Papers by Keyword: Continuous Cooling

Abstract: The present study has been undertaken to compare the microstructure of the plain carbon steel, containing 0.65 carbon, which was formed during varying isothermal and continuous cooling conditions following austenitisation at the same temperature and soaking time. After austenitisation, one set of samples was subjected to isothermal treatment which was carried out at a temperature varying in the range of 650–400 °C, and the other one was continuously cooled to ambient temperature using different cooling rates ranging from 500 to 1.4 °Cs^–1. The metallographic examination of the samples was fulfilled using light and TEM microscopy. Additionally, Vickers hardness measurements were performed.

Abstract: Physical simulation of steel Mn3Ni1CrMo continuous cooling with different speeds from austenitic state was performed using GLEEBLE 3500 complex. The phase transformations are analyzed and the effect of the cooling rate on the structure and hardness is investigated. A continuous cooling transformation diagram of the undercooled austenite decomposition is constructed. It was concluded that it is possible to reduce the hardness of the hot-rolled billet by reducing the cooling rate compared to the existing in the processing at the STELMOR line of PJSC “MMK”, and this will eliminate the heat treatment of welding wire on the hardware processing.

Abstract: To understand the effect of vanadium on the austenite decomposition of a 0.7 %C steel used in railway wheels the Continuous Cooling Transformation (CCT) diagrams were obtained and the microstructures analyzed with optical, SEM, TEM and XRD techniques. Vanadium refined the austenitic grain (12 and 6 μm for 7C and 7V, respectively), what can be explain by the presence of fine (10 nm in diameter) V₄C₃ precipitates, which restricts the austenitic grain growth. In addition, vanadium, in solid solution, reduced the pearlite interlamelar spacing (0.13 and 0.11 μm for 7C and 7V, respectively) by depressing the initial temperature pearlite formation (644 and 639 °C for 7C and 7V, respectively). He increased the ferrite volume fraction from 1 to 3 % at cooling rate of 1 oC/s, due the fact that vanadium is a ferrite stabilizer. Vanadium addition did not affect the initial temperature for martensite formation, but increased the hardenability with martensite formation at slower cooling rates (10 and 5 oC/s for 7C and 7V, respectively). For higher cooling rates (20 to 100 oC/s), the austenite transformation to martensite at room temperature was incomplete and all steels presented martensite and retained austenite, which volumetric fraction was near the same for both steels varying from 20 to 40 %.

Abstract: The microstructure and magnetic properties of Fe-Co-Cr alloys with 15 wt % Co were investigated using transmission electron microscopy and magnetic measurements. The secondary decomposition within both the α₂-phase matrix and the α₁-phase particles was observed for magnets subjected thermo-magnetic treatment and subsequent stepped aging or continuous-cooling treatments. During high-temperature treatments (630-600 ^оC), when the α₂ phase is dominant (the volume fraction is more than 50%), the secondary decomposition of this phase takes place (α₂ → α_1' + α_2'). The deterioration of magnetic insulation of α₁-phase particles results in the decrease in the coercive force of alloys. Below 600 ^оC, when the α₁ phase is dominant (the volume fraction is more than 50%), the splitting of elongated α₁-phase particles occurs. When the temperature of stepped-aging decreases in high steps, the secondary decomposition (α₁ → α_1' + α_2') leads to the splitting of initial α₁-phase particles into fine slightly elongated particles and the decrease in the coercive force.

Abstract: The continuous cooling phase transformation behavior of niobium microalloyed steel was studied by Thermecmastor-Z thermomechanical simulator; the continuous cooling transformation curves (CCT) were established. The change of microstructure under different cooling rates was observed, and the influence of deformation in austenite non-recrystallization region on transformation was discussed. Based on these work, it was possible to know that the phase transformation is retarded and the ferritic grain is refined dramatically as the cooling rate increasing. The deformation in austenite non-recrystallization region caused deformation stored-energy, which improved the grain refinement of transformation to some extent, but not significant.

Abstract: This paper considers for transformation behavior of Nb microalloyed steels, experiments had demonstrated the effect of Nb was obvious: lowered start temperature of ferrite transformation remarkably and forming more refined ferrite grain size. In this study, computer simulation of Nb-containing steels transformation during continuous cooling was carried out by adopting a classical nucleation and growth theory, the model was derived based on the theories and the experimental results, and the calculated start temperatures of ferrite transformation were compared with the results of experimental.

Abstract: The first part of this document demonstrates the creation and use of continuous cooling (CC) diagrams, which are built up from Temperature-time T-t elements. The second part of the document shows the possibility of the creation of virtual CC diagrams by numerical approximated base transformation diagrams, based on measured data.

Abstract: The dilatation curves of continuous cooling transformation at different cooling rates were determined for U75V rail steel by THERMECMASTOR-Z thermal simulator, and continuous cooling transformation curve was obtained. The influence of cooling rate on microstructure and hardness was studied. The softening behavior after isothermal deformation in the austenite region 850-1000°C but before the second pass was also studied by double-pass compression tests. The results show that the product of austenite decomposition was pearlite when the cooling rate was lower than 10°C. Troostite and martensite were gained at the cooling rate of 10°C•s-1. Only martensite was obtained when the cooling rate was in the range of 10-50°C•s-1. The hardness of the steel increased with the increase of cooling rate. Under the condition of 30% deformation and 3s-1 deformation rate, the relaxation time for completing recrystallization was shorter than 100s when the deformation temperature was higher than 1000°C. When the deformation temperature was lower than 880°C, full recrystallization was difficult to achieve even if the relaxation time was extended.

Abstract: The properties and precipitation behavior of Cu-bearing steels have been investigated. The optical microscope and transition electron microscope were employed to study the influence of interrupted cooling and quenching temperature on the precipitation behavior. Also, the properties of samples with different quench processes were tested. The results show that when the steel is interruptedly cooled and quenched from 650-700°C, with the quenching temperature increasing the volume fraction of martensite becomes larger and the hardness becomes higher. When the microstructure is ferrite the second-phase precipitates occurs and they are proved copper-rich particles. However there are no obvious precipitates in martensite. The copper-rich second phase forms by the way of inter-phase precipitation.

Abstract: The precipitation behavior of several Cu-bearing steels with various copper contents during continuous cooling has been studied. The optical microscope and HRTEM were employed to study the influence of cooling rate on the precipitation process. Also, the hardness of samples with different processes is tested. The results show that when the steels was cooled at a cooling rate between 0.1-1°C/s with the cooling rate increasing the second phase precipitates become finer but the precipitates become denser. When the cooling rate is 1°C /s the density of the second phase precipitates are the largest. When the cooling rate is quicker than 1°C /s as the cooling rate increase the precipitates become finer and fewer. The hardness tests also show that the sample will get the highest hardness. When the samples are cooled at a rate larger than 5°C /s， there is few precipitates in samples. The copper-rich second phase form by Inter-phase precipitation, and the copper-rich phase i.e. G.P zone is the main cause to strengthen the alloy. As the copper content varies from 1.5wt% to 2.5wt% the highest hardness could be obtain when the samples is cooled at a rate of 1°C /s and the density of the precipitates is the largest