The dilatometer study of the austenite transformations in steels with different chemical composition was conducted. The studied steels were classified as the air hardened steels of different alloying ...systems (Cr-Ni-Mo, Cr-Mn-Si-Mo and Cr-Mo-V) designed for the mining applications (rock drilling equipment, drilling instrument). The microstructure of the steels was investigated after continuous cooling at the rates of 0.1...30 °C/s from the austenitization temperature down to the ambient temperature. The CCT diagrams of the studied steels were plotted showing that the alloying with different set of elements can provide the desired hardenability and microstructure.
The neural network model of Van der Wolk et al.
describes the effect of composition on the phase regions of the continuous cooling transformation (CCT) diagram, yet does not consider the fractions ...of microstructural components and the hardness data that are often quoted in CCT diagrams. In the present paper, the construction of two more neural network models, one for the fractions of ferrite, pearlite, bainite and martensite in the microstructure, and one for the hardness after cooling, using the data of 338 and 412 diagrams, respectively. The accuracy of each model was found to be similar to the expected experimental error; moreover, the models were found to be mutually consistent, although they have been constructed independently. Furthermore, the trends in these properties for alloying elements can be quantified with the models, and are largely in line with metallurgical expectations.
A neural network model for the calculation of the phase regions of the continuous cooling transformation (CCT) diagram of engineering steels has been developed. The model is based on experimental CCT ...diagrams of 459 low-alloy steels, and calculates the CCT diagram as a function of composition and austenitisation temperature. In considering the composition, 9 alloying elements are taken into account. The model reproduces the original diagrams rather accurately, with deviations that are not larger than the average experimental inaccuracy of the experimental diagrams. Therefore, it can be considered an adequate alternative to the experimental determination of the CCT diagram of a certain steel within the composition range used. The effects of alloying elements can be quantified, either individually or in combination, with the model. Nonlinear composition dependencies are observed.
To optimize reverse transformation treatment, which is effective in preventing hot rolling cracking in the CC-HCR (Continuous Casting - Hot Charge Rolling) process, three-dimensional ...metallo-thermo-mechanical analyses were performed. The metallo-thermo-mechanics and a CCT (Continuous Cooling Transformation) diagram estimation method using JMatPro were used to obtain the required cooling time for reverse transformation in immersion cooling with water jet and to elucidate the effects of nonuniform cooling and γ grain size on thermal deformation and stress generation behaviors during cooling and the mechanisms of these events.These analyses clarified the following. When diffusion-controlled transformation occurs during cooling, the required cooling time increases as Dγ (Diameter of γ grain) increases, and becomes substantially constant when only martensitic transformation occurs. In addition, the difference of Dγ causes a difference in the type of transformation that occurs during cooling and the temperature range where transformation occurs during cooling, and these differences produce differences in the amount of transformation expansion, which greatly affects the bloom deformation behavior during cooling. Furthermore, there is a difference in the level of the maximum generated stress during cooling depending on whether the transformation that occurs near the bloom surface layer during cooling is diffusion-controlled transformation or martensitic transformation. In addition, this difference in transformation behavior also causes a difference in the mechanism of maximum stress generation.
Using standard continuous cooling transform (CCT) diagrams for finding hardness of surfaces obtained by laser or small-size induction hardening is discussed. Their misuse may lead to differences ...between the values obtained from the model and experimental data because unlike hardening of large surfaces, the produced heat is mostly transferred away not by convection to the environment, but mainly by conduction to the interior of the metal material at a very high rate (at the level of many hundred Kelvins per second). The paper explains the details and offers a methodology of suppressing errors based on a combination of theoretical and experimental approaches. The methodology is illustrated with an example.
To optimize reverse transformation treatment, which is effective in preventing hot rolling cracking in the CC-HCR (Continuous Casting - Hot Charge Rolling) process, three-dimensional ...metallo-thermo-mechanical analyses were performed. The metallo-thermo-mechanics and a CCT (Continuous Cooling Transformation) diagram estimation method using JMatPro were used to obtain the required cooling time for reverse transformation in immersion cooling with water jet and to elucidate the effects of nonuniform cooling and γ grain size on thermal deformation and stress generation behaviors during cooling and the mechanisms of these events.These analyses clarified the following. When diffusion-controlled transformation occurs during cooling, the required cooling time increases as Dγ (Diameter of γ grain) increases, and becomes substantially constant when only martensitic transformation occurs. In addition, the difference of Dγ causes a difference in the type of transformation that occurs during cooling and the temperature range where transformation occurs during cooling, and these differences produce differences in the amount of transformation expansion, which greatly affects the bloom deformation behavior during cooling. Furthermore, there is a difference in the level of the maximum generated stress during cooling depending on whether the transformation that occurs near the bloom surface layer during cooling is diffusion-controlled transformation or martensitic transformation. In addition, this difference in transformation behavior also causes a difference in the mechanism of maximum stress generation.
•Obtaining of real continuous cooling transformation diagrams for β-Ti alloys.•Correlation between cooling rate, microhardness, elastic modulus and phases.•Experimental continuous cooling ...transformation diagrams through thermal analyzes.•The higher the cooling rate imposed for β-Ti alloys the lower elastic modulus.
Considering an increase in the interaction time between a patient and a metallic implant, new problems can emerge, such as stress shielding and fracture due to mechanical failure. Thus, metallic biomaterials that are used as implants need to be improved decreasing their elastic modulus as the mechanical biocompatibility between a bone and an implant can be improved and prevent the stress shielding phenomena. Therefore, β Ti alloys have gained ground over the last decades as both the β phase and the martensitic α″ phase can lead to a decrease in the elastic modulus. This research aimed to obtain experimental continuous cooling transformation (CCT) diagrams for metastable β Ti-12Mo-6Zr-2Fe (TMZF) and stable β Ti-40Nb (wt. %) alloys through dilatometry tests and differential scanning calorimetry (DSC) analysis. The microstructure characterization by optical (OM) and scanning electron microscopy (SEM), the elastic modulus, E (GPa) and the Vickers microhardness (HV) were analyzed under varied cooling rates from the β field, as well as rapidly solidified by copper mold casting. The results showed that the higher the cooling rate imposed, the lower the Vickers microhardness and elastic modulus values for both alloys, which were 56 GPa and 144 HV for Ti-40Nb and 74 GPa and 333 HV for the best condition (rapid solidified).
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•Intercritical continuous cooling transformation diagram for multiphase steels.•Intercritical austenite transforms into proeutectoid ferrite, bainite and martensite.•Multiphase steels ...obtained in a wide range of cooling rates (1 °C/s to 100 °C/s).•Temperatures for martensite decrease with the decrease in cooling rate.
This paper deals with the construction of an experimental intercritical continuous cooling transformation (CCT) diagram for the manufacture of low-alloyed low-carbon multiphase steels. An in-situ dilatometric study was conducted both to determine the critical transformation temperatures and to follow the evolution of austenite on continuous heating. A quantitative analysis of the transformed austenite was conducted from the dilation curves using the lever rule method to further investigate the intercritical austenite decomposition for different cooling rates. Time and temperatures required for phase transformations were determined from the first derivative of the dilation curves, obtained as a function of cooling rate. Critical points were then plotted to construct the corresponding CCT diagram. Results show that the experimental CCT diagram can be used to design thermal cycles for the development of multiphase steels.
The research was mainly focused on the phase transformation of Ti-42Al-5Mn (at%) alloy produced by vacuum induction melting (VIM) and vacuum arc remelting (VAR) followed by wrought process. The phase ...transformation kinetics of the alloy during continuous cooling under the cooling rates of 0.1 °C/s, 0.5 °C/s, 2 °C/s, 10 °C/s, 50 °C/s, and 200 °C/s were identified by the Gleeble-3800 system, which is finally used to construct a schematic continuous cooling transformation (CCT) diagram of this alloy. The related phase composition, microstructure and property of the alloy were studied using X-ray diffraction (XRD), electron probe micro analyzer (EPMA), transmission electron microscope (TEM) and Vickers hardness (HV). It shows that six kinds of phase transformation are existed during continuous cooling from 1300 °C with the cooling rates of 0.1 °C/s, 0.5 °C/s, 2 °C/s, 10 °C/s, 50 °C/s, 200 °C/s and WQ, including β→α2′, β→α, β→γ, β→βo/α→α2, α2→α2/γ and α2/γ→βo,sec. It reveals that partial transformations would be inhibited when the cooling rate is relatively high. The martensitic structures (α2′) obtained by β→α2′ were formed under the WQ condition after holding at 1300 °C for 5min, and it will be completely restrained below the cooling rate of WQ. For the β→γ, it is restrained if the cooling rates are higher than 50 °C/s. The α2→α2/γ could be also suppressed when cooling with 200 °C/s, and the γ lath within the supersaturated α2-grains would be formed at lower cooling rate below 50 °C/s. For 0.5 °C/s and 0.1 °C/s, a small amount of dotted βo (βo,sec) phases can be formed in the lamellar interfaces, which is proved the reaction products of α2/γ→βo,sec. Furthermore, the effect of cooling rates on the microstructure, including interlamellar spacing (λ) and γ grains are also identified and discussed.
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•Five kinds of phase transformations including β→α, β→γ, β→βo/α→α2, α2→α2/γ and α2/γ→βo,sec occur during our CCT test.•This paper clarifies specific transformation temperature range of α2→βo,sec for the wrought Ti-42Al-5Mn alloy.•5 at%Mn addition tends to decrease the increasing trend of interlamellar spacing with the cooling rate reducing.
The approach for coupled experimental and numerical estimation of the heat treated steel part microstructure and hardness is presented. The method is based on the investigation of the austenite ...transformation in a steel during continuous cooling, Jominy hardenability test and numerical modeling of a quenching process. The presented approach is verified by estimation of the 20CrMo5 steel gear shaft microstructure and hardness. The estimated results are in good agreement with the experimental ones.
