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Tool-grade steels designed for the manufacture of hot-forming dies have been studied. An economically alloyed modified steel 70Kh3G2FTR(m) is proposed, which has a fine metal base structure with uniform carbide hardening in the heat-treated state. The comparative structural studies with traditional tool-grade steels (5KhGM, 4Kh5MFS) at different stages of heat treatment, as well as the statistical analysis of mechanical properties (hardness and toughness) from thermal hardening parameters, allowed us to develop an optimal heat treatment technology, which provided the required indicators for the structure, hardness, and heat resistance of the material. It is shown that 70Kh3G2FTR(m) steel retains its strength and the effect of microalloying at elevated operating temperatures, which is confirmed by data from transmission electron microscopy, dynamic mechanical analysis, and thermophysical properties in the field of operating temperatures up to 400 °C, as well as studies of the samples' texture under thermal exposure. The assessment of the mechanical properties, wear resistance, and economic effect of the introduction of the developed material and its thermal hardening technology make it possible to reasonably recommend 70Kh3G2FTR(m) steel as a rational replacement for traditional materials. [ABSTRACT FROM AUTHOR]

Copyright of Automobile Technology & Material is the property of Automobile Technology & Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the general environment of lightweight automobiles, the integrated die-casting technology proposed by Tesla has become the general mode to better achieve weight reduction in automobiles. The die-casting mold required by integrated die-casting technology has the characteristics of large scale and complexity. Hence, higher requirements are put forward for the comprehensive performance of the die steel. Despite the stagnation in the progress of conventional strengthening methods, enhancing the performance of die steel has become increasingly challenging. Indeed, it necessitates exploring novel die steel and optimizing heat treatment and reinforcement technologies. This article summarizes and analyzes the development status of die steel and corresponding heat treatment and microstructure manipulation as well as strengthening methods and elaborates on an excellent nano-strengthening technology. Furthermore, this review will aid researchers in establishing a comprehensive understanding of the development status of die steel and the processes utilized for its strengthening. It will also assist them in developing die steel with improved comprehensive performance to meet the high demand for mold steel in the integrated die-casting technology of the new era. [ABSTRACT FROM AUTHOR]

The structure and mechanical properties of 4Kh4N5M4F2 steel in thermodeformed and cast states after quenching and tempering, and additional heating are investigated. After additional heating of hardened and tempered 4Kh4N5M4F2 steel, which models the operating conditions of the equipment (operating temperature during quasi-stationary exposure), at 630–650°C steel softens, which is associated with the formation of Me7C3 carbides. Such carbide phase in the metal structure of the cast steel under mentioned conditions is absent and is accompanied by the increase in its heat resistance. The expansion of the operating temperature range of cast 4Kh4N5M4F2 steel after the optimal mode of hardening and tempering allows using a tool made of this steel up to the operating temperature of 650°C. It is recommended not to use such steel in the cast and thermodeformed states for the manufacture of tools for hot deformation of non-ferrous metals and alloys, which operate under cyclic impact loading. [ABSTRACT FROM AUTHOR]

A strategy combining intercritical quenching, pre-tempering, and tempering processes was implemented to optimize the microstructures and mechanical properties of 5CrNiMoV steel. By intercritically quenching at 1050 °C, pr-tempering at 600 °C, and tempering at 550 °C, the steel exhibited a comprehensive performance with a yield strength of 1120 MPa, an ultimate tensile strength of 1230 MPa, and an elongation of 8.2%. The high strength of the steel is attributed to the presence of tempered martensite and abundant secondary carbides. The favorable ductility is mainly provided by the pearlite inherited from intercritical quenching and tempering. Additionally, the precipitation of secondary carbides not only enhances precipitation strengthening, but also reduces the dislocation density and lattice strain of the matrix, thereby enhancing strength and ductility. This study offers a scheme for producing strong and ductile 5CrNiMoV steel. [ABSTRACT FROM AUTHOR]

In the current context, an attempt is being made to improve the electrical discharge machining (EDM) process by using powder particles in a suitable combination. To improve the quality of such procedures, the process parameters should be optimized. The present study proposes to utilize Taguchi–Grey relational analysis to discover the optimal combination of process parameters for SKD61 die steel specimens using titanium powder-mixed EDM (PMEDM). Among the machining parameters chosen, the optimal combination of current (3 A), pulse on-time (37 μs), pulse off-time (37 μs), and powder concentration (4 g/L) was determined experimentally. Due to its relevance in spark energy production, peak current is a more significant factor in PMEDM processes. A superior surface topography was obtained with increased microhardness and fewer microfractures over machined specimens with optimal process parameter in PMEDM. The titanium particles can effectively enhance the surface performance measures during PMEDM-based machining owing to tiny craters and pores with better lubrication.

To improve the surface roughness of SKD61 die steel and reduce the secondary overflow of the molten pool, a steady magnetic field-assisted laser polishing method is proposed to study the effect of steady magnetic field on the surface morphology and melt pool flow behavior of SKD61 die steel. Firstly, a low-energy pulsed laser is used for the removal of impurities from the material surface; then, the CW laser, assisted by steady magnetic field, is used to polish the rough surface of SKD61 die steel to reduce the material surface roughness. The results show that the steady magnetic field-assisted laser polishing can reduce the surface roughness of SKD61 die steel from 6.1 μm to 0.607 μm, which is a 90.05% reduction compared with the initial surface roughness. Furthermore, a multi-physical-field numerical transient model involving heat transfer, laminar flow and electromagnetic field is established to simulate the flow state of the molten pool on the surface of the SKD61 die steel. This revealed that the steady magnetic field is able to inhibit the secondary overflow of the molten pool to improve the surface roughness of SKD61 slightly by reducing the velocity of the molten pool. Compared with the molten pool depth obtained experimentally, the molten pool depth simulation was 65 μm, representing an error 15.0%, thus effectively demonstrating the accuracy of the simulation model. [ABSTRACT FROM AUTHOR]

A strategy combining intercritical quenching, pre-tempering, and tempering processes was implemented to optimize the microstructures and mechanical properties of 5CrNiMoV steel. By intercritically quenching at 1050 °C, pr-tempering at 600 °C, and tempering at 550 °C, the steel exhibited a comprehensive performance with a yield strength of 1120 MPa, an ultimate tensile strength of 1230 MPa, and an elongation of 8.2%. The high strength of the steel is attributed to the presence of tempered martensite and abundant secondary carbides. The favorable ductility is mainly provided by the pearlite inherited from intercritical quenching and tempering. Additionally, the precipitation of secondary carbides not only enhances precipitation strengthening, but also reduces the dislocation density and lattice strain of the matrix, thereby enhancing strength and ductility. This study offers a scheme for producing strong and ductile 5CrNiMoV steel.

Pressed steel with adjustable (regulated) austenitic transformation (RAT) is used for the hot deformation of a copper-nickel alloy at operating temperatures > 850°C (above the critical point A3 = 850°C). We recommend to extend the temperature range of forged steel with RAT (4Kh4N5М4F2 grade) and to use it in the martensitic state at operating temperatures < 630°С. For this purpose, we study the phase-structural state of this steel after optimized temperature modes of heat treatment (hardening and tempering). The relationship between the parameters of crystal structure and the mechanical properties of thermally hardened steel is established, as well as the temperature mode of hardening used for the process of primary recrystallization of steel with RAT. We compare the parameter of crystal structure and mechanical properties of the analyzed steel with the corresponding characteristics of two operated forged die steels, namely, steel for hot deformation of H13 grade (ASTM, USA; its analogs are the 4Kh5МF1S steel according to GOST 5950-2000, and SKD6 steel according to JIS, Japan) and 4Kh4N5M4F2 steel with RAT used to produce large-size wheels (extruders) for the hot deformation of copper. We justify the temperature mode of tempering for the process of softening of forged steel with RAT. Based on the established relationship between the parameters of crystal structure and hardness, it is shown that, at room temperature, the level of hardness should be lower than 40 HRC. [ABSTRACT FROM AUTHOR]

The control forging and cooling experiments of H13 and Cr8 die steel were carried out on a MMS-200 thermal simulator. When the cumulative strain of H13 steel reached 2.302 by drawing once, the number of recrystallized grains increased, the recrystallized grains were refined and the corresponding grain grade was about eight. The grain was refined with deformation bands at 750 °C in non-recrystallization region. With increasing cooling rate, the distorted austenite grains evolved into fine recrystallized grains and distorted austenite grains. The microhardness value of annealed H13 steel increased and then decreased with increasing cumulative strain and cooling rate, decreased and then increased with increasing drawing temperature. When the cumulative strain was 1.609 by drawing twice for Cr8 steel, the distribution and quantity of carbide particles were improved. With increasing deformation temperature, the size and number of carbide particles decreased and the dissolution degree increased significantly. Moreover, the intragranular carbide particles dissolved preferentially into matrix. With increasing cooling rate, it presented acicular martensite with granular carbides. The microhardness value of Cr8 decreased first and then increased with increasing cumulative strain and cooling rate, and increased and then decreased with increasing drawing temperature. [ABSTRACT FROM AUTHOR]

Effect of Al content on the microstructure, hardness, corrosion resistance, and thermal conductivity of the die steel was examined. It was shown that after adding 0.37 wt.% Al, the microstructure is still composed of lath-shaped tempered martensite, and the hardness is increased slightly. However, when the Al content rises to 1.34 wt.%, ferrite occurs in the microstructure besides tempered martensite, and the hardness is decreased significantly. The thermal conductivity of the die steel is decreased gradually with increasing Al content from 0.37 to 1.34 wt.% at all the tested temperatures. Thermal conductivity is decreased with the increase of temperature without Al addition. However, the maximum thermal conductivity occurs at 450 °C whenever 0.37 or 1.34 wt.% Al is added. Potentiodynamic polarization tests indicate that the corrosion current density in 0.5 mol·L−1 HCl solution is decreased from 3.08 to 2.62 mA·cm-2 when 0.37 wt.% Al is added. However, the corrosion current density is slightly increased from 2.62 to 2.74 mA·cm−2 when Al content is increased to 1.34 wt.%. The corrosion resistance of the die steels with Al addition by potentiodynamic polarization is in agreement with the electrochemical impedance spectroscopy (EIS) results. [ABSTRACT FROM AUTHOR]

Hot-work die steels are widely used to meet the requirements of industrial applications in which the steels must endure high temperature and mechanical loads, such as the hot stamping of very-high-strength steel. In the field of hot-stamping technology applications, the tool materials must have excellent high-temperature performance, such as the high-temperature stability of the microstructure. Research on hot-stamping die materials began somewhat late in China because high-quality die steel products had typically been imported. A new type of hot-stamping die steel with high thermal conductivity and high wear resistance was developed to meet the requirements of hot-stamping technology. In this study, we used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine the high-temperature tempering performance and microstructural characteristics of this new Mo−W−V alloyed hot-work die steel. Based on the results, we derived the precipitation and evolvement rules of the carbides in the new type hot-stamping die steel during the tempering process, which indicate that the new Mo−W−V alloyed test steel has an excellent secondary hardening property. We find the hardness of the microstructure to increase after tempering at 500 ℃–600 ℃; however, at tempering temperatures above 600 °C, the matrix obviously softens and the hardness of the test-steel microstructure decreases. The hardness of the test die steel is strongly linked to the segregation, precipitation and growth of the alloy carbides in the matrix. No alloy carbide precipitation is observed at tempering temperatures below 560 ℃; however, M2C-type carbide precipitation is observed at tempering temperatures higher than 560 ℃. MC-type alloy carbide is observed in the test-steel matrix at tempering temperatures up to 600 ℃. At tempering temperatures above 620 ℃, the M2C-type alloy carbides transform into M6C-type alloy carbides and the hardness curve of the test steel sharply declines. The MC-type and M6C-type alloy carbides are the main carbides in the matrix of the new Mo−W−V alloyed hot-work die steel.

In the work, the heat treatment conditions of 4H4N5M4F2 die steel for hot deformation are investigated. The physico-mechanical properties of the investigated ingot steel were determined after quenching 1100 ± 5 °С and tempering. Given the importance of cooling regimes after tempering, various cooling regimes (in oil, in a furnace, in air) were investigated. Physical-mechanical properties of cast steel 4X4H5M4F2 after tempering at 550 ± 5 °C and 600 ± 5 °C were determined. The optimal tempering regime for steel at 550 ± 5 °C with air cooling was established: the ultimate strength of 1860 MPa and the yield strength of 1760 MPa. The optimal tempering regime for steel at 600 ± 5 °C with air cooling has been established: the ultimate strength is 1600 MPa, the yield strength is 1500 MPa, and the heat resistance is 48.5 HRC. It was established that twofold hardening and tempering of steel at 600 ± 5 °C temperature with oil cooling leads to an increase in its fracture toughness (75 J/cm2) compared with the fracture toughness after air cooling (30 J/cm2). It is established that the temperature range of tempering brittleness of the studied steel is 465 ‑ 495 °С. The optimized temperature regime of tempering of the investigated steel (590 ± 5 °С) made it possible to increase the impact strength by a factor of two (up to 30 J/cm2) in the temperature range 465 ‑ 495 °С. A pilot test of the punch tool made from the investigated steel was carried out. During hot pressing of the AK7ch aluminum alloy, the life of the dies was at the level of forged steel 4Kh5MF1S with a nitrided surface layer, which was used at the factory. After the operation of both matrices (hot deformation), samples were cut and tested for hardness and toughness. The latter turned out to be higher for the forged steel, however, the service life of the matrices from both steels was at the same level.

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, effect of Mo content on the microstructure, thermal conductivity, and corrosion resistance of the die steels was investigated by optical microscopy, scanning electron microscopy, x-ray diffraction, laser thermal conductivity meter, electrochemical experiments, and pitting tests. The microstructure of the die steels is mainly composed of lath-shaped tempered martensite. At all the tested temperatures, the thermal conductivity of the die steels is decreased with the increase in Mo content from 1.2 to 5.0 wt.%. However, electrochemical experiments indicate that increase in Mo content in the die steels can reduce the corrosion current density and increase the charge transfer resistance in 0.5 mol·L−1 HCl solution. Furthermore, it was found that Mo in the die steels is beneficial to decrease weight loss and pitting corrosion rate, which improves the pitting corrosion resistance of the die steels. [ABSTRACT FROM AUTHOR]

This paper reports the investigation on parametric optimization of the abrasive aqua jet (AAJ) and cryogenic assisted abrasive aqua jet (CAAAJ) processes for cutting AISI D2 steel using multi objective TOPSIS approach. The input parameters considered were aqua jet pressure, abrasive grit size and jet impingement angle. In this study, depth of penetration, metal removal rate, kerf taper ratio and average roughness were taken as the performance characteristics. The results showed that the CAAAJ process exhibited better performance characteristics than the AAJ process. The AAJ machining process with an inclined jet impact angle influences the output responses, which is evident from an optimal selection of parameters. Besides, the influencing process variables were determined by using the analysis of variance. The overall machining performance of the AAJ and CAAAJ processes were improved by using the optimum process variables through the TOPSIS method.

Steels with adjustable austenitic transformation during the exploitation (RAPE) are designed for applied in the temperature range of 800 – 950 °C, which corresponds to the austenitic structure, but at the lower temperature range (630 – 650 °C) tempering fragility of the second kind occurs, which makes it difficult to operate. This is inconvenient when the die tool works in a wide range of temperatures during deformation of various metals and alloys. An improved steel composition (4H4N5M3F2) (RAPE) for press molds for hot pressing of copper and its alloys at temperatures of 630 – 650 °C is proposed. Steel was obtained by electroslag remelting, it was heat treated and the properties were determined. It is shown that the heat resistance of the investigated steel is higher by 2 HRC than the heat resistance of steels grade 4H5MF1S and 3H3M3F, which are used under the same operating conditions. The yield strength and impact strength of steel 4H4N5M4F2 considerably exceeds the characteristics of steel 3H3M3F (high –grade rolled products). The annealing temperature limits, which allow obtaining the necessary technological properties of steel, were established. It is shown that the steel structure consists of two areas: dark (obviously it is released martensite) and light (the area with a lower content of the carbide component). With an increase in tempering temperature from 640 to 660 °C, the hardness (HV) of the dark and light components decreases from 478.6 to 459.8 and from 427.8 to 376.0, respectively. The heat resistance of the investigated steel after quenching and tempering in optimal conditions increased to 650 °C (41 HRC).

To improve the surface roughness of SKD61 die steel and reduce the secondary overflow of the molten pool, a steady magnetic field-assisted laser polishing method is proposed to study the effect of steady magnetic field on the surface morphology and melt pool flow behavior of SKD61 die steel. Firstly, a low-energy pulsed laser is used for the removal of impurities from the material surface; then, the CW laser, assisted by steady magnetic field, is used to polish the rough surface of SKD61 die steel to reduce the material surface roughness. The results show that the steady magnetic field-assisted laser polishing can reduce the surface roughness of SKD61 die steel from 6.1 μm to 0.607 μm, which is a 90.05% reduction compared with the initial surface roughness. Furthermore, a multi-physical-field numerical transient model involving heat transfer, laminar flow and electromagnetic field is established to simulate the flow state of the molten pool on the surface of the SKD61 die steel. This revealed that the steady magnetic field is able to inhibit the secondary overflow of the molten pool to improve the surface roughness of SKD61 slightly by reducing the velocity of the molten pool. Compared with the molten pool depth obtained experimentally, the molten pool depth simulation was 65 μm, representing an error 15.0%, thus effectively demonstrating the accuracy of the simulation model.

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The plasma-based electron beam (PBEB) irradiation with a maximum diameter of 60 mm has been used to smoothen the workpiece surface. After PBEB irradiation, the machined surface roughness is reduced, and its corrosion resistance is improved. However, for die and tool steels, some craters still exist on the surface after PBEB irradiation, which remain a big problem for the roughness improvement and quality control of the machined surfaces. In this study, four types of work materials have been tested during PBEB irradiation. The effects of non-metallic inclusions (MnS and carbide) and impurities on the generation of craters were investigated. In addition, craters formed on the work materials with different nitrogen concentrations have also been observed after PBEB irradiation. Finally, a case study is given, and it is found that PBEM irradiation can achieve good surface finish of die steel materials. (c) 2006 Elsevier B.V. All rights reserved.

Effects of tempering temperature on impact wear of 30Cr3Mo2WNi hot-working die steel are investigated by SEM, TEM, hardness, and impact wear tests. From 300 to 680°C, the hardness of the steel decreases and the impact toughness increases with increasing tempering temperature, while a secondary hardening with maximum hardness, 48.6 HRC, is achieved at 550°C. Fatigue delamination wear is the main mechanism during the impact wear, and three typical damage features are identified with different tempering temperatures. Brittle fatigue cracks are easy to occur in the steels tempered at 300°C. Ductile fatigue cracks occur at medium temperatures. Surfaces of steel tempered are extruded at 680°C.

In practice, the improvement of surface roughness (SR) after die sinking electric discharge machining (EDM) is simple and inexpensive when compared with the microhardness of machined-surface layers (HV). In addition, when HV is low, the improvement of SR will be less effective and have no significance to the mold surface layer. Therefore, the HV of molds after die sinking EDM is improved and plays a more important role than the improvement of SR. Currently, powder-mixed die sinking EDM is a technological solution that can improve both the HV and SR simultaneously. However, SR is given a priority criterion popular choice for many studies into powder-mixed die sinking EDM. In this current study, the researchers improve the quality of the steel surface layer of the mold using titanium (Ti) powder-mixed die sinking EDM. In the research, HV is selected as a criterion to optimize input parameters, and SKD61, SKD11, and SKT4 mold steels as well as Cu and Gr electrode materials are used. The effects of the workpiece material (A), electrode material (B), electrode polarity (C), pulse-on time (D), pulse-off time (F), current (E), Ti powder concentration (G), and some interactive A × B, A × G, and B × G to HV surface layers are analyzed and evaluated. Finally, the Taguchi method is used to optimize the parameters. Results indicated that parameters such as the electrode material, the pulse-on time, the concentration powders, A × G, and B × G significantly affect the HV. The Ti powder concentration has the largest effect on HV. When the powder concentration increased, HV was increased; its largest increase was 41.81%, and the optimal value of HVopt = 864.363 ± 61.68 HV at a Ti powder concentration of 10 g/l. The machined surface analysis of SEM and SR after powder-mixed die sinking EDM using Ti powder at optimal conditions showed that the quality of the surface layer was significantly improved. The qualities of surface layers, such us mechanical properties, topography, and the microstructure after EDM with titanium powder mixed into dielectric fluid, was significantly improved under optimal conditions for various mold steels. [ABSTRACT FROM AUTHOR]

In this article, the wire electrical discharge machining of different heights of die steel workpieces has been carried out for different control strategies, i.e. proportional control mode, constant speed mode, constant voltage mode, and constant area feeding mode. It is very crucial to understand the thermo-mechanical aspect of the machining gap during machining of changing job height. For the efficient machining of variable thickness of jobs, these observations are extremely essential. Here, it is observed how job height influences cutting speed, surface roughness, kerf width, gap voltage, gap current, input power, and specific energy consumption under these control strategies. So far, very little research work has been reported in this area. Thus, it is quite imperative to carry out an intensive research study of wire electrical discharge machining (WEDM) during machining of different job thickness under those control strategies. An attempt has been made to understand the nature of variation of these important response parameters. The average and variance of some of the most influential parameters, i.e., cutting speed, surface finish, and kerf width were also calculated. Along with this, to predict the different important response parameters, i.e., cutting speed, surface finish, and kerf width for any given height job under any specified control strategy, regression analysis was carried out. [ABSTRACT FROM AUTHOR]

• Failure analysis of a cold rotary swaging die which bears high-frequency impact loads is investigated. • A large amount of dislocations are believed to have accumulated in the near outer layer of the arc surface. • The common single circle design leads to the concentrated forming stress during rotary swaging process on the die surface. • Phase inhomogeneity caused in heat treatment process and internal damage accumulation are two other reasons for the failure. • Fillet and surface designs are proposed to improve the wear and stress distribution. Failure analysis was carried out on a cold rotary swaging die for batch production of small shafts and tubes. Characteristics of top and bottom surfaces were examined. Hardness distribution on the cross section and microstructure were analyzed. Stress distribution and wear on the die during rotary swaging were investigated by finite element analysis (FEA). The study showed that the internal damage, phase inhomogeneity, concentrated forming stress were the main three reasons for premature failure of the die. The internal damage caused the tensile strength to reduce by more than 55%. The content of 33.55% martensite near the arc surface was not high enough to prevent the cracks from propagating inward. The stress concentration at the bottom of the arc surface further decreased the bearing ability. Increasing the fillet angle can decrease the high stress by around 60% at the transition area and improving surface design can disperse the high stress area while reducing maximum stress by more than 35%. [ABSTRACT FROM AUTHOR]

The effect of cooling intensity on the carbide segregation and solidification microstructure of an H13 as-cast ingot with Mg addition was studied during the electroslag remelting process. The solidification microstructure and the carbide characteristics of the steel were analyzed by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. The results show that the solidification microstructure of the ingot consists of martensite, retained austenite and primary carbides. Carbides in the electroslag remelting ingot are V8C7, MC, M23C6 and M6C. With the increasing of cooling intensity, the size of carbides in the edge of the electroslag remehing ingot decreases, the distribution of these carbides becomes more homogeneous, but the types of carbides remain unchanged. Increasing the cooling intensity improves the modification of inclusions by Mg. The formed MgO. Al2O3 arising from Mg treatment provides preferred nucleation sites for TiN. These complex inclusions promote the heterogeneous nucleation of primary carbides, consequently refining primary carbides.

This paperattempted to study the induced surface residual stressesduethe effect of Electrical discharge machining (EDM) input parameters, (the pulse current,the pulse-on time and the type of electrode).The work includedthe use of two types of electrode, the copper and graphite as well as using or without using the graphite powder mixing with the kerosene dielectric (PMEDM) for machining AISI D2 dies steel. The response surface methodology (RSM) was usedfor design the experimental work matrices. The analysis of variance (ANOVA) was used, and models were builtto predict the surface residual stresses.The obtained results showed that the minimum tensile surface residual stresses obtained when using the copper electrodeswith pulse current (22 A) and pulse on duration (40 µs) when working with kerosene dielectric alone and (8 A) with (120 µs) when working with graphite powder mixing. The results concluded that the using of graphite electrodes and kerosene dielectric alone or with powder mixing induced minimum residual stresses with pulse current (22 A) and pulse on duration (120 µs). The copper elec-trodes with kerosene dielectric and graphite powder mixing improved the induced tensile residual stresses by about (80 %) lower than when using kerosene dielectric alone and about (50%) lower than with graphite electrodes and the kerosene dielectric alone or with graphite mixing powder.

The curves of contact temperature-time between TA15 titanium alloy and H13 die steel with glass lubrication and without glass lubrication were obtained and the characteristics of the interface heat transfer were analyzed. The corresponding graph and empirical formula between the interfacial heat transfer coefficient (IHTC) and the temperatures of both the titanium alloy and the die steel were established. The results show that glass lubricant can reduce the interfacial heat transfer between the titanium alloy and the die steel effectively. When the initial temperatures of the titanium alloy and the die steel are respectively 700–800 °C and 340–400 °C, the temperature of the contact interface tends to be stable at the time of about 15 s under the condition of glass lubrication, which is about 50% longer than that without glass lubricant. The IHTC is increased from 125 W/(m 2 °C) to 1000 W/(m 2 °C) with the increase of the contact time under the condition of glass lubrication, while it is increased from 150 W/(m 2 °C) to 1800 W/(m 2 °C) without glass lubrication. The empirical formula of IHTC obtained in this paper has high accuracy that the error between the simulated and experimental results is less than 10%. [ABSTRACT FROM AUTHOR]

Powder mixed electric discharge machining (PMEDM) is one of the new innovations for the enhancement of capabilities of the electric discharge machining process. This paper is an attempt to study the effect of SiC powder mixed in the kerosene dielectric fluid. The type of electrodes, the peak current and the pulse-on time are the main selected EDM input parameters. The workpiece and the electrodes materials are the AISI D2 die steel and copper and graphite materials, respectively. The output responses considered are the workpiece surface roughness (SR), the material removal rate (MMR) and the tool wear ratio (TWR). The experiments are planned using the response surface methodology (RSM) design procedure. Empirical models are developed for SR, MRR and TWR using the analysis of variance (ANOVA) and regression models to study the effect of process parameters. The best results for the productivity of the process (MRR) were obtained when using graphite electrodes at pulse current (22 A), pulse on duration (120 μs) and with silicon carbide (SiC) powder mixing in kerosene dielectric at reaches (76.76 mm³/min). These results improved the material removal rate by (264%) with respect to the corresponding value obtained when using copper electrodes with kerosene dielectric alone. The best (TWR) results of the process were obtained when using graphite electrodes at pulse current (8 A), pulse on duration (40 μs) and using the kerosene dielectric alone reduced to the level (0.1023 %)...

A new apparatus is proposed for the freeform surface diamond machining on die steel in this paper. Fast tool servo-based diamond turning is considered to be the most effective and efficient generating technology for freeform surfaces, but freeform surfaces of die steel cannot be machined very effectively by this technology because of the severe tool wear and the surface quality degradation. Elliptical vibration cutting has demonstrated excellent performances in machining die steel materials. Therefore, this paper proposes a double-frequency elliptical vibration cutting apparatus, which combines fast tool servo and elliptical vibration cutting. The device is designed to be a flexure hinge structure and driven by two piezoelectric actuators to generate tool motions. A series of testing experiments are conducted, in which the device performs well. In addition, the freeform surfaces are generated on the 40Cr die steel workpieces with the device, and the surface machined by double-frequency elliptical vibration cutting shows much better surface integrity and form accuracy than the surface machined by conventional fast tool servo, which validates the principle and the proposed apparatus. [ABSTRACT FROM AUTHOR]

For the process of plastic materials working, there is a minimum cutting thickness. When the real effective cutting thickness is less than the minimum cutting thickness of workpiece materials in the actual cutting process, it will cause abnormal cutting of the tool and the workpiece, mainly in the sliding friction. So the machining accuracy is hard to guarantee. It is significant to determine the minimum cutting thickness of the materials to improve the machining quality and precision. A test method was provided to determine the minimum cutting thickness of workpiece material, focusing on the material of hardened steel Crl2MoV and the minimum cutting thickness for different cutting speed was determined by this lest method. The test results show that; the thermal softening effect has greater effect on the chip formation mechanism of hardened steel Crl2MoV (58 HRC) than strain rate effect in the selected speed range. The determination of the minimum cutting thickness has provided a theoretical basis for selecting the allowance of finish machining of automobile covering mold. [ABSTRACT FROM AUTHOR]

Abstract: With the increasing demand for the replication of structured optical elements such as Fresnel lenses and prism arrays, more attention is being paid to the development of ultra-precision diamond machining technology for the fabrication of die steel molds. However, the machining process would be a catastrophic failure because of rapid and excessive tool wear if a diamond tool is used to machine die steel. In the present paper, a micromachining method for fabricating microstructures on die steel using single crystal diamond tool is presented. The presented technology is based on a thermochemical technique that uses plasma nitriding treatment to suppress the rapid and excessive tool wear in the diamond machining of steel. Experimental findings revealed that severe chemical tool wear, which is the main wear mechanism in the diamond machining of steel, was reduced significantly after plasma nitriding treatment, and a mirror-quality surface with an average surface roughness of 20nm root-mean-square (RMS) was achieved over a cutting distance of approximately 5.4km. Furthermore, a Fresnel microstructure with surface roughness RMS better than 40nm was precisely fabricated on AISI 4140 die steel using single crystal diamond tool. [Copyright &y& Elsevier]

Abstract: Various non-smooth surfaces on the 3Cr2W8V, H13 and HD die steel that were similar to the animals’ surfaces were processed by laser. The size, microstructure and hardness of the striate non-smooth units processed with various laser parameters were studied. The abrasive particle wear behaviors of three materials with various distributing distance striate non-smooth units were measured at 200A current intensity and 3.0ms impulse duration. And the wear behaviors of three materials with various shape 2mm distributing distance non-smooth units were also measured at the same laser parameters. At the same time the wear mechanism of the die steels with non-smooth surfaces were discussed. The results show that the wear-resistances of several materials with non-smooth surfaces are better than that of the smooth materials. The changing trend of wear-resistance of three materials with non-smooth surfaces remains the same at same laser parameters regardless of their shape or the distributing distance. Namely, the wear-resistance of HD non-smooth specimens is the best, and that of the 3Cr2W8V is secondary, and that of the H13 is the worst. The size and hardness of non-smooth units are the major factors influencing the wear-resistance of non-smooth material. The bigger volume and higher hardness of non-smooth units result in the better wear-resistance of material with non-smooth surface. [Copyright &y& Elsevier]