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The combination of additive and subtractive manufacturing processes is especially useful for repairing complex geometries and high-added-value components. The best solution for combining both processes is to integrate them in a single machine. Nevertheless, this combination entails a series of challenges, such as the impact that the use of cutting fluids in the subtractive operation may have on the subsequent additive process. In view of this situation, the present work aims to evaluate the effects of the deposition of AISI H13 hot work tool steel on a substrate impregnated with cutting fluid. For this purpose, different oil concentrations have been considered, and the attained results have been compared with the reference tests, performed on a clean substrate. In addition to morphological variations, it has been observed that when high oil concentrations are used, the deposited material is cracked, invalidating the parts manufactured through this approach. Therefore, in the case of AISI H13 tool steel, it has been determined that a cleaning stage is highly necessary in order to remove any cutting fluid that may be on the surface of the substrate before the additive operation is performed.; Fabrikazio-prozesu gehigarri eta kengarrien arteko konbinaketa oso erabilgarria da geometria konplexuko eta balio-erantsi altuko piezen konponketarako. Prozesuak bateratzeko aukera onena haiek makina bakarrean barneratzea da. Alabaina, bateratze horretan erronka anitz agertzen dira, besteak beste, mekanizazio-prozesuan erabiltzen diren ebaketa-jariakinek jarraiko gehitze-prozesuan izan dezaketen eraginaren ezjakintasunaren ondorioz.Egoera horren aurrean, berotako trokelgintzan ohikoa den AISI H13aren kasurako ebaketa-jariakinarekin kutsaturiko gainazalean laser bidez materiala eranstean ager daitezkeen akatsen azterketa gauzatu da. Olio-maila anitzekin egin dira saiakuntzak, eta gainazal garbian egindako erreferentziazko saiakuntzarekin alderatu dira lorturiko emaitzak. Aldaera morfologikoak nabaritzeaz gain, % 100 olio-kontzentrazioko ebaketa-jariakina erabiltzen den kasuan erantsitako materiala arrakalatu egiten dela ikusi da, eta egoera horretan fabrikaturiko piezak baliogabetu egiten dira. Hortaz, beharrezkoa dela ikusi da AISI H13aren kasuan gehitze-prozesuaren aurretik gainazalean egon daitezkeen ebaketa-jariakinen garbiketa .

Made available in DSpace on 2020-12-10T19:47:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-15 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Tool steels are applied in a variety of industrial operations providing a good balance of properties. Surface engineering has the potential to improve productivity and further extend the lifetime of metallic components. In the present work plasma nitriding is applied to the hot work AISI H13 tool steel to improve wear and corrosion characteristics. The steel was nitrided in the tempered condition at three different temperatures and pressures for 5 h of duration. At 450 degrees C of nitriding temperature mainly a diffusion zone is observed while a compound layer is produced at 550 and 650 degrees C. Both surface and bulk hardness decrease as nitriding temperature is increased. Xray diffraction indicates that a mixture of both epsilon and gamma' iron nitrides is produced in all cases. The content of epsilon-nitride appears to decrease with temperature while gamma'-nitride and CrN increase. Working pressure does not lead to significant alterations in phase proportion, hardness and wear resistance after plasma nitriding at a given temperature. However, increasing processing temperature, from 450 to 650 degrees C, reduces the wear coefficient from 1.19.10(-7) to 7.06.10(-8) mm(3)/N.m, respectively, while from the base steel such coefficients are in the order of 10(-5) mm(3)/N.m. Regarding the corrosion behavior, plasma nitriding at 450 and 550 degrees C yields higher corrosion potentials, lower current densities and an extensive passivation range, while the tempered substrate, irrespective the condition, exhibits no passivation. From the wear and corrosion perspective it is concluded that plasma nitriding at 450 or 550 degrees C leads to better corrosion properties while nitriding at 650 degrees C yields a better wear performance. Univ Fed ABC, Ctr Engn Modelagem & Ciencias Socials Aplicadas, Alameda Univ S-N, BR-09606045 Sao Bernardo Do Campo, SP, Brazil Univ Sao Paulo, Dept Engn Mat, Escola Engn Sao Carlos, Av Joao Dagnone 1100, BR-13563120 Sao Carlos, SP, Brazil Univ Estadual Paulista, Fac Engn Ilha Solteira, Dept Fis & Quim, Av Brasil Ctr 56, BR-15385000 Ilha Solteira, SP, Brazil Univ Estadual Paulista, Fac Engn Ilha Solteira, Dept Fis & Quim, Av Brasil Ctr 56, BR-15385000 Ilha Solteira, SP, Brazil

Cargo operations on tanker vessels involve high risks to crew and the marine environment. At the time of loading and unloading of cargoes and tank cleaning operations, consequences of accidents may be severe such as loss of lives, property loss and marine pollution. One of the most critical accidents is an explosion which may advance to a large fire. An explosion may occur due to flammable and combustible materials, electric arcs, dangerous operations, like hot work on deck, or static electricity. This study focuses on the issue of static electricity, which is one of the serious threats onboard and can cause large explosions under hazardous conditions if a discharge is in contact with nearby flammable gases or air mixture. In a bow-tie structure, static electricity-related explosion and fire accident was determined as the top event. In the fault tree diagram, intermediate events were considered as the flammable atmosphere in a tank, operational failures, technical failures, and unsafe practices which cover direct human errors. Fuzzy logic and Cognitive Reliability and Error Analysis Method (CREAM) were used for quantitative failure analysis, and the probability of accident risk was found as 6.31E-02. Findings show that the most critical contributions to the top event are minimal cut sets of lack of monitoring cargo tank atmosphere, inadequate actions for reducing the O2 level in tank, failure to understand safety data sheets, failure to follow procedures, non-bonded ullage & sample apparatus. The research provides a significant contribution to the literature and gives information regarding static electricity risks to ship officers, tanker safety superintendents and other maritime authorities to improve the safety of cargo operations.

In this work, we have attempted to prepare a comparative machinability study of wire electrical discharge machining of different difficult-to-machine materials, viz., stainless steel (SS) 316, H21 hot work tool steel and M42 high-speed steel (HSS). The key features, which are compared during the analysis, are mainly material removal rate, average surface roughness, kerf width, wire consumption rate (WCR), recast layer (RL), elemental diffusion, surface morphology and micro-hardness of the machined surface. They are found to be greatly influenced by pulse energy. The pulse energy is calculated in terms of ‘specific discharge energy’. Apart from the discharge energy, the thermal conductivity of the material also plays an important role in the formation of RL and inclusion of foreign elements such as carbon, oxygen, copper and zinc in RL. H21 steel has been found to be more prone to thermal defects due to its high-thermal conductivity and high tensile residual stresses, whereas more re-solidification of foreign materials is observed in SS316 and M42 HSS due to their high adhesive properties and low-thermal conductivity. But, in low-energy cutting, more uniform surfaces are observed in H21 steel in comparison with other two types of steel.

The recent development of study on H13 hot-work die steel is reported in this paper. Microstructures and mechanical properties and their changes with some factors are briefly introduced. The factors are included in melting, heat treatment, surface treatment, and so on.

A NiCrBSi alloy coating was sprayed on H13 hot work mould using a high velocity oxygen fuel. The surface and cross-section morphologies of obtained NiCrBSi coating were observed using a field emission scanning electron microscope (SEM), its phases were analyzed using an X-ray diffractometer (XRD). The friction-wear behaviors of NiCrBSi coating were investigated using a high temperature wear tester, the morphologies and chemical elements of worn tracks were analyzed using a SEM and its configured energy dispersive spectrometer (EDS), respectively. The results show that the average COF of NiCrBSi coating at 500, 600, and 700 °C is 0.4046, 0.4039, and 0.3975, respectively. The wear mechanism of NiCrBSi coating at 500 and 600 °C is abrasive wear, adhesive wear and oxidation wear, while that at 700 °C is abrasive wear and oxidation wear, the wear resistance of NiCrBSi coating is dependent on the compounds of Ni, Si and Cr.

Decarburisation is found as an undesirable consequence of the heat treatment cycle in hot work tool steels. In this work, an increase in the decarburisation resistance of tool steel through...

Dilatometry is a useful technique to obtain experimental data concerning transformation. In this paper, a dilation conversional model was established to calculate carbides fraction in AISI H13 hot-work tool steel based on the measured length changes. After carbides precipitation, the alloy contents in the matrix changed. In the usual models, the content of carbon atoms after precipitation is considered as the only element that affects the lattice constant and the content of the alloy elements such as Cr, Mo, Mn, V are often ignored. In the model introduced in this paper, the alloying elements (Cr, Mo, Mn, V) changes caused by carbides precipitation are incorporated. The carbides were identified using scanning electron microscope and transmission electron microscope. The relationship between lattice constant of carbides and temperature are measured by high-temperature X-ray diffraction. The results indicate that the carbides observed in all specimens cooled at different rates are V-rich MC and Cr-rich M23C6, and most of them are V-rich MC, only very few are Cr-rich M23C6. The model including the effects of substitutional alloying elements shows a good improvement on carbides fraction predictions. In addition, lower cooling rate advances the carbides precipitation for AISI H13 specimens. The results between experiments and mathematical model agree well.

The effects of two conventional heat treatments and one innovative processing by laser surface remelting of modified X37CrMoV5-1 tool steel on its abrasion wear resistance were investigated. Conventional heat treatments consisted of quenching from 990 °C, individually followed by two different tempering treatments to achieve secondary hardness either at 520 °C or 560 °C. Laser surface remelting was performed using optimized parameters of continuous laser beam scanning mode. The results showed that the highest wear resistance was obtained for almost carbide-free, surface remelted microstructure with the highest hardness due to microstructural refinement and martensitic transformation hardening. The observed differences in wear resistance among individual material states are discussed in relation to their microstructures, hardness, and wear mechanisms characteristics.

AISI H13 (4Cr5MoSiV1) is one of the commonly used materials for extrusion tool, and it suffers from fatigue–creep damage during the hot extrusion process. Stress-controlled fatigue and creep–fatigue interaction tests were carried out at 500 °C to investigate its damage evolution. The accumulated plastic strain was selected to define the damage variable due to its clear physical meaning. A new fatigue–creep interaction damage model was proposed on the basis of continuum damage mechanics. A new equivalent impulse density for fatigue–creep tests was proposed to incorporate the holding time effect by transforming creep impulse density into fatigue impulse density. The experimental results indicated that the damage model is able to describe the damage evolution under these working conditions.

The X40CrMoV5-1 (H13) hot work tool steel was densified by selective laser melting (SLM) using different laser parameters and preheating temperatures. The porosity and crack densities of the processed specimen were determined, the resulting microstructure characterized, tempering hardness diagrams recorded and the reusability of the powder assessed. The X40CrMoV5-1 steel showed a good densification behaviour. Relative densities of above 99.5% were obtained. After SLM densification, the specimen showed a fine-grained microstructure, with a cellular arrangement consisting of ferrite and austenite. Although the microstructure did not change with preheating temperature, a decrease in crack density could be observed for higher preheating temperatures. By combining microstructural observations with some simulations, a new model describing the microstructural evolution of SLM-densified X40CrMoV5-1 is suggested. The peak in secondary hardness after tempering SLM-densified X40CrMoV5-1 was observed at higher temperatures compared to the cast reference steel in the same heat treatment condition.

The corrosion behavior of an Fe–20Mn–11Al–1.8C–5Cr alloy prepared by spark plasma sintering was investigated via immersion tests in molten aluminum at 750 °C for 1 and 4 h, respectively, and a hot work steel (AISI H13) was included as a reference. The experimental results show that the corrosion rate of Fe–20Mn–11Al–1.8C–5Cr alloy is ~ 24% of that of H13 steel, suggesting that Fe–20Mn–11Al–1.8C–5Cr alloy in molten aluminum possesses better corrosion resistance than H13 steel. Detailed analysis show that κ-carbide ((Fe, Mn)3AlC x ) and Cr7C3 carbide precipitated in the matrix play a key role in enhancing the corrosion resistance of Fe–20Mn–11Al–1.8C–5Cr alloy in molten aluminum. Both of them show better corrosion resistance than γ-Fe matrix and H13 steel, and can also take on the role of roots in grasping the corrosion product and restrain them from spalling into the molten aluminum.

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.

Gas nitriding has become a popular thermo-chemical surface treatment, which is being used to develop thermal/mechanical fatigue and wear characteristics of iron and steels. In this study, the gas nitriding of AISI H13 hot work die steel was carried out in flowing NH 3 gas at 550 °C for 5–15 h. By adjusting the nitrogen potential ranging from 0.18 to 2.8, three types of nitrided surface layer consisting of e-Fe 2-3 N and γ′-Fe 4 N phases, γ′-Fe 4 N single-phase, as well as the α-(Fe, N) phase had been prepared, respectively. The corresponding microstructure, hardness and thickness of the nitrided layer were systematically characterized. A contrastive analysis of influence of nitrided-layer microstructure control on wear behavior of AISI H13 hot work die steel was conducted. The nitrided surface layer consisting of e-Fe 2-3 N and γ′-Fe 4 N phases showed excellent wear resistance under loads of 100 N but poor wear properties at 300 N. The wear mechanism was revealed based on the microstructure characteristics, surface hardness and toughness of each nitrided surface layer.

Friction stir welding is an emerging solid state joining process which is used to join metals and alloys having low weldability. In this research work experimental analysis has been performed on FSW for AA 6061. Effect of FSW parameters like tool rpm, tool transverse speed and tool pin profile are investigated. A vertical milling head is used to produce FSW joints. Hot work tool steel (H13) is used as a tool material and total 3 number of tools are manufactured namely as cylindrical pin, tapered pin and square pin. Tool transverse feed of 10, 15 and 20 mm/min and tool rotational speed of 2250, 2500 and 2750 rpm are taken for the study. A full factorial method is used for three numbers of parameters and their three levels and total 27 numbers of experiments are conducted keeping all other parameters constant. As a response weld tensile strength of joint is tested according to ASME-IX. Response surface method (RSM) and Analysis of variance (ANOVA) is adopted for the statistical analysis. As a conclusion it has been derived that feed of 15 mm/min, tool rotational speed of 2750 rpm and tapered pin profile gives better weld strength for the given experimental conditions.

AISI H13 hot work steel with fatigue cracks was repaired by a biomimetic laser remelting (BLR) process in the form of lattice units with different sizes. Detailed microstructural studies and microhardness tests were carried out on the units. Studies revealed a mixed microstructure containing martensite, retained austenite and carbide particles with ultrafine grain size in units. BLR samples with defect-free units exhibited superior thermal fatigue resistance due to microstructure strengthening, and mechanisms of crack tip blunting and blocking. In addition, effects of unit size on thermal fatigue resistance of BLR samples were discussed.

The aim of this work is to investigate the durability of tool steels for hot stamping by comparing the wear resistance of three hot work tool steels. Friction and wear behaviours of different tool steels sliding against a 22MnB5 uncoated steel at elevated temperatures were investigated using a high-temperature version of the Optimol SRV reciprocating friction and wear tester at temperatures of 40 and 200°C. Our results show that friction decreased with increasing temperature, whereas wear of the tool steel increased with temperature for the second and the third tested tool steels. The slightly better wear behaviour of steel specimen 1 comes from the hardness of the carbides in the martensitic microstructure, which are rich in vanadium. The authors gratefully acknowledge the funding provided by the Department of Research and Universities of the Basque Government under Grant no. IT947-16 and the University of the Basque Country UPV/EHU under Program no. UFI 11/29.

The aim of this research was to determine the effect of vacuum-heat-treatment process parameters on the material properties and their correlations for low-Si-content AISI H11-type hot-work tool steel using a single Circumferentially Notched and fatigue Pre-cracked Tensile Bar (CNPTB) test specimen. The work was also focused on the potential of the proposed approach for designing advanced tempering diagrams and optimizing the vacuum heat treatment and design of forming tools. The results show that the CNPTB specimen allows a simultaneous determination and correlation of multiple properties for hot-work tool steels, with the compression and bending strength both increasing with hardness, and the strain-hardening exponent and bending strain increasing with the fracture toughness. On the other hand, the best machinability and surface quality of the hardened hot-work tool steel are obtained for hardness values between 46 and 50 HRC and a fracture toughness below 60 MPa√m.

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.

The paper deals with the influence of thermal load on functionality of the Toolox 33 hot work tool steel equivalent to the materials of W.Nr. 1.2311, 1.2312, 1.2738 and P20 in order to assess its suitability as a material for glass manufacture preform. Using light and electron microscopy it was shown that the steel was highly unfitting for this application where the steel comes into contact with the hot glass. Regarding the evaluation of the microstructure, it was shown that intense decarburization reflecting on the fracture behaviour of the surface layer during the thermal load has occurred. This fact was confirmed by a static tensile test and hardness measurements. Moreover, the thick layer of flakes has formed on the surface.

The microstructure of a hot-work tool steel additively manufactured using laser powder-bed fusion (L-PBF), and its response to post heat treatment, is studied in detail by microstructure characterization and computational thermodynamics and kinetics. The high solidification and cooling rates during the L-PBF process lead to suppression of δ-ferrite and instead solidification of an austenite phase directly containing a cellular substructure where the alloying elements have segregated to the inter-cellular regions and where solidification carbides have formed in the cell junctions. The austenite is then partly decomposed into martensite at lower temperatures. The micro-segregation can be predicted by reducing the complex solidification behavior to a diffusion problem in one dimension enabling detailed comparisons with the measured segregation profiles quantified at a nanometer scale. Martensite start temperature (Ms) calculations along the spatially varying composition show that the Ms temperature decreases in the inter-cellular regions where austenite is observed. The network of austenite in the as-built microstructure can be understood from the combined influence of the composition dependence of the Ms temperature in relation to the build plate temperature and the mechanical stabilization of the small-sized austenite regions. This work demonstrates the power of computational tools based on computational thermodynamics and kinetics for designing tool steels for additive manufacturing by predictions of the steel's response to the L-PBF process and post heat treatments.

The present study deals with the effects of laser surface treatment on microstructure evolution and wear resistance of AISI H11 hot work tool steel in quenched and tempered condition. The most upper laser-affected zone is characterized by re-melted microstructure consisting of dendrite cells with fresh non-tempered martensite, retained austenite and inter-dendritic carbidic network. The subsolidus microstructure just beneath the re-melted zone represents the most laser surface hardened zone consisting of fresh non-tempered martensite with fine and coarse carbides as a result of overheating the original QT substrate microstructure. The highest microhardness values in the range from 775 to 857 HV were measured for the LSH microstructure and the most softened microstructure exhibited the minimum hardness of 530 HV. The laser treated samples showed the improvement of their surface wear resistance by 35%.

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.

Influence of cryogenic treatment on AISI H13 hot work die steels has been studied to correlate carbide density with surface roughness and dry sliding wear. This work includes hardening of AISI H13 ...

The increasing demands for light-weight components in vehicles contribute to the global expansion of hot sheet metal forming technologies. Structural components are typically produced using hot sta ...

Hot work tool steels are widely used as thermal and mechanical highly stressed tools, amongst others for pressure die casting. Advanced die-casting processes require further increase regarding the size of the molds, the complexity of the geometries, and the tool life of the dies, resulting in a multifaceted stress profile for the used tool steel. Thus, an optimum combination of certain properties, such as a high thermal stability and toughness as well as a particularly good through hardenability for large cross-sections, is hence necessary. The mechanical properties of engineering structural materials are highly dependent on their microstructure and are achieved after heat treatment, which is therefore crucial for the good performance of the tool steel. Depending on the size of the tools, the hardening process in these materials can lead to varying microstructures and properties through their cross-section resulting from the quenching step and the inconsistent cooling rates. Particularly slow cooling rates can lead to the formation of bainite, which is known to decline the toughness and hence degrade the mechanical performance. In this work large dimensioned samples of 5%Cr martensitic steel with a size of 810 x 510 x 350 mm and a well-defined geometry are prepared and heat treated under standard conditions for die casting molds. Subsequently impact energy and fracture toughness in different zones of the samples are determined. The corresponding microstructures are investigated using optical microscopy and scanning electron microscopy. The results are compared with those of numerical simulations and discussed in this presentation.

A low-speed hot-ring compression test has been proposed to be helpful in classifying the tribological performances of lubricants in hot forging of steel under severe conditions. In this previous work, we used calibration curves with considering heat transfer between the air and the hot work, the die and the hot work; however, without considering contact time and compression velocity. This calibration curves were insufficient to evaluate the frictional coefficient between the die and the work. To use more precise values of the frictional coefficients, we updated calibration curves with considering heat transfer between a die and lubricant, a lubricant and a work, air and a work by an experiment and a FEM analysis. It was found that the frictional coefficient between a die and a work was underestimated without considering heat transfer and velocity of the press.

Shot peening is one of the most popular surface enhancement technique used to improve fatigue performance of different materials. This paper focuses on to study the effect of different shot peening parameters on micro-structural and mechanical properties of DIN 1.2714 tool steel specimens. Shot peening treatments were carried out by varying shot size and peening intensity. X-ray stress analysis, micro-hardness testing and micro-structural analysis were performed to characterize these specimens. In addition, pin on disk wear testing was executed to recognize wear behavior of this shot peened tool steels. It was observed that along with compressive residual stress generation, shot peening also induces work hardening effect and modifies surface structure which are responsible for significant improvement in this tool steel.

Compared with the traditional technological process, hard milling of hot work tool steel (AISI H13) can significantly improve the physical/mechanical performances of machined components. A three dimensional (3D) finite element (FE) simulation model was built in this research to investigate the complex nonlinear process. First, the geometric model of workpiece was established considering the previous machined surface profile in actual milling process. Secondly, the prediction validation of the simulation model about hard milling process was verified by comparing the simulated cutting forces with the experiment results. Finally, the effect of cutting speed and feed rate on cutting forces and cutting temperature were researched by using the FE simulation model. The results indicate that cutting forces increase with the increase of feed rate, while cutting temperature increases with the increase of cutting speed. The effects of cutting speed on cutting forces and feed rate on cutting temperature are not significant. The simulated temperature is much lower than the austenitizing temperature of AISI H13 steel which means white layer is unlikely to be formed under the cutting conditions used in this study. The research can contribute to the fundamental understanding of mechanism and optimization of cutting parameters in hard milling.

In this study, CrN and TiAlN thin films were deposited on plasma-nitrided QRO 90 Supreme hot work tool steel by physical vapor deposition process and analysed with regard to their erosion performance under hydro-abrasive erosion conditions. The as-received specimens were quenched to room temperature from 1050°C and tempered gradually at 605°C for 2 h and at 560°C for 4 h. These specimens were plasma-nitrided for 10 h at 500°C at a pressure of 250 Pa in a gas mixture of 80% N2 + 20% H2 and then coated with TiAlN or CrN coatings by cathode arc evaporation. The specimens were characterized by metallographic techniques, SEM, EDS and micro-hardness test. Plasma nitriding and duplex surface treatments significantly increased the hardness of the specimens and thus significantly reduced the erosion of the specimens. The hardnesses on the surface of plasma-nitrided, CrN-deposited and TiAlN-deposited QRO 90 steels were 1092 HV0.025, 2436 HV0.025 and 3578 HV0.025, respectively. TiAlN-coated specimens were about 17-fold harder than the as-received specimens and over 3-fold harder than the plasma-nitrided specimens. The erosion resistance of CrN-coated specimens was increased by a factor of 3.6 and 1.5 compared with that of the as-received and plasma-nitrided specimens, respectively. A brittle fracture phenomenon was observed on the eroded surface of the duplex-treated specimens while a ductile material removal was observed on the as-received and the tempered specimens. The plasma-nitrided specimens showed a mixed behaviour of ductility and brittleness.

[Graphic][1] The amount of energy that an animal can burn could be limited by the food available in its environment, or how well its body can digest and utilize nutrients. Additionally, because energy metabolism characteristically produces warmth, it has been suggested that some animals have

The management of hot work is the key element of petroleum refinery safety management. A large amount of hot-work data has been accumulated, which is underexploited. Driving new insights using big data analytics is the trend. However, there have been few scientific studies on solving a specific problem using big data method in the field of safety management. Hence, the unstructured-data analysis of the hot-work permit-to-work text was investigated. The professional corpus in the hot-work field was constructed using word segmentation, stop list elimination, standardized process, and manual proofreading. All hot-work content collocates were manually grouped into semantic domains in the light of experts’ experience. The data-driven reduction models of hot work number were proposed aiming at possible invalid hot work, long-time hot work, repetitive hot work and possible equipment defect. Based on the proposed reduction models, we mined the patterns of hot work and the unnecessary or high-risk hot work could be identified automatically. The result of the reduction model in training set indicated that the reduction models are reasonable. The reduction model 1, reduction model 2, reduction model 3, reduction model 4 could reduce the proportion of hot work number 5%, 3%, 4%, and 2%, respectively. Thus, the targeted measures could be put forward to optimize the safety management of hot work.

International audience; In hot forming processes, steel tools are subjected to rapid temperature transients and cyclic oxidation. AnT²COK, a new analytical model based on diffusion-controlled oxide growth in cyclic conditions, is proposed to predict the parabolic oxidation kinetics in spallation-free conditions. Compared to cyclic oxidation models of the literature (COREST, COSP, DICOSM, etc.), it is applicable for any shape of thermal cycle, fully transient or with dwell time. The model is applied to thermal fatigue tests on X38CrMoV5 steel, for Tmax between 500 and 685 °C. Its validity is demonstrated above 550 °C, using frequency factor and activation energy calculated from isothermal tests.

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

Boride layer characterization and dry sliding wear behaviors of borided H13 steel at different durations and temperatures with nanoboron powder have been investigated. A single phase boride layer was formed at 800 °C and a double phase boride layer was obtained at 900 °C and 1000 °C. According to the boriding process with Ekabor II, higher ratio FeB/FeB + Fe2B and total boride layer were formed when nanoboron was used in the boriding process. It has been observed that the increment in the boriding temperature and boriding duration has increased the boride layer thickness from 6,34 μm to 103.26 μm. Manganese boride and chromium boride phases were determined along with iron borides in the boride layer. The hardnesses of borides formed on the H13 steel reached 2028 HV0.1 and the change in hardness from the surface to the interior was slower at samples which were borided at higher temperatures and durations. Fracture toughness was found to be in the range of 1.32–5.23 MPa-m1/2 depending on boronizing time in samples which were borided at 1000 °C. The increase in the boriding temperature and boriding duration led to increased wear resistance. At high temperature, microcrack-induced plastic deformation and fatigue; at room temperature, microcrack formation were dominant wear mechanisms.

This paper is a part of experimental research in the area of high pressure die casting (HPDC) mould wear. Influence of mould preheat temperature and molten aluminium alloy impact speed on total mould wear was researched using novel laboratory die casting testing equipment. Testing parameters were set to simulate HPDC of aluminium alloy AlSi9Cu3(Fe). The specimens were made from X38CrMoV5-1 hot work steel (H11). Experiment was designed using central composite design. Following the experiment design, 13 specimens were heat treated and the surface was modified by “Tenifer” nitrocarburizing. Specimen wear was measured by a Mettler B5 scale (Kusnacht, Switzerland) and shown graphically by 3D scan before and after the experiment; the 3D scans were overlapped to determine main wear areas. Response surface was acquired. Most influential tribological wear mechanisms were determined by ANSYS CFX 17.2 analysis. It was found that preheat temperature and molten aluminium alloy impact speed directly affects total wear of the mould surface. An increase of preheat temperature decreases total wear, while an increase of molten aluminium alloy impact speed increases total wear. Conditions for minimum and maximum wear were quantified; most significant wear was observed on sharp edges of nitrided mould material specimens. ANSYS CFX 17.2 hard particle erosion rate simulation suggested erosion occurrence mostly at impact angles perpendicular to the specimen surface. Other ANSYS CFX 17.2 simulation suggested occurrence of cavitation erosion. SEM analysis indicated an occurrence of intermetallic compounds between molten alloy and hot work steel.

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.