thermal-cyclic was rolled (5 cycles at a reduction of 10-15 % in each cycle and cooled to a temperature below the Ar1). And normalizing annealing was carried out in the range from 100 to 900 °C increments to 100 °C for 1 hour. The possibility to reduce the magnitude of the specific electrical resistance of the hot-rolled steel manufactured using DTCT mode through the use of subsequent normalizing at 700 °C on average 10 %, and by annealing – no more than 5 %. A further increase in the time of normalization at 700 °C to 3, 5 and 10 hours has no significant effect on the value of the electrical resistance of the steel subjected DTCT. However, the downward trend in resistivity is maintained. Overall reduction of electrical resistivity of the hot-rolled steel Ст3пс by using
    mode DTCT and subsequent normalizing at 700 °C for 1 hour is more than 12 %.

  • Heat processing of low alloyed steels with cooling in an air flux of varying velocity

    Machines. Technologies. Materials., Vol. 12 (2018), Issue 10, pg(s) 402-406

    Using an originally developed laboratory controlled air cooling automatic device regimes of controlled fasted normalization of low and middle carbon steel were studied. Significant improving of the steel structure was shown. The proposed technologies of controlled air cooling could be useful for small metal products of middle carbon steels heat treatment as an advanced normalization process.

  • TRANSFORMATION OF HETEROPHASE NON-METALLIC INCLUSIONS “PHASES ARE BESIDE” IN STEELS UNDER LASER ACTION

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 4 (2018), Issue 1, pg(s) 7-11

    Melting and crystallization of heterophase non-metallic inclusions “phases are beside” was investigated. It was shown that under laser action the initial structure of inclusion-steel matrix boundaries transits into unstable equilibrium high-energy condition that cause development of the dissipation processes connecting with aspiration of system inclusion-matrix to the state with minimum of the free energy. In the result of the system heterophase inclusion-matrix transits to the state of unstable equilibrium which determines structure and properties of laser-quenched interphase boundary. Processes of melting, fusion and dissolution of non-metallic inclusions “phases are beside” and also of the melting of steel matrix play the great role in transformation of interphase inclusion-matrix boundaries under laser action.

  • MATERIALS

    APPLICATION OF NONLINEAR CONTROLLED COOLING REGIMES FOR STRUCTURE FORMATION MANAGEMENT IN EUTECTOID STEEL

    Machines. Technologies. Materials., Vol. 12 (2018), Issue 2, pg(s) 80-81

    Using computer modelling with originally developed semi empirical physical grounded models study of structure formation when austenite transformation during cooling by certain regime in eutectoid steel was carried out. The model allowed us to predict final structure. Cooling curves leading to fine pearlite (almost without bainite) and lower bainite (with a small part of fine pearlite) structures were find out. The results obtained could be useful for high carbon ordinary instrumental and constructional steels with higher manganese production and processing (rails, cord and rope wire, springs, low stressed instruments). Realization of the fine pearlite obtaining regime needs equipment that could provide cooling rates from 0.04 deg./sec. to 6.6 deg./sec. with average value of 1.1 deg./sec.. For bainitic structure obtaining the range of cooling rates provided shoud be from 0.14 deg./sec. to 14.0 deg./sec. with average value of 2.2 deg./sec. The cooling intensivity must have an ability to arbitrary and controlled changing during process.

  • MATERIALS

    TRANSFORMATION OF HETEROPHASE NON-METALLIC INCLUSIONS “HIGHMELTING PHASE SURROUNDING WITH LOW-MELTING COVER” IN STEELS UNDER LASER ACTION

    Machines. Technologies. Materials., Vol. 11 (2017), Issue 6, pg(s) 315-319

    Melting and crystallization of heterophase non-metallic inclusions “high-melting phase surrounding with low-melting cover” was investigated. It was shown that under laser action the initial structure of inclusion-steel matrix boundaries transits into unstable equilibrium high-energy condition that cause development of the dissipation processes connecting with aspiration of system inclusionmatrix to the state with minimum of free energy. In the result of the system heterophase inclusion-matrix transits to the state of unstable equilibrium which determines structure and properties of laser-quenched interphase boundary. Processes of melting, fusion and dissolution of non-metallic inclusions “high-melting phase surrounding with low-melting cover” and also of the melting of steel matrix play the great role in transformation of interphase inclusion-matrix boundaries under laser action.

  • MATERIALS

    TRANSFORMATION OF EUTECTIC NON-METALLIC INCLUSIONS IN STEELS UNDER LASER ACTION

    Machines. Technologies. Materials., Vol. 10 (2016), Issue 11, pg(s) 60-62

    Melting and crystallization of eutectic non-metallic inclusions was investigated. It was shown that under laser action the initial structure of eutectic inclusion-steel matrix boundaries transits into unstable equilibrium high-energy condition that cause development of the dissipation processes connecting with aspiration of system inclusion-matrix to the state with minimum of free energy. In the result of the system eutectic inclusion-matrix transits to the state of unstable equilibrium which determines structure and properties of laser-quenched interphase boundary. Processes of melting, fusion and dissolution of eutectic non-metallic inclusions and also of the melting of steel matrix play the great role in transformation of inclusion-matrix boundaries under laser action.

  • TECHNOLOGIES

    WELDABILITY ASSESMENT OF STEEL FOR LINE PIPES

    Machines. Technologies. Materials., Vol. 10 (2016), Issue 11, pg(s) 40-43

    The steel for the production of welded pipes must possess good weldability to achieve high efficiency and effectiveness of the production process in production lines (in line) and ground, during welding of pipes in long distance pipelines and in lower temperature conditions. The main focu of this research was on weldability assessment of API Grade X52 steel at low temperature (0°C), which is used for the production of welded pipes, respectively pipelines. Carbon equivalent (CE), mechanical testing and metallographic analysis of the welded joint were conducted in order to assess the weldability. The results of mechanical tests and metallographic analysis show that steel API Grade X52, at low temperature (0°C) has excellent weldability, so the pipes produced can be welded in long distance pipelines, easy and unhindered, thereby ensuring high production efficiency and effectiveness.

  • IN-SITU STRESS-STRAIN TESTING OF STEELS IN CO2-CONTAINING SALINE SOLUTIONS

    Machines. Technologies. Materials., Vol. 8 (2014), Issue 12, pg(s) 23-25

    In CCS environment (carbon capture and storage) pipes and in geothermal power plants the materials used in pumps are loaded cyclically and exposed constantly to the highly corrosive hot thermal water. The lifetime reduction of AISI630 (X5CrNiCuNb16-4, 1.4542) is demonstrated in in-situ-laboratory experiments (T=60 °C, geothermal brine: Stuttgart Aquifer flow rate: 9 l/h, CO2). S-N plots, micrographic-, phase-, fractographic- and surface analysis were applied to obtain sustainable information on the corrosion fatigue behavior.