Recrystallization Of Steel Research Articles

Specific Features of Stresses Relaxation and Recrystallization of Steel under Laser Heating

Specific Features of Stresses Relaxation and Recrystallization of Steel under Laser Heating

Influence of vanadium, niobium and boron on kinetics of austenite recrystallization of steels with different strength levels under hot deformation conditions

Summarized results of research of the dynamic and static austenite recrystallization kinetics of low-carbon low-alloy and alloyed steels of strength classes 420, 620, 690, 750 and 890 and medium-carbon steels of strength class 1700 containing different amounts of vanadium, niobium and boron are presented. Studies were carried out by the plasmetric method under deformation conditions close to hot rolling. It was found that vanadium has a weak effect on recrystallization, and niobium in all the studied steels significantly slows it down in the hot rolling temperature range, regardless of the total doping level; microalloying of steels with boron leads to acceleration of austenite recrystallization.

Improving the technology of chemical-thermal treatment of tool steels

The paper presents data on the study of the intensification of chemical-thermal treatment processes. Diffusion saturation of the surface of steels and alloys is most often carried out under high-temperature isothermal or isothermal-step exposure with complete recrystallization of steel into an austenitic state. This leads to overheating — the structure and mechanical properties, in addition to hardness and wear resistance, deteriorate. the main regularities and mechanisms of boration of ferritoperlite steels are investigated and described. It is shown that cyclic heating and cooling significantly accelerate the kinetics of the CTO process of iron-carbon alloys. It was found that thermal cycling during boration leads to an increase in the layer thickness up to 80% on carbon steels, with an increase in the degree of alloying, the effect decreases from 70% (cast steel 5KHNM) to 20% (steel X12M). With an increase in the carbon content in steel, the depth of the borated layer decreases both after isothermal high-temperature boration and after thermocyclic boration.

Study on critical condition of dynamic recrystallization of large back-up roll steel

70Cr3Mo alloy steel is mainly used to produce large back-up roll for cold rolling mill, which has higher processing quality requirements. In this paper, the hot compression test of 70Cr3Mo large back-up roll steel was carried out, and the flow stress curves under different deformation temperatures and strain rates were obtained. The critical condition of dynamic recrystallization of the steel was determined by calculation and fitting, and the critical stress formula of dynamic recrystallization was obtained.

Effect of La-Ce Mixed Rare Earth on High Temperature Deformation Behavior of 685 Armor Steel and Its Mathematical Model

A thermal simulation test machine was used to conduct high-temperature compression tests on two sets of 685 test steels with and without rare earths. Through linear fitting analysis and microstructure observation, the effect of rare earths on the high-temperature deformation behavior of 685 armored steel was studied. The results show that when the deformation temperature is 1000°C, La-Ce mixed rare earth can increase the deformation resistance of steel, and the influence varies with the amount of compression deformation, while at 1100°C, the rare earth has no obvious influence on the deformation resistance of steel. After adding rare earth, the recrystallization activation energy of steel is increased by 6.78%. Mixed rare earth (La-Ce) has an inhibitory effect on the recrystallization of steel. Using Origin8.0 software for regression analysis, a mathematical model of armored steel containing rare earths is established. The model has good curve fitting characteristics, and the calculated values are basically in agreement with the experimental values.

Modeling the Dynamic Recrystallization and Flow Curves Using the Kinetics of Static Recrystallization.

The results of modeling the dynamic recrystallization of steels during hot deformation on the basis of information on their static recrystallization kinetics are presented. The results of predicting the amount of deformation accumulated in the metal under the conditions of dynamic recrystallization development were used for calculating the metal flow curves. The model was validated by comparing the calculated flow curves with the experimental flow curves determined on the 1045 steel by means of hot torsion tests carried out from 1000 °C to 1100 °C and at strain rates from 0.1 to 10 s‒1. The difference between the experimental and predicted flow stress values did not exceed 6%. The influence of the chemical element content in low-alloyed steels on the magnitude of the critical strain for the initiation of dynamic recrystallization is assessed. The method of predicting the kinetics of dynamic recrystallization by recalculating the kinetics of static recrystallization to the conditions of continuous growth of the strain degree during metal deformation implemented in the model can be used in designing and optimizing technologies associated with metal hot forming processes.

Modeling Deformation Flow Curves and Dynamic Recrystallization of BA-160 Steel During Hot Compression

The hot deformation behavior of a high strength low carbon steel was investigated using hot compression test at the temperature range of 850–1100 °C and under strain rates varying from 0.001 to 1 s−1. It was found that the flow curves of the steel were typical of dynamic recrystallization at the temperature of 950 °C and above; at tested strain rates lower than 1 s−1. A very good correlation between the flow stress and Zener–Hollomon parameter was obtained using a hyperbolic sine function. The activation energy of deformation was found to be around 390 kJ mol−1. The kinetics of dynamic recrystallization of the steel was studied by comparing it with a hypothetical dynamic recovery curve, and the dynamically fraction recrystallized was modeled by the Kolmogorov–Johnson–Mehl–Avrami relation. The Avrami exponent was approximately constant around 1.8, which suggested that the type of nucleation was one of site saturation on grain boundaries and edges.

STRUCTURE FORMATION OF HIGH STRENGTH NITROGEN-BEARING STEEL UNDER HOT DEFORMATION

Deformation resistance characteristics of nitrogen-bearing steel of Cr-Ni-Mn alloying composition have been defined with the help of universal research complex Gleeble 3800 at various temperatures between 1200 and 800 : C depending on the strain rate. Temperature and deformation conditions of dynamic recrystallization depending on the strain rate have been determined by analyzing the deformation diagrams, namely that of the deformation limit beginning the process. Optimum temperature regimes for industrial hot stamping, forging and rolling have been recommended. It has been found that at a degree of true strain e = 0.9 the dynamic recrystallization of steel occurs in the range of 10~ 2 + 2 s _1 of strain rate at temperatures not lower than 900°C. The experimental data have been confirmed by metallographic research. Studies have shown that the processes of structure formation during isothermal deformation of steel at different speeds have some differences at temperatures above 900°C. The higher the temperature and the lesser the strain rate, the greater is the development of relaxation. It was found that at a strain rate of 0.01 s _1 corresponding to hot stamping, dynamic recrystallization in the temperature range of 1200 - 1100°C deformation starts at values equal to e = 0.1 (about 10 % of relative reduction). When the temperature lowers to 1000 and 900°C it is necessary to accumulate deformation to 20 and 30 %, respectively. Increasing the strain rate to 0.1 s _1 (when forging) leads to the fact that at temperatures above 1100° : C dynamic recrystallization begins at a degree of deformation about 20 %; at temperatures of 1000 and 900°C about 28 and 35 %, respectively. When the strain rate is 1-2 s _1 (when rolling) dynamic recrystallization starts when the temperature range is 1100 -1000°C and degree of deformation equals to 30 %. Lowering the temperature to900°C, as well as increasing to1200°C, increases the limit degree to 36 %.

Recrystallization Kinetics and Texture Evolution of Nb Stabilized Ferritic 430 Stainless Steel Cold Rolled and Isothermal Annealed

The ferritic stainless steel type 430 stabilized with Nb, with and without annealing after hot rolling, was cold rolled and subjected to isothermal annealing at temperatures 650, 700 and 750°C for times ranging between 10 to 86400 s. The recrystallization kinetics was evaluated by JMAK model through microhardness measurements and KAM and GOS parameters. The Avrami exponent data indicate the occurrence of an unidimensional grain growth due only to high angle boundaries migration, with values ranging between 0.9 and 1.2. The nucleation rate and grain growth decreased continuously with time. The evolution of the texture was analyzed via EBSD analysis by ODF maps. The steel recrystallization is based on combination of ON and SG theories, due to presence of {111}<121>, {554}<225> and {111}<112> related to γ fiber. The rotated cube component, feature of the hot rolled steel, decreased with annealing time.

Static recrystallisation of steels produced by direct strip casting – The effect of carbon and vanadium concentration

Six steel alloys containing a range of carbon and vanadium concentrations have been prepared by simulated strip casting. The alloys were cold rolled and annealed to examine the recrystallisation behaviour. The annealing treatment resulted in three processes occurring concurrently: recrystallisation; spheroidisation of cementite, and precipitation of vanadium-enriched nano-precipitates. These nano-precipitates had a much higher concentration of Fe than would be expected from traditional processing methods, and this increased their maximum attainable volume fraction. In the two alloys that did not contain second phase particles, recrystallisation showed typical reaction kinetics, and the recrystallised grain size continued to increase with increasing time at temperature. However, in those alloys with second phase particles the recrystallised grains showed unusual behaviour, rapidly reaching an upper limit to their size. Continued time at temperature was not accompanied by an increase in the grain size. This growth limit has been attributed to Zener pinning, with the limiting grain size being proportional to the Zener pinning pressure. It has been proposed that the delayed recrystallisation that is typically observed in strip cast steels is likely to be the result of nano-scale precipitation which is unique to rapidly cooled materials, such as those produced by strip casting.

Evaluation of the Possibility of Retarding Steel Recrystallization During Hot Rolling with Precipitation of Manganese Sulfide Particles

The article is devoted to finding new production methods making it possible to prepare rolled product of carbon or low-alloy steels with a fine-grained structure, and this means greater strength with limitation or exclusion of expensive alloying with niobium. The possibility is considered of retarding recrystallization during hot rolling as a result of reprecipitation of manganese sulfide particles previously dissolved on heating for rolling. Laboratory tests are performed with the aim of determining the optimum heating temperature for rolling in order to implement the mechanism described.

Applied Aspects of Low-carbon and Low-alloy Steel Recrystallization

The efficient use of low-carbon and low-alloy structural steels in Russia depends on the degree of structure fineness. The most acceptable method of providing the fine-grain structure is the recrystallization annealing. The main purpose of annealing is to build a uniform structure providing for better workability of steel products and higher level of mechanical properties thereof. It becomes possible as a result of recrystallization in solid state to correct such a significant defect of steel structures as the coarse-grained structure obtained as a result of overheating. The possibilities of passive flux-gate test method have been studied to check shaping the fine-grained structure in the course of recrystallization annealing.

On ball-milled ODS ferritic steel recrystallization: From as-milled powder particles to consolidated state

Recrystallization of a ball-milled ferritic ODS steel is studied towards its evolution from as-milled powder to consolidated state. This characterization has been made possible by using a combination of X-ray Diffraction (XRD) and an innovative method based on an Automated Crystallographic Orientation Mapping (ACOM) tool attached to a Transmission Electron Microscope (TEM). Focus Ion Beam preparation has been essential to obtain a thin section of the ODS steel powder particle and perform the ACOM-TEM study. Relevant temperatures regarding recovery and recrystallization during the heat treatment had first been identified with XRD profile analysis. Selected states were further characterized using ACOM-TEM that provides key information on microstructure, i.e. grain size and morphology, crystallite size, local texture and distortion. ACOM-TEM cartographies have revealed for the first time that the microstructure of as-milled ODS ferritic steel particles consists in very anisotropic grains containing undistorted domains and dislocation walls. This is in agreement with the nanosized crystallites measured by XRD results. The mutual benefits of XRD and ACOM-TEM methods to analyse and describe the microstructure are discussed as well as the reliability of dislocation density measurements provided by ACOM-TEM misorientation measurements. In addition, of the ACOM-TEM results, the microstructural evolution during the processing route is interpreted in terms of a competition between recovery, recrystallization, grain growth and precipitation.

Discrimination Between Cracks and Recrystallization in Steel Using Nonlinear Techniques

One major problem in ultrasonic NDT for steel products and welding inspection is that standard linear methods are often unable to distinguish the nature of signals. Partially recrystallized grains, voids, small cracks or inclusions in the piece under investigation could produce indications very similar in terms of acoustic energy reflected and ultrasonic peaks envelope. Here, we analyze the nonlinear response to ultrasonic excitations of steel bars with both kind of imperfections purposefully generated. Using the Scaling Subtraction Method as a tool for the analysis, we show differences in the nonlinear signature, which can be used to distinguish nondestructively a crack/delamination from a region with imperfect grains formation, with possible applications of this technique in the production cycle.

Experimental Study on the Influence of Single-Pass Deformation on Recrystallization Behavior and Microstructure

By using Gleeble1500-D thermal simulation machine, Rare Earth(RE) adding Q345B steel of single-pass compression test were carried out. A study had been made of the effect of different deformed conditions in hot rolling process on Nd-modified Q345B steel recrystallization behavior and microstructure evolution.The result shows that RE steel Q345B of single compression test are consistent with the general experimental rule. Rare Earth additions significantly increased hot- deformed resistance at low temperature compression, however, it is not obvious at high temperature. The increased hot-deformed resistance and the degree of the retardation is more obvious for heavy RE Tb than light RE Nd.

On the Onset of Dynamic Recrystallization in Steels

The knowledge of the flow behavior of metallic alloys subjected to hot forming operations is of particular interest for designers and engineers in the practice of industrial forming processes simulations (i.e. rolling mill). Nowadays dynamic recrystallization (DRX) is recognized as one of the most relevant and meaningful mechanisms available for the control of microstructure. This mechanism occurs during hot forming operations over a wide range of metals and alloys and it is known to be as a powerful tool which can be used to the control of the microstructure and properties of alloys. Therefore is important to know, particularly in low stacking fault energy (SFE) materials, the precise time for which DRX is available to act. At constant strain rate such time is defined by a critical strain, εc. Unfortunately this critical value is not directly measurable on the flow curve; as a result different methods have been developed to derive it. Focused on steels, in the present work the state of art on the critical strain for the initiation of DRX is summarized and a review of the different methods and expressions for determining εc is included. The collected data is suitable to feeding constitutive models.

Study and Practice of Recrystallization Annealing Process of High-Plasticity Cold-Rolled Steel Sheet

More detailed analysis of chemical compositions, cold plastic deformation and microstructure and properties change of 40Mn and 65Mn steel in recrystallization annealing process were made in the paper. How to get high plasticity and improve the performance of cold pressure processing technology as to cold-rolled 40Mn, 65Mn steel in recrystallization annealing technology, it was suggested that hardness was appropriately sacrificed to ensure the high plasticity. The paper analyzed concretely the reason of the influence of ball Fe3C to plasticity. Recrystallization annealing process and metallographic structure analysis were made. Basically set the process of 40Mn and 65Mn steel recrystallization annealing. Initially carry out the practical application, receive a better effect and have more potential applications foreground.

Hot Deformation Behavior of V-Microalloyed Steel

Through the expansion curve of continuous cooling transformation at different cooling rates measured by THERMECMASTOR-Z thermal simulator for U75V rail steel, the continuous cooling transformation curve was obtained. The influence on steel microstructure and hardness at different cooling rates was studied. The softening behavior of isothermal deforming in austenite area of 850–1000 °C in the interval of passes was also studied by double-pass compression test. The results show that the product of austenite transformation is pearlite when the cooling rate is lower than 10 °C. When the cooling rate was in the range of 10–50 °C · s −1, only martensite was received. The hardness of the test steel increases with increasing the cooling rate. Under the condition of deformation of 30% and deformation rate of 3 s −1, the relaxation time for complete recrystallization was shorter than 100 s when deformation temperature was higher than 1000 C. When deformation temperature was lower than 880 °C, complete recrystallization of steel was difficult to achieve even if the relaxation time is extended.

The study of recrystallisation and crystallographic texture genesis in industrial steels

Abstract Charles Crussard actively participated in the foundation of the IRSID laboratory in 1948. He integrated this institute in 1952 as chief of the Physical Metallurgy Department and among the scientific fields that he initiated were the plasticity and the recrystallisation of steels. Nowadays, these are still active research fields at the ArcelorMittal Research laboratory (formerly called IRSID) and the purpose of this paper is to illustrate the heritage of the research subjects that Crussard initiated and how his vision has influenced our work at IRSID.

<i>In Situ</i> Observation of Grain Growth and Recrystallization of Steel at High Temperature

An in-situ observation method for structures at high temperature is developed. The new observation device can reveal grain boundaries at high temperature and enables dynamic observation of these boundaries. Grain growth while maintaining microstructure at high temperature is observed by the new observation device with only one specimen for the entire observation, and grain sizes are quantified. The quantifying process reveals two advantages particular to the use of the new observation device: (1) the ability to quantify grain sizes of specified sizes and (2) the results of average grain size for many grains have significantly less errors because the initial structure is the same for the entire observation and the quantifying process. The new observation device has the function to deform a specimen while observing structures at high temperature, so that enables it to observe dynamic recrystallization of steel. The possibility to observe recrystallization is also shown.