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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]

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]

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]

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]

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 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]

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The friction and wear of stamping die surface can affect the service life of stamping die and the quality of stamping products. Surface texturing and surface coating have been widely used to improve the tribological performance of mechanical components. This study experimentally investigated the effect of triangular surface texture on the friction and wear properties of the die steel substrate with TiN coatings under oil lubrication. TiN coatings were deposited on a die steel (50Cr) substrate through a multi-arc ion deposition system, and then triangular surface texturing was fabricated by a laser surface texturing. The friction and wear test was conducted by a UMT-3 pin-on-disk tribometer under different sliding speeds and different applied loads, respectively. The adhesion test was performed to evaluate the effectiveness of triangular texturing on the interfacial bonding strength between the TiN coating and the die steel substrate. Results show that the combination method of surface texturing process and surface coating process has excellent tribological properties (the lowest frictional coefficient and wear volume), compared with the single texturing process or the single coating process. The tribological performance is improved resulting from the high hardness and low elastic modulus of TiN coatings, and the generation of hydrodynamic pressure, function of micro-trap for wear debris and micro-reservoirs for lubricating oil of the triangular surface texture. In addition, the coating bonding strength of the texturing sample is 3.63 MPa, higher than that of the single coating sample (3.48 MPa), but the mechanisms remain to be further researched. [ABSTRACT FROM AUTHOR]

In order to research the wear property of die steel, based on the bionic theory, bionic units were manufactured by laser remelting treatment on the surface of five kinds of die steels with varying chemical compositions alloying element contents (1.77%, 5.73%, 8.66%, 9.38% and 14.39%). The differences and regularities in the characteristics (depth, width, area and depth to width ratio), microstructure and hardness of samples with varying laser energy density and compositions of the matrix were analyzed. Then, the wear property of die steel was experimentally evaluated. The results displayed that the cross-sectional area of the bionic unit increased with the increase of laser energy density for the same material. Meanwhile, when the energy density was constant, the cross-sectional area of the bionic unit increased with an increase in alloying element content, but the average hardness of the bionic unit first increased and then decreased. Compared with the untreated sample, the bionic sample is beneficial to enhance the wear property. Moreover, the wear property of die steels with chemical compositions alloying element content of 8.66% reinforced with bionic unit was more effective than other samples. The wear enhancement mechanism of the bionic sample was discussed. • Bionic units of die steels with varying chemical compositions were manufactured by laser remelting treatment. • The differences in the microstructure and hardness of samples with varying laser energy densities and compositions of the matrix were analyzed. • The mathematical models between the bionic unit characteristics and the compositions of die steel were established. • The wear property of bionic unit with chemical compositions alloying element content of 8.66% was the best. [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: Rapid tool wear in diamond machining of steel can cause catastrophic failures. Despite several approaches to reducing tool wear, diamond machining of steel for industrial applications remains limited. We investigated two solutions, namely plasma nitriding treatment for workpiece surface modification and elliptical vibration cutting for cutting process modification, to determine their effect on reducing tool wear in diamond machining of AISI 4140 die steel. Furthermore, a new approach by combining the two solutions was also explored. Experimental results showed that diamond tool wear could be reduced by several orders of magnitude and mirror-quality surface can be obtained by using either the plasma nitriding treatment or the elliptical vibration cutting. However, in contrast to our expectations, combining the two solutions did not yield further improvement of either the surface finish or the reduction of tool wear compared with that of elliptical vibration cutting alone due to microchipping. Care has been taken to investigate the mechanism responsible for microchipping, and it was found that microchipping is highly dependent on the crystal orientation of the diamond. A diamond tool with the (110) plane as the rake face and the (100) plane as the flank face was more resistant to damage, and the microchipping induced in the combined cutting process was almost completely suppressed. [Copyright &y& Elsevier]

Abstract: Microstructure, hardness and wear behavior of AISI D2 steel subjected to varied sub-zero treatments have been examined with reference to conventional heat treatment. Part I of this work presents the variations of microstructure and hardness, whereas part II deals with the wear behavior. The sub-zero treatments studied are cold treatment, shallow cryogenic treatment and deep cryogenic treatment. The developed microstructures have been characterized by XRD, optical microscopy and SEM examinations coupled with EDX and image analyses. Macrohardness and microhardness of the specimens have been evaluated by Vickers indentation technique. The obtained results infer that (i) retained austenite content is reduced by cold treatment, but is almost completely eliminated by both shallow and deep cryogenic treatments, (ii) the sub-zero treatments modify the precipitation behavior of secondary carbides; lower the temperature of sub-zero treatment higher is the degree of modification, (iii) the deep cryogenic treatment refines the secondary carbides, increases their amount and population density, and leads to more uniform distribution, and (iv) bulk hardness increases marginally but apparent hardness of the matrix improves considerably by deep cryogenic treatment. [Copyright &y& Elsevier]

In this study, nitriding behavior of plasma nitrided X32CrMoV33 die steel was investigated. Nitriding process was carried out at temperatures of 450, 500, and 550°C for treatment time in the range of 2-32 h. Depending on nitriding temperature and time, the thickness of compound layer ranged from 2 µm to 15 µm. The presence of γ'-Fe4N, ε-Fe2-3N, α-Fe, and Cr2N phases formed in the compound layer was confirmed by XRD analysis. Using cross-sectional samples and a microhardness indenter, hardness depth profiles were also obtained; it was found that the hardness of compound layer was over 1000 HV. Kinetic studies revealed that the effective diffusion coefficients for plasma nitrided X32CrMoV33 are approximately 40.3 × 10-14, 99.2 × 10-14, and 427 × 10-14 m2s-1 for 450, 500, and 550°C process temperatures, respectively. The activation energy for plasma nitrided X32CrMoV33 steel is 118.77 kJ mol-1. [ABSTRACT FROM AUTHOR]

Milling cutters were evaluated by tool wear, cutting force and vibration. Surface integrity of grinding and milling were investigated by comparing residual stress distributions, metallurgical structure, hardened layer depth and surface roughness. And influence of cutting tool wear on surface integrity was investigated. Experimentations revealed that the preferable surface integrity would be obtained if the proper milling cutter as well as a small wear criterion were adopted to avoid the advent of tempered martensite. The research results pointed out the feasibility of taking milling as the finish machining process instead of grinding in machining hardened steel with high efficiency. [ABSTRACT FROM AUTHOR]