Rolling Heat Research Articles

Optimized Tension for AZ31B Thin Sheets Rolled with On-Line Heating Rolling

On-line heating rolling mill which could efficiently preheat sheet and apply tensile force on both ends of the sheet along rolling direction (RD) was used to investigate the effect of tension on mechanical behavior and shape quality of magnesium sheets. For revealing the influence mechanism, many analysis techniques including optical microscope, electron backscattered diffraction, macrotexture and transmission electron microscope were performed. The shape defect, edge wave, could be eliminated under higher tension along RD, which was attributed to more uniform distribution of microstructure and microstrain. Nevertheless, it is undesirable that the forward tensile force exceeds 3 kN in present work because the strength decreased for high recrystallization level when the tensile force is beyond this value. Furthermore, the main deformation mode was still slip during rolling process despite of accompanying twining, e.g., double twins, but more prismatic slip activated when tensile force exceeds 3 kN. The distribution of shear bands was affected by the applied tensile force that they appear as “V” shape along RD at a low forward or backward tensile force, while they appear as reticulate shape under applied tensile force of 5 kN.

The Phase Composition and Mechanical Properties of the Novel Precipitation-Strengthening Al-Cu-Er-Mn-Zr Alloy

The microstructure, phase composition, and mechanical properties during heat treatment and rolling of the novel Al-5.0Cu-3.2Er-0.9Mn-0.3Zr alloy were evaluated. A new quaternary (Al,Cu,Mn,Er) phase with possible composition Al25Cu4Mn2Er was found in the as-cast alloy. Al20Cu2Mn3 and Al3(Zr,Er) phases were nucleated during homogenization, and θ″(Al2Cu) precipitates were nucleated during aging. The metastable disc shaped θ″(Al2Cu) precipitates with a thickness of 5 nm and diameter of 100–200 nm were nucleated mostly on the Al3(Zr,Er) phase precipitates with a diameter of 35 nm. The hardness Vickers (HV) peak was found after the annealing of a rolled alloy at 150 °C due to strengthening by θ″(A2Cu) precipitates, which have a larger effect in materials hardness than do the softening processes. The novel Al-Cu-Er-Mn-Zr alloy has a yield strength (YS) of 320–332 MPa, an ultimate tensile strength (UTS) of 360–370 MPa, and an El. of 3.2–4.0% in the annealed alloy after rolling condition.

Improved Edge Quality for AZ31 Sheets Using Online Heating Rolling Technique

The edge quality of AZ31 sheets prepared by online heating rolling (O-LHR) technique under different rolling temperatures has been investigated. The AZ31 sheets are rolled from 3 mm to around 1 mm via four passes under three different temperatures. Each pass reduction keeps a constant about 25%. For comparison, a series of sheets are also rolled by conventional rolling (CR) under the same condition. The macroscopic observation for sheets rolled by both processes and microstructure examination for the rolled sheets via O-LHR are performed to characterize the edge cracking behavior. The results reveal that the edge quality of sheets after O-LHR is better than that through CR and remarkably improves with the increase in temperature. No obvious edge crack appears in AZ31 sheet rolled by O-LHR at a rolling temperature of 250 °C. This can be attributed to the enhanced dynamic recrystallization and the activation of non-basal slip, which results in a homogeneous microstructure at the edge.

Optimization of the Schedule for the Whole Process in Hot Strip Manufacturing

Optimization of the schedule is an effective way to reduce energy consumption in hot strip manufacturing. The heating energy and the rolling energy contribute the vast majority of the energy consumption. In order to reduce the energy consumption for the whole process, an optimization method based on the multi-objective function was applied, and the heating energy and rolling energy were both taken into consideration during the function modeling. Meanwhile, process constraints and equipment limitations were taken as objective function boundary conditions, and the tapping temperature in the furnace exit and thickness of each pass were decision variables. Further, to obtain the optimal solution of the objective function, the differential evolution algorithm was used, finally, the optimal tapping temperature and the thickness were obtained successfully. Meanwhile, the validity of the calculated results was verified by comparing with the actual process in a hot rolling production line in Hebei province, the results indicated that with the proposed method, a more reasonable schedule were obtained; compared with the existing actual schedule of typical specification, the energy consumption can be reduced by about 1.5%.

Structure and properties of high strength low alloyed cold-resistant steel after reheat and direct quenching with tempering

The paper shows comparative investigations of structure of rolled plates from low alloyed coldresistant steel 08CrNi2MoCuNb with guaranteed yield strength 750 MPa after traditional reheat quenching and quenching from rolling heat (direct quenching) with subsequent high temperature tempering. The research is carried out by means of optical metallography, SEM and TEM. The peculiarities of parameters of bainitemartensite structure, which influence the strength level in initial (quenched) state, are revealed. Also, the impact of tempering on structure and properties of rolled plates after reheat and direct quenching is shown.

Effect of pass reduction on distribution of shear bands and mechanical properties of AZ31B alloy sheets prepared by on-line heating rolling

Abstract Preheating and rolling process were simultaneously achieved by on-line heating rolling system. The effect of pass reduction on distribution of shear bands and mechanical properties of AZ31 Mg alloys sheet was investigated by analyzing microstructure and texture. With pass reduction increasing, the shear bands become denser and distribute more uniformly. In all rolled sheets, shear bands distribute symmetrically along the middle layer in the side of the sheets. With reduction increasing from 15 % to 50 %, the tilting angle between the shear bands and the rolling direction decrease approximately from 27° to 14°, which is due to the higher velocity difference between surface-layer and middle-layer at higher reduction. In addition, rolled sheets show lower yield strength at higher reduction. The decrease of yield strength is due to the increase of dynamic recrystallization degree and weaker texture at high pass reduction.

Characterisation on Al-bearing hot-rolled TRIP steel produced through isothermal bainite transformation

In this study, an energy-efficient processing route involving hot rolling and on-line heat treatment was proposed, which is applied to Nb-alloyed and Al-containing hot-rolled TRIP steel. The experiments were carried out involving hot rolling and on-line heat treatment, where the samples were subjected to different bainite hold times. The results shows that during isothermal bainite transformation, film-like and blocky retained austenite were present in microstructures at bainite hold times of 10 and 20 min. The sample subjected to bainite hold time of 20 min exhibited excellent mechanical properties, with tensile strength of 839 MPa, total elongation of 38% and product of strength and elongation of 31.9 GPa%. The instantaneous work hardening exponent increased gradually with true strain at bainite hold time of 20 min.

Effect of tension on edge crack of on-line heating rolled AZ31B magnesium alloy sheet

Edge crack is a common defect in the rolled magnesium alloy sheet which increase the rolling cost. In this study, the effect of tension on the edge crack of AZ31B sheet rolled with on-line heating rolling was investigated. The sheets were rolled under different tension at the rolling temperature of 523 K with thickness reduced from 1 mm to 0.6 mm in 1 single pass. The microstructures, texture, and mechanical properties, fracture surfaces of the sheets were characterized. The results show that the number of edge crack and crack depth increase with the increase of the tension. EBSD results show the crack tip area are mainly composed of fine recrystallized grains.

The Effect of Microalloying on Mechanical Properties of Low-Carbon Chromium–Nickel–Molybdenum Steel

Abstract—The work covers the effect of niobium, as well as both niobium and vanadium, on mechanical properties of high-strength chromium-nickel-molybdenum steel after thermal refining. The mechanical properties of steels were determined after applying various tempering temperatures (from 580 to 660°C) and durations of tempering (from 1 to 16 h), and also after quenching from rolling heat and furnace heat with subsequent tempering. It is shown that, after quenching and tempering in the temperature range of 580–660°C of the high-strength steel of the Cr–Ni–Cu–Mo composition alloyed with 0.02% Nb and 0.07% V, the yield strength is higher as compared with steel alloyed with niobium (0.05%), at only an insignificant decrease in the impact strength and ductility. Increase of the total composition of the basic alloying elements does not result in a significant change in the mechanical properties within the investigated tempering temperature interval. Quenching from rolling heat increases the strength while maintaining high toughness, and the increase in strength is most noticeable for steel microalloyed only with niobium.

Scientific and Technological Bases for Developing Cold-Resistant Steel with a Guaranteed Yield Strength of 315–750 MPa for Arctic Conditions: Part 2. Manufacturing Technology, Structure, Properties, and Serviceability of Sheet Products

Abstract—The paper presents results of the industrial implementation of hot plastic deformation and thermal treatment schemes for the production of rolled sheet products based on cold-resistant steel with yield strength not lower that 315–750 MPa for the Arctic. On the basis of the studies performed, a set of scientific and technological techniques has been developed for various technological processes (thermomechanical treatment followed by accelerated cooling, quenching from the rolling heating, and separate furnace heating with high-temperature tempering). The developed complex method provides the formation of a structure having an acceptable heterogeneity and anisotropy level corresponding to different morphological and crystallographic parameters throughout the entire thickness of rolled products up to 100 mm based on low-alloy steels with a yield strength not lower than 315–460 MPa and up to 60 mm based on economically alloyed steels with a yield strength not lower than 500–750 MPa. The structure of sheet products is presented that provides guaranteed characteristics of strength, cold resistance (impact energy KV at a testing temperature ranging from –60 to –80°C, critical ductile-to-brittle transition temperature Tkb, and nil ductility temperature NDT), and crack resistance according to a CTOD criterion in a low-temperature range to meet the requirements of the RMRS “Rules for the Classification and Construction of Ships” for steel with the Arc40 index.

Scientific and Technological Bases for Developing Cold-Resistant Steel with a Guaranteed Yield Strength of 315–750 MPa for Arctic Conditions. Part 1: Alloying Principles and Requirements for Sheet Product Structure

Abstract—The results obtained upon choosing rational alloying and microalloying for cold-resistant steels with a guaranteed yield strength of 315–750 MPa on the basis of established interrelations between phase transformations, structure, mechanical properties, serviceability parameters, and the content of main alloying elements are presented. Quantitative requirements for various structural parameters and their maximum permissible difference throughout sheet product thickness up to 100 mm have been developed, depending on the strength category and manufacturing technology (thermomechanical treatment with accelerated cooling, quenching from separate furnace heating or rolling heating with high temperature tempering) to provide guaranteed characteristics of strength, cold resistance (impact energy KV at a testing temperature from –60 to –80°С, critical ductile-to-brittle transition temperature Тkb, and nil ductility temperature NDT), and crack resistance according to the criterion of critical crack tip opening displacement (CTOD).

The effect of annealing and anisotropic behaviour on tensile and fatigue properties of AA 8090

Purpose: This paper aims to assess microstructures and mechanical properties of annealed and un-annealed Al-Li alloys (AA8090) and provide valid information regarding influence of anisotropy on tensile properties, fatigue lives. Design/methodology/approach: The methodology included investigating the influence of annealing on grain size, tensile strength and fatigue lives of AA8090. Optical microscope, scanning electron microscope and X-ray diffraction were utilized to analyse the crystallographic texture. Findings: The results showed that the un-annealed alloy exhibited much finer grain structure in three directions, namely longitudinal (L) rolling direction, L-45° and Long transverse (LT) combined with stronger crystallographic texture. Regarding to mechanical properties, un-annealed alloy presented superior tensile strength with strong anisotropic behaviour. L and LT grains direction showed highest tensile strength value of 550 MPa and L-45° showed lowest tensile strength value of 420 MPa. Results of fatigue test revealed that annealed Al-Li alloy has lower fatigue lives with high influence of test direction on fatigue properties. Higher variation in fatigue life to failure links with un-annealed alloy over annealed alloy. Examination of fractured surface showed that the morphology of fractured surface is a mixture of ductile and brittle fractures in both annealed and un-annealed alloys with more brittle behaviour in un-annealed alloy. Research limitations/implications: The main challenge of this work is the determination of the test direction (test angle in respect to rolling direction), which is necessary to provide correct information regarding mechanical properties. Further study of low cycle fatigue can be done in future, which will be an excellent indication to mechanical properties of this alloy since it provides more understanding to the behaviour of the material and better comprehend crack propagation and strain stress concentration. Practical implications: AA8090 alloy is an important candidate for aerospace and aircraft industries. Influence of annealing heat treatment and rolling direction on mechanical properties of AA8090 alloy provides more accurate information to the manufacturers who deal with this alloy. Originality/value: This study is affording a significant information regarding the effect of annealing and anisotropic behaviour on mechanical properties of AA8090. To our knowledge, there are few reports that study this combination of factors on AA8090 alloy.

The effect of microalloying on mechanical properties of low-carbon chromium-nickel-molybdenum steel

The work covers the effect of niobium, as well as niobium and vanadium together, on mechanical properties of high-strength chromium-nickel-molybdenum steel after thermal improvement (heat treatment). The mechanical properties of steels are determined after applying various tempering temperatures (from 580 to 660°C), durations of tempering (from 1 to 16 hours), and also after quenching from rolling heat and furnace heat with subsequent tempering. It is shown that after quenching and tempering in the temperature range 580– 660°C, simultaneous microalloying by niobium and vanadium, compared to microalloying by niobium alone, increases the yield strength but in significantly decreases toughness and ductility. Quenching from rolling heat increases strength while maintaining high toughness and the increase in strength is most noticeable for steel microalloyed only by niobium.

Integrated problem of soaking pit heating and hot rolling scheduling in steel plants

This paper considers an integrated problem of soaking pit heating and hot rolling scheduling that arises in steel plants. Both soaking pit and hot rolling mill are batching machines with capacity considerations. The processing time of a batch in the soaking pit is equal to the longest processing time of the jobs in the batch, whereas the processing time of a batch on the hot rolling mill is equal to the sum of the processing times of the jobs in the batch. Setup time is required whenever a batch is formed on the hot rolling mill. For this problem, we must determine the formation of batches and the sequences of these batches in the soaking pit and on the hot rolling mill such that makespan is minimized. First, we formulate the problem as a mixed integer linear programming model (MILPM) and analyze its computational complexity. Second, we provide a fast heuristic algorithm with worst-case bound to generate near-optimal solutions, and a branch and bound algorithm to solve the problem to optimality. Finally, computational experiments using randomly generated data demonstrate that our heuristic algorithm is very efficient and effective, and the branch and bound algorithm significantly outperforms CPLEX on MILPM in terms of computational time and the number of instances solved to optimality within the given time limit.

Effect of scheme of rolling and post-deformation cooling on mechanical properties of rolled sheet made of V−Nb−Al-alloyed steel

Problem statement. Structural steel products are the bulk of the production of modern metallurgy. It is advisable to increase the mechanical properties of rolled products in the framework of technologies involving the use of rolling heating, which saves energy and reduces the production cost. Purpose. The choice of a rational scheme of rolling and post-deformation cooling of rolled steel made of structural steel. Material and Methods. The study material is 20 mm thick sheet steel made of S355J2 steel (EN 10025) micro-alloyed with V−Nb−Al complex. Methodology − tests for mechanical properties according to the requirements of EN 10025. Results. The mechanical properties of sheet metal are compared after performing standard hot rolling, normalizing rolling, controlled rolling, and also after controlled rolling with subsequent accelerated cooling in various modes. Conclusions. It is shown that by using controlled rolling with accelerated cooling to 460…530 °C, it is possible to significantly (by one third, up to category 500Q) increase the strength of steel with an increase in its cold resistance and at the same time maintaining plasticity at an acceptable level. Such an increase in the complex of properties is achieved without the use of heat treatment with special heating, which is an economically advantageous direction.

Influence of V and Nb Micro‐Alloying on Direct Quenched and Tempered Ultra‐High Strength Steels

The construction of mobile crane booms requires the usage of ultra‐high strength steels. Micro‐alloying elements promote grain refinement during hot rolling and result in increased toughness. The relevant strength is given through a martensitic microstructure, which is accomplished by elements retarding the γ to α transformation. Direct quenching (DQ) from the rolling heat and quenching after a preceding re‐austenitization (RQ) are two different production routes. They differ regarding their productivity, their achievable strength levels, and their resulting microstructures. In order to explore the influence of the production route in combination with prominent micro‐alloying elements, which come to application during hot‐rolling, six steels with varying content of V and Nb are investigated concerning their different properties after DQ and RQ as well as their behavior after tempering. It is found, that Nb strongly improves the strength after thermomechanical processing in the as‐rolled condition. Furthermore, Nb compensates the loss of strength during tempering. This effect is not thoroughly discussed in literature so far. Although Nb leads to grain refining during re‐austenitization, the effects on the strength of RQ steels are minimal. The effect after tempering is also weaker than after direct quenching. It is also shown, that V offers a high strength potential after tempering, however weakens the impact toughness significantly.

Scientific and technological bases for creation of cold-resistant steel with a guaranteed yield strength of 315–750 MPa for the Arctic. Part 1: Principles of alloying and requirements for sheet metal structure

The results of the choice of rational alloying and microalloying of cold-resistant steels with a guaranteed yield strength of 315–750 MPa are presented on the basis of the established interrelationship of phase transformations, structure, mechanical properties and performance characteristics when varying the content of basic alloying elements. Quantitative requirements for various structural parameters and their maximum permissible difference in sheet metal thickness up to 100 mm have been developed, depending on the strength category, manufacturing technology (thermomechanical treatment with accelerated cooling, hardening from separate furnace or rolling heating with high temperature tempering), which provide guaranteed characteristics of strength, cold resistance (impact work KV at test temperature –60 ... –80°С, critical temperatures of viscousbrittle transition Ткand zero ductility NDT) and crack resistance under the criterion of the critical opening in the top CTOD fracture.

The Edge Crack, Texture Evolution, and Mechanical Properties of Mg-1Al-1Sn-Mn Alloy Sheets Prepared Using On-Line Heating Rolling

A series of Mg-1Al-1Sn-Mn magnesium alloy sheets were rolled from 3 mm to 1 mm under temperatures of 150 °C, 200 °C, and 250 °C in four rolling passes using on-line heating rolling. The conventional rolling was also performed for comparison. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) technologies were utilized to characterize the edge cracks as well as the microstructure of rolled thin sheets. The result revealed that the number of edge cracks decreased dramatically with the increase of rolling temperature. No visible edge cracks were found on the surface of sheets rolled at 250 °C by on-line heating rolling, while the conventional rolling at the same temperature still resulted in severe edge cracks. The intensity of the basal texture for on-line rolled sheets increased from 4.982 to 9.596 as the rolling temperature increased from 150 °C to 250 °C, which was related to the reorientation of new grains and deformation grains remained after rolling. The direction of the basal pole slightly tilted towards the rolling direction (RD), which may be mainly attributed to the activation of a pyramidal slip, as well as the tension imposed on the samples. Moreover, mechanical properties were improved after rolling on the basis of the strong texture and grain refinement. The highest yield strength (YS), ultimate tensile strength (UTS), and the maximum elongation of the rolled sheets were 148 MPa, 298 MPa, and 14.6% along the RD, respectively.

Effect of Tempering and Rolling on Fatigue Crack Growth Behavior of Modified 9Cr-1Mo Steel

In the present work, fatigue crack growth (FCG) behavior of modified 9Cr-1Mo steel has been investigated near fatigue threshold and Paris regime at room temperature (RT) and 650 °C. The modified 9Cr-1Mo steel was subjected to normalizing at 1050 °C followed by tempering (650-750 °C) and warm rolling at 550 °C followed by tempering in order to improve its precipitation state and refine microstructure. The microstructural parameters such as grain size, block size, lath width and precipitate size were examined and correlated with FCG and tensile properties of investigated samples. The results showed that decreasing tempering temperature significantly reduces the fatigue threshold at RT while increases the yield strength at elevated temperature (i.e., 650 °C). Increase in fatigue threshold is found to increase with the increase in block size, whereas high density of fine precipitates contributed the high temperature strength. The FCG rate in Paris regime was less affected by heat treatment and rolling process at RT. However, rolled sample tested at 650 °C shows a decrease in FCG rate as compared to heat-treated samples. In terms of higher FCG resistance and yield strength, warm rolling followed by tempering at low temperature (i.e., 700 °C) can be considered optimum. For the numerical simulation of FCG behavior, extended finite element method (XFEM) along with Paris law has been implemented in ABAQUS using python script. The simulated FCG behavior is found in good agreement with the experimental results.

The interlaminar shear failure characteristics of asphalt pavement coupled heating cables

Nowadays, heating cables are used as heat sources for heating pavements in practical engineering. However, there is a contradiction between the snow melting function and the interlaminar stability of heating pavement. In order to solve the contradiction, the interlaminar failure behavior of asphalt mixture coupled heating cables specimen (AMCS) was researched, through experiments and the finite element method. Under the different conditions of heating cables and rolling times, a series of direct shear tests was performed at the interface of AMCS, to compare the interlaminar stability of three different AMCS. Meanwhile, based on the bilinear cohesive zone model and coulomb friction model a 2D finite element model was established, to simulate this shear failure processes and make up for the limitations of the experiment. According to above test and simulation results, the failure mechanism and the weakest interface in AMCS were found, and the influence of the heating cable’s diameter and embedded spacing on the interlaminar shear strength were found. Then, a modified coulomb theorem model was proposed to predict the shear strength of the AMCS. This research enriches the design theory of the heating pavement and it has great significance for its structural design of heating asphalt pavement.