Continuous Forging Research Articles

Galling-Free Dry Near-Net Forging of Titanium Using Massively Carbon-Supersaturated Tool Steel Dies.

Massively carbon-supersaturated (MCSed) tool steel dies were developed to make galling-free forging products from titanium bar feedstocks in dry conditions without lubricating oils. Two types of tool steel dies were used, SKD11 and ACD56, following the Japanese Industrial Standard (JIS). The plasma-immersion carburizing process was employed to induce massive carbon supersaturation in two kinds of tool steel dies at 673 K for 14.4 ks. A pure titanium bar was upset in a single stroke up to the reduction of thickness of 70% using the MCSed SKD11 die. Very few bulging displacements of the upset bar proved that μ = 0.05 on the contact surface of the MCSed SKD11 die to pure titanium work. Two continuous forging experiments were performed to demonstrate that an in situ lubrication mechanism played a role to prevent the contact surface from galling to titanium works in both laboratory- and industry-scaled forging processes. After precise microstructure analyses of the contact surface, the free-carbon film formed in situ acted as a lubricating tribofilm to reduce friction and adhesive wear in continuous forging processes. The MCSed ACD56 dies were also used to describe the galling-free forging behavior of manufacturing eyeglass frames and to evaluate the surface quality of the finished temples. The applied load was reduced by 30% when using the MCSed ACD56 dies. The average surface roughness of the forged product was also greatly reduced, from 4.12 μm to 0.99 μm, together with a reduction in roughness deviations. High qualification of forged products was preserved together with die life prolongation even in dry manufacturing conditions of the titanium and titanium alloys.

Optimization design of laser-EMAT and its application in high-temperature forgings detection

In high-temperature continuous forging process, according to the real-time monitoring of workpiece thickness and flaws, the processing parameters can be adjusted accordingly, so we can remove defective components in time, which has essential research value for avoiding the interruption of production line and improving their yield and quality grade. We established a finite element (FE) model of the carbon steel’s laser-electromagnetic acoustic transducer (laser-EMAT) testing process. Based on the simulation model, we analyzed the effects of laser parameters, EMAT parameters, and sample thickness on the detected ultrasonic signal amplitude, and we also achieved the optimized Laser-EMAT design parameters. Subsequently, we developed a high-temperature resistant spiral coil EMAT and measured the high-temperature forging with a thickness of 100 mm and temperatures from 300 °C to 730 °C. Based on the experiments, we researched the effect of specimen temperature on the received ultrasonic wave amplitude. The results show that the excitation efficiency of laser-induced ultrasonic waves improves by decreasing pulse duration, decreasing laser spot radius, and increasing pulse laser energy. The receiving efficiency of the shear wave (SW) detected by the EMAT enhances when reducing the diameter of the EMAT wire and increasing the permanent magnet height. When the radius of the permanent magnet is equal to the radius of the EMAT coil, the receiving efficiency of SW is the highest. As the sample thickness increases, the size of the EMAT should increase accordingly to the acoustic beam divergence for obtaining a higher ultrasonic wave intensity. The amplitude of the SW signal received by the EMAT increases by 679% after the optimization design. With rising carbon steel forging temperature, the SW signal amplitude increases first and then decreases sharply, reaching its maximum at 617 °C, which is 29% higher than at room temperature, and the signal-to-noise ratio (SNR) of the SW is 20.5 dB.

Effect of parent β-texture on α-texture evolution during dynamic precipitation in a continuous forging process of Ti-6Al-4V alloy

The α-texture evolution during dynamic precipitation in a continuous forging process was investigated in Ti-6Al-4 V alloy. The relationship between α-phase transformation texture and deformation texture was studied. It was found that the {10−10} transformation texture gradually weakened during deformation, and the texture intensity was lower than that of traditional β-forging and (α + β)-forging under a constant deformation strain. In addition, it was also observed that the (001) parent β-texture led to a weaker {10−10} α-texture development than the other β-textures. According to the Schmid factor (SF) analysis, the α-lath in the (001)//FD parent β-grains exhibited a higher SF value of the {10−10}< 11–20 > prismatic slip system than that in the other β-grains. The high-dislocation-density region locally appeared in the α-lath under the activation of prismatic slip system, which led to inhomogeneous deformation and partial lattice rotation. Therefore, the misorientation angle developed within the α-lath and the {10−10} transformation texture was weakened.

Effects of optimizing continuous forging extrusion process on the microstructure and mechanical properties of AZ31 magnesium alloy

Continuous forging extrusion (CFE) is a newly developed extrusion process to refine grains of wrought magnesium alloys. However, at lower extrusion temperatures, CFE also easily leads to material failure during extrusion, resulting in poor mechanical properties. In this paper, a high-pressure holding stage was added to the CFE process to effectively heal cracks in Mg–3Al–1Zn (AZ31) alloy. Meanwhile, the high-pressure holding leads to a large number of {10–12} tensile twinning, which acts as potential recrystallization nucleation points and promotes grain refinement during extrusion. By optimizing CFE process with this high-pressure holding, the strength and ductility of AZ31 alloy are greatly improved. AZ31 alloy specimens with a diameter of 60 mm before extrusion exhibit good mechanical properties with a tensile yield strength (TYS), ultimate tensile strength (UTS), compressive yield strength (CYS), fracture elongation (FE), and tensile compressive yield asymmetry (σCYS/σTYS) of 327 MPa, 365 MPa, 303 MPa, 23.5%, and 0.93, respectively. Deformation mechanism and microstructure evolution during the high-pressure holding stage are discussed in detail.

Dry Cold Forging of Pure Titanium Wire to Thin Plate with Use of β-SiC Coating Dies.

Dense β-SiC coating with 3C-structure was utilized as a dry cold forging punch and core-die. Pure titanium T328H wires of industrial grade II were employed as a work material. No adhesion or galling of metallic titanium was detected on the contact interface between this β-SiC die and titanium work, even after this continuous forging process, up to a reduction in thickness by 70%. SEM (Scanning Electron Microscopy) and EDX (Electron Dispersive X-ray spectroscopy) were utilized to analyze this contact interface. A very thin titanium oxide layer was in situ formed in the radial direction from the center of the contact interface. Isolated carbon from β-SiC agglomerated and distributed in dots at the center of the initial contact interface. Raman spectroscopy was utilized, yielding the discovery that this carbon is unbound as a free carbon or not bound in SiC or TiC and that intermediate titanium oxides are formed with TiO2 as a tribofilm.

Novel continuous forging extrusion in a one-step extrusion process for bulk ultrafine magnesium alloy

Highly-uniform ultrafine Mg–3Al–1Zn alloy was successfully fabricated by a simple conventional extrusion method called continuous forging extrusion (CFE). After CFE, the average grain size of Mg–3Al–1Zn alloy was refined to 0.6 μm. The ultra-fine grain (UFG) AZ31 alloy exhibited an excellent combination of yield strength of 307 MPa and ductility of 26.3%. The improved mechanical properties were mainly attributed to grain boundary strengthening and texture weakening. The formation of dynamic recrystallized submicron grain in the CFE was also discussed.

Grain Refinement Mechanism and Microstructural Evolution of M50NiL Steel during Multi-directional Impact Forging

This study investigated the effect of varying temperatures and cumulative strains on M50NiL steel during multi-directional impact forging (MDIF). The grain size was found to increase gradually with increasing temperature, after being held at 1050, 1100, 1150 and 1180 °C for 30 min, with the minimum grain size observed at 1100 °C during the MDIF process. The M50NiL steel subjected to MDIF at 1100 °C and at varying cumulative strains of 0.6, 1.8, 3.6 and 7.2 exhibited grain sizes that decreased with increasing cumulative strain. The mean grain size gradually decreased to ~ 1 μm at a cumulative strain of 7.2. New small grains were nucleated at grain boundaries via dynamic recrystallization, and microbands were formed via the temperature drop during the continuous forging process. The grains were subdivided into subgrains by the microbands, and these subgrains were converted to new refined grains via transformation of their boundaries into high-angle boundaries. Further, martensite transformation was restrained owing to the grain refinement. Improved tensile strengths values are obtained after MDIF process.

Multi-phase microstructures in Anatolian Seljuks iron-steel objects: classification and production techniques

In this paper a collection of iron objects from the Anatolian Seljuks Period, ca. 12th–13th century AD, are analysed and discussed from a metallurgical perspective. A total number of 21 iron-steel objects, small knives and flat bodied (with thin cross-section) arrowheads was examined. These objects are coming from the Seljuks’ cultural layers of Eğirdir (Isparta, Central Anatolian Caravanserai), Kubad Abad (Konya, Central Anatolian Sultan’s Palace Complex), and Samsat (Adıyaman, Eastern Anatolian Fortress). In the samples which were taken from iron tools, composite-like structures formed by different ferrous phases were revealed by metallography, SEM-EDX and micro hardness examinations. These structures are classified according to the production materials and techniques. The first group revealed signs of continuous forging and, in some cases, bloomery iron folding, which can lead to such composite-like structures. The second group consisted of tools which were produced from different starting materials which were forge-welded before or during shaping process. The crucible steel knives can be classified as another group, in which the composite-like structure exhibits totally different constituents leading to more homogeneous mechanical character. In modern times, composite materials have gained importance and become key engineering materials due to their outstanding specific properties. This study reveals that skilled Seljuks’ blacksmiths made similar materials design choices in the production of iron or steel objects, despite limited materials and metallurgical knowledge.

Microstructure, texture and mechanical properties in an as-cast AZ61 Mg alloy during multi-directional impact forging and subsequent heat treatment

Abstract Multi-directional impact forging (MDIF) and subsequent heat treatment were applied to an as-cast AZ61 Mg alloy and the microstructure, texture evolution and mechanical properties were systematically investigated. The microstructural evolution during MDIF was classified into twinning-active and dynamic recrystallization (DRX)-predominant stages. During the early forging passes, a complicated twinning behavior was observed, including {10–12} primary, {10–12}–{10–12} secondary and {10–12}–{10–12}–{10–12} ternary twins with various twin variants, and even detwinning behavior. With further continuous forging, {10–12} twins disappeared leading to the formation of coarse DRXed grains, and fine DRXed grains began to nucleate at serrated grain boundaries of the coarse DRXed grains due to discontinuous DRX mechanism and progressively consumed the coarse DRXed grains, eventually resulting in a bimodal microstructure. Meanwhile, as-cast random texture turned into a special non-basal texture. After subsequent heat treatment at 400 °C for 2 h, the coarse eutectic network completely disappeared with fine β-Mg17Al12 particles uniformly locating at grain boundaries and the non-basal texture stayed stable, thereby resulting in a good balance of strength (ultimate tensile strength of 259 MPa) and ductility (20.6%).

Twinning, recrystallization and texture development during multi-directional impact forging in an AZ61 Mg alloy

Multi-directional impact forging (MDIF) with high strain rate shows high grain refinement efficiency and texture randomization effect in magnesium alloys. AZ61 Mg alloy was subjected to MDIF process, and the related grain refinement mechanisms and texture development were investigated. MDIF resulted in a homogeneous microstructure with fine grains of 11 μm and non-basal texture, which was ascribed to the consecutive twinning and dynamic recrystallization (DRX). During the early forging passes, twin-induced DRX associated with {10–11} contraction and {10–11}-{10–12} double twins, and the coalescence and intersection of {10–12} extension twins with various variants effectively refined the coarse original grains and randomized the texture. With continuous forging, continuous and discontinuous DRX subsequently took place and eventually led to the fully DRXed microstructure and double-peak texture. Besides, fine spherical β-Mg17Al12 particles were dynamically precipitated along the original grain boundaries, acting as the preferred nucleation sites for DRX by particle-stimulated nucleation mechanism (PSN). Meanwhile, these particles became effective pinning obstacles for suppressing the DRXed grain growth.

유한요소법을 이용한 SCM435 Bolt의 성형 공정에 관한 해석 및 공정 개선 방안

A bolt manufacturing process is completed with continuous forging. Technical and economical success of each process will depend on the appropriate process design and metal mold design for each procedure. This study aims to analyze the moldings of first and second steps among the multi-step molding processes of SCM435 bolt by use of the finite element method in order to achieve the reasonable process. Since the processes of first and second steps analyzed by use of the finite element method consist of axial symmetry, the transformed configuration of material satisfy the dimensions expected in process. In addition, the uniflow line formed in material becomes smooth and consistent over the entire process. Therefore neither molding of material nor inherent defect is expected.

フランジヘッダー試験による線材用&lt;br&gt;潤滑皮膜評価法の提案

In the production of fasteners, the lubrication of wire films plays an important role in determining formability and die life. Zinc phosphate is one of the most popular lubricants for wires because of its high performance in terms of lubrication and cost. A one-liquid lubricant has been developed and an attempt has been made to apply it in place of conversion lubricants such as zinc phosphate. However, the performance of the one-liquid lubricant is generally unstable, thus; its improvement is strongly desired. The lubrication of wire films is enhanced by gluing powdered metal soap together at the time of drawing. Therefore, a tribosimulator at the side face of a testpiece is desired. Thus, we designed the shape via finite element (FE) simulation. This tribosimulator test was named the “flange header test”. In this test, forging load is increased at a point known as the lubrication limit. In addition, from the measurement of knockout load, the test enables us to evaluate the galling of a lubricant. Moreover, the test simulates the tendency to bring about die damage as in the case of mass production by continuous forging.

テーパーカップ試験による硬質被膜&lt;br&gt;工具のトライボ特性評価

Hard coatings on tools are very effective for wear resistance and the prevention of scuffing in forging; thus, many new coatings are developed yearly. The function of hard coatings in the reduction of friction has markedly improved recently; however, a method for its effective evaluation under practical forging conditions has not yet been developed. In this research work, we discussed the effectivity of the taper cup test, which we developed, as a new evaluation method. The taper cup test estimates the friction coefficient under a high surface expansion ratio, which is almost the same level to as those for mass-produced forging components. In the case of using no lubricant, diamond-like carbon (DLC) has a much lower friction coefficient than TiAlN and TiN. In the case of using one-liquid lubricant, friction coefficient is affected by surface roughness depending on the type of hard coating. In addition, continuous forging smoothened the surface, there by decreasing friction coefficient.

Japanese State of the Art Continuous Casting Process.

In the Japanese steelmaking industry, continuous casting technologies for manufacturing defect-free slab or bloom with high productivity are becoming increasingly important. The surface and internal defects of steel products attributable to steelmaking conditions originate in the entrapment of inclusions or gas bubbles by the solidifying shell in the casting mold or strand, and in the formation of center-line segregation at the final stage of solidification. To suppress such defects and ensure high quality in continuous casting process, many advanced technologies have been developed and applied in industrial plants as follows:(1) To promote the removal of inclusion from molten steel in the tundish, centrifugal flow tundish (CF-tundish) or H-shaped tundish was developed.(2) To prevent the entrainment of inclusion or gas bubbles into molten steel in the mold, flow control devices using the electromagnetic brake and electromagnetic stirrer have been adopted. Flow control mold is one example which is characterized by two static magnetic fields imposed on the entire width of a slab. Surface and internal defects in cast slabs are remarkably reduced by this newly designed tool.(3) To reduce the degree of center-line segregation, the solft-reduction process with a plane reduction unit or short-pitched roll segment for cast slab and continuous forging process with an anvil for cast bloom were applied to practical operations.

Improvement of properties of rods and bars by continuous forging process. Kawaberi, M., Yamamoto, Y. and Asoh, K. Kawruaki Steel Giho (1994) 26 (1), 26–32 (in Japanese)

Two-dimensional semiconductors have attracted immense research interests owing to their intriguing properties and promising applications in electronic and optoelectronic devices. However, the performance of these devices is drastically hindered by the large Schottky barrier at the electric contact interface, which is hardly tunable due to the Fermi level pinning effect. In this review, we will analyze the root causes of the contact problems for the two-dimensional semiconductor devices and summarize the strategies on the basis of different contact geometries, aiming to lift out the Fermi level pinning effect and achieve the ohmic contact. Moreover, the remarkable improvement of the device performance thanks to these optimized contacts will be emphasized. At the end, the merits and limitations of these strategies will be discussed as well, which potentially gives a guideline for handling the electric contact issues in two-dimensional semiconductors devices.

Control of Centerline Segregation in Continuously Cast Blooms by Continuous Forging Process.

The continuous forging equipment was constructed at No. 3 Continuous Casting Machine of Mizushima Works in 1990 to prevent the centerline segregation in continuously cast blooms. To clarify the mechanism of prevention of centerline segregation of blooms by this process, a mathematical model was developed by considering the discharge of the solute-enriched liquid between dendrites. The model shows that the segregation ratio in the central portion of the bloom decreases as the solid fraction at the forging point decreases. The solute concentration in the central portion of the bloom during forging calculated from the model is in good agreement with the observed values. The solute concentration in the central portion of the bloom can be predicted and controlled to a desired value by changing the solid fraction at the forging point by use of casting speed as a variable. As forging proceeds, a solute-enriched liquid region is formed in the upstream liquid region close to the forging point. The carbon concentration in the solute-enriched liquid region, where the solute accumulates, becomes constant after several meters from the forging point.

Long and continuous forging machines-development and field of application

AbstractThe historical development of the mechanically driven 4-hammer long forging machine is described. Comparisons are made of the operation and economic performance of the 4-hammer machine with conventional forging equipment, such as the hammer and hydraulic press. The 2-hammer long forging machine and its use to forge construction steels are outlined. Continuous forging machines, their use to forge continuously cast steel billet, and their combination with rolling stands for the production of bar steel are then described.