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The IHTC (Interfacial-Heat-Transfer-Coefficient) between 22MnB5 and KDAHP1 hot work tool steel during the hot stamping process is an important thermal parameter to reflect the heat transfer efficie...

This research focuses on specimen geometry and the associated surface roughness of H13 hot-work tool steel, processed using laser-directed energy deposition additive manufacturing, and varying both the powder feed rate and the laser scanning speed. Under the examined conditions, the test sample measurements of length and width did not vary, but the sample heights were significantly affected by the scanning speed. An increase in scan speed resulted in ‘underbuilding’, while a decrease resulted in ‘overbuilding’, as might be anticipated. The top surface roughness of the samples was found to be greater than the side surface roughness, due to the capture of extra powder particles. For the single-track and multitrack clad samples, the surface roughness was increased when decreasing the scan speed. The addition of a draft angle, when producing 3-D components, was shown to reduce the side surface roughness. Using a finer layer thickness results in overbuilding the target height, while a coarser layer thickness results in underbuilding. Finally, the surface roughness exhibited no clear trend when the layer thickness was changed.

In industry, thermally shocked components lead to early failures and unexpected breakdowns during production resulting in huge losses in profit. Thus, the present study investigates the as-received, hardened and hardened and nitrogen treated H13 tool steels subjected to a thermal shock gradient similar to the actual industrial applications. The thermal shock gradients were created by using an in-house-built thermal shock fatigue cyclic treatment machine. The effect of thermal shock fatigue cyclic treatments at 1000 and 2000 thermal shock cycles in hot and molten metal chambers was noticed. All the thermal shock fatigue cyclic-treated samples were analysed by hardness, X-ray diffraction, microscopy and magnetic tests. The interesting changes in hardness, distorted crystal structure and crack initiation were found to be different for differently treated H13 tool steel specimens. The molten aluminium was more prone to stick to the surface of as-received as well as hardened and nitrogen treated steel compared to the hardened H13 steel specimens, which would delay the crack initiation. The wear resistance properties of the hardened H13 steel specimens were found to be higher than as-received and hardened and nitrogen treated H13 steel specimens after thermal shock fatigue cyclic treatment. The loss in magnetic properties was significant for the hardened and hardened and nitrogen treated samples compared to as-received H13 tool steel specimens. Therefore, the present 1000 and 2000 thermal fatigue cycles for 30 s at 670 °C would be worthy to predict the proper heat treatment method to design the parameters as well as the life of die-casting components and to help in the economical production of casting.

To elevate the friction and wear performances of hot work mold, CrNi coatings with the different TiO2 mass fractions were fabricated on H13 steel using laser cladding (LC). The morphologies and phases of obtained coatings were analyzed using a scanning electron microscope (SEM) and x-ray diffraction (XRD), respectively. The effects of TiO2 mass fraction on the friction and wear performances of CrNi coatings at 600 °C were investigated using a high-temperature wear tester, and the wear mechanism was also discussed. The results show that the TiO2-reinforced CrNi coatings are mainly composed of Fe0.64Ni0.36, Cr and Cr2Fe14C phases; their porosity decreases with the increase in TiO2 mass fraction. The average coefficients of friction (COFs) of CrNi-5%TiO2, -10%TiO2 and -15%TiO2 coatings are 0.77, 0.74, and 0.67, respectively, and the corresponding wear rates are 1.164 × 10−5, 0.942 × 10−5, and 0.614 × 10−5 mm3·s−1·N−1, respectively. The TiO2 plays a role of friction reduction and wear resistance, and the wear mechanism is abrasive wear and oxidation wear.

Purpose This paper aims to experimentally determine the influence of the tool shoulder depth value on the structural and strength properties of the single lap joints made of 7075-T6 aluminium alloy made with friction stir welding (FSW) technology. The aim of the preliminary tests is to optimize the parameters of joining process of thin-walled structures such as the skin-stringer joint or skin-frame joint of the aircraft fuselage. The tests were carried out for materials commonly used in such structures, i.e. 1.6 mm thick sheet 7075–T6 aluminium alloy with cladding on both sides (cladding thickness 4% per each side). The layer of clad protects plates from corrosion. Design/methodology/approach This study shows the results of the investigation for the joining of 7075–T6 ALCLAD aluminium alloy sheets. The welding process was carried out on a computer numerical control milling machine SOLARUCE TA–20A. Linear FSW welding was performed using a commercial tool from RSS SCHILLING with the symbol 10–K–4–Z–M–O, which is fabricated of hot work tool steel. Constant parameters of the technological process were applied. The welding process was executed for different values of the shoulder depth ZS. Findings This paper investigated the dependence between the thinning of the welded material and the depth value of the tool shoulder during the FSW process. The influence of the depth value of tool shoulder on joint strength in the static tensile/shear test was also performed. With the increase of the depth of the tool, the size of flash and structures of the face of the joint changes as well (its annular surface resulting from the tool’s work and the accompanying process of material flow on the run-off side). Such conditions in the process require a proper tool depression to reduce the occurrence of flash and minimize material thinning to achieve high joint strength and maintain the conditions for plasticizing the material. Practical implications Based on the experimental tests carried out, a number of guidelines for the correct conduct of the welding process can be outlined. Originality/value Taking into account the various aspects of the process, the optimal range of the tool depth into the material is a value of approximately 0.06 mm. At this value, the face of the weld is not porous; the flash is easily removed; and the strength of the joint and the deformation of contact line are at an acceptable quality level.

Recently, micro-milling has been one of the most important technologies to produce miniature components, because optional geometrical structures can be machined with a high material removal rate. In terms of conventional dimensions, dynamic milling definitely signals the direction of development in modern technologies: dynamic milling results in higher productivity, better thermal circumstances, and increased tool life. The current paper gives a summary of the possible applications of dynamic milling tool paths in the case of micromachining. The major problems of this technology are the issue of minimum chip thickness and relatively large tool deformation. Different milling strategies, i.e. up milling and down milling, will be compared in detail. A systematic series of experiments were performed in order to generate data for the investigation. A special measuring system was established to perform related data collection. The experiments were carried out on a 5-axis micromachining centre using a tool steel workpiece with a hardness of 50 HRC. Based on the results of the experiments, the force components and the vibrations were also analysed at different radial depths of cut and different feed per tooth values, where productivity was also an important factor. It was found that dynamic milling can be applied in micro sizes, too. It is concluded that in the case of small contact angles, setting as high a feed per tooth value as 23.52 μm is also justified. During the investigation, optimal cutting parameters were also determined within the applied parameter range, these are ae = 34.80%, fz = 8.28 μm, and the use of the down milling strategy.

H13 steel is a typical hot work die steel with good strength and toughness that is often used to manufacture high-temperature disk springs. However, disk springs occasionally fail after use in the petrochemical industry. Therefore, the effects of the quenching and tempering temperatures on the microstructure and mechanical properties of H13 steel after quenching and tempering processes are investigated herein. The results show that the lath width (lath) controls the strength of the H13 steel. The precipitated phases mainly comprise Cr23C6, Cr7C3 and VC. The coarsening of the Cr23C6 phase reduces the hardness, while reducing the dislocation density improves the toughness of the H13 steels after quenching and tempering. When the quenching temperature is 1040 °C and the tempering temperature is 570 °C, the H13 steel after quenching and tempering has a uniform microstructure with good strength and toughness.

In the past few decades, demand for precise miniature components has grown significantly. Modern production technologies required for the production of such components, including micro milling, have become extensively researched areas. In spite of the intensive research in this field, there are still many topics and aspects that merit investigation. Through a systematic series of experiments, this paper analyses the special characteristics of micro milling including cutting forces, vibrations, burr formation, and surface quality. A 5-axis micromachining centre with 60.000 rpm maximum spindle speed was used for the experiments carried out in the scope of this paper, and the machining of hardened hot-work tool steel (AISI H13) with a hardness of 50 HRC was investigated in detail. Also, a special measurement environment was prepared in order to collect machining data. Based on the results of the experiments, a power regression prediction model for cutting forces was created. As part of the analysis in the scope of the experiments, fast Fourier transformation was carried out in order to analyse the dynamic characteristics of the micro milling process, and to determine dominant frequencies. In addition, an analysis of variance (ANOVA) was applied to extensively analyse the main effects and interactions of different cutting parameters on different characteristics. Based on the investigations carried out in a comprehensive parameter range, an optimal parameter combination was also determined. The results of the experiments introduced in this paper contribute to a deeper understanding of the micro milling process, and this research provides information directly applicable in the industry.

Since the popularization of press hardening in the early noughties, die and tooling systems have experienced considerable advances, with tool refrigeration as an important focus. However, it is still complicated to obtain homogeneous cooling and avoid hot spot issues in complex geometries. Additive Manufacturing allows designing cavities inside the material volume with little limitation in terms of channel intersection or bore entering and exit points. In this sense, this technology is a natural fit for obtaining surface-conforming cooling channels: an attractive prospect for refrigerated tools. This work describes a pilot experience in 3D-printed press hardening tools, comparing the performance of additive manufactured Maraging steel 1.2709 to conventional wrought hot work tool steel H13 on two different metrics: durability and thermal performance. For the first, wear studies were performed in a controlled pilot plant environment after 800 hot stamping strokes in an omega tool configuration. On the second, a demonstrator tool based on a commercial tool with hot spot issues, was produced by 3D printing including surface-conformal cooling channels. This tool was then used in a pilot press hardening line, in which tool temperature was analyzed and compared to an equivalent tool produced by conventional means. Results show that the Additive Manufacturing technologies can be successfully applied to the production of press hardening dies, particularly in intricate geometries where new cooling channel design strategies offer a solution for hot spots and inhomogeneous thermal loads.

Increasing the service life of die casting dies is an important goal of the foundry industry. Approaches are either material- or process-related. Despite new material concepts, hot work steels such as H11 are still predominantly used in the uncoated condition for die casting dies. In order to withstand the stresses that occur, this steel is used exclusively in the quenched and tempered condition. Required properties such as high high-temperature strength and high hardness combined with high toughness are, in principle, contradictory and can only be adjusted consistently over the entire die by furnace-based heat treatment. However, the results of various investigations have shown that improvements in the thermal shock resistance and wear resistance of hot work tool steels can be achieved by thermally influencing the microstructure near the surface. Based on these studies and related findings, an approach to surface heat treatment using the electron beam was developed. Due to the particle character of the radiation and the associated possibility of high-frequency beam deflection, the electron beam offers significantly greater flexibility in energy input into the workpiece surface compared with lasers or induction. The overall technological concept envisages replacing furnace-based heat treatment in the production of casting dies by localized and demand-oriented boundary layer heat treatment with the electron beam. The experiments include, on the one hand, the experimental determination of a suitable temperature–time interval with a focus on short-term austenitization. On the other hand, a simulation-based approach of boundary layer heat treatment with validation of a suitable heat source is investigated. Regarding short-term austenitization, the corresponding temperature and time range could be narrowed down more precisely. Some of these parameter combinations seem to be very suitable for practical use. The test specimens show a hard surface layer with a depth of at least up to 6 mm and a very tough buffer layer. Numerical simulation is used to estimate the resulting metallurgical microstructure and the achievable hardness as a function of the temperature–time interval. In addition, the results provided show the possibility of determining and optimizing the material properties by means of a simulation-based approach within the framework of a purely digital process planning and subsequently transferring them into a process planning. In the technical implementation, a temperature control was first established by means of a two-color pyrometer. In the further course of research, the pyrometer will be supplemented by an internally installed infrared camera, which will allow the reproducible setting of specified temperature profiles even for complex, large-area contours in the future.

The economic efficiency of die-casting processes is largely determined by the lifetime of the die. Such dies are exposed to high cyclical loads of thermal, mechanical, tribological and chemical loads during operation. These loads cause various types of damage, which reduce the lifetime. If the production comes to an unexpected stop due to a critical defect in the casting tool, repair welding is often the only way to return the tool to production immediately. At present, primarily manual TIG or plasma-welding processes are used for this purpose, which, however, exhibit insufficient process reliability and thus achieve an insufficient extension of lifetime. The primary objective of the research project is therefore the development of a technology for the economical regeneration of locally damaged die-casting dies with improved metallurgical properties compared with conventional repair welds. This forms an elementary basis for extending the service life of dies in series production. For this reason, electron-beam welding is to be qualified because of its possibilities for variable, need-adapted designs of the overall heat balance and the use of filler material as a welding process for industrially used hot-work steels.

Thermal fatigue resistance of a high Cr hot work roller steel is evaluated at 500, 600 and 700 °C. Surface layer degradation was investigated and characterised after a finite number of thermal cycles. Degradation mechanisms of the cooled surface layer in relation to the size, shape, orientation, distribution of carbides and crack oxidation progress were elucidated. Complex phenomena of crack growth is discussed where internal cracks nucleate due to stress at crack tip and oxidation along carbides follows from crack tail. Quantitative evaluation of cracks shows increased crack length with increasing temperature and number of thermal cycles.

The aim in this article is to evaluate microstructural changes, hardness variations, and wear behavior of H13 hot work tool steel as a function of austenitizing and tempering temperature us...

One of the major advantages of micromachining is the high achievable surface quality at highly flexible capabilities in terms of the machining of workpieces with complex geometric properties. Unfortunately, finishing operations often result in extensive process times due to the dependency of the resulting surface topography on the cutting parameter, e.g., the feed per tooth, fz. To overcome this dependency, special tool shapes, called wipers, have proven themselves in the field of turning. This paper presents the transfer of such tool shapes to solid carbide milling tools for micromachining. In this context, a material removal simulation (MRS) was used to investigate promising wiper geometries for micro end mills (d = 1 mm). Through experimental validation of the results, the surface topography, the resulting process forces, and tendencies in the residual stress state were investigated, machining the hot work tool steel (AISI H11). The surface-related results show a high agreement and thus the potential of MRS for tool development. Deviations from the experimental data for large wipers could be attributed to the non-modeled tool deflections, friction, and plastic deformations. Furthermore, a slight geometry-dependent increase in cutting forces and compressive stresses were observed, while a significant reduction in roughness up to 84% and favorable topography conditions were achieved by adjusting wipers and cutting parameters.

The aim of this work is to develop a die material selection criterion for aluminum hot stamping applications. The criterion has been based on the back-to-back comparison of a set of reciprocating friction and wear tests. Three representatives belonging to different stamping die material families have been selected for the study: a cold work steel, a hot work steel, and a cast iron. These tool materials have been combined with an exemplary member from two heat treatable aluminum families: 2XXX and 6XXX. Each die-material/aluminum–alloy combination has been tested at three temperatures: 40, 200, and 450 ºC. The temperatures have been selected according to different stamping scenarios: long takt time press quenching, short takt time press quenching, and very short takt time hot forming without quenching, respectively. The results show that, among the three die material options available, the cold work steel turned out to be the most favorable option for high volume production and long takt time, the hot work steel fitted best for high volume production coupled with short takt time, and cast iron turned to outstand for short runs with prototype dies and for hot stamping without die quenching.

In recent years, hard turning, an alternative to grinding, which provides low cost and good surface quality, has become an attractive method to the manufacturers. In this experimental study, AISI H11 hot work tool steel that has been hardened up to 50 HRC was subjected to hard turning tests with coated carbide tooling. The analyses were carried out by applying response surface methodology with the analysis of variance method. A total of 27 experiments were modeled utilizing 3 3 full factorial design and were carried out using a CNC lathe. The effects of the cutting parameters on surface roughness, energy consumption, electric current value, and sound intensity level were investigated. Optimum cutting parameters and levels were determined according to these optimum values. The relationship between cutting parameters and output variables was analyzed with two-dimensional and three-dimensional graphics. The results show that while the most effective parameter on the surface roughness was the feed rate (88.62%), the most effective parameter on the sound intensity level was the cutting speed (44.92%). In addition, the cutting depth was the most effective parameter on both electric current (52.20%) and energy consumption (46.15%). Finally, regression coefficients were determined as a mathematical model, and it was observed that this estimated model gave results that were very similar to those achieved with real experiment (correlation values: 97.64% for surface roughness, 98.72% for energy consumption, 97.22% for electric current value, and 91.38% for sound intensity level).

This part of the study aimed to investigate the effects of cryogenic treatment applied to uncoated high speed steel (HSS) end mills on cutting forces (Fc), surface roughness (Ra), and tool life. The milling tests were performed at four cutting speeds (40, 50, 60, and 70 m/min), three feeds (0.018, 0.024, and 0.03 mm/rev), and a depth of cut (2 mm) under dry and wet conditions. Three categories of uncoated HSS end mills were used in the tests: conventional heat treated (CHT), cryo-treated (CT), cryo-treated and tempered uncoated (CTT), and TiAlN/TiN multilayer coated (MLC) end mills. The test results showed that the lowest values of Fc and Ra were measured with the use of MLC end mills. However, the cryogenic treatment provided in a reduction in Fc and Ra values. In addition, under wet conditions, the CTT end mills exhibited better performance than the CHT ones by 71.4%. The test results showed while cryogenic treatment is a useful and cheap application in steels, it does not have the ability to compete with coating technology in terms of tool life in milling of hot work tool steel. This paper is organized into two sections. In the first section, cutting performance of cryo-treated and multilayer coated end mills is evaluated. In the second section, performance comparison of cryo-treated WC-Co (Part 1), HSS (Part 2), and MLC end mills in milling of AISI H13 hot work tool steel is presented. Duzce University Scientific Research Project DivisionDuzce University [BAP - 2011.03.02.065] The authors wish to place their sincere thanks to Duzce University Scientific Research Project Division for financial support for the Project No: BAP - 2011.03.02.065. WOS:000632341800005 2-s2.0-85103206693

This paper focused on the performance of tungsten carbide end mills in machining of AISI H13 hot work tool steel under dry and wet conditions. The tool performance was evaluated in terms of resultant cutting force (Fc), average surface roughness (Ra) and tool life. In the milling tests, four categories of end mills were used: untreated (U), cryo-treated (CT), cryo-treated and tempered uncoated (CTT) and TiAlN/TiN multilayer coated (MLC). The tests were performed at four cutting speeds (80, 100, 120, 140 m/min), three feeds (0.08, 0.12, 0.16 mm/rev) and a depth of cut (2 mm). The test results showed that the lowest values of Fc and Ra were obtained with the use of MLC end mills. However, the cryogenic treatment was also effective on decreasing Fc and Ra. In addition, while the CTT end mills provided a slight improvement in tool life under dry conditions, they showed a remarkable improvement of 126.1% in comparison with the untreated ones under wet conditions. Although the CTT end mills exhibited a superior performance to U and CT ones, the MLC end mills were much more resistant to abrasive wear. This study is organized into two parts (WC-Co and HSS) to observe the effects of deep cryogenic treatment on performance of two different tool materials and to compare cryo-treated end mills with multilayer coated ones. This part is related to the cryogenic treatment of tungsten carbide end mills, whereas part two is regarding cryo-treated HSS end mills. Duzce University Scientific Research Project DivisionDuzce University [BAP - 2011.03.02.065] The authors wish to place their sincere thanks to Duzce University Scientific Research Project Division for financial support for the Project No: BAP - 2011.03.02.065 WOS:000632341800007 2-s2.0-85103008043

Turning parameters for cutting DAC-10 tool steel was optimized using surface response methodology (RSM). Turning was performed with TiAlN coated single point tool bit on CNC lathe. Cutting speed, feed rate, and depth of cut were considered as the cutting parameters and relative effect of process parameters on surface roughness and tool wear rate was analyzed. Outcomes revealed that feed rate and cutting speed are the governing parameters for surface quality and cutting speed for tool wear rate respectively. Optimization method confirms reasonable zone for responses and gives optimal condition for turning with cutting speed 150 m/min, feed rate 0.1 mm/rev and depth of cut 0.4 mm.

This study evaluates the surface roughness and current values using cutting parameters in the turning of AISI H11 being hot work tool steel under dry machining conditions. The selected design factors are the depth of cut, feed rate, cutting speed. A design of experiments was used to carry out this research. The obtained results were analyzed to determine the effects of input parameters on the resultant surface roughness, current using the analysis of variance (ANOVA) and the Response Surface Methodology (RSM). The experimental results showed that increasing feed rate increased the surface roughness, and current values. The most effective cutting parameter on all the output parameters was found to be the feed rate on the surface roughness. Also, the motor current values were influenced by the 38,48% depth of cut, 23,98% cutting speed, 25,52% feed rate, respectively.

The increasing demand for complex components with filigree secondary functional elements promotes the application of new process technologies to extend the process limits of sheet-bulk metal forming (SBMF). The filling of cavities poses great challenges for manufacturing with sufficient quality. In cold forming, a considerable potential could be observed regarding mould filling, through a local adaptation of friction properties by surface structuring. In this study the transferability to hot sheet-bulk metal forming, which offers specific advantages due to thermal support, is to be investigated. The machinability of a hardened (53 HRC) hot work tool steel (HWS) AISI H11 by micro- and high feed milling is investigated related to tool wear and surface quality. Functional surface structures are applied on dies and adapted within the scope of hot sheet-bulk metal forming. Subsequent a developed hot ring compression test is to be used for tribological investigation of the structure-dependent material flow. In addition, an increase in the wear resistance of the structures by wet abrasive jet machining is to be focused on. Finally, the improvement of the surface modifications by introducing selected structures into a prototype tool is to be evaluated under real operating conditions with regard to their durability and mould filling.

The aim of this study was to evaluate the effect of dissolution of the small carbides residual from annealing and earlier processing, on the mechanical and wear properties of hot-work tool steel. Recommended as well as extreme austenitization temperatures (950 °C, 1030 °C and 1150 °C) with subsequent tempering were used aiming at same hardness level of specimens of same material. This allows correlation in wear resistance variation to the microstructural elements and variations in other mechanical properties of the investigated steel. M23C6 and MC are still present at the Taus = 950 °C, which are being dissolved with higher austenitization temperature. Optimal combination of mechanical properties are obtained at recommended austenitization. Specimens subjected to lowest austenitization showed the worst abrasive wear resistance.

Shape memory alloys are generally produced by casting processes and are subsequently homogenized. However, to obtain semifinished products on an industrial scale, the ingots from the casting process must be hot worked. In particular, final bar and sheet products can be obtained by hot rolling process. During intense hot work, surface oxidation of the material and microstructural changes may cause modifications to its original thermomechanical properties. In this sense, the present work aimed to study the correlation of the superelastic behavior in a Cu-Al-Be-Cr alloy before and after subjecting it to the hot rolling thermomechanical process. Abnormal grain growth was observed for a hot rolled sample with 30% reduction in initial alloy thickness. This abnormal growth in relation to non-rolled alloy caused an increase in phase transformation temperatures, a reduction in residual strain, a reduction in induction stress and an increase in alloy superelasticity.

Good mechanical and wear properties of hot-work tool steels are needed for tools to withstand severe service conditions during their operational lifetime. Thus, the aim of this investigation was to correlate mechanical and wear properties with changes in microstructure of commercially available hot work tool steel Sitherm S361R. Hardness, impact toughness, tensile strength and wear tests were performed. Hot-work tool steel was heat treated at austenitizing temperature 1030 °C for 15 min in a horizontal vacuum furnace and gas quenched using nitrogen. One set of samples was investigated in as quenched state. Double tempering of samples was performed after quenching for 2 h at each of chosen temperatures, with first tempering temperature of 500 °C for the whole set of tempered samples. The second tempering was conducted at temperatures from 520 °C to 640 °C with increment of 30 °C for each set of samples. Microstructure of differently heat treated samples showed martensitic matrix, but different fraction and distribution of carbides, consequently influencing hardness, impact toughness, tensile strength, yield strength and wear resistance. Reciprocating sliding wear tests were carried out at room temperature in order to correlate microstructure of differently heat treated hot-work tool steel with wear. In order to achieve adhesive and abrasive wear mechanisms, 100Cr6 and Al2O3 balls were used as counter-body, respectively. Combination of adhesive and abrasive wear was observed for all specimens with different hardness when using 100Cr6 material as a counter body. However, in the case of Al2O3 abrasive wear was found as the prevailing wear mechanism.

In this paper, the temperature dependent cyclic mechanical properties of the martensitic hot work tool steel 1.2367 after tempering are investigated. To this end, hardness measurements as well as monotonic and cyclic tests at temperatures in the range from room temperature to 650 °C are performed on material tempered for different tempering times and temperatures. To describe the observed time and temperature dependent softening during tempering a kinetic model for the evolution of the mean size of secondary carbides based on Ostwald ripening is developed. Furthermore, mechanism-based as well as phenomenological relations for the cyclic mechanical properties of the Ramberg-Osgood model depending on carbide size and temperature are introduced. A good overall agreement of the measured and the calculated stress-strain hysteresis loops for different temperatures and heat treatments is obtained using the determined material properties of the kinetic and mechanical model.

In this work, the influence of heat treatment on the microstructure and machinability of AISI H13 tool steel was investigated for the as-received (AR), water-quenched (Q), quenched and single-tempered (QST) and quenched and double-tempered (QDT) conditions. The machining tests were carried out through turning method at various cutting speeds. The results indicated that heat treatment conditions and the cutting speed affected the surface roughness of samples. However, cutting forces were not affected by steel microstructure and cutting speed except to those of water-quenched samples.

A new test rig for thermal fatigue testing was used to investigate and characterise surface layer degradation of indefinite chill double pour (ICDP) cast iron hot work roller. Thermal fatigue tests were performed at three temperatures (500 °C, 600 °C and 700 °C) using a Gleeble 1500 D thermomechanical simulator. Appearance of cracking was evaluated quantitatively for each test temperature by following the average length of the seven longest cracks, the average length of all cracks and crack density after the preselected number of thermal cycles. We found that crack nucleation, crack propagation (growth), their linking and subsequent material spalling are related to the cementite and graphite particles characteristics. Revealed, were the appearance of internal cracks in cementite and graphite, propagation towards and from the test surface, cracks linking and material chipping. Based on observations, a better understanding of degradation mechanisms and their temperature related intensity was gained. Finally, suggestions for improved thermal fatigue resistance of cast iron rollers are given.

A magnetic method for the in-situ inspection of the combined effects of both, clamping force (CF) and the distribution of the surface residual stress (RS) on a face milled workpiece are presented. FE simulations have been conducted and evaluated, illustrating the impact of clamping on the workpiece surface deflection and thus, the machining accuracy. Furthermore, magnetic Barkhausen noise (MBN) signals were acquired on a hot-work tool steel workpiece after three different milling procedures: Face milling, one pass of micro-milling and 38 passes of micro-milling. Finally, the MBN signal on the unclamped workpiece was obtained. The MBN signal energy MBNenergy presented the highest values with the probe oriented in the pick (clamping) direction for all stages of milling process where the CF was applied. After unclamping the workpiece, the higher value of the MBNenergy was obtained with the probe oriented in feed direction of the milling processes revealing the true effect of the RS. These results were in agreement with the literature and confirmed by numerical simulations and X-ray diffraction based residual stress measurements.

We used the isothermal compression test (conducted in a Gleeble-3500 system) to study the hot deformation behaviors of SiCp/Al composites over a wide range of temperatures (623-773 K) and strain rates (0.001-10 s−1). A 3D hot-processing map was constructed based on the Malas stability criteria and experimental data. An artificial neural network model of four hot work quality characteristic parameters (strain rate sensitivity m, its derivative m′, temperature sensitivity s, and its derivative s′) were established. A new hot-processing map, known as a hot-processing critical strain map, has been proposed based on the smallest strain prior to instability. Two optimized processing regions at 623-660 K, 0.05-0.075 s−1 and 720-773 K, 0.04-0.18 s−1 were determined based on this map.

The hysteresis loops, stress and strain behavior, lifetime behavior and fracture characteristic of 4Cr5MoSiV1 hot work die steel at a wide range of mechanical strain amplitudes (from 0.5% to 1.3%) during the in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) tests cycling from 400 °C to 700 °C under full reverse strain-controlled condition were investigated. Stress-mechanical strain hysteresis loops of 4Cr5MoSiV1 steel are asymmetric, and stress reduction appears at high-temperature half cycles owing to a decrease in strength with increasing temperature. 4Cr5MoSiV1 steel always exhibits continuous cyclic softening for both types of TMF tests, and the cyclic softening rate is larger in OP loading condition. OP TMF life of 4Cr5MoSiV1 steel is approximately 60% of IP TMF life at the same mechanical strain amplitude and maximum temperature. Lifetime determined and predicted in both types of TMF tests is adequately described by the Ostergren model. Fracture surfaces under IP TMF loading display the striation and tear ridge, showing quasi-cleavage characteristics, and the cracks are less but longer. However, fracture surfaces under OP TMF loading mainly display the striation and dimple characteristics, and the cracks are more and shorter.

A WC-12Co coating was sprayed on AISI H13 hot work mold steel using a high-velocity oxygen fuel. The morphologies, phase compositions, and distributions of chemical elements of the obtained coatings were analyzed using a field emission scanning electron microscope, x-ray diffraction, and energy-dispersive spectroscope (EDS), respectively. The friction-wear behaviors under different loads were investigated using a reciprocating wear tester; the morphologies and distributions of the chemical elements of worn tracks were analyzed using a SEM and its configured EDS, respectively. The results show the reunited grains of WC are held together by the Co binder; the primary phases of the coating are WC, Co, and a small amount of W2C and W, owing to the oxidation and decarburization of WC. Inter-diffusion of Fe and W between the coating and the substrate is shown, which indicates a good coating adhesion. The values of the average coefficient of friction under the loads of 40, 80, and 120 N are 0.29, 0.31, and 0.49, respectively. The WC grains are pulled out of the coating during the sliding wear test, but the coating maintains its integrity, suggesting that the coating is intact and continuously protects the substrate from wearing.

Tool steel matrix composites show improved hardness and remarkable wear resistance but generally also a systematic lower fracture toughness than the base material. The present work deals with the feasibility and characterization of a powder metallurgical hot work tool steel reinforced with partially stabilized zirconia (PSZ). Selection of PSZ as the reinforcement is aimed at improving the strength and fracture toughness of the composite by taking advantage of the transformation toughening effect of PSZ. The specimens were produced by mechanical alloying (MA) followed by spark plasma sintering (SPS) using two different types of PSZ, different volume fractions (10 and 20 vol %) and sizes of reinforcement. The influence of processing parameters on density and microstructure was investigated. The chemical stability of the tool steel-PSZ system was also studied looking at the possible formation of complex oxides and precipitates during the fast consolidation by SPS.

A high velocity oxygen fuel (HVOF) sprayed NiCrBSi coatings on H13 hot work mould steel were processed using a laser remelting (LR). The surface–interface morphologies, chemical compositions and phases of the obtained coatings were analyzed using a scanning electronic microscope (SEM), energy dispersive spectroscope (EDS), X–ray diffractometer (XRD), respectively. The friction–wear behaviors of the coatings at high temperatures were investigated using a high temperature wear tester, the effects of loads on the coefficients of frictions (COFs) of the coatings were discussed. The results show that the average COF of the coatings under the loads of 4, 8, and 12 N is 0.34, 0.47, and 0.36, respectively. The coating has excellent wear resistance properties, the wear rates decrease with increasing of the loads. The wear mechanism of the coating is primarily oxidation wear under the load of 4 N, there is a small amount of wear debris on the worn track. While the worn tracks surface under the load of 8 and 12 N appear furrows and spalling pits, the wear mechanism is abrasive wear and oxidation wear. At 600 °C, the Ni, Fe and Si of the coating are oxidized, the wear resistance of the coating is improved by the oxides.

Additive manufacturing (AM) is increasingly used for the manufacturing of tools and dies; in this respect, apart from the optimization of processing parameters, it is important to establish the most proper heat treatment conditions for the fabricated parts. In this paper, the microstructure, and some properties of H13 hot work tool steel fabricated by selective laser melting (SLM) have been evaluated after direct tempering and in quenched and tempered condition. The as-built microstructure consists of a partially tempered martensite and a much higher amount (up to 19%vol) of retained austenite (RA) compared to the quenched steel (RA

International audience; The interaction between thermal fatigue and aluminizing and/or oxidation is investigated using an experimental approach based on decoupling of mechanisms. Virgin and pre-aluminized steel specimens are tested in air and nitrogen between 100 and 650 °C. Homogeneous uniaxial micro-crack network forms on the oxidised or pre-aluminized surface in air, with a better resistance to micro-cracking for the intermetallic coating. The propagation of the micro-cracks is delayed in nitrogen, whilst no evidence of micro-cracking is observed on the virgin specimen. The premature cracking of the steel depends on the formation of the superficial micro-crack network, and the crack propagation is assisted by oxidation.

In industry the increasing variety of products leads to shorter product life cycles. For parts made by forging processes this trend results in very high prizes, as the tool costs have to be assimilated with only few parts. To reduce the tool costs new, flexible processes have to be investigated and established in tool manufacturing. Laser based additive manufacturing is noted for its high flexibility and especially laser metal deposition (LMD) gets in the focus of the research as it allows adding material on free formed surfaces. Therefore it is already used for coating and repairing of forming tools. New investigations are made to qualify this process for the production of forging tools. The aim is to generate active elements onto a geometrical simple base unit. Within first investigations the manufacturing of high carbon hot work tool steel 1.2343 was analysed. The measured mechanical properties were similar to those of conventional manufactured material.The focus of this paper is the connection strength of the additively built structures to the substrate. Therefore cylindrical specimens for tensile tests are manufactured with the linkage zone in the parallel area, in which the highest tension will be achieved. To assess the strength of the connection a comparison with conventional manufactured steel will be made. Furthermore specimens produced with various settings will be tested to analyse the influence of the LMD process. Additionally post heat treated samples will be analysed to recognize the effect of the hardening on the strength of the specimens.

In the present paper a thermodynamics based constitutive modeling of coupled dissipative phenomena is discussed. In the proposed analysis special attention is paid to the problem of thermo-mechanical coupling in rate equations of thermodynamic conjugated forces. As an example of thermo-plastic coupling, the non-isothermal fatigue behavior of tempered martensitic hot work tool steel is considered. The numerical simulations are performed, to illustrate the qualitative and quantitative influence of temperature rate on the response of constitutive model when cyclic thermo-mechanical loading is applied.

The friction and wear behaviors of a new hot-work die steel, SDCM-SS, were studied at high temperature under dry air conditions. The wear mechanism and microstructural characteristics of the SDCM-SS steel were also investigated. The results showed that the SDCM-SS steel had greater wear resistance compared with H13 steel; this was owed to its high oxidizability and temper stability. These features facilitate the generation, growth, and maintenance of a tribo-oxide layer at high temperature under relatively stable conditions. The high oxidizability and thermal stability of the SDCM-SS steel originate from its particular alloy design. No chromium is added to the steel; this ensures that the material has high oxidizability, and facilitates the generation of tribo-oxides during the sliding process. Molybdenum, tungsten, and vanadium additions promote the high temper resistance and stability of the steel. Many fine Mo2C and VC carbides precipitate during the tempering of SDCM-SS steel. During sliding, these carbides can delay the recovery process and postpone martensitic softening. The high temper stability postpones the transition from mild to severe wear and ensures that conditions of mild oxidative wear are maintained. Mild oxidative wear is the dominant wear mechanism for SDCM-SS steel between 400 and 700 °C.

To investigate the evolution mechanism of Al2O3 inclusions after Mg treatment in H13 die steel, the determination of inclusions characteristics and thermodynamic calculation were carried out in the present study. The results showed that irregular and cluster Al2O3 inclusions in H13 die steel were modified to MgO·Al2O3 and MgO after Mg treatment. Two types of MgO·Al2O3 were detected after Mg treatment. The long-range gravity between the MgO-containing inclusions is weaker than that of the MgO-free inclusions. The long-range gravity between the inclusions decreases with the increasing of Mg content of the steel. The evolution mechanisms of inclusion in low Mg-containing and high Mg-containing H13 die steel were comprehensive discussed. The different reaction mechanisms result in the different of the core of the MgO·Al2O3 inclusion.

T This paper examines the abrasive and erosive wear of duplex multilayer TiN/TiCN and TiN/TiBN coatings deposited on quenched and tempered hot work tool steel grade X37CrMoV5-1. The coatings were produced by duplex method composed of a plasma nitriding and pulsed direct current (DC) plasma-assisted chemical-vapor deposition (PACVD). Measurements of the thickness of the deposited coatings were determined by calotest. Adhesion of the layers were determined by the Rockwell-C indentation test and the microhardness profile in a diffusion zone beneath the surface was determined by Vickers method (HV 0.05). Tests of abrasive wear resistance were carried out using "Dry Sand-Rubber Wheel” method. Test of erosion resistance of the base material and of duplex layers was carried out by exposing test samples to impact erosion of fine sand particles and determining the loss of mass after 60 minutes of wear. Worn surface were analysed by stereomicroscopy. The results show increasing wear resistance of duplex multilayer coatings of TiN/TiCN and TiN/TiBN in relation to plasma nitrided and uncoated steel (in the quenched in tempered condition).

Advanced die manufacture demands hot work die steels with superior strength. Unfortunately, due to the rare understanding of the crystallographic structures and strengthening mechanisms of H13 steel, the contradictory between ultra-high strength and low ductility remains inevitably as far as authors known. In this work, we developed a strategy combining rare earth addition, electroslag remelting and pre-tempering treatment, and prepared rare earth (Re) H13 steel with ultra-high ultimate tensile strength up to 2 gigapascals (GPa) and good ductility. The Re H13 steel underwent pre-tempering treatment exhibited hardness of ca. 53.6 HRC, ultimate tensile strength of ca. 2029 MPa, yield strength of ca. 1654 MPa, total elongation of ca. 9.3% and impact energy of ca. 16.0 J (superior grade of NADCA#207–2003 standard), respectively. The good ductility of Re H13 steel mainly attributed to high density of high angle grain boundaries (45°

A successful attempt at laser cladding of H13 (AISI) hot work tool steel by the laser engineered net shaping technique is presented. Technological parameters, such as laser spot diameter, powder flow rate, and deposition velocity, were changed during the experiment. The influences of the different technological parameters on the efficiency of the cladding, geometry of the clads and properties of the deposited material were investigated. As a result, 75 different samples were deposited. The efficiency of the cladding varies significantly within the chosen range of parameters and is as low as several percentage points. The chosen parameters also appear to affect the shape of the clad, size of the heat-affected zone, microstructure and hardness of the steel, which ranged from 500 to 800 HV after deposition. The proper choice of parameters led to the desired surface hardness of the deposited material, and a heat treatment of the final product may not be necessary.