In this paper, we present a thermokinetic diagram of the decomposition of supercooled austenite of steel R350LHT built based on the results of dilatometric, metallographic, and durometric studies of ...the decomposition of supercooled austenite of steel R350LHT upon continuous cooling and under isothermal conditions. In the study of the decomposition of supercooled austenite during continuous cooling, cooling at a rate of 0.1 and 1°C/s was found to cause the decomposition of austenite in steel R350LHT according to the pearlite mechanism. After cooling at a lower rate, the pearlite structure is coarser and has a lower (289 HV) hardness. This is due to a higher temperature range of transformation, in which diffusion processes associated with the transformation of austenite into pearlite occur more actively. In the rate range from 5 to 10°C/s, the austenite decomposition undergoes according to the pearlite and martensite mechanism, which leads to the formation of a pearlite-martensite structure. When the austenite of the studied steel is cooled at a rate of 30 and 100°C/s, the transformation occurs according to the martensitic mechanism, and a martensitic structure with high hardness is formed. At an increase in the cooling rate of steel R350LHT, an increase in hardness from 289 (at 0.1°C/s) to 864–896 HV (at 100 and 30°C/s, respectively) is observed. The performed studies allow narrowing the boundaries of the search for the optimal parameters of the welding and heat treatment modes of the studied rail steel. To obtain the required structures and physical and mechanical properties (the austenite of R350LHT steel undergoes decomposition according to the pearlite mechanism), cooling should be carried out at a rate of no more than 1°C/s.
Overview of the CMD-3 recent results Ryzhenenkov, A E; Akhmetshin, R R; Amirkhanov, A N ...
Journal of physics. Conference series,
04/2020, Volume:
1526, Issue:
1
Journal Article
Peer reviewed
Open access
The CMD-3 detector started data taking at the electron-positron collider VEPP-2000 in December 2010 with a goal to collect about 1 fb−1. The collected data sample corresponds to an integrated ...luminosity of 200 pb−1 in the center-of-mass energy range from 0.32 up to 2 GeV. This paper reports recent results on the hadronic cross sections measurements with the CMD-3 detector.
The structural-phase state, dislocation substructure and fracture surface of the low-carbon Sv-08GA steel coating deposited by arc spraying under a flux made of the slag of silicomanganese production ...with a low manganese oxide content are studied using the methods of modern physical metallurgy. The deposited metal is shown to have a banded structure. The elemental compositions of metal bands and interband regions are found to be substantially different. The coating is shown to fail preferentially according to a ductile mechanism. The scalar and excess dislocation densities are estimated quantitatively, and the contributions of a dislocation forest and internal long-range stress fields are also estimated. The maximum hardening due to the dislocation substructure of the material is shown to be in pearlite grains.
During contact flash welding of rails, the metal in the area of thermal impact is heated and continuously cooled. Accelerated heating and subsequent intensive cooling during pulse flash welding lead ...to the formation of quenching structures, which subsequently leads to cracking and to brittle destruction upon operation of rail weld joint. This work studies capabilities of contact heating after welding in order to eliminate formation of quenching structures in metal weld joint of R350LHT rail steel. Thermal cycles during welding and subsequent contact heating have been recorded. The regularity of structure formation of metal weld joint (including the area of thermal impact) was determined during pulse contact heating for R350LHT rail steel. It is demonstrated that the contact pulse heating allows to prevent the formation of quenching structures and decelerates cooling of weld joint. In the case of non-optimum modes, the contact pulse heating can result in reverse effect. It has been determined that upon significant contribution of heat by contact heating, the metal cooling rate exceeds critical value and the transformation runs according to diffusion free mechanism with formation of coarse grain martensite structure. The use of thermal kinetic and isothermal diagrams of austenite decomposition with known thermal welding cycles allows to restrict significantly the search ranges of optimum modes of electric welding of railroad rails and subsequent contact heating. The use of optimum modes of contact heating allows to obtain minimum length of areas of thermal impact without the formation of quenching structures in weld joint of railroad rails.
Isothermal diagram of decomposition of overcooled austenite of R350LHT steel has been plotted on the basis of dilatometric, metallographic, and durometric studies. While comparing thermal kinetic and ...isothermal diagrams of decomposition of overcooled austenite of R350LHT steel, it has been established that the thermal kinetic diagram plotted during continuous cooling is displaced downwards and rightwards in comparison with the isothermal diagram. This result completely agrees with the known regularities. During the studies, the critical points of R350LHT steel have been determined: Ac
1
= 711°C; Ms = 196°C. Using the isothermal diagram of decomposition of overcooled austenite of R350LHT steel, the temperature of minimum resistance of overcooled austenite has been determined equaling to 500°C. Under the isothermal conditions, the pearlitic structures are formed in the temperature range from 700 to 600°C. A mixture of pearlitic and bainitic structures is formed at 550°C. In the range from 500 to 250°C, the bainitic structures are formed: at 500–400°C, the upper bainite is formed; at 350°C, the mixture of upper and lower bainite is formed; at 300–250°C, the lower bainite is formed. The increase in the hardness of transformation products upon decrease in the holding temperature from 246 HV (at 700°C) to 689 HV (at 250°C) is observed nearly in the overall studied temperature range of isothermal decomposition of overcooled austenite. However, at 500°C, the hardness slightly drops, which could be attributed to the occurrence of residual austenite in the course of bainitic transformation.
The process e+e−→K+K− has been studied using 1.7×106 events from a data sample corresponding to an integrated luminosity of 5.7 pb−1 collected with the CMD-3 detector in the center-of-mass energy ...range 1010–1060 MeV. The cross section is measured with about 2% systematic uncertainty and is used to calculate the contribution to the anomalous magnetic moment of the muon aμK+K−=(19.33±0.40)×10−10, and to obtain the ϕ(1020) meson parameters. We consider the relationship between the e+e−→K+K− and e+e−→KS0KL0 cross sections and compare it to the theoretical prediction.
The structure and composition of the arc sprayed coatings formed using a flux cored Fe–C–Si–Mn–Cr–Ni–Mo wire are studied. A carbon-fluorine-containing additive, namely, the gas purification dust of ...aluminum production ((wt %) 21–46 Al
2
O
3
, 18–27 F, 8–15 Na
2
O, 0.4–6 K
2
O, 0.7–2.3 CaO, 0.5–2.5 SiO
2
, 2.1–3.3 Fe
2
O
3
, 12.5–30.2 C
tot
, 0.07–0.9 MnO, 0.06–0.9 MgO, 0.09–0.19 S, 0.10–0.18 P) is introduced into the charge of the flux cored wire instead of amorphous carbon. The problems of the influence of the carbon–fluorine additive on the weldability and the contamination of the deposited metal with oxide nonmetallic inclusions are considered; the microstructure and the contamination of the deposited metal are studied. The microstructure of the deposited layer formed using a flux cored electrode of the Fe–C–Si–Mn–Cr–Ni–Mo system consists of acicular and lath martensite arranged in the former austenite grains, along the boundaries of which ferrite layers precipitate. Silicates (undeformable) and oxides (point) are found to exist in the deposited metal. According to the results of quantitative analysis of the chemical composition of the nonmetallic inclusions obtained using a Teskan Mira 3 scanning electron microscope, the nonmetallic inclusions in the deposited metal are at most 10 μm in size; their globular shape positively influence the wear resistance of the deposited layer. The chemic composition of the nonmetallic inclusions shows that they mainly consist of silicon, aluminum, and manganese oxides; there are also traces of sulfur, calcium, and magnesium. The metallic matrix contains iron (dominant amount), chromium, manganese, and silicon; the molybdenum content is substantially lower.
The characteristics of metallurgical production and metal products of Kuzbass enterprises, their heat and energy supply, environmental safety, training of specialist for their needs, directions of ...their innovative development are considered. It was confirmed that the metallurgy of Kuzbass forms the basis of Siberian metallurgical cluster in Russia and includes 7 enterprises, of which ZSMK is the undisputed leader. Metallurgy takes the 2nd place with the volume of 26.6% in the structure of the industrial sector of Kuzbass.
During the manufacturing of continuous welded rail track, the problem of the local hardened points in the welded joint during rail joint welding is resolved by using local heat treatment of the ...welded joint. As a result, the quenching structure formation is excluded. However, the appearance of new heat-affected zones with reduced hardness is possible. During operation, such rails are characterized by increased tread surface wear in these areas and rail flattening at the welded joint, which is the main reason for retiring the rails from service earlier than the guaranteed service life. A new technology based on the dependence of the structural component dispersion (primarily perlite and carbide particles formed in the process of rail butt welding) is proposed for the steel composition and cooling conditions. The cooling rate has a decisive influence on the dispersion degree of the ferrite-cementite structure formed during the austenite decomposition. During the welding rail process, the granular perlite formation is possible in a butt weld in areas with a temperature ranging within points
Ac
1
and
Ac
m
. To determine these critical temperatures, thermodynamic calculations were performed using the Thermo–Calc® software (TCFE database) allowing the chemical composition of the samples obtained by spectrometry. The iron–carbon state diagrams for rail steel 76KhSF with the minimum and maximum alloying element content according to GOST R 51685–2013 are modeled. To obtain the minimum number of sections with reduced hardness, it is possible to weld rails using shot discontinuous flash welding. In order to eliminate the formation of defective areas with a quenching structure, it is possible to control the cooling of the welded joint by contact heating. Temperature distribution measurement during welding according to given modes and controlled cooling confirms the theoretical conclusions.
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