Hot Rolling Conditions Research Articles

On the occurrence of dynamic strain aging in near-alpha alloy Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si

Alloy Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si (IMI 834) is the most recently developed near-alpha type titanium alloy for high-temperature application up to 873 K, as discs and blades in the high pressure part of compressors, in advanced jet engines. It possesses a good combination of creep and fatigue resistance at elevated temperature, in properly heat-treated condition, and has a fine bimodal microstructure, consisting of a small volume fraction of equiaxed alpha in a fine-grained matrix of transformed beta. Some investigations have already been done on the tensile behavior of this alloy, in different heat-treated conditions, over a wide range of temperature from 293 to 923 K. However, no report has been made on the occurrence of dynamic strain aging (DSA) in this alloy. The purpose of this article is to present the observation on the occurrence of DSA in the titanium alloy IMI 834, in the as-received (hot-rolled and mill-annealed) condition, over the temperature range 623 to 823 K.

The tensile failure of mild steel oxides under hot rolling conditions

The failure of oxide scales formed on mild steel (mass contents of 0.17% C, 0.13% Si, 0.72% Mn) was investigated using a high‐temperature tensile test technique over the temperature range 830 – 1150°C. Strain and strain rates used were 1.5 – 20% and 0.02 – 4.0 s−1, respectively. The scales were 10 – 300 μm thick. The variations of these test parameters were chosen to approximate the tensile loading of the oxidised surface layer at the slab faces just before roll contact at the upper or lower surfaces. Oxide scales formed cannot be assumed either to be perfectly adhering during tensile loading, in the sense of slipping, or to be fully brittle. Two limit modes leading to oxide spallation have been observed which are strongly influenced by the temperature, strain rate and strain. For the first mode initial through‐scale cracking occurs followed by initiation and propagation of a crack along the oxide‐metal interface between adjacent cracks. The second mode corresponds to the slipping of the oxide scale relative to the metal surface before spallation. The delamination and following slipping of the oxide raft can take place along the interface within the non‐homogeneous oxide scale.

Influence of Coiling Temperature on Toughness of Hot Rolled Microalloyed Steels

The effect of coiling temperature on the toughness of hot rolled microalloyed steels was investigated. Heats with different Nb and/or Ti contents were laboratory hot rolled in austenitic conditions. Coiling temperatures were varied between 400°C and 700°C. A reduction of more than 50% was given below the recrystallization-stop temperature of the steels. Finishing temperature was around 860°C and thickness of the finished strips was about 6 mm. The transformation behaviour of the steels was studied by deformation dilatometry in order to select an appropriate thermomechanical treatment and to correlate the influence of coiling temperature with transformation kinetics. The influences of grain size, grain boundary cementite, pearlite morphology, coherency of precipitates and solute carbon on toughness of the steels were examined. It was found that the most important parameter in achieving a good toughness in the hot rolled condition is the carbide morphology. By selecting coiling temperatures below the pearlite start temperature of the particular steels, a fine carbide (pearlite) dispersion was obtained with excellent toughness properties. Although a possible harmful influence of the presence of coherent precipitates on the toughness of the microalloyed steels should not be completely excluded, it is thought to have a minor effect at these temperatures.

Influence of Thin Slab Casting on the Properties of Microalloyed Steel for High Cold Forming Requirements

The grain refining influence of a TiN-precipitation during conventional continuous casting is already well established /1/. During direct hot processing of thin slabs, TiN-precipitation should occur in the liquid phase during solidification /2, 3/ and in the austenite /4/. Various experiments have been carried out in order to examine the effect of a TiN-precipitation before and during hot rolling of thin slab casted Ti- and TiNb- microalloyed high strength structural steels. The precipitation behaviour has been determined by TEM investigations. The samples show a large variety of TiN and Ti(N,C) precipitates. Number and size of the precipitates are depending on the holding and rolling-start temperatures. The impact of the individual hot rolling conditions on precipitation state, grain size as well as strength- and toughness-properties have been determined.

Efecto del procesado termomecánico sobre las propiedades mecánicas de la aleación MA956. I Caracterización microestructura

Both the microstructural characteristics and the texture of the ferritic oxide dispersion strengthened MA956 alloy have been studied after different stages of processing. The material was supplied by INCO Alloys International in three conditions: hot isostatically pressed (HIP), hot extruded + 1,330°C/1 h and hot rolled. Two annealing treatments: 1,100°C/100 h and 1,330°C/1 h were performed on the HIP and hot rolled materials to observe the effect of previous microstructure (or the thermomechanical history) on the final microstructure. In the hot-extruded condition, the initial strong fibre texture evolves towards a very strong texture after 1,330°C/1 h treatment, whereas in the hot rolled condition the initial fibre texture with components and results in a after the same thermal treatment. It is pointed out that this difference in the final texture could be due to the differences in the volume fraction of primary grains with and orientations.

Effect of Hot Rolling Conditions on the Microstructure and Mechanical Properties of Fe-C-Mn-Si Multiphase Steels

There is a growing need for the high strength steels with high formability for many applications. Using the concept of transformation induced plasticity (TRIP) observed in austenitic steels, one can obtain the combination of high strength and high formability. However, these austenitic steels require a fairly large amount of alloying elements which impose several practical problems for their widespread applications. On the other hand, it has been shown that the dual phase steels possess the relatively good combination of strength and formability due to their characteristic microstructure. The major microstructural constituents of dual phase steels are soft ferrite and hard martensite/bainite with small amount of retained austenite. In recent years, the beneficial effect of retained austenite on the mechanical properties of dual phase steels have been re-recognized and accordingly, there have been several investigations on developing the so-called TRIP-aided dual phase steels having increased amount of retained austenite in the microstructure. Most investigations on these TRIP-aided dual phase steels have been concentrated on the effects of heat treatment conditions and alloying elements such as Si, Mn, C and P on the microstructure and mechanical properties of cold rolled sheet steels. There have also been a few studies on developing suchmore » steels by hot rolling, and the emphases of these studies are placed mostly on increasing the amount of retained austenite. However, the microstructure of these hot rolled steels is far from optimum, consisting of large packets of hard second phase particles. The main objective of the present study is to modify the microstructure of this class of steels by varying the hot rolling conditions. The steel used in the present study is Fe-0.2C-2Si-1.5Mn.« less

Effect of Roll and Rolling Temperatures on Sticking Behavior of Ferritic Stainless Steels.

The sticking behavior of several austenitic and ferritic stainless steels under the hot rolling conditions was examined in detail using a two disk type hot rolling simulator. The sticking of bare metal to roll surfaces was strongly dependent on the high temperature tensile strength and the oxidation resistance of the stainless steel. A steel having higher tensile strength and lower oxidation resistance exhibited better resistance against sticking. The sticking occurred in increasing severity in the order of 430J1L, 436L, 430 and 409L. It was clarified that a high speed steel (HSS) roll was more beneficial to prevent sticking compared to a Hi-Cr roll.

Recrystallization and Related Phenomena. Influence of Hot Rolling and Cooling Conditions on the Grain Refinement of Hot Rolled Extralow-carbon Steel Bands.

In this paper, the effect of various operational parameters in a hot strip rolling process on the grain refinement of hot rolled plain extralow-carbon steel bands has been investigated. The finishing temperature and the onset time of cooling after hot rolling influence the grain refinement significantly. The finishing temperature just above Ar3 is optimum for the grain refinement. The reducing of the onset time of cooling not only refines the grain size, but also decreases the finishing temperature-dependence of grain size. The increase in the reduction of the final hot rolling refines the grain size as well. The cooling rate does not affect the grain size of hot bands in the range between 40 and 120°C/sec significantly. The mechanism of the grain refinement has been discussed with a relation of recrystallization and transformation behavior of austenite and it is concluded that in the case of extralow-carbon steel without Ti and Nb addition, the grain refinement of hot bands is strongly influenced by not only the recrystallization but also grain growth behavior of austenite.

Recrystallization and Related Phenomena. Effect of Hot Band Microstructural Factors on Recrystallization Texture in Ti-added Ultra-low Carbon Cold-rolled Sheet Steels.

An examination has been made of the effect of hot rolling conditions, considered as thermal history, on the deep drawability and recrystallization texture formation in Ti-added ultra-low carbon cold-rolled sheet steels. The findings show that the average r-value of IF steel is significantly improved by refining the hot band grains, by decreasing the finish-rolling temperature in large thermal drop, to temperature even below the Ar 3 transformation temperature, during hot rolling process. However, the average r-values of sheets hot-rolled almost isothermally at a finish-rolling temperature below the Ar 3 transformation temperature deviate detrimentally, when compared with hot band of the same grain size. In this study, an attention has paid to the formation of texture throughout the hot rolling, cold rolling and annealing processes, in relation to deep drawability.

Effects of Cu and Other Tramp Elements on Steel Properties. Effect of Cu, Sn and Ni on Hot Workability of Hot-rolled Mild Steel.

The effect of tramp elements Cu and Sn on the hot workability of mild steels was investigated in this paper. A hot rolling condition was simulated by oxidizing followed by tensile-deforming and the hot workability was assessed by measuring the number of surface cracks. The microstructure at the scale/steel interface was closely observed, and the relationship between the surface cracking and the microstructure was established. Sn as low as 0.04 % increased the number of cracks in an 0.3 % Cu bearing steel, while 0.3 % Ni suppressed the cracking in an 0.3%Cu-0.04%Sn bearing steel. An energy dispersive X-ray spectroscopy (EDX) at the subscale layer of the oxidized Cu-Sn bearing steel revealed that an 82%Cu-7%Sn-Fe alloy phase formed at the scale/steel interface. The phase calculation using the Thermo-Calc computer program showed that Sn decreased the solubility limit for Cu in Fe, thus increasing the amount of liquid Cu enriched alloy and enhancing the surface cracking by Cu liquid embrittlement. On the other hand, an addition of 0.3 % Ni to the 0.3%Cu-0.04%Sn bearing steel formed two different Cu-Sn phases at the surface of the steel; a 12%Cu-19%Ni-Fe layer under the steel surface and a liquid 63%Cu-12%Sn-12%Ni-Fe alloy placed above the layer. The amount of the 63%Cu-Sn-Ni-Fe alloy was a little, and the 12%Cu-Ni-Fe layer was in a large amount. In addition, the phase calculation at an oxidation temperature 1 100°C showed that the Cu and Ni enriched layer was solid. Therefore, the addition of 0.3 % Ni suppressed the surface cracking in the Cu-Sn bearing steel. A mechanism of the reduced amount of liquid by increasing Ni content was discussed in terms of local equilibrium and inward diffusion of Cu atoms from the Cu enriched layer into the steel.

Microstructural characteristics of an ultrafine grain metal processed with equal-channel angular pressing

Equal-channel angular pressing is a procedure for producing a fully dense material with an ultrafine grain size, typically in the submicrometer or nanometer range, by subjecting the material to a very high plastic strain. This paper describes the principle of equal-channel angular pressing and illustrates the capability of the technique by reference to a series of detailed experiments conducted on an Al-3%Mg solid solution alloy in which the grain size was successfully reduced by equal-channel angular pressing from an initial size of ~500 μm in the hot-rolled condition to a final size of ~0.2 μm.

Age Hardening in a Cu-bearing High Strength Low Alloy Steel.

The copper age hardening response in a low alloy variant of the ASTM A710 type steel has been investigated at temperatures of 450, 500, and 550°C for three pre-treated conditions (as rolled ferrite, bainitic ferrite, and martensite). Transmission electron microscopy has been used to follow microstructural changes and their relation to the variations in the hardness curves. The results indicate that the age hardening responses of both the martensitic and bainitic ferrite structures are much higher than that of the as rolled condition, and this observation is rationalised in terms of higher solute Cu content, higher density of dislocations and greater uniformity of solute copper atoms in the pre-treated condition providing a multitude of nucleating sites for copper precipitation. Moreover, it has been found that the peak hardness in the martensitic and bainitic structures was attained when fine e-copper precipitates are predominantly observed on dislocations. Compared to the martensitic and bainitic structures, the presence of pre-existing interphase e-copper precipitates, as well as the formation of additional copper-rich clusters and precipitates from supersaturated ferrite contribute to the aging response in the hot rolled condition.

Experimental investigation of the transformation texture in hotrolled ferritic stainless steel using single orientation determination

Two ferritic stainless steels (≈16.5 mass pct Cr) were hot-rolled using seven subsequent passes. The first sample was rolled within the range 1280 °C to 750 °C,i.e., the deformation started in the ferritic region. The second sample was rolled within the range 1080 °C to 770 °C,i.e., the deformation started in the ferritic-austenitic region. In both cases, up to 40 vol pct of the ferrite transformed into austenite during hot rolling. During the last passes, the austenite transformed into cubic martensite. After hot rolling, these former austenitic regions were identified using a selective etching technique and examined using single orientation determination in the scanning electron microscope. The regions which remained ferritic throughout the hot-rolling process were investigated as well. Whereas the texture of the martensite considerably depended on the hot-rolling conditions, especially on the temperature and on the intervals between the rollings, the texture of the ferrite was less affected. The textures of the martensite were interpreted in terms of the crystallographic transformation rules between austenite and martensite. The textures of the ferrite were discussed in terms of recovery and recrystallization.

Mechanical behavior of aluminum deformed under hot-working conditions

The stress-strain behavior of aluminum 3–9 purity deformed at elevated temperatures has been analyzed on a rational basis. Emphasis has been given to the analysis of the curves corresponding to typical deformation conditions of interest for hot rolling of commercial aluminum alloys. The strainhardening behavior has been modeled assuming the validity of the typical saturation exponential equation earlier proposed by Voce. The temperature and strain dependence of the flow stress parameters involved in such an equation has been introduced by means of a model based on the power law relationship, where the stress-sensitivity exponent of the strain rate is considered to be temperature dependent. The strong temperature dependence of this parameter precluded the use of the exponential relationship expressed in terms of the Zener-Hollomon parameter. Therefore, a different temperature-compensated strain rate parameter similar to the MacGregor-Fisher parameter has been employed following the earlier developments put forward by Kocks. Thus, a satisfactory correlation of the flow stress parameters with the deformation conditions has been obtained. The final constitutive equation derived provides a satisfactory reproduction of the experimental values of the flow stress and follows quite closely the strain-hardening behavior. The mean activation energy determined by the different models confirmed the predominance of both climb of edge dislocation segments and motion of jogged screw dislocations as the rate-controlling mechanisms during deformation of this material under hot-working conditions. The use of a constitutive equation which expresses the flow stress of the material in terms of the applied strain, rate of straining, and deformation temperature to calculate the power dissipation efficiency of the material(η) deformed under hot-rolling conditions has shown that it could be strongly strain dependent, particularly toward the end of the rolling schedule. Hence, it has been concluded that the calculation of both the power co-content as defined in dynamic material modeling (DMM) and its maximum value, taking into consideration the constitutive equation previously developed, represents a more plausible and soundly based approach toward the determination of η.

Simulation of the hot rolling and accelerated cooling of a C-Mn ferrite-bainite strip steel

By means of torsion testing, the microstructures and mechanical properties produced in a 0.14 Pct C-1.18 Pct Mn steel were investigated over a wide range of hot-rolling conditions, cooling rates, and simulated coiling temperatures. The austenite grain size present before accelerated cooling was varied from 10 to 150 μm by applying strains of 0 to 0.8 at temperatures of 850 °C to 1050 °C. Two cooling rates, 55 °C/s and 90 °C/s, were used. Cooling was interrupted at temperatures ranging from 550 °C to 300 °C. Optical microscopy and transmission electron microscopy (TEM) were employed to investigate the microstructures. The mechanical properties were studied by means of tensile testing. When a fine austenite grain size was present before cooling and a high cooling rate (90 °C/s) was used, the microstructure was composed of ferrite plus bainite and a mixture of ferrite and cementite, which may have formed by an interphase mechanism. The use of a lower cooling rate (55 °C/s) led to the presence of ferrite and fine pearlite. In both cases, the cooling interruption temperature and the amount of prior strain had little influence on the mechanical properties. Reheating at 1050 °C, which led to the presence of very coarse austenite, resulted in a stronger influence of the interruption temperature. A method developed at Institut de Recherche Siderurgique (IRSID, St. Germain-en-Laye, France) for deducing the Continuous-Cooling-Transformation (CCT) diagrams from the cooling data was adapted to the present apparatus and used successfully to interpret the observed influence of the process parameters.

Some new results in thermomechanical processing of microalloyed steels

In recent times, efforts have been directed towards a better understanding of the mechanisms associated with deformation and restoration of austenite during continuous multipass hot rolling of microalloyed steels. The correspondence between the condition of austenite before transformation and the resultant microstructure upon cooling holds the key to the attainment of interesting properties.In the present paper, some results obtained on the deformation of austenite in a microalloyed steel, using a hot compression machine, are presented. Here, the idea was to simulate actual plate rolling or hot strip rolling conditions and study the evolution of microstructure at different stages of the hot deformation process i.e. after precise reductions at given strain rate and temperature of deformation.The paper further discusses recent results obtained by us on the influence of hot deformation parameters (strain, finish rolling temperature, temperature of deformation) and cooling rates (air cooling, spray water cooling) on the microstructure of microalloyed steel. The precise conditions leading to the evolution of acicular ferrite and bainitic microstructures have been identified. New information on the influence of short tempering treatments (15 min at 550, 600 and 650°C) on the microstructure and properties of a microalloyed steel are also outlined.

Effect of hot rolling condition on the development of textures in ultra low carbon steel

The development of hot and cold rolling textures in Ti-bearing ultra low carbon steel has been investigated laying emphasis on effects of various processing parameters such as slab reheating temperature, hot rolling temperature, partition of hot rolling and cold rolling reductions. {225}〈554〉, {001}〈110〉 and {225}〈110〉 are suggested as attractors of texture components during deformation, which have 29.5° rotation relationship to a common 〈110〉 axis with respect to each other. In chaotic rotation of grains during deformation, if the material lies under shear condition, {225}〈554〉 appears as a main texture component. Due to crystallographic instability, {225}〈554〉 easily alters to {001}〈110〉 and further to {225}〈110〉 under plane strain condition and/or with increasing rolling reduction.

Influence of the hot rolling conditions on texture formation in Fe-Si sheets

The hypothesis that hot rolling conditions and the microstructure of the hot band produced thereby are the basic factors in developing distinct textures in sheet materials is confirmed by the results given. Starting from hot rolled plates of Fe-1% Si alloys with different carbon contents it was possible to obtain the three technically important textures ({110}〈001〉, {100}〈001〉 and {111} fibre) simply by varying the microstructure by applying final hot rolling under different conditions, while keeping cold rolling and final heat treatment unchanged.

Formation of metastable phases in a spray deposited 2024 aluminium alloy

The microstructures of a spray deposited 2024 aluminium alloy in the hot rolled condition were investigated by transmission electron microscopy. It was found that there exist amorphous and quasicrystalline phases in the spray deposited preform, and neither metastable phase is able to undergo structural change in the 400 °C as-rolled condition, showing high termal stability. A reasonable mechanism for the formation of both metastable phases is described using a spray model.

Structure and properties of steels 32G2F and 32G2FRT

Currently there is extensive use of low-alloy steels with microadditions of vanadium, boron, titanium, and other alloying elements which are introduced with the aim of refining austenite grains, preventing softening during subsequent welding, and attaining quite high strength and ductility properties mainly in the hot-rolled condition. In the present work, austenite transformation kinetics are studied for steels 32G2F and 32G2FRT in order to evaluate the possibility of using them for manufacturing high-strength drilling pipes.