Continuous Heat Treatment Research Articles

Introduction of flatness gage IP-4 on the continuous Wean-Damiron heat-treatment line at the Samara Metallurgical Plant

Results are presented from the practical application of opto-electronic flatness gage IP-4 on a continuous heat-treatment line. The gage is being used to increase the flatness of aluminum alloys after their quenching and combination straightening by bending and tension. The gage allows quality adjustment of straightening machines and makes it possible to quantitatively measure flatness in real time. The machine operator can adjust the parameters of the straightening operation and significantly improve the quality of the product. When coils are being straightened, the gage makes it possible to reliably predict the flatness of the rolled product at the outlet of the machine and decide on the need for additional straightening without having to prepare samples of the metal.

Modification of the Submerged Coil To Prevent Microbial Carryover Error in Thermal Death Studies

A submerged coil unit generates death rate data for foodborne pathogens through precise computer-controlled sequential sampling rather than the usual manually timed, labor-intensive single sampling associated with other approaches. Our work with Yersinia pseudotuberculosis and Listeria monocytogenes Scott A using the submerged coil unit indicated non–log-linear death rates with large degrees of tailing. Varying degrees of cell adhesion to the surface of the exit port resulted in carryover that was likely the primary cause of these non–log-linear kinetics. This carryover also resulted in erroneously high measured levels of thermal resistance for both organisms. To address the carryover problem, modifications were made to the exit port of the submerged coil unit to ensure continuous and uniform heat treatment. These modifications resulted in a 2-fold decrease in measured D-values for L. monocytogenes Scott A and a 10-fold decrease in measured D-values for Y. pseudotuberculosis. D-values measured with the modified machine for L. monocytogenes Scott A were similar to those found in the literature. Slight tailing in survival curves persisted with the modified method, particularly for Y. pseudotuberculosis. These results indicate that kinetic data for microbial death rates obtained using an unmodified submerged coil unit must be viewed with suspicion in light of the significant potential for carryover.

Structural transformations in NANOPERM-type alloys studied by Mössbauer spectrometry and diffraction of synchrotron radiation

As-quenched Fe91 − x Mo8Cu1B x NANOPERM-type alloys (x = 12, 15, 17, 20) were exposed to continuous heat treatment up to 800°C. During the temperature increase (ramp of 10 K/min), an in situ acquisition of diffracted synchrotron radiation intensities was performed. The obtained data are correlated with those derived from the volume and surface Mossbauer effect experiments. The onset of individual crystallization steps as well as identification of the crystalline phases created is discussed.

Effects of Molybdenum on Continuous Cooling Transformation Behavior and Heat Treatment Characteristics for Low Alloyed Ductile Iron

Effects of Molybdenum on Continuous Cooling Transformation Behavior and Heat Treatment Characteristics for Low Alloyed Ductile Iron

Nanocrystallization kinetics and glass forming ability of theFe65Nb10B25metallic alloy

The crystallization kinetics of glassy ${\mathrm{Fe}}_{65}{\mathrm{Nb}}_{10}{\mathrm{B}}_{25}$ melt-spun ribbons is studied by differential scanning calorimetry in the mode of continuous heating and isothermal annealing and by x-ray diffraction and transmission electron microscopy. Continuous heat treatments of the ribbons show the presence of multiple exothermic peaks before melting. The low-temperature peak corresponds to the precipitation of nanoscale ${\mathrm{Fe}}_{23}{\mathrm{B}}_{6}$-type crystalline metastable phase, and further annealing leads to its transformation into the metastable ${\mathrm{Fe}}_{3}\mathrm{B}$ phase and subsequent formation of $\mathrm{bcc}\text{\ensuremath{-}}\mathrm{Fe}$, ${\mathrm{Fe}}_{2}\mathrm{B}$, and FeNbB stable crystalline phases. The nucleation frequency and the growth rate are determined at selected temperatures from the analysis of the microstructures that emerge during the ${\mathrm{Fe}}_{23}{\mathrm{B}}_{6}$-type nanocrystallization. The master curve method is used to obtain the apparent activation energy and the Avrami exponent at the nanocrystallization onset. The nanocrystallization kinetics is explained in the framework of the Kolmogorov-Johnson-Mehl-Avrami theory. The rejection of insoluble alloy atoms during primary crystallization, the formation of diffusion layers around the crystals, and the decrease in the nucleation frequency caused by alloy enrichment of the residual disordered matrix is modeled through a soft impingement factor. Estimated values for the interfacial energy that provide a satisfactory agreement between experiments and modeling are derived considering that homogeneous nucleation frequency and interface-controlled grain growth are dominant at the onset of the nanocrystallization. Consequently, the time-temperature-transformation diagram is also drawn and the critical cooling rate estimated for this glass forming alloy.

Precipitation of Cr-rich phases in rapidly solidified Ni–20Al–8Cr (at.%) powders

The evolution of the microstructure in rapidly solidified Ni–20.9Al–8Cr–0.49B (at.%) powders after different continuous and isothermal heat treatments at temperatures up to 1100 °C has been studied by electron microscopy and microanalysis. Powders in the rapidly solidified condition have a dendritic microstructure consisting of Ni 3Al dendrites and a NiAl phase in the interdendritic regions. Chromium is in solid solution in both phases. This microstructure is stable when heating at 10 K min −1 up to 750 °C. When the powders are heated up to 950 °C, partial dissolution of the NiAl phase and the precipitation of very small chromium-rich particles take place. The microstructure of the powders after annealing at temperatures between 750 and 1100 °C for different times is characterised by the dissolution of the β-NiAl phase and the simultaneous precipitation of various Cr-rich phases. α-Chromium, the metastable X-phase, and dark polygonal Cr 5B 3 precipitates have been identified. The segregation of chromium and boron in the form of borides removes these elements from the intermetallic matrix, so the content of both elements should be optimised to preserve their beneficial influence on the ductility of the γ′-Ni 3Al phase.

Effects of Manganese on Continuous Cooling Transformation Behavior and Heat Treatment Character for Spheroidal Graphite Cast Iron

Effects of Manganese on Continuous Cooling Transformation Behavior and Heat Treatment Character for Spheroidal Graphite Cast Iron

간접 가열방식의 연속식 열처리로내 판(Plate) 온도해석에 관한 연구

This study has been performed to predict the transient thermal behavior of the plate in indirectly-fired continuous heat treatment furnace. The temperature profiles in the plate are determined solving the transient one-dimensional heat conduction equations. To verify the validity of the present numerical results, the present results obtained from the transient analysis are compared with those of experiments. Extensive parametric investigations are performed to examine the effects of the emissivities of the plate and refractory, plate thickness and velocity, as well as the gas temperature, on the thermal behavior of the plate.

BSCCO-2212 conductor development at oxford superconducting technology

Three types of BSCCO-2212 conductor are in development at Oxford Superconducting Technology (OST). Prototype size batches of multifilament tape continue to be manufactured for use in a 5 T high field insert magnet demonstration in collaboration with the National High Magnetic Field Lab. Progress will be reported in improving uniformity of microstructure and transport properties in these tapes. Development of multifilament wire has been renewed in response to interest from the high energy physics community. Issues of interest in these wires include the effects on J/sub c/ from filament size and distribution, as well as chemical composition and impurity content in the ceramic. Progress in J/sub c/ and J/sub E/ at 4.2 K in these wires will be discussed. Optimization of dip-coated 2212 tape for MRI magnet applications is also underway, as part of a Superconductivity Partnership Initiative. Various cost and performance tradeoffs will be considered, including the silver/ceramic ratio, the thickness of the ceramic, and the choice of batch or continuous heat treatment. The status of these optimization efforts will be reported.

Precipitation and recrystallization behavior of beta titanium alloys during continuous heat treatment

Precipitation and recrystallization behavior during the continuous heat treatment of three beta-titanium alloys with various molydenum equivalents (VT22, Ti-15-3, and TIMETAL-LCB) was established. Following solution treatment, the materials were cold deformed to various reductions and then heated at rates between 0.17 and 50 K s−1 to peak temperatures below and above the beta-transus temperature. Precipitation below the transus was most rapid for the alloy with the least amount of beta stabilizing elements (VT22) and next fastest for the most-highly-alloyed material (TIMETAL-LCB), an effect ascribed to its large iron content. The reduction level was found to have a very strong influence on the uniformity of recrystallization and the recrystallized grain size. Because of the competition between precipitation and the temperature dependence of recrystallization nucleation and growth, the heating-rate dependence of the recrystallization temperature for the beta-titanium alloys was weak.

Microstructure of as-melt spun Al−Cu−Mg−Fe−Ni alloy and its variation in continuous heat treatment

A commercial AA2618 alloy was treated through melt spinning at rotating speeds of 20 and 40 m·s−1. The as-melt spun ribbons were characterized by a combination of optical microscopy (OPM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The microstructural evolution of the ribbons in a continuous heating process was investigated, and the microhardness was also measured under different conditions. It was found that AlxFeNi is prone to precipitate in AA2618 alloy due to the minimal solubility of iron and nickel. Fine AlxFeNi particles appeared along the grain boundaries at the chilling sides of as-melt spun ribbons, and at both the grain boundaries and in the interior of grains at the free sides. On continuous heating AlxFeNi precipitated steadily and uniformly throughout the matrix until melting. The microhardness of as-melt spun ribbons decreased significantly from the chilling surfaces to free surfaces. Precipitation of AlxFeNi lowered the hardness of the alloy.

A production planning and design model for assessing the thermal behaviour of thick steel strip during continuous heat treatment

This paper presents a theoretical model to determine the temperature variation of steel strip as it passes through a continuous-cooling line. The model permits the temperature along the strip to be determined and includes the effect of strip thickness to be taken into account. The model may be used in three ways. These are: to determine the strip temperature distribution having specified the external surface heat transfer coefficient as a boundary condition and hence to specify the required length of the cooling line and the nature of the cooling technology appropriate to the thermal duty required to examine the effect of changing operational parameters, such as the strip thickness and line speed, on an existing cooling line so that required production rates are matched to the thermal characteristics of the line and to specify the distribution of the heat transfer coefficient along the cooling line in order to achieve a metallurgical prescribed timewise cooling history. The paper includes a set of examples that illustrate these applications of the model.

The microstructure of as-melt spun Al–7%Si–0.3%Mg alloy and its variation in continuous heat treatment

The commercial A356 alloy was treated using melt spinning at rotating speeds of 20 and 40 m s −1, respectively. The as-melt spun ribbons were characterized by a combination of optical microscopy (OPM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). DSC tests were carried out to measure the microstructural evolution and melting of the ribbons during continuous heating, and microhardness of the ribbons under different conditions was also measured. It was found that at the chilling sides of A356 ribbons the matrix was composed of non-dendritic equiaxed grains, while at free sides the matrix was composed of dendritic grains. Silicon particles were found to preferentially precipitate along the grain boundaries on a nanometer scale at free sides. DSC tests indicated that in A356 ribbons the endothermic peaks of ternary Al–Mg 2Si–Si eutectic melting drastically weakened, while the peaks of binary Al–Mg 2Si eutectic melting vanished. The microhardness of the aluminum matrix at chilling sides of as-melt spun ribbons was significantly raised.

Accelerated artificial ageing regimes of commercial aluminum alloys. I. Al–Cu–Mg alloys

Abstract The effects of temperature and exposure on the phase composition and morphology of hardener precipitates, strength and plasticity of commercial Al–Cu–Mg alloys were carried out. These results are submitted as TTT (time–temperature transformation) and TTP (time–temperature properties) diagrams for ageing. In Al–Cu–Mg alloys within a wide temperature range (160–260°C) the structure of hardener precipitates is the same. The age hardening rate is determined by identical diffusion processes subjected to the Arrhenius equation. For this system short-term accelerated artificial ageing regimes with exposure of less than 10 min is possible for reception of high strength. Examples of such regimes used for thin sheets from D16 and 1161 alloys in commercial conditions on a continuous heat treatment line are given. For thicker products accelerated regimes depend on the heating duration determined by the type of thermal device, the modes of stacking products, their thickness and non-uniformity on thickness. The examples of the accelerated ageing regimes in commercial conditions for forgings from AK4-1 alloy (type of 2618 alloy) are presented. The comparison of the mechanical properties, damage tolerance, corrosion resistance, technological plasticity of the semiproducts processed by standard and accelerated ageing regimes is given.

The Effect of Continuous Cooling Heat Treatment on Interface Properties of SK3/Copper Compound Casting

The bonding of an SK3 steel insert to copper during cast welding and heat treatment was studied. The interface shear strength was made with a push-out test. After cast welding, a cast welding layer formed between SK3 steel and copper. After a continuous cooling heat treatment, there was a cast welding layer near the SK3 steel matrix, an irregular layer near the copper matrix, and a middle layer between them. X-ray diffraction analysis was used to determine that the interface layer consisted of carbon and CuFeO2. Through electron probe x-ray microanalysis (EPMA), it was shown that mainly iron atoms and carbons diffused into the copper matrix. The interface shear strengths of the compound casting while with water quenched, oil quenched, air cooled, and furnace cooled, were 23.42, 18.74, 12.29, 13.43, and 8.33 MPa, all of heat treatment fractures in the cast welding layer near the SK3 steel matrix.

Reaction mechanism and kinetics analysis of lithium nickel oxide during solid-state reaction

The reaction mechanism and kinetics analysis for the formation of lithium nickel oxide (LiNiO2) during solid-state reaction have been investigated. The atmosphere during the reaction has a pronounced effect on the stoichiometry and cation arrangement of LiNiO2. It is obligatory to supply adequate oxygen partial pressure to overcome the diffusion barrier existent in the precursor powder. It is difficult to synthesize stoichiometric LiNiO2 with the Rm structure if the oxygen partial pressure is too low. The formation of LiNiO2 requires continuous heat treatment for a certain period of time which depends on the heating temperature and the oxygen partial pressure provided. Based on the Johnson–Mehl–Avrami equation, LiNiO2 formation is governed by a three-dimensional diffusion controlled mechanism. The reaction kinetics of LiNiO2 formation are satisfactorily expressed by the Brounshtein–Ginstling model, and the activation energy of the formation process is estimated to be 76.1 kJ mol−1. A microscopic reaction model for the formation of LiNiO2 has been established.

Changes in cell morphology and actin organization during heat shock in Dictyostelium discoideum: does HSP70 play a role in acquired thermotolerance?

In response to heat shock (34 degrees C, 30 min), cell morphology and actin organization in Dictyostelium discoideum are drastically changed. Loss of pseudopodia and disappearance of F-actin-containing structures were observed by using fluorescence microscopy. These changes were paralleled by a rapid decrease of the F-actin content measured by a TRITC-phalloidin binding assay. The effects of heat shock on cell morphology and actin organization are transient: After heat shock (34 degrees C) or during a long-term heat treatment (30 degrees C), cell morphology, F-actin patterns and F-actin content recovered/adapted to a state which is characteristic for untreated cells. Because F-actin may be stabilized by increased amounts of heat shock proteins, their response and interaction with F-actin was analyzed. After a 1 h heat treatment (34 degrees C), the major heat shock protein of D. discoideum (HSP70) showed maximally increased synthesis rates and levels. During recovery from a 34 degrees C shock or during a continuous heat treatment at 30 degrees C, the HSP70 content first increased and then declined slowly toward normal levels. Pre-treatment of cells with a short heat shock of 30 min at 34 degrees C stabilized the F-actin content when the cells were exposed to a second heat shock. Furthermore, a transient colocalization of HSP70 and actin was observed at the beginning of heat treatment (30 degrees C) using immunological detection of HSP70 in the cytoskeletal actin fraction.

Changes in cell morphology and actin organization during heat shock in Dictyostelium discoideum: does HSP70 play a role in acquired thermotolerance?

In response to heat shock (34°C, 30 min), cell morphology and actin organization in Dictyostelium discoideum are drastically changed. Loss of pseudopodia and disappearance of F-actin-containing structures were observed by using fluorescence microscopy. These changes were paralleled by a rapid decrease of the F-actin content measured by a TRITC-phalloidin binding assay. The effects of heat shock on cell morphology and actin organization are transient: After heat shock (34°C) or during a long-term heat treatment (30°C), cell morphology, F-actin patterns and F-actin content recovered/adapted to a state which is characteristic for untreated cells. Because F-actin may be stabilized by increased amounts of heat shock proteins, their response and interaction with F-actin was analyzed. After a 1 h heat treatment (34°C), the major heat shock protein of D. discoideum (HSP70) showed maximally increased synthesis rates and levels. During recovery from a 34°C shock or during a continuous heat treatment at 30°C, the HSP70 content first increased and then declined slowly toward normal levels. Pre-treatment of cells with a short heat shock of 30 min at 34°C stabilized the F-actin content when the cells were exposed to a second heat shock. Furthermore, a transient colocalization of HSP70 and actin was observed at the beginning of heat treatment (30°C) using immunological detection of HSP70 in the cytoskeletal actin fraction.

Numerical and experimental analysis of an electro-thermal coupled problem for transverse flux induction heating equipment

This paper describes a quasi 3D-FEM electromagnetic and thermal computation of transverse flux inductors used in the metal industry for the continuous heating of metal strips. The coupled steady-state eddy current and thermal problem is solved for the prediction of the temperature distribution in the workpiece, a fundamental step towards the optimum design of the inductors. The computation has been used for the design of a heater for the continuous heat treatment of golden or silver metal strips. The suitability of the method presented here for the optimum design of transverse flux inductors has been confirmed by measurements on a laboratory prototype with thin silver strips workpieces.

Fabrication and properties of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ multilayer superconducting tapes and coils

A flexible 100 m-class Bi-2212 multilayer superconducting tape was fabricated by the continuous heat treatment technique using a Ag-0.2 at% Mg sheath. The sheath material did not change the J/sub c/ value of the multilayer superconducting tape and doubled the tensile stress tolerance compared with pure Ag sheathed Bi-2212 tape. The J/sub c/ value of the Ag-0.2 at% Mg alloy sheathed tape was above 10/sup 5/ A/cm/sup 2/ at 4.2 K, 21 T and 1.3/spl times/10/sup 5/ A/cm/sup 2/ at 20 K, 0 T. A stacked pancake coil fabricated by the "react & wind" technique carried 120 A at 10 K and 90 A at 20 K. The coil could be operated for 24 hours under 18 K with operating current of 75 A.