Transformation Of Supercooled Austenite Research Articles

Application of neural networks to forecasting the CCT diagrams

The paper presents the methodology of modelling using the neural networks of the relationship between the chemical composition and austenitizing temperature, and the supercooled austenite transformation kinetics during the continuous cooling. The model worked out makes it possible to calculate a complete CCT diagram for the steel with a known chemical composition and analysis of the influence of particular elements on the characteristic points and transformation curves of the supercooled austenite, and also the hardness resulting from cooling. It makes also possible forecasting of the structure developed in steel as a result of cooling at a particular rate, by the quantitative description of the percentages of ferrite, pearlite, bainite, and martensite with the retained austenite.

Application of neural networks for prediction of critical values of temperatures and time of the supercooled austenite transformations

The own model is proposed in the paper making it possible to predict the Ac1, Ac3, Bs, Ms temperatures and time to begin the bainitic transformation. The original method was used for calculating the anisothermic diagrams of the supercooled austenite transformations of the constructional steels using the artificial neural networks. The set of training data was compiled to carry out this task (400 charges of constructional steels) including their chemical compositions, austenitising temperatures, and the supercooled austenite transformation diagrams during their continuous cooling. The obtained results were compared with results obtained based on those cited in literature and with commonly used empirical relationships, indicating in many cases to the better consistency of calculations made using the new method with the empirical data. Examples of application of the developed model for evaluation of the effect of the alloying elements on the Ac3 temperature value and time to beginning of the bainitic transformation was presented.

Application of neural networks for prediction of critical values of temperatures and time of the supercooled austenite transformations

The own model is proposed in the paper making it possible to predict the A c1 , A c3 , B s , M s temperatures and time to begin the bainitic transformation. The original method was used for calculating the anisothermic diagrams of the supercooled austenite transformations of the constructional steels using the artificial neural networks. The set of training data was compiled to carry out this task (400 charges of constructional steels) including their chemical compositions, austenitising temperatures, and the supercooled austenite transformation diagrams during their continuous cooling. The obtained results were compared with results obtained based on those cited in literature and with commonly used empirical relationships, indicating in many cases to the better consistency of calculations made using the new method with the empirical data. Examples of application of the developed model for evaluation of the effect of the alloying elements on the A c3 temperature value and time to beginning of the bainitic transformation was presented.

Acicular ferrite formation during hot plate rolling for pipeline steels

The transformation of supercooled austenite in a commercial pipeline steel was investigated by means of continuous cooling transformation (CCT) and hot simulation experiments. Based on the obtained results, an improved thermomechanical control process (TMCP) was proposed, which could produce a mixed microstructure dominated by acicular ferrite. Results indicated that an increase in the cooling rate could improve the percentage of acicular ferrite in the final microstructure under the present experimental conditions. Furthermore, the acicular ferrite dominated microstructure could be obtained by a two stage controlled rolling in the austenite recrystallisation region plus the non-recrystallisation region and controlled cooling at a cooling rate of 30 K s-1.

The fatigue strength of electron beam transverse butt welds in low alloy NiCrMo steels - further endurance and fracture mechanics tests: Andrews, R. M. and Punshon, C. S. TWI Journal (1992) 1 (4) 457–485

The paper presents the methodology of modelling using the neural networks and regression method of the relationship between the chemical composition and austenitizing temperature, and the supercooled austenite transformation kinetics during the continuous cooling. The worked out model makes possible to calculate a CCT diagram for the steel with a known chemical composition and analysis of the influence of particular elements on the characteristic points and transformation curves of the supercooled austenite. In order to work out the methods the set of experimental data worked out on the basis of information available in the literature consisting of 300 CCT diagrams made for constructional and engineering steels was used. Model presented in the paper features a useful assistance in selection of the chemical composition of steel for machine elements subjected to heat treatment.

Effect of aging of supercooled austenite on the mechanical properties of vanadium-containing steels

1. The development of the processes of dispersion hardening of supercooled austenite leads to improved strength properties of steels 30Kh3N3MFB and 30KhNSMFB (with a slight reduction of ductility and real fracture stress) after hardening with isothermal holding in the range of subcritical temperatures and low tempering compared with the properties of these steels obtained by conventional hardening and the same tempering. 2. The uniform distribution of regions enriched with vanadium and carbon forming in the process of isothermal transformation of supercooled austenite and inherited by martensite, the possibility of their being cut by dislocations cause the uniform development of plastic deformation throughout the bulk of the steel without stress concentrations arising. Such a structural state ensures the possibility of attaining good strength properties. Then failure of steels 30Kh3N3MFB and 30KhNSMFB proceeds by the ductile micromechanism, but when the isothermal holding before quenching is extended to more than 10 min, the tendency of steel 30KhNSMFB to brittle failure increases; this may be due to the effect of silicon. 3. The good strength properties combined with satisfactory ductility and real fracture stress enable us to recommend the newly devised steels, especially 30Kh3N3MFB, as material for improtant machine parts.

Kinetic characteristics of the diffusional transformation of supercooled austenite in P/M steels

Kinetic characteristics of the diffusional transformation of supercooled austenite in P/M steels

Properties of die steels hardened with vanadium carbonitride

1. The particles of vanadium carbonitride formed in steels of the 50Kh6MFB type alloyed with nitrogen in amounts up to 0.07% are less soluble in austenite than vanadium carbides, and thus inhibit austenite grain growth to a greater extent with heating to 1210°. 2. In the range of subcritical temperatures investigated the transformation of supercooled austenite begins with precipitation of carbide and carbonitride phases from it. This process leads to some additional hardening of the steel after isothermal hardening as compared with standard quenching. The resistance of austenite to the γ→α transformation during cooling is lower for steels with nitrogen than for steels without nitrogen. 3. After tempering, the bending strength and fracture toughness of steels with nitrogen are higher than for the steel without nitrogen, which is due to the finer austenite grain size of the steels with nitrogen after heating. For all steels tested (with and without nitrogen) these properties are somewhat superior after standard oil quenching than after isothermal hardening, although the hardness is higher after isothermal hardening. 4. An analysis of the combination of properties and structure of steels of the 50Kh6MFB type confirms the expediency of adding 0.06–0.07% nitrogen to the steel.

Transformation of supercooled austenite in now-alloy steel 16GFR during continuous cooling

A C−C−T diagram was plotted for steel 16GFR, which makes it possible to predict with adequate reliability the character of the structure formed during cooling of pipe at given rates under plant conditions and thus to correct the heat-treatment process for pipe made of steel 16GFR with strength σb=720 MPa and guarantee the mechanical properties and cold resistance required.

Transformation of supercooled austenite in sintered steels during continuous cooling

In the present work thermokinetic diagrams were constructed using data yielded by austenite transformation investigations carried out with a high-speed magnetometer fitted with a ferromagnetic probe [3, 4]. Magnetometric measurements were made on specimens with densities of 6.50, 7.00, and 7.78 g/cm 3, machined from impact test specimens produced by single pressing and sintering and also by hot forging. Transformations were studied in ZhGr0.5 and ZhGr0.5N2M sintered steels of the following chemical compositions (%):

Transformation of austenite in low-alloy steel 10GDKhFRL

Replacing nickel in steel 08GDNFL with chromium and microalloying with boron leads to hardly any changes in the kinetics of the transformation of supercooled austenite. The C-C-T diagrams make it possible to determine roughly the quantitative characteristics of the structural components in parts differing in cross section and through the cross section and also make it much simpler to select the proper heat treatment.

Kinetics of the transformation of supercooled austenite in steel 12Kh1MF

1. For open hearth steel 12Kh1MF the stability of the austenite is higher in the pearlitic region and lower in the intermediate region than that of the steel melted in an electric furnace. The normalized open-hearth steel has a larger bainitic component than the steel melted in the electric furnace. 2. A ferritic—bainitic structure with Widmanstatten arrangement of the carbides ensures a longer time to rupture at elevated temperatures than a ferritic—pearlitic structure.

Kinetics of the transformation of supercooled austenite in steel 19KhGN

Kinetics of the transformation of supercooled austenite in steel 19KhGN

Effect of alloying on transformation of supercooled austenite in low-alloy steel of the 14G2S type

Effect of alloying on transformation of supercooled austenite in low-alloy steel of the 14G2S type

Effect of heat treatment on conditions of formation, shape, and stability of vanadium carbides in vanadium steels

1. It was found that the structure of steels 22F1B, 27F1B, and 35F2B resulting from isothermal transformation of supercooled austenite at 680–720°C consists of evenly distributed high-strength, oriented, dispersed vanadium carbide in a ferrite matrix. Such vanadium carbides impart high strength at normal and elevated temperatures, while ferrite provides fairly high ductility. 2. The structure of the steels after the double heat treatment (normalization at 1130°C for 5 min, tempering at 720°C for 3 h) consists of ferrite and unevenly distributed vanadium carbides. The strength characteristics at normal and elevated temperatures are lower than after the isothermal treatment at 680–720°C for 30 min. 3. The original structure of the steel after quenching or after isothermal treatment has different effects on the hardness during subsequent tempering. Tempering at 400–450°C after quenching or incomplete decomposition of supercooled austenite leads to reduction of the hardness due to coalescence of cementite, while complete decomposition of austenite, with formation of a ferrite-carbide structure, leads to an increase in hardness beginning at very low temperatures.

High-temperature X-ray analysis of the isothermal transformation of supercooled austenite in steel R6M5

1. Measurements of the lattice constant of M6C and MC carbides, and α- and γ-phases, and the width of lines of α- and γ-phases in the process of heating at 20–1200°C make it possible to calculate the partial coefficients of linear and volume expansion of these phases and demonstrate the relationship between the type of solid solution and the partial coefficients of expansion of M6C carbides. 2. Measurements of the lattice constants and line width of α- and γ-phases and the intensity of the lines (quantity) of M6C carbides in the process of isothermal holding for as long as 3 h at 1200–250°C after austenitizing at 1220 made it possible to substantiate the processes and the temperature-time range for such technological operations as HTTMT, LTTMT, austempering, etc.

Isothermal transformation of supercooled austenite in high-speed steel �P733

1. Isothermal transformation diagrams of supercooled austenite were plotted for high-speed steel EP733. 2. The effect of isothermal temperature and holding time on the properties of the steel was determined.

Isothermal transformation of supercooled austenite in steel 75KhSMF

A T-T-T diagram for steel 75KhSMF was plotted. It was found that the transformation ceases in the pearlitic and intermediate temperature ranges.

Effect of deformation by upsetting on the transformation of supercooled austenite in 40KhS steel

Effect of deformation by upsetting on the transformation of supercooled austenite in 40KhS steel

Influence of ultrasonics on the kinetics of the transformation of supercooled austenite in certain steels

1. Ultrasonic vibrations applied to the sample during isothermal transformation have different effects on the phase transformations in the pearlitic and bainitic regions. 2. Ultrasonic vibration has opposite effects on steels with and without nickel. 3. In steels 30KhGSNA and 30KhGSA ultrasonic vibration induces more complete transformation of austenite in the bainitic region.