Showing papers on "Forging published in 1999"

Heat treatment of UDIMET 720Li: the effect of microstructure on properties

Abstract: The evolution during heat treatment of the as-forged microstructure of the high strength superalloy UDIMET 720Li has been studied. Particular emphasis has been placed on the characterisation of γ ′ precipitation kinetics using optical and transmission electron microscopies (TEM) and subsequent image analysis. The observations are interpreted using thermodynamic, phase transformation and precipitate hardening theories. The results have implications for the gas turbine manufacturers. Through a better understanding of the evolution of the microstructure during ageing, a heat treatment of 24 h at 700°C is proposed, which is believed to be optimal. This allows full advantage to be taken of the properties of the alloy, whilst reducing the costs and time associated with the heat treatment schedules. Moreover, the data presented allows the variation in properties across a U720Li forging to be estimated.

Processing high-temperature refractory-metal silicide in-situ composites

Abstract: High-temperature, refractory-metal, intermetallic, in-situ composites consist of high-strength, niobium-based silicides with a niobium-based metallic toughening phase. A variety of processing schemes have been used to generate these in-situ composites, including solidification and vapor phase processes. Secondary processing, such as forging and extrusion, has also been employed. These composites offer an excellent balance of high-and low-temperature mechanical properties with promising environmental resistance at temperatures above 1,100°C.

Friction stir welding tool

Abstract: A stir weld tool of the present invention is used to weld two pieces of metal together through frictional heating, plasticizing, mixing, and forging of the plasticized metal into a uniform weldment. The stir weld is accomplished by rotating the stir weld tool with a pin having at least one boss on its surface to create the mechanical friction in the metal in contact with the rapidly rotating pin. As the rotating pin travels along the weld joint, the plasticized metal of the work pieces is extruded to the back face of the pin while undergoing a mechanical stirring and forging from action imparted by the at least one boss on the surface of the pin, and while confined from above by the pressure exerted on the metal by a shoulder on the stir weld tool.

Synthesis and Structural, Ferroelectric, and Piezoelectric Properties of SrBi4Ti4O15 Ceramics

Abstract: SrBi 4 Ti 4 O 15 ceramics were prepared via ordinary firing (OF) and hot forging (HF). Characterization using scanning electron microscopy and X-ray diffractometry shows platelike grains that were highly oriented (F = 0.95) after hot forging. Ferroelectric, dielectric, and piezoelectric characterizations revealed that polarization reorientation was restricted to the ab plane of the orthorhombic structure, parallel to the (Bi 2 O 2 ) 2+ layers. The thickness coupling factor for OF samples was only half that for HF samples oriented parallel to the HF direction (in the ab-plane), as a consequence of poling restrictions in randomly oriented grains.

Process for forging titanium-based material, process for producing engine valve, and engine valve

Abstract: The invention provides a process for forging a titanium-based material comprises the steps of: preparing a titanium-based sintered workpiece including at least one of ceramics particles and pores in a total amount of 1% or more by volume, the ceramics particles being thermodynamically stable in a titanium alloy; and heating the workpiece to a forging temperature and forging the same. In the production process, the pores or the ceramics particles inhibit the grain growth during forging. Accordingly, it is possible to carry out the forging at a relatively high temperature at which the titanium-based material exhibits a small resistance to deformation. Moreover, the titanium-based material can maintain an appropriate microstructure even after the forging. Consequently, the impact value and the fatigue strength are inhibited from decreasing.

Superplastic Sinter-Forging of Silicon Nitride with Anisotropic Microstructure Formation

Abstract: The microstructure and mechanical properties of silicon nitride, produced by a superplastic sinter-forging technique, were investigated. The obtained silicon nitride exhibited a highly anisotropic microstructure, where rod-shaped grains tended to be aligned perpendicular to the forging direction. A very high bending strength of 2108 MPa as well as a high fracture toughness of 8.3 MPa.m 1/2 were achieved when a stress was applied perpendicularly to the pressing direction. This very high strength was considered to be due to the reduced flaw size by the superplastic sinter-forging process and the steep R-curve behavior caused by the grain alignment.

Precision forging of spur gears with inside relief

Abstract: Conventional closed-die forgings as applied to the forging of spur gears require high forging pressure. In this paper, a precision forging technology has been developed for the forging of spur gears with alloy steel (SCM415). The technology developed includes two steps in the forging process. Well-shaped products are forged successfully using a lower forging pressure than that of conventional forging. The accuracy of the forged spur gear obtained by the new precision forging technology is set nearly equal to that of a cut spur gear of the fourth and the fifth classes in the Korean industrial standard.

Cavitation and failure during hot forging of Ti-6Al-4V

Abstract: The occurrence of cavity initiation and gross, free-surface fracture during subtransus hot pancake forging of Ti-6Al-4V with a transformed beta (colony) microstructure was established. Cavity initiation mechanisms were one of two distinct types. At temperatures approximately 75 °C or more below the beta transus temperature (T β ), cavity initiation occurred at relatively low strains in the beta phase lying between the grain-boundary alpha phase and the lamellar colonies. By contrast, at temperatures near the transus (i.e., T≈T β −25 °C), cavity initiation occurred at much larger strains as a result of microfracture of partially-to-fully globularized alpha phase. Finite element method (FEM) modeling of the pancake forging process revealed that secondary tensile stresses had been developed in the regions that had exhibited cavitation/fracture. The FEM analyses were used to correlate both the cavity initiation and the gross free-surface fracture results to previous observations from uniaxial hot tension tests in which identical damage mechanisms had been observed. The tensile work criterion of Cockcroft and Latham (C+L) gave moderately good (quantitative) correlation between the forging and uniaxial tension behaviors. An alternate comparison based on the Rice and Tracey cavity growth model gave reasonable predictions of free-surface fracture but tended to overestimate the incidence of subsurface cavity initiation.

Technology, properties and applications of intermetallic {gamma}-TiAl based alloys

Abstract: This paper reviews industrial scale thermomechanical and near-net shape processing of {gamma}-TiAl based alloys (``{gamma} alloys``). The progress achieved in forging of large ingots, rolling of sheets from forged ingots as well as HIPed powders, single and multistep extrusion of ingots and HIPing of prealloyed powders to near-net shape parts is presented. The impact of the different prematerial routes on process economy and the quality of semi-finished products will be discussed. The problems which arise when heat treatments are transferred from small lab furnaces to large industrial furnaces are outlined. The superplastic behaviour of {gamma}-TiAl sheet material is described and results of superplastic forming are presented. Different joining techniques have been screened for {gamma}-TiAl based alloys including laser welding, brazing and solid-state diffusion bonding. Although the oxidation resistance of {gamma} alloys is remarkably higher than that of Ti alloys the need for reliable oxidation resistant coatings for long-term application at temperatures >700 C is anticipated. Results of cyclic oxidation tests on coated {gamma}-TiAl samples are presented. Finally, some potential application fields for {gamma}-TiAl alloys are outlined. (orig.) 58 refs.

Improvement of room temperature tensile properties for Fe3Al-based alloys by thermomechanical and annealing processes

Abstract: The effects of thermomechanical and annealing processes on room temperature tensile properties of Fe 3 Al-based alloys have been investigated. It is found that the thermomechanical process affects the room temperature tensile properties of Fe 3 Al-based alloys greatly. It is very important to control the hot deformation process so that a fine grain microstructure can be obtained before the final warm-rolling process. A higher room temperature ductility combined with a higher yield stress can be obtained by refining grains of Fe 3 Al-based alloys and obtaining the B2 ordered structure with a suitable surface state, such as oil film, Al 2 O 3 film and an aluminium-poor region near the surface. The intrinsic factors, such as microstructure and crystal structure, and extrinsic factors, such as surface condition, must be considered when the sensitivity to environmental embrittlement is investigated. An advanced thermomechanical process, named controlled thermomechanical process, to further improve room temperature tensile properties has been developed. It consists of hot forging an ingot to 20 mm at 1000–1200°C, hot rolling it to 10 mm at 850–1000°C, warm rolling to 5 mm thickness at 500–680°C, then annealing at 800°C for 1 h, then warm rolling to 2 mm thickness at 500–680°C.

Prediction of ductile fracture in cold forging of aluminum alloy

Abstract: In this paper, the limitation and applicability of the ductile fracture criteria based on a work hypothesis and Cockcroft and Latham were investigated. For this purpose, experimental and numerical investigations for simple upsetting were conducted for aluminum alloys Al1100-O, Al2024-T3, Al6061-T4, and A17075-T4. As a result, the fracture mode of each alloy was observed. The study was extended for pin-shape cold forging of Al1100-O and Al6061-T4 to compare the likeliness of fracturing according to two criteria. Based on experimental data of simple upsetting, the damage factors for the same two criteria were calculated by adopting rigid-viscoplastic finite element analysis. With this approach, the prediction of surface cracking was attempted by comparing the calculated limiting damage factors between simple upsetting and pin-shape forging. It was observed in simple upsetting that Cockcroft and Latham's criterion gave a more reasonable prediction for crack initiation site than work hypothesis, but the limiting damage factors differ depending on the process. In spite of the differences, however, Cockcroft and Latham's criterion might be useful in designing upsetting-like cold forging processes in which the influence of the induced circumferential tensile stress on failure is dominant.

Silicon carbide based composite material and manufacturing method thereof

Abstract: A silicon carbide based composite material includes as a first component, a metal mainly consisting of aluminum or copper, and as a second component, particles mainly consisting of silicon carbide having high purity and few defects. The material is obtained by heating a compact of the raw material powder containing the first and second components at a temperature not lower than the melting point of the metal mainly consisting of aluminum or copper, and by forging and solidifying under pressure. Preferably, the silicon carbide raw material powder is prepared to have high purity by carrying out a preliminary treatment, or the material after forging or a material obtained through a conventional infiltration process is further heated at a temperature lower than the melting point of the first component. In this manner, an improved superior thermal conductivity can be obtained.

Analysis and prevention of cracking phenomenon occurring during cold forging of two AISI 1010 steel pulleys

Abstract: This study is concerned with the effects of microstructural parameters on the cracking phenomenon occurring during cold forging of two AISI 1010 steels that were fabricated by converter steel making and electric furnace steel making, respectively. This allowed a comparison between microstructures that contained a small or large amount of nitrogen. Detailed microstructural analyses of the cracked region showed that a number of adiabatic shear bands, along which cracks initiated and propagated, were formed in the top interior part of the cold-forged pulley. Dynamic torsional tests were conducted using a torsional Kolsky bar in order to investigate the dynamic deformation behavior during cold forging, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. From the dynamic shear stress-strain curves, the steel containing a considerable amount of nitrogen showed a smaller shear strain of 0.2 at the maximum shear stress point, after which the shear stress decreased rapidly prior to fracture, whereas the other steel containing a smaller amount of nitrogen showed relatively homogeneous shear deformation. This dynamic torsional behavior correlated well with the cracking and adiabatic shear banding behavior, together with the yield-point phenomenon occurring in the steel containing more nitrogen. Because the cracking occurring during cold forging was associated with the adiabatic shear banding and the yield-point phenomenon, the minimization of nitrogen and the fast cooling rate after hot rolling were suggested to prevent the cracking.

Analysis of tapered preforms in cold upsetting

Abstract: Upset forging is usually carried out with a sequence of stages and the tapered preforms are commonly used. The preforms should be free from flash formation and buckling injuries. In this paper, the results that depend on elastic–plastic finite element analysis of taper upset forging are given. The buckling analysis was realized by using the Modified Riks method. For a given upset ratio which is the ratio of unsupported length to diameter of the initial billet, reduction in the height of the billet and the diameter ratio are the important design parameters in taper upsetting. For several values of the design parameters, the analysis has been carried out and the results have been compared with the results of the well-known Meyer's experiment and Gokler's suggestions. In the analysis, the perfectly square end (ideal billet case) and the end with face inclination angle were considered as two different end conditions of the billet. The results for the ideal billet case are in good-agreement with Meyer's results. The end-face inclination angle, which is a significant imperfection on the billet, reduces the limits of allowable upset ratio. It has been observed that although the tapered header dies designed at the limits suggested by Meyer produce flashless preforms, in some of the cases, injuries due to buckling are not eliminated. However, Gokler's suggested limits provide elimination of both flash formation and injuries due to buckling.