Pass Hot Rolling Research Articles

Effect of variable thickness cross rolling on microstructure gradient of 2205 duple stainless steel

Quantitative description of the complex relationship between rolling process and microstructure is crucial for improving the performance of 2205 duplex stainless steel products. In this work, four distinct rolling processes were used for three passes of hot rolling of 2205 duplex stainless steel. The study delved into the macroscopic morphology, microstructural gradients, and texture evolution of 2205 duplex stainless steel sheets in various rolling states. In addition, a data expansion method was used to expand the original experimental data, and the support vector machine model optimized by genetic algorithm was used to accurately describe the complex relationship between different rolling processes and microstructures. The results indicate that the proposed variable thickness cross-rolling method renders a more uniform microstructure in the rolled piece, with significantly refined grains and the formation of a distinct structural gradient. Among them, when using process 3 rolling, the grain size in the edge area of the plate after three passes of rolling is finer and the degree of recrystallization is higher, which is conducive to improving the problem of poor thermal plasticity at the edges and providing a basis for studying the suppression of edge crack damage in 2205 duplex stainless steel. In addition, the proposed machine learning model accurately predicted the grain size of plates in different rolling states, aligning closely with experimental findings.

Rolling theory-guided prediction of hot-rolled plate width based on parameter transfer strategy

Machine learning performs well in many problems. However, the tendency to generate predictions that violate theoretical knowledge makes it difficult to apply to practical processing. To resolve this situation, this paper combines domain knowledge with a data-driven model, proposes a theory-guided machine learning framework based on a parameter transfer strategy, and applies it to the width prediction of plates after multiple passes of hot rolling. The framework applies a swarm optimization algorithm to the original theoretical model and generates numerous highly-physical consistent samples. The established deep neural network (DNN) model is trained with simulated data, and the parameters are fine-tuned using a parameter transfer strategy combined with actual data to ensure excellent adaptation to the actual environment based on adequate learning of theoretical knowledge. In tests, the proposed model had the best overall prediction performance in this paper. Meanwhile, the developed model is consistent with the existing perception of rolling theory. This allows for the quick and reliable application of machine learning models in production.

Fabrication of TiB-reinforced titanium matrix composite via spark plasma sintering and vertical bidirectional reactive hot rolling

TiB/Ti6Al4V composite was prepared using spark plasma sintering followed by bidirectional reaction hot rolling. The TiB whiskers were synthesized in situ during the rolling process, thereby preserving a relatively high structural integrity. TiB whiskers were distributed within the composite in three distinct locations: intragranular, intergranular, and transgranular distribution. After eight passes of vertical bidirectional reaction hot rolling, the average grain size of the matrix was refined to 1.36 μm, and the grains exhibited random crystallographic orientations. Tensile properties in different directions demonstrated high consistency, with a strength of 1220 MPa ± 30 MPa and an elongation of 8.0% ± 0.5%. The primary strengthening mechanisms in the composite included grain refinement, dislocation strengthening, and load transfer strengthening from the TiB.

Impact of uneven distribution of grain characteristics on yield strength and martensitic transformation of as-hot-rolled medium-entropy alloys

As-hot-rolled medium-entropy alloys (MEAs) with unevenly distributed grain sizes of face-centered cubic grains exhibit better yield strength without uniform elongation loss compared to cold-rolled and annealed ones. Successive operation of dynamic recrystallization (DRX) during several hot rolling passes leads to a wide range of grain sizes from submicrons to tens of micrometers due to the grain growth after nucleation: early recrystallized grains are coarser than recently recrystallized ones. Not only the grain size but internal dislocation density of the recently recrystallized grain is low. During the tensile deformation of the hot-rolled MEAs at –196 °C, dislocation pile-ups in the relatively soft and fine DRX grains enhance yield stress and hetero-deformation-induced strain hardening. Thanks to the enhanced yield stress of the as-hot-rolled MEAs, stress-induced martensitic transformation easily occurs. Notably, partially DRXed MEAs hot-rolled at 800 °C have lower yield stress than fully DRXed ones, hot-rolled at 900 and 1000 °C. This is attributed to the softening effect of the stress-induced body-centered cubic martensitic transformation in unrecrystallized coarse grains prior to the yielding, which lowers the yield stress of the partially DRXed ones. After yielding, the martensitic transformation facilitates strain hardening and early necking is precluded. This study presents a fresh outlook on the uneven distribution of grain sizes by hot rolling beneficial to mechanical responses of uniform elongation of ∼45% despite the as-rolled states with an advantage of simplified thermo-mechanical processes.

Delta ferrite formation and evolution during slab processing from an 80-ton industrial heat of AISI 304 austenitic stainless steel

Although delta ferrite is a very common phase in most austenitic stainless steels, studies about its formation and evolution during slab processing from industrial heats of tens of tons are scarce. The main objective of this research is to study the evolution of delta ferrite (quantity, chemical composition, morphology, and distribution) along the production route from the cast slab to the coil of an industrial heat of 80 tons of 304 stainless steel. Samples were extracted after the following processing steps: continuous casting, first and second hot-rolling pass, and solution-heat-treating, arriving at the final commercial condition. Sample analyses were carried out with several complementary microstructural characterization techniques: optical microscopy, scanning electron microscopy with energy dispersive spectroscopy (EDS), X-ray diffraction, and magnetic measurements of delta ferrite content (feritscope). Thermocalc® indicates that the present continuous cast slab solidifes according to the FA (ferrite-austenite) mode and the final microstructure should be completely austenitic in equilibrium conditions. Nevertheless, delta ferrite is detected along the processing steps, indicating that the steel is out of phase equilibrium. The ferrite content measured after solidification varies significantly across the as-cast slab thickness. Lower values are detected on the surfaces, followed by a gradual increase when moving into the slab, reaching a peak, and finally decreasing at the slab center. This pattern of delta ferrite content is named “M type” distribution. The average content of delta ferrite decreases after each subsequent processing step, namely the two hot-rolling passes and the solution heat-treating.

Digital simulation of aluminum alloy slab rolling with low relative reduction

It is noted that the traditional process for obtaining of aluminum alloys sheet metal is associated with semicontinuous casting of thick billets and their subsequent hot rolling. The first hot rolling pass is characterized by low reduction, which leads to strain localization in the surface layers of the metal. The finite element modeling of the first pass is performed and the stress-strain state is determined. It is found that the degree of deformation in the surface layer is approximately an order of magnitude higher than the value calculated through the total compression of the strip. At the center of the band, the deformations are practically equal to zero. Two zones along the length of the strip are revealed, in which the penetration depth of the deformation is additionally reduced. They are located at a distance from the ends of the strip, approximately equal to half of its thickness. The stress intensity is distributed quite uniformly over the thickness, but the average normal stress is distributed sharply unevenly over the thickness and is compressive near the surface and tensile in the center of the strip. This can provoke an increase in porosity, or the appearance of internal ruptures.

Finite Element Modeling of Hot Rolling of 1075 Carbon Steel Process with Variable Cross Section

Currently, it is common to use steel poles for applications in livestock and agriculture. In this work, finite element analysis of five hot rolling passes for the manufacture of farm poles using 1075 carbon steels from recycled railway material was developed. The steel industry in Mexico imports products from other countries or from companies specialized in metallurgy at an excessive cost. To be more competitive and save costs, companies seek the reutilization of existing resources such as the railway 1075 steel, which has good mechanical properties. SFTC DEFORM-3D software was used to model five hot rolling passes considering a variable cross section railway profile. The effect of rolling speed and temperature were considered to analyze flow behavior. Rolling loads were also determined.

On the grain boundary character evolution in non equiatomic high entropy alloy during hot rolling induced dynamic recrystallization

Grain boundary character evolution during dynamic recrystallization (DRX) in a non-equiatomic Fe40Mn40Co10Cr10 high entropy alloy has been examined systematically through single pass hot rolling of 30, 50 and 70 pct reduction. It was observed that the extent of DRX is highly dependent upon the hot rolling reduction. The recrystallization area fraction was considerably higher at 50 pct as compared to 30 pct and 70 pct rolling reduction. In recrystallized regions, a significant proportion of coincidence site lattice (CSL) boundaries (Ʃ≤29) were observed regardless of the rolling reductions. Interestingly, a higher proportion of CSL boundaries (particularly Ʃ3 and Ʃ9) were observed amongst the grain boundaries between recrystallized grains of last and second last necklace layer (L-S); and grain boundaries between recrystallized grains of the last necklace layer (L-L). However, most of the grain boundaries between last necklace layer and the parent deformed matrix (L-D) have been observed to be random high angle grain boundaries (HAGBs). Generation of significant fraction of second order twin boundaries (Σ9) along with first order twin boundaries (Σ3) adjacent to the recrystallization front (i.e. behind the migratinggrain boundary) is a consequence of multiple twinning processes expected to occur during DRX. Here, role of Σ3 twin boundaries on the recrystallization process has been discussed. Grain boundary character evolution and its influence on DRX in the presently studied High-Entropy Alloy (HEA) has been inferred to be similar to previously reported observations on conventional low stacking fault energy materials.

Influence of Process Parameters on Grain Size and Texture Evolution of Fe-3.2 wt.-% Si Non-Oriented Electrical Steels.

The magnetic properties of non-oriented electrical steel, widely used in electric machines, are closely related to the grain size and texture of the material. How to control the evolution of grain size and texture through processing in order to improve the magnetic properties is the research focus of this article. Therefore, the complete process chain of a non-oriented electrical steel with 3.2 wt.-% Si was studied with regard to hot rolling, cold rolling, and final annealing on laboratory scale. Through a comprehensive analysis of the process chain, the influence of important process parameters on the grain size and texture evolution as well as the magnetic properties was determined. It was found that furnace cooling after the last hot rolling pass led to a fully recrystallized grain structure with the favorable ND-rotated-cube component, and a large portion of this component was retained in the thin strip after cold rolling, resulting in a texture with a low γ-fiber and a high ND-cube component after final annealing at moderate to high temperatures. These promising results on a laboratory scale can be regarded as an effective way to control the processing on an industrial scale, to finally tailor the magnetic properties of non-oriented electrical steel according to their final application.

Predictive integrated numerical approach for modeling spatio-temporal microstructure evolutions and grain size dependent phase transformations in steels

A computational modeling for predicting microstructure evolutions and mechanical properties of steels under thermo-mechanical-metallurgical process is established, for the first time, by integrating the finite element (FE) simulation, cellular automaton simulation (CA), and phase transformation kinetics. In this microstructural-integrated modeling, various recrystallization processes, such as dynamic recrystallization (DRX), meta-DRX, and static recrystallization (SRX), are formulated based on dislocation density based constitutive laws. With microstructure information provided by the CA modeling, the austenite grain size (AGS)-dependent phase kinetics in the form of continuous cooling transformation (CCT) diagram is applied for addressing the effect of AGS on transformations under various cooling conditions. The integrated numerical approach implemented in the FE software via user defined subroutines can simulate the morphology and size distribution of constituent grains, transformed fractions of various phases, hardness profiles and flow stresses after thermo-mechanical process with large plastic deformation. As a validation of the integrated modeling, the multiple oval-round pass hot rolling and subsequent cooling process are simulated for the seismic reinforcing steel bar and the predicted microstructure and mechanical properties are compared to those of experimental data.

Modeling and simulation of mass flow during hot rolling low carbon steel I-beam

Abstract Continuously cast near net shape blanks have been widely used in industry owing to the benefit of producing items close to final shape. However, for complicated shaped blanks, such as I and H beams, using near net shape blanks is not enough to prevent unwanted mass flow and deformation during hot rolling. The strength of the rolled material, pre-existing defects, and hot rolling parameters all have a major influence on the final shape of the rolled beam. In this study, the shaping of a low carbon steel during the breakdown mill hot rolling process was investigated using finite element analysis. The geometry of the as cast beam blank, mill roll profiles and hot rolling pass schedule were modeled identically to that used during the production hot rolling operation. The results showed that the I-beam has more deformation in the flange than in the web for breakdown mill rolling. A small depression or waviness was found to develop along the beam flange during the simulation. A parametric study of the effect of the roll gap on mass flow and beam blank surface depressions was performed. It was observed that for a larger roll gap, the surface depression increased in size. In contrast, the depression was found to decrease with a smaller rolling gap due to greater mass flow. These results agreed with the industrial produced I-beam. It was also predicted that the presence of a pre-existing surface defect on the beam blank flange has a significant influence on final size of the depression.

Influence of Rolling Temperatures on Interface Microstructure and Mechanical Properties of Multi-Pass Rolling TA1/Q235B Explosive Welded Sheets

The effect of rolling temperatures on the interface microstructure and mechanical properties is investigated using 2-mm-thick TA1/Q235B composite sheets, which were prepared after nine passes of hot rolling of explosive welded plates. The results show that the vortex region and the transition layer exist in the interface at the explosive welded plate, while only the transition layer exists in the interface after hot rolling. The transition layer is composed of α-Ti, TiC, Fe, and FeTi, and the thickness increases with the increasing rolling temperature. The microhardness of the explosive welded plate is higher than that of the hot-rolling sheet, and the microhardness of interface are higher than that of matrix metals. The interface shear strength and tensile elongation of the hot-rolled sheet increase with the increasing hot rolling temperature, while the ultimate tensile strength (UTS), yield strength (YS) and Young modulus decrease with the increase of hot rolling temperature. The shear strength of sheets is related to the interfacial compounds, and the tensile strength is mainly affected by the grain morphology of the matrix.

Microstructure and mechanical properties of hot rolled ODS copper

• The previous thermal treatment of the powder affects to the alloy densification. • Higher hot rolling passes are necessary in order to close the voids. • The as HIP material exhibits the higher mechanical strength. • The hot rolling process increases the thermal conductivity. Dispersion strengthened copper alloys have been produced by following a powder metallurgy route that have consisted of milling copper and yttrium acetate powders in a planetary ball milling and subsequently sintering by hot isostatic pressing (HIP). In order to increase the degree of densification of the materials, they were subjected to a thermal treatment in vacuum and to a hot rolling process at 1173 K. The decomposition of the yttrium acetate during the thermal treatments resulted in the formation of voids, with a loss of densification that could not be satisfactorily improved with the hot rolling processing. The microstructure and the mechanical and thermal properties of the alloys were analyzed by scanning electron microscopy, electron backscattering diffraction, micro and nanohardness measurements, and compression tests and thermal conductivity measurements, both in the range 300–780 K. The best mechanical properties were obtained for the as-HIP material, with a mean grain size of 0.3 ± 0.3 μm and a yield strength value at room temperature of 520 MPa. In contrast, the material with the highest thermal conductivity for the entire range of temperature was found to be the alloy thermal treated in vacuum at 1273 K and later subjected to the hot rolling processing. The different microstructural characteristics of the alloys such as grain size, defects present in the grains and size of voids seems to be responsible of the differences on their thermal conductivity values.

Development of thermo-mechanical processing to form high density of uniformly distributed nanosized carbides in austenitic stainless steels

Model alloys and thermomechanical processing (TMP) were developed to form a high density of uniformly distributed nanosized (<10 nm) carbides in an austenitic stainless steel matrix. The composition of the model alloys was determined to control the formation of precipitates during the TMP. The TMP consisted of homogenization at 1200 °C for 1 h, multiple hot-rolling passes above and below the non-recrystallization temperature (TNR), and precipitation heat treatment at 800 °C for 2 h. By proper division of the rolling passes above and below TNR, a microstructure with a homogeneous grain size and a well-developed dislocation structure was obtained. Then, subsequent precipitation heat treatment produced a microstructure containing a high density (~1.1 × 1022/m3) of uniformly distributed and coherent NbC precipitates in the austenitic matrix. The evolution of the nanosized NbC during the precipitation heat treatment was coupled with the dislocation characteristics, such as the density and distribution, which were controlled by the hot-rolling conditions.

Hot workability of 420 J1 martensitic stainless steel

Steel grade 420 J1 is martensitic colonies embedded with ferritic phase stainless steel. The steel under investigation contains mainly 12.42 % chromium and 0.2% carbon.Hot workability of the 420 J1 steel grade became the most critical issue to suit the different application requirements. The present article is dealing with the parameters controlling successful hot workability of the steel grade 420 J1.4-conscutive hot rolling passes were designed for a thickness reduction from 7 to 3 mm. Hot deformation passes were designed to score two parallel goals. The first goal is to avoid instability regions, while the second one is to create dynamic softening.It was found that austenite is subjected to grain refinement to reach about 17 micron.The flow stress is calculated. Dynamic recovery is clearly noticed at the last two deformation passes. Microstructural investigation as well as mechanical properties for final hot rolled steel strips was executed.

Dynamic recrystallization control in hot rolling

Recrystallization is important for steel processing because it modifies microstructure along the process route and thus determines the final properties of steel products. Loads in various deformation operations and consistency of dimensions and shape of deformed steels are also influenced by recrystallization and its homogeneity. These factors are especially important in hot rolling that aims at uniform refined hot rolled microstructure. This can be achieved by avoiding dynamic recrystallization (DRX) of austenite during hot rolling passes and static recrystallization between them and before cooling. Alternatively, microstructure can be refined by stimulating recrystallization. Experimental data and constitutive analysis show that for a given steel there exist two limiting values of Zener-Hollomon parameter Z that delineate three temperature – strain ranges for DRX: no-DRX range (high Z) where DRX cannot be initiated irrespective of the applied strain, full DRX range (low Z) and partial DRX range (intermediate Z). Avoiding DRX in finishing rolling sequence implies setting up rolling speeds and temperatures in no-DRX range of Z. Alternatively, for roughing sequence the mill settings should be such as to keep rolling speeds and temperatures in the full DRX range. In any case it is imperative to avoid partial DRX, i.e., to avoid rolling speeds and temperatures that correspond to intermediate Z range. This approach can be directly utilized to control DRX in hot strip mills and plate mills based on the experimental data.

Characterization of Thermomechanically Processed High-Temperature Ni-Lean NiTi–20 at.% Hf Shape Memory Wires

The thermomechanical processability of Ti(Hf)-rich Ni49.8Ti30.2Hf20 (at.%) high-temperature shape memory alloy (HTSMA) wires was examined. Hot-extruded rods with an initial diameter of 6.35 mm were hot-rolled and cold-drawn into a final diameter of 260 µm. For all samples, processing was performed in open air without extrusion canning. The HTSMA rods were processed to an area reduction of 99.83%. Experimental results showed that hot-rolling at 800 °C decreased the grain size and introduced a small amount of retained austenite, while breaking up the Ti4Ni2Ox intermetallic oxide phase, resulting in a 10 °C decrease of the austenite start temperature (As). While both hot-rolling and cold-drawing exhibited clear effects on the thermomechanical properties, neither the number of hot-rolling passes nor the number of cold-drawing passes affected the transformation temperatures of the material. Additionally, the NiTiHf HTSMA showed similar thermomechanical responses after the 5th and 25th hot pass when subjected to room temperature loading to 500 MPa (uniaxial tension) and thermally induced shape recovery.

Influence of hot rolling on the microstructure of lean duplex stainless steel 2101

In this work, the microstructure and the strain partitioning of lean duplex stainless steel 2101 (LDX 2101) during different hot-rolling processes are investigated by optical microscopy and electron-backscattered diffraction (EBSD). The results show that the LDX 2101 exhibits poor thermoplasticity at high temperature. The four-pass hot-rolled plates show fewer edge-cracking defects and superior thermoplasticity compared with the two-pass hot-rolled plates prepared at different temperature. The phase boundary is the weakest site in the LDX 2101. The cracks are initiated and propagated along the phase boundaries during the hot-rolling process. According to the EBSD analysis, the increase of the hot-rolling pass can dramatically improve the strain distribution in ferrite and austenite phases and promote the strain transmission in the constituent phases, thereby improving the coordinated deformation ability of the two phases. This effect further increases the thermoplasticity and reduces the formation of edge cracks in LDX 2101.

Effects of rolling on microstructures and properties of in-situ (TiB2 + ZrB2)/AlSi9Cu1 composites

In this paper, the (TiB2 + ZrB2)/AlSi9Cu1 composites were fabricated via in situ reaction from Al-K2TiF6-K2ZrF6-KBF4 reaction system. The effects of rolling on microstructures and properties of the composites were investigated by XRD, SEM, TEM and mechanical tensile test. In addition, the influence mechanisms of plastic deformation on aluminum alloy composites were discussed in detail. The results show that the in situ TiB2 and ZrB2 particle well distributed in the matrix with the size of 20∼50 nm and the morphology is short-stick or plate. The rolling technology could obviously optimize the microstructure, enhance the properties of the composite especially, after 6 passes hot rolling and 4 passes cold rolling, the TiB2 and ZrB2 particles clusters with size range from 80 to 150 nm were uniformly distributed in the matrix, the Si phases were fractured into different small parts with the size of less than 1 μm and the grains size were further reduced. The ultimate tensile strength (UTS) and elongation (EL) of in situ composite are 282 MPa, 17.6%, respectively. Also, the Portevin-Le Chatelier (PLC) phenomenon found in the composite was discussed.

Cracking of Electrolytic Tough Pitch Copper Plates During Hot Rolling

Failure analysis is performed in electrolytic tough pitch copper plates that have been severely fractured during the initial hot rolling passes. A comprehensive investigation was conducted, including mainly macroscopic examination, fractographic and metallographic evaluation. Moreover, numerical simulation of the solidification front using a computational fluid dynamics software was also employed to analyze the influence of the variation of casting parameters on the solidification front development. Fracture areas manifested poor ductility, while in many cases a prior cast pattern consisting of coarsely solidified dendritic crystals was revealed. The obtained evidence is suggestive of microstructural embrittlement caused by the synergistic contribution of the manufacturing process conditions and the potential elemental and particle segregation, such as cuprous oxide aggregation, that might promote failure susceptibility.