Showing papers on "Hot working published in 1992"

On deformation-induced continuous recrystallization in a superplastic AlLiCuMgZr alloy

Abstract: The microstructural changes of a warm rolled AlLi alloy occurring during static annealing and superplastic deformation at 515°C were studied by means of transmission electron microscopy. Deformation induces a continuous recrystallization with a rapid subgrain growth and a rapid increase in boundary misorientations. The higher strain rate results in a faster subgrain growth and a finer recrystallized grain size. The increasing rate of boundary misorientations and the strain at which the average misorientation reaches about 20° increase with increasing strain rate. The increase in boundary misorientations is proportional to the subgrain growth during the whole static annealing process. Deformation results in a more rapid increase in boundary misorientation with subgrain size than static annealing. Dislocation gliding plays an important role before the formation of high angle grain boundaries during superplastic deformation. The absorption of dislocations into subgrain boundaries results in a more rapid increase in boundary misorientation during deformation. Thus, the mechanism of the deformation-induced continuous recrystallization is suggested to be the generation of dislocations in grains and the absorption of gliding dislocations into subgrain boundaries.

The origin of crystallographic texture produced during hot deformation in rapidly-quenched NdFeB permanent magnets

Abstract: The authors present a model for the development of crystallographic texture by hot deformation in NdFeB magnets produced by rapid solidification Favourably oriented grains, with their c-axis parallel to the compression axis, grow by mass transport through a Nd-rich liquid grain boundary phase, forming large platelet grains The driving force is the elastic energy difference between grains with c-axes making different angles with the compression axis Numerical calculations based on the known properties and conditions of these materials are consistent with a liquid diffusion model >

Computer Model for Prediction of Carbonitride Precipitation during Hot Working in Nb-Ti Bearing HSLA Steels.

Abstract: A computer model which predicts complex precipitation behavior quantitatively in Nb-Ti bearing steel has been developed on a theoretical basis. The solubility and composition of the complex precipitates, and the chemical driving force of the precipitates from supersaturated austenite are estimated by means of thermodynamic analysis of regular solution composed of four-binary compounds. The change in dislocation density which acts as a nucleation site during hot working is calculated by using dislocation theory. And the time dependence of volume fraction and the particle radius of strain induced precipitation are also predicted on the basis of classical nulceation theory. In order to estimate the effect of deformation on nucleation, the change in elastic energy of dislocation with nucleation is calculated.Experimental results showed that combination of Nb and Ti addition, decreased the solubility of carbonitrides and accelerated the precipitation rate from supersaturated austenite because of the formation of complex precipitates. Such experimental results are in good agreement with the prediction by the present model. And both the acceleration of precipitation rate and the refinement of precipitates particles due to hot deformation are also quantitatively explained.

Modelling of microstructure evolution during recrystallization controlled rolling

Abstract: The static recrystallization characteristics (grain size, kinetics) have been established for Ti-V-(Nb) austenites and used as the basis for a theoretical evaluation of microstructural evolution during hot rolling of plate. In this context, particular attention has been focussed on so-called recrystallization controlled rolling, whereby a fine as-rolled ferrite garin size is obtained via transformation from an austenite which has been substantially grain refined via static recrystallization. The model is shown to forecast a behaviour which is in acceptable accord with practical plate-rolling experience. Furthermore, the rolling model has been used in a systematic theoretical investigation of the effect of principal rolling variables on the degree of microstructural refinement during processing of Ti-V-(Nb) steels via recrystallization controlled rolling.

Effects of Casting Conditions and Deformation Processing on A356 Aluminum and A356-20 Vol. % SiC Composites:

Abstract: The effects of casting conditions and deformation processing on the mechanical properties of unreinforced A356 aluminum and A356-20 vol pct SiC composite were investigated by tensile properties in these compounds fabricated by either sand casting or squeeze casting techniques followed by hot working to 33, 50, 90, and 95 percent reductions. The evolution of the microstructure and values of tensile properties were evaluated for the cast materials in each of the hot worked conditions. It was found that, while the deformation processing of the sand-cast composite resulted in banding of the Al and SiC particles within the microstructure, such features were not observed in the squeeze-cast microstructure. The tensile strengths of the squeeze cast materials was found to be higher than those of the sand cast materials, for both the unreinforced and composite samples, while increased amounts of deformation were found to improve the ductility of the composite.

Optimization of hot workability in stainless

Abstract: The hot working behavior of 304L stainless steel is characterized using processing maps developed on the basis of the Dynamic Materials Model and hot compression data in the tem- perature range of 700 °C to 1200 °C and strain-rate range of 0.001 to 100 s♪-1. The material exhibits a dynamic recrystallization (DRX) domain in the temperature range of 1000 °C to 1200 °C and strain-rate range of 0.01 to 5 s-1. Optimum hot workability occurs at 1150 °C and 0.1 s-1, which corresponds to a peak efficiency of 33 pct in the DRX domain. Finer grain sizes are obtained at the lower end of the DRX domain (1000 °C and 0.1 s-1). The material exhibits a dynamic recovery domain in the temperature range of 750 °C to 950 °C and at 0.001 s"1. Flow instabilities occur in the entire region above the dynamic recovery and recrystallization domains. Flow localization occurs in the regions of instability at temperatures lower than 1000 °C, and ferrite formation is responsible for the instability at higher temperatures.

Influence of oxygen on dynamic recrystallization during hot working of polycrystalline copper

Abstract: The characteristics of dynamic recrystallization (DRX) during hot working of copper containing various amounts of oxygen are studied in the temperature range 650–950 °C and strain-rate range $0.001–100 s^{-1}$. Using the dynamic materials model, the efficiency of power dissipation given by [2m(m + 1)], where m is the strain-rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. One of the domains in the processing map has been correlated with DRX, and in the DRX domain the temperature and strain rate for the efficiency peak dependend on the oxygen content. Up to about 150 ppm of oxygen, the DRX strain rate and temperature decrease; at higher oxygen contents, a steep decrease in DRX strain rate and an increase in DRX temperature have been recorded. The results are qualitatively explained on the basis of a simple DRX model where the rate of nucleation of a recrystallized grain boundary and the rate of its migration are considered. Oxygen present both as interstitial atoms and as oxide particles increases the rate of dislocation generation and hence the rate of nucleation of DRX. This results in lowering of the DRX strain rate. The large back stress caused by the presence of the oxide particles is responsible for the increase in DRX temperature.

Flow softening and microstructure evolution during hot working of wrought near-gamma titanium aluminides

Abstract: The hot-working behavior of two wrought ingot-metallurgy near-gamma titanium aluminides was established using the isothermal, hot compression test Experiments were conducted in both the two-phase (alpha+gamma) and single-phase (alpha) regimes at strain rates typical of conventional metalworking operations (01 to 10 s−1) As for conventional titanium alloys, the flow stress showed a strong dependence on temperature and strain rate In addition, the stress-strain curves revealed substantial levels of flow softening Under subtransus conditions, the majority of this softening was ascribed to deformation heating effects and, secondarily, to microstructural effects By contrast, microstructural changes, associated with the dissolution of remnant gamma grains and redistribution of solute, appeared to lead to the majority of the softening observed in the nominally single-phase alpha regime Metallography on as-received (isothermally forged), heat-treated, isothermally upset, and upset and heat-treated samples revealed the persistence of segregation which appears to be a signature of the solidification process characteristic of near-gamma titanium aluminides

Alloy Design for Improvement of Ductility and Workability of Alloys Based on Intermetallic Compound TiAl

Abstract: Two drawbacks of TiAl, deficiency of room temperature ductility and difficulty of hot working have been surmounted substantially by the authors, and at present active research work of light heat-resisting TiAl-base alloys has been performed over a wide range from academic to technical fields aiming at practical uses. In this overview it is described that room temperature ductility is improved by the addition of Mn and, in connection with this improvement, concepts of the authors for the nature of TiAl and the roles of third elements which are soluble in TiAl are discussed

Method involving modified hot working for the production of a titanium alloy part

Abstract: A method of producing a part having high strength and improved ductility from a titanium alloy having a composition, in percent by weight, or Mo equivalent 5 to 13 and Al equivalent 3 to 8, the balance being titanium and impurities, comprising the steps of hot working an ingot of the alloy including a roughing down under heat and preparation of a blank under heat, preheating to a temperature situated above the real beta transus of the hot worked alloy, and then final working of at least a part of this blank, after which the blank obtained is subjected to a solution heat treatment and then aged. The hot worked blank is cooled from the preheating temperature to a temperature for the beginning of final working which, under the conditions of the cooling of the blank, is at least 50° C. below the real beta tansus and at least 10° C. above the temperature of appearance of the alpha phase, so that the final working is sufficient to end within the alpha nucleation range.

Processing map for hot working of powder

Abstract: The constitutive flow behavior of a metal matrix composite (MMC) with 2124 aluminum containing 20 vol pct silicon carbide particulates under hot-working conditions in the temperature range of 300 °C to 550 °C and strain-rate range of 0.001 to 1 s-1 has been studied using hot compression testing. Processing maps depicting the variation of the efficiency of power dissipation given by [2m/(m + 1)] (wherem is the strain-rate sensitivity of flow stress) with temperature and strain rate have been established for the MMC as well as for the matrix material. The maps have been interpreted on the basis of the Dynamic Materials Model (DMM). [3] The MMC exhibited a domain of superplasticity in the temperature range of 450 °C to 550 °C and at strain rates less than 0.1 s-1. At 500 °C and 1 s-1 strain rate, the MMC undergoes dynamic recrystallization (DRX), resulting in a reconstitution of microstructure. In comparison with the map for the matrix material, the DRX domain occurred at a strain rate higher by three orders of magnitude. At temperatures lower than 400 °C, the MMC exhibited dynamic recovery, while at 550 °C and 1 s-1, cracking occurred at the prior particle boundaries (representing surfaces of the initial powder particles). The optimum temperature and strain-rate combination for billet conditioning of the MMC is 500 °C and 1 s-1, while secondary metalworking may be done in the super- plasticity domain. The MMC undergoes microstructural instability at temperatures lower than 400 °C and strain rates higher than 0.1 s-1.

Method for making fatigue crack growth-resistant nickel-base article

Abstract: Fatigue crack growth-resistant articles are made from powder metal or cast and wrought gamma prime precipitation strengthened nickel-base superalloy material, wherein a relatively high predetermined minimum strain rate, emin, is employed during hot working at or near the alloy's recrystallization temperature; or alternatively a relatively high strain level, emin, is employed during cold or warm working at temperatures below the alloy's recrystallization temperature. The worked articles are characterized by a uniform fine grain size, and grains which coarsen uniformly after heating at the supersolvus solutioning temperature, thereby alleviating non-uniform grain growth within the material.

Plastic-flow behavior and microstructural development in a cast alpha-two titanium aluminide

Abstract: Plastic-flow behavior and microstructural development were investigated for a cast α2 titanium aluminide, Ti-24Al-11Nb (atomic percent), using the isothermal hot-compression test. Regimes of warm- and hot-working behavior were inferred from flow curves adjusted for deformation heating effects. Plots of flow stress as a function of inverse temperature and estimates of the strain-rate-sensitivity index confirmed the transition from warm to hot-working conditions over a rather narrow temperature range. Hot working in theα 2 +β phase field was also marked by a rather high activation energy (viz., ∼1080 kJ/mole) for the controlling deformation process, which appeared to consist of dynamic globularization of the ordered-α 2 phase. A sharp decrease in the activation energy was noticed when the deformation temperature was increased above the β-transus. Microstructural observations also indicated development of an unrecrystallized structure during warm working, with cavities and wedge cracks being found near the bulged free surfaces of the upset specimens. The plastic-flow phenomenology exhibited a number of similarities to that found in the wrought version of the Ti-24Al-11Nb alloy.

Processing map for controlling microstructure in hot working of hot isostatically pressed powder metallurgy NIMONIC AP-1 superalloy

Abstract: The hot deformation behavior of hot isostatically pressed (HIP) NIMONIC AP-1 superalloy is characterized using processing maps in the temperature range 950 °C to 1200 °C and strain rate range 0.001 to 100 s•1. The dynamic materials model has been used for developing the pro-cessing maps which show the variation of the efficiency of power dissipation given by [2m/ (m + 1)] with temperature and strain rate, withm being the strain rate sensitivity of flow stress. The processing map revealed a domain of dynamic recrystallization with a peak efficiency of 40 pct at 1125 °C and 0.3 s•1, and these are the optimum parameters for hot working. The microstructure developed under these conditions is free from prior particle boundary (PPB) de-fects, cracks, or localized shear bands. At 100 s•1 and 1200 °C, the material exhibits inter-crystalline cracking, while at 0.001 s•1, the material shows wedge cracks at 1200 °C and PPB cracking at 1000 °C. Also at strain rates higher than 10 s•1, adiabatic shear bands occur; the limiting conditions for this flow instability are accurately predicted by a continuum criterion based on the principles of irreversible thermodynamics of large plastic flow.

Martensitic chromium@ steel - has good wear resistance and high temp. tensile strength, used in building parts

Abstract: Martensitic Cr-steel consists of a wt.%:- 0.005-0.5 C; 0.2-2.0 Si; max. 1.0 Mn; max. 0.025 P; max 0.025 S; 14-18 Cr; 0.5-3 Mo; 0.5-3 W; 0.3-2 Ni; 0.2-1.0 N; 0.2-1.0 V; max. 0.5 Nb and/or Ti; max. 0.01 B; balance Fe and usual impurities. The ratio of C:N is 0.4-0.8 and (C+N):V is 1.5-2.5. After hot working the steel is air cooled before being heated to 950-1200 deg.C and then rapidly quenched in oil or water to below the martensite forming temp. Finally it is tempered at 500-650 deg.C before being air cooled to room temp. USE/ADVANTAGE - In building parts. Steel has high tensile strength of above 1800 MPa at room temp., high strength of above 1000 MPa at 500 deg.C and excellent corrosion resistance esp. in acids and/or chloride solutions. Also has the necessary wear resistance with a hardness of 40 HRC.

Process for producing amorphous alloy material

Abstract: A process for producing an amorphous alloy material characterized by imparting ductility to an amorphous alloy having a supercooled liquid region by giving a prescribed amount of strain at a prescribed strain rate to the alloy in the glass transition temperature region of the alloy. The amorphous alloy may be in the form of spherical or irregular-shaped powders or thin ribbons or in the form of primary consolidated shapes thereof or an amorphous alloy casting. The amount of strain and strain rate are preferably 50% or greater and 2×10-2 /sec or higher, respectively, and the worked amorphous alloy material is preferably allowed to cool in a furnace or spontaneously. Suitable examples of the amorphous alloy to be employed include Al-TM-Ln, Mg-TM-Ln, Zr-TM-Al and Hf-TM-Al alloys, wherein TM is a transition metal element and Ln is a rare earth metal element. The thus obtained amorphous alloy is greatly improved in the prevention of embrittlement in hot working peculiar to the alloy.

Hot pressed magnets in open air presses

Abstract: This invention describes a practice for the hot-pressing and/or hot working of rare earth element-containing alloy powders (52) using open-to-the-air presses (10;100). The rare earth-containing powder (52) is pressed into a compact body (34) at ambient temperatures using a solid lubricant only on the die wall. This compact body (34) is then hot-pressed in an open-air press (100) utilizing a heated die (114) flooded with argon (130).

Effect of zinc content on the processing map for hot working of α brass

Abstract: The hot deformation behavior of α brass with varying zinc contents in the range 3%–30% was characterized using hot compression testing in the temperature range 600–900 °C and strain rate range 0.001–100 s−1. On the basis of the flow stress data, processing maps showing the variation of the efficiency of power dissipation (given by 2m (m+1) where m is the strain rate sensitivity) with temperature and strain rate were obtained. α brass exhibits a domain of dynamic recrystallization (DRX) at temperatures greater than 0.85Tm and at strain rates lower than 1 s−1. The maximum efficiency of power dissipation increases with increasing zinc content and is in the range 33%–53%. The DRX domain shifts to lower strain rates for higher zinc contents and the strain rate for peak efficiency is in the range 0.0001–0.05 s−1. The results indicate that the DRX in α brass is controlled by the rate of interface formation (nucleation) which depends on the diffusion-controlled process of thermal recovery by climb.

Interstitial free steels

Abstract: The strength of interstitial free steels is increased by up to 100 % and the ductile to brittle transition temperature is decreased by up to 100 °C by warm finish rolling in the single phase ferrite region below Arl to effect ferrite dynamic recrystallization of the steel microstructure to a ferrite structure of grain size having a grain size of up to 5 νm, and especially an ultra fine grain size of 1 to 2 νm; the method may be employed in various hot working methods including strip and rod mills, planetary hot rolling and extrusion.

Magnetrostrictive materials and methods of making such materials

Abstract: The magnetostriction alloys of the present invention are composed basically of Tb-Dy-iron which is partially substituted by at least one element selected from the group consisting of Y, La, Cs, Pr, Nd and Sm, and have been grown in the direction of face index or contain Mn and M element (at least one metallic element selected from the group consisting of C, Mg, Al, Si, Ca, Zr, Y, Ga and B. The magnetostrictive alloy may be formed by melting the constituent materials by high frequency induction dissolution. The molten materials are cast in a heated mold having a temperature gradient. The solidified material may be further treated by hot working.

Production of precipitation type copper alloy

Abstract: PURPOSE: To obtain a precipitation type Cu alloy material having high workability, strength, and electric conductivity by improving the solution heat treatment, recrystallization treatment, and aging treatment for a precipitation hardening Cu alloy containing Cr, Sn, etc. CONSTITUTION: A cast ingot of a Cu alloy which has a composition consisting of, by weight, 0.1-0.35% Cr, 0.05-0.5% Sn, and the balance Cu or further containing 0.05-5.0% Zn or further containing 0.0005-1.0%, in total, of one or ≥2 kinds among specific small amounts of Si, Mn, Mg, V, Ti, B, and P is subjected to hot working starting at 880-1050°C and then cooled rapidly to undergo cold working. Subsequently, heat treatment, in which holding is done at 360-650°C for 45-1800sec or holding is done at 880-1020°C for 5-60sec, and a high density pulse current applying treatment are simultaneously performed. Then, cold working is done, and, at the time of performing aging heat treatment, an electric field of (1 to 10)KV/cm is impressed simultaneously. By this method, an electronic and electrical equipment material combining superior workability with a high strength and electric conductivity can be obtained. COPYRIGHT: (C)1994,JPO&Japio

Lubricant for hot plastic working

Abstract: PURPOSE:To exhibit good lubricating performance and to excellently prevent the seizure of dies, etc., by forming the lubricant for hot plastic working by mixing graphite powder, glass powder and water. CONSTITUTION:The lubricant for hot plastic working is formed by mixing the graphite powder, the glass powder and the water. The glass powder is preferably such glass powder which can attain a molten state in correspondence to 1000 poise dynamic viscosity in the range of the temp. (hereafter described as a heating temp. range) at which the lubricant is heated by the heat transfer effect, etc., during hot plastic working. Since the molten glass component has flowability, the glass elongates smoothly with the material surface deformed by the plastic working, thereby preventing the direct contact of tools, such as dies, and the material and exhibiting the lubricating effect. On the other hand, the graphite causes oxidation, etc., at the hot working temp. and is poor as the lubricant but acts sufficiently as a release agent.

Characterization of the hot-working behaviour of a P/M Al-20Si-7.5Ni-3Cu-1Mg alloy by hot torsion

Abstract: Hot torsion tests were performed to investigate the mechanical and microstructural responses of a quinary Al-20Si-7.5 Ni-3Cu-1Mg (wt %) alloy, consolidated from a rapidly solidified powder, to deformation at varying temperatures and strain rates. It was found that, under most of the deformation conditions applied, stress-strain curves were characterized by distinct stress peaks, which are usually absent from the curves shown by conventional aluminium alloys. Temperature and strain rate strongly influenced the stress and ductility of the material. Their combined influence on the peak stress has been expressed with a hyperbolic sine equation. The material also exhibited an extraordinarily high strain rate sensitivity,m, and a largem value variation with temperature. A relatively high value of activation energy for deformation was determined, which clearly reflects additional thermal barriers to metal flow, arising from a high volume fraction of multi-phase particles dispersed in the material. Additionally, the microstructure developed in the course of deformation was examined, which showed evidence of the co-operation of dynamic recovery and recrystallization. The initiation of local dynamic recrystallization is a result of a low level of dynamic recovery achievable in the material, which is again different from conventional aluminium alloys.

Method for hot-working magnesium alloy

Abstract: PURPOSE:To establish the method for hot-working a magnesium allay at a high working rate as well as at a high strain rate. CONSTITUTION:The magnesium allay having an allay compsn. constituted of, by weight, 6.0 to 10.0% Al, to 10 sec strain rate and 200 to 350 deg.C working temp. Before the working, solution treatment of 380 to 420 deg.CX>=5hr may be executed.

Hot tool steel

Abstract: PURPOSE:To provide a tool steel for hot working having excellent high temp. strength, high in hardenability, provided with excellent toughness, in which a nitriding layer is hard to be diffused and having good nitriding properties. CONSTITUTION:This steel contains, by weight, 0.36 to 0.45% C, 4.0 to <4.35% Cr, one or two kinds of W and Mo by 1.9 to 3.5% as 1/2W+Mo, 0.5 to 1.6% V and the balance Fe with inevitable impurities. If required, 0.5 to 5.0% Co can furthermore be incorporated therein. By forming the alloy compsn. in the above-mentioned manner, the steel is provided with high temp. strength and toughness, the softening and diffusing of the nitriding layer are suppressed and the service life of a die can be improved.

Production of ferritic stainless steel sheet excellent in ridging characteristic and workability

Abstract: PURPOSE:To produce a ferritic stainless steel sheet excellent in ridging characteristic and workability by subjecting a slab of a ferritic stainless steel having a chemical composition specified by a specific equation to hot roughing and finish hot rolling under respectively specified conditions, coiling the resulting plate, and then applying cold rolling and annealing to the plate. CONSTITUTION:A slab of a ferritic stainless steel where chemical components are balanced so that FIX represented by an equation becomes 35-80 and which has a dual phase structure of ferrite and austenite at hot working temp. is produced. Hot roughing is started by heating the slab up to 1150-1250 deg.C, and finish hot rolling is completed while regulating the finish rolling outlet side velocity and the finish rolling outlet side temp. to >=7.0m/s and >=860 deg.C, respectively, followed by coiling at 650 deg.C. Then the resulting hot rolled steel strip is subjected to a combination of cold rolling and annealing treatments, by which a cold rolled steel sheet is produced. By this method, the ferritic stainless steel having superior surface characteristics and excellent in ridging characteristic and workability can be obtained without causing reduction in productivity and rise in costs.

The Elastic-Plastic Finite-Element Method

Abstract: The rigid-plastic and viscoplastic finite-element techniques described in the previous chapters are useful approaches to the modelling of metal deformation when the elastic component of strain may reasonably be ignored. This is often the case, for example, for hot working conditions. In other situations, it is important to take into account the elastic as well as the plastic deformation of the material, and it is vital to do so if the unloading behaviour is to be predicted.