Bar Rolling Process Research Articles

Artificial intelligent analyzer for mechanical properties of rolled steel bar by using neural networks

In this paper, an artificial intelligent (AI) analyzer for mechanical properties of rolled steel bar by using neural networks was proposed. Based on the learning capability of neural network, the nonlinear and complex relationships among the steel bar’s properties, the billet compositions and the control parameters of manufacture could be automatically developed. Such an AI analyzer could help the technician to precisely set the related control parameters on the bar rolling process. Not only the quality of steel bar could be improved, the production cost of the bar could also be greatly reduced.

Numerical prediction of austenite grain size in a bar rolling process using an evolution model based on a hot compression test

A microstructure evolution model was formulated by characterizing the kinetics of static (SRX) and metadynamic (MDRX) recrystallization in consideration of the experimental data using single and double compression tests of AISI 4135 at various temperatures and strain rates. The evolution model consisted of equations for SRX, MDRX, and grain growth was implemented into an in-house finite element program to simulate the process. Numerical prediction of austenite grain size (AGS) evolution during a hot bar rolling of AISI 4135 was conducted and presented. The predicted results were compared with the experimental data obtained from the hot bar rolling and the numerical results based on other AGS models available in the literature which were derived based on torsion tests. The present model determined in the current investigation based on compression tests shows better agreement with the experimental data than the earlier works. The critical strains determined from compression tests were relatively smaller than those from the torsion tests, which influenced the overall recrystallization and grain growth behaviors. Also, the current model was beneficial to understand the effect of recrystallization behavior and control the microstructure evolution during hot bar rolling.

Surface wrinkle defect of carbon steel in the hot bar rolling process

It is well known that surface defect is a common problem encountered in the multi-stage hot bar rolling process of carbon steel. In this study, the phenomenon was investigated by simulating the process by the finite element technique to identify the location where the surface defect might occur and checking the surface qualities obtained from the compression tests at various temperatures and strain rates to clarify the important parameter governing the possible surface defect formation. Also, the surface temperature was measured by employing pyrometer to support the experimental observation. The levels of temperature and specific deformation energy obtained from finite element simulations depending on the roll groove geometry were compared with the experimental observation to better understand the formation of the surface defect in the hot rolled bar. Based on this study, the surface defect might be formed by dissipating the excessive deformation energy accumulated by generating the new surface at the lower level of temperature where recrystallization cannot occur. According to this work, the comparison of the specific deformation energy level for determining the instability of the hot working process might be interesting for further investigation.

Plastic work approach for surface defect prediction in the hot bar rolling process

In this study, a numerical technique was developed to study the effect of processing parameters on instability of the steel during five passes hot bar rolling process. For this a processing map developed based on the plastic work approach was used with finite element analyses to judge occurrence of instability during the process. The effect of roll geometry and processing temperature on hot rolled bars was examined with the help of a parametric study by employing the numerical technique developed. Based on this parametric study, the improved roll pass design and initial processing temperature were determined, respectively, for reducing flow instability during the process. The laboratory rolling mill was used to validate the numerical results. It was found that with the increase of the initial temperature in the process the less flow instability was observed compared to the change of the roll geometry introduced at each pass under the present investigation condition. It was found that the current numerical technique implemented will be useful in identifying the important parameters governing the formation of surface cracks in the multi-stage hot bar rolling process.

Using of FEM to Analyse of the Reinforcement Bar Rolling Process

Reinforcement bars are chiefly used in the building industry at production of reinforced concrete constructions and as working elements in bridge building. An important factor for strength joining bar and concrete are dimensions and positioning of ribs at the bar’s surface. In this paper the computer simulation of the rolling of the round reinforcement bar is presented. It has been performed in order to define the specific features of the mode of metal flow in the roll gap and to determine the effect of the shape and dimensions of the roll on the pitch of the ribs of the finished bar.

A novel approach for the prediction of surface profile of outgoing workpiece and the calculation of mean roll radius in alloy bar rolling

In alloy bar rolling process, the component of alloyed steel influenced the spread coefficient greatly, therefore, the component influence coefficient m of different alloyed steel has been determined firstly to calculate the maximum spread. Then the curvature radius of stress free surface and the “critical point on the contact boundary” have been solved, the surface profile of outgoing workpiece has been obtained. Furthermore, the formula of the equivalent contact section area has been proposed and the mean roll radius has been calculated. The bar rolling experiment and the rigid-plastic FEM (finite element method) simulation have been carried out to verify the novel approach. Compared with experimental data and simulation results, the novel approach can be used in setting processing parameter and design of finishing groove.

Effect of Processing Parameters on Precipitation Reactions Occurring in a Ti-Bearing IF Steel

The investigation was focused on the detailed description of precipitation/formation processes of TiN, TixSy, Ti4C2S2, TiC, and (Fe,Ti)P particles occurring in the production of thin sheets of titanium-bearing interstitial-free steels. The knowledge concerning this reactions was gained based on the thermodynamic calculation and physical simulations conducted on Gleeble 3800 thermal – mechanical simulator. The formation process of titanium carbosufide of Ti4C2S2 is the crucial reaction for the thin sheets properties. The investigation confirmed the in-situ mechanism of this phase formation, involving carbon diffusion in the TiS and TixSy sulfides’ crystal lattice. Thus, the precipitation of the substantial fraction of these sulfides is a prerequisite for further intense carbosulfide formation. Titanium sulfides are formed at the rough rolling stage of the transfer bar rolling process. The most intense precipitation of the sulfides occurs at around 1000°C. Besides the effect on the carbosulfide formation, it was found out that the sulfides substantially retard the recrystallization and grain growth in the IF steels. The most favourable Ti4C2S2 formation conditions prevail in the temperature range of approximately 950 - 920°C, which corresponds to the plate finish rolling stage. Both reactions, i.e. sulfides and carbosulfide formation, are deformationinduced processes.

Process design for refinement and homogenization of microstructure in bar rolling

Depending on process design of the bar rolling process, the final microstructure distribution varies. In this final distribution two perspectives should be taken into account: homogenization and refinement. Most of the studies carried out so far are focused on minimization of the grain size but the uniformity of the grain size is also important because the locally coarse grain sizes significantly deteriorate the overall performance of the rolled bar. In this study two criteria are proposed as a measure of the refinement and homogenization of the austenite grain size (AGS) distribution. The effect of process parameters on these two parameters was investigated to determine the major controlling parameter for better process design of round-oval-round pass sequence in the bar rolling under the isothermal and non-isothermal conditions. The investigation revealed that the temperature was the most important controlling parameter and the decrease of initial processing temperature was effective not only in the grain refinement but also in the grain homogenization.

Modeling of recrystallization and austenite grain size for AISI 316 stainless steel and its application to hot bar rolling

In this study, we have developed a model for predicting recrystallized volume fraction (RXN) and austenite grain size (AGS) of AISI 316 stainless steel by using hot torsion test and then applied it to bar rolling process. It was found that the proposed model coupled with the analytic equation for bar rolling could in a general way predict average values of RXN and AGS across material section. Results also revealed that for predicting them more precisely in a point-wise manner, the proposed model should be incorporated with equations that take into account inhomogeneous distribution of deformation state and temperature across the section during rolling.

Analytical model of pass-by-pass strain in bar rolling and its verification

This paper presents an analytical model for predicting the pass-by-pass strain, defined as maximum averaged effective (equivalent) plastic strain at a given pass, in a bar (or rod) rolling process. The model has been based on the equivalent rectangle approximation method which makes the curved configuration of the deformed section into a simplified rectilinear configuration and the hypothesis of parallelepiped deformation of material. Experimental and numerical studies were carried out to investigate the validity of the analytical model. For experimental verification, plate rolling and bar rolling experiments were designed that consisted of a four-pass oval-round (or round-oval) rolling sequence such that during rolling the material experiences the same amount of the strain at each pass. The microstructures and mechanical behaviors of specimens acquired from the two types of experiment were compared. A commercial finite element analysis program, DEFORM, was also used to examine the validity of the analytical model numerically. A similarity between the mechanical behaviors of the plate-rolled and bar-rolled specimens was found at each pass. It was also seen that the strains calculated by the analytical model were in agreement with the averaged effective plastic strain computed by finite element simulation.

A three-dimensional finite element analysis of the three-roll planetary mill

The purpose of this paper is to analyze the bar rolling process by means of the three-roll planetary mill with a three-dimensional elastic–plastic finite element model. The problems can be solved with the aid of finite element program MARC by adopting the large deformation—large strain theory with the updated Lagrangian formulation (ULF) and considering the contact problem between the rigid three-rolls and the deformable bar billet. In addition, a remeshing procedure was adopted to improve the unexpected run-time error of turning an element inside out. Furthermore, a new subdivided element model of the divided layers was created, and two different kinds of deformable bar billet were used to simulate the process. The numerical results obtained, such as the equivalent von Mises stress and plastic strain distribution, rolling force, rolling speed of the entrance and exit plane, etc., are very useful in designing the rolling process of the three-roll planetary mill.

Analytic model for the prediction of mean effective strain in rod rolling process

This paper presents an analytic model for predicting the mean effective strain, defined as a maximum average effective (equivalent) plastic strain at a given pass, in bar (or rod) rolling process. The proposed model has been based on the elementary theory of plasticity and the equivalent rectangle approximation method which transforms a non-rectangular cross-sectional shape into a rectilinear one. Then, the mean effective strains are calculated using the hypothesis of parallelepiped uniform deformation of material during rolling. A numerical analysis using three-dimensional finite element method was also carried out to examine the validity of the analytic model proposed. The analysis shows that considering the assumption of uniform deformation of workpiece introduced in the formulation of the model, the mean effective strains calculated by the analytic model are in agreement with those computed by finite element analysis. The results of this study might be important for the study of the pass-by-pass microstructural evolution and temperature increment due to plastic deformation associated with rod rolling where the mean effective strain becomes a critical parameter.

Bulge predictions in steady state bar rolling processes

AbstractA new algorithm for free surface corrections in Eulerian finite element computations is presented and applied to a steady state bar rolling process to predict lateral spread. A variety of rolling geometries are examined, including differing height to width ratios and reductions. The bulge profiles, as well as the maximum and mean bulge amounts, are compared in detail with experiments.