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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.)

Abstract—The possibility of improving the performance characteristics of Kh12MF die steel using gas–powder laser cladding and a nickel-based powder alloy containing 60% tungsten carbide as a cladding material is investigated. Laser cladding is carried out using a domestic SVAROG-1-5DR laser installation equipped with a 5-kW fiber diode laser. Laser cladding conditions have been experimentally selected. The microstructure, microhardness, and chemical composition of the deposited layer and the substrate are studied on transverse metallographic sections. Laser cladding is found to provide reliable melting of a carbide-containing powder material to the substrate and to significantly increase the surface hardness of Kh12MF steel. The hardness of the Kh12MF steel increases to 75.3 HRC upon cladding at P = 5 kW, V = 7 mm/s, and F = 30 mm. [ABSTRACT FROM AUTHOR]

The paper presents the results of metallographic analysis of the microstructure of high-alloy Uddeholm Sverker 3 steel (AISI Type D2). Cold treatment of high-alloy steels is used as a way to reduce the amount of retained austenite and, as a consequence, to stabilize the mechanical properties and dimensions of precision parts. In this work, we have used deep cold treatment by immersion in liquid nitrogen after heat treatment according to the traditional technology (quenching for primary hardness and low tempering). Exposure to liquid nitrogen has been carried out for 24 h. At the end of the exposure, the parts have been removed from liquid nitrogen and kept at room temperature until they reached room temperature. Then, the parts have been subjected to tempering at a low temperature of 170°C. The cryogenically treated sample has more noticeable fluctuations in the chemical composition and a larger amount of the carbide phase (30 and 27 vol %, respectively). Fluctuations in the chemical composition are expressed in more intense coloring of carbide particles using color etching, which indicates differences in their chemical composition. In the case of cryogenic treatment, the average specific size of carbides is less than in the absence of it. In addition, an increase in the content of ultrafine carbides is observed in the cold-treated sample, which is logically explained by their precipitation from retained austenite during its decomposition at cryogenic temperatures, decay of retained austenite and, as a result, the release of additional volumes of carbide particles. Particles formed during cryogenic treatment can be classified as ultrafine, with an average diameter of about 1 μm. [ABSTRACT FROM AUTHOR]

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]

RE and Mg co-treatment can significantly improve the cleanliness of steel and refine carbide， but RE and Mg are prone to be burned during electroslag remelting. Therefore， two kinds of electroslags containing Ce2O3 and MgO were designed， which are 55% CaF2-30% Ce2O3-10% MgO-5% Al2O3 (1#) and 60% CaF2-30% Ce2O3-10% MgO (2#)， respectively. Ce and Mg co-treatment of H13 die steel was carried out using a resistance-heated tube furnace， and the slag-metal equilibrium behavior between H13 steel and the aforementioned slags at 1873K was studied. The results show that the main inclusions in H13 steel are Ce2O3 and MgO. Some Ce2O3 inclusions are coated with MgO. At 15min after adding Ce and Mg， the dissolved Ce in the steel was almost completely burned， and only insoluble Ce in Ce2O3 inclusions was remained. During the whole deoxidation period， the content of dissolved Mg in steel changed little. The contents of dissolved Mg in 1# and 2# H13 steel at 60min were 0.0034% and 0.0053%， respectively， MgO solubility in 1# and 2# slags are 10.6% and 6.7%， respectively. Due to MgO supersaturation， both slags have very weak absorption capacity for MgO inclusions. The rmodynamic calculation shows that both the Al2O3 component and minor amounts of SiO2 in the slags lead to serious burning loss of Ce and Mg. [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.

The dies and molds made up of higher strength materials with complex shape can be easily machined using unconventional machining processes. The surface roughness and machining productivity during roughing phase has a very significant effect on increasing the efficiency of electrical discharge machining process. The optimization approach can enhance the mechanism of the machining process. In the present study, data envelopment analysis based ranking method was utilized to apply the multi criteria decision making in the process on machining SKD61 die steel. The influence of the input process factors such as voltage, pulse current and pulse-on-time were considered as input indicators in electrical discharge machining process. The material removal rate and surface roughness were selected as performance measures under rough mode to enhance the machinability in the process. From the experimental study, it was found that material removal rate and surface roughness were significantly improved under the optimal process parameter combinations of voltage (90 V), current (10 A) and pulse-on-time (100 µs). The optimal combination could produce 5% higher material removal rate with better surface finish. The surface quality of the surface layer can be improved under optimal parameters with lower white layer thickness owing to its importance on evaluating spark energy. [ABSTRACT FROM AUTHOR]

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]

Copyright of Electroplating & Finishing is the property of Electroplating & Finishing 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.)

The processes of modifying the surface properties of 3Cr2V8F and 5CrNM tool steels by electron-beam alloying (EBA) in vacuum with boron and aluminum treatment mixtures are considered. Metallographic analysis of the cross sections showed that as a result of EBA, uniform layers with a high roughness and without visible signs of zoning (layering) with a thickness of up to ~500 μm are formed. The modified layers have a distinct boundary with the base metal. The crystallization process starts after the end of electron-beam heating; Thus, a dendrite-like structure of the modified layer is formed. An increase in the microhardness from 350 to 1550 HV occurred in the surface zone of the layer due to phase and structural transformations from the liquid state (X-ray phase analysis revealed the presence of Fe2B, Fe3Al, FeAl3, AlB2, and AlFe2B2 phases). Thermal stresses develop, contributing to the hardening and plastic deformation processes. Wave oscillations of the microhardness profiles are observed over the modified-layer thickness. It is established that the maximum microhardness after two-component (B4C + Al) alloying is higher than after alloying with only boron carbide. [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]

• The synergistic effect of cyclic temperature and mechanical load on 4Cr5Mo3V steel was investigated by TMF testing. • Martensite decomposition, oxidation and carbide segregation contributed to the final thermo-mechanical fatigue failure. • Severe deformation existed in the vicinity of the newly precipitated M2C carbide during the TMF process. • The thermo-mechanical fatigue life of 4Cr5Mo3V steel was well described by four models. Thermo-mechanical fatigue (TMF) testing was used to study the fatigue behavior of 4Cr5Mo3V hot work die steel to reflect the in-service conditions. The synergistic effect of cyclic temperature and mechanical load was investigated using a strain-controlled method. Our results confirmed that the cyclic softening degree of 4Cr5Mo3V steel increased as the mechanical strain amplitude get bigger, leading to a reduction of the fatigue life. The microstructure evolution was studied before and after the TMF testing, and it was found the maximum texture strength in as-received steel decreased from 7.22 to 2.34 when the strain amplitudes was set as ± 1.1 %. Experimental evidence showed that martensite decomposition, oxidation, dislocation density reduction and carbide segregation all contributed to the final TMF failure. Severe deformation existed in the vicinity of the newly precipitated M 2 C carbide during the TMF process, acting as fatigue crack initiation sources due to stress concentration. Four different models were interrogated including Basquin-Coffin-Manson model, Smith-Watson-Topper (SWT) model, Ostergren model and 3SE energy model; and it was found that SWT model yielded the best fatigue life description. Nevertheless, all the four models showed reasonable fitting capability within the 2x scatter band, which proved the reliability of the experiments established in this study. [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.

The softening of a hot-deformed die steel under thermocycling used in thermal fatigue tests is studied. The changes in the microstructure, in the dislocation structure and in the hardness of the surface layer and of the core of the thermocycled sample are analyzed. It is shown that the thermocycling process is accompanied by softening of the hot-deformed die steel, because the total concentration of structural flaws grows or decreases in turns at a general tendency to lowering. [ABSTRACT FROM AUTHOR]

The possibility of raising the wear resistance and prolonging the service of forging die inserts is analyzed with the aim to elevate the efficiency of the production process and to reduce the cost of forgings. Three sets of inserts fabricated from the same grade of die steel and subjected to the same heat treatment are studied. Additional nitriding (gas or ion plasma one) is applied to two sets for comparison. It is shown that the inserts subjected to ion nitriding have the highest wear resistance and endurance. [ABSTRACT FROM AUTHOR]

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.

JMatPro software was used to simulate the H13 steel with different mass fraction Ti. According to the calculation results, the new mold steel with different Ti mass fraction was designed. The mechanical properties and microstructure of H13 steel with different Ti mass fraction after heat treatment were analyzed. The results show that it is reasonable to add Ti element mass fraction less than 0.600%. The tensile strength, hardness and plasticity of H13 steel containing trace Ti increase first and then decrease with the increasing of Ti content after quenching and tempering at room temperature. The performance achieves the best when the mass fraction of Ti is 0.127%. The maximum tensile strength and hardness at room temperature are 1 788 MPa and 51.5HRC, respectively. Compared with H13 steel without Ti, it increases 264 MPa and 3.7HRC respectively, and the reduction of area increases from 35.0% to 47.0%. The quenching and tempering micro structure of H13 steel with Ti mass fraction of 0%, 0.044% and 0.127% respectively is a mixture micro structure of tempered sorbite and tempered troostite. The quenching and tempering micro structure of H13 steel with Ti mass fraction of 0.325% and 0.536% is tempered sorbite. [ABSTRACT FROM AUTHOR]

In this paper, we studied the phase and elemental composition of the surface layer of die steel 5KhNM subjected to electro-explosive sputtering deposited composite TiC–Ni–Mo coating and subsequent pulsed irradiation with a high-intensity submillisecond electron beam. The modes of electron-beam processing providing the formation of a dense, with a mirror gloss, surface layer with a submicrocrystalline structure based on titanium carbide and intermetallic compounds based on Mo, Ni, and Ti are determined. The electron-beam processing of an electro-explosive coating in the melting mode is shown to lead to the formation of a structurally uniform and concentration-uniform surface layer. TiC–Ni–Mo coatings have a 1.26 times higher wear resistance compared to die steel 5KhNM used as a substrate. The microhardness of the formed coatings is 450–2400 HV, the nanohardness is 25.5 GPa, and the modulus of elasticity is E = 398 GPa. [ABSTRACT FROM AUTHOR]

EN31 steel is a potential member in automobile industry, and achieving dimensional accuracy with outstanding surface characteristics is a challenging task while machining this alloy. The current investigations deal with wire electrical discharge machining (WEDM) of EN31 die steel and establish a fundamental understanding of the process parameters on micro-scale machined surface characteristics. WEDM parameters such as pulse on-time, servo voltage, wire feed and wire tension are grouped in an efficient way to understand the influence of these parameters on edge roughness, kerf width and cutting rate. The current study revealed that low pulse on-time and servo voltage decreased kerf width and edge roughness. However, cutting rate decreased with pulse on-time but increased with servo voltage. Wire tension and wire feed were found to have diverse effects on the response parameters. While edge roughness varied inversely, kerf width was directly proportional to the wire feed corresponding to lower wire tension. [ABSTRACT FROM AUTHOR]

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.