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İnsanlar gün içerisindeki faaliyetlerinin büyük bölümünü kapalı alanlarda geçirir. Bu nedenle insanlar için kapalı mahallerde iyi bir havalandırma ve iklimlendirme sistemi tasarlamak son derece kritiktir. İyi bir havalandırma, insanlarda hem vücut sağlığı hem de çalışma verimleri adına önemli bir kıstastır. Sıcaklık maruziyeti, vücudun fizyolojik ve psikolojik dengesini, çalışma verimini önemli ölçüde etkileyen ve çalışma ortamında sıkça karşılaşılan problemlerdendir. Isıl konfor ise, kişinin bulunduğu ortamın sıcaklığı ile uyumun sağlanması ve memnuniyetsizliğin bertaraf edilmesi anlamına gelmektedir. Termal konfor şartlarının tam olarak sağlanamadığı ortamlarda çalışmak zorunda kalan çalışanların verimlerinin düştüğü, güvenli çalışma durumunun zayıfladığı ve buna bağlı olarak iş kazasına maruz kalma sıklıklarının arttığı gözlemlenmiştir. Bu yüzden ısıl işlemin zorunlu olduğu, sıcaklık maruziyetinin kaynağında yok edilemediği durumlarda çalışan kişilerin termal konfor şartlarının iyileştirilmeleri öncelikle çalışanların sağlığına sonrasında ise üretim verimine olumlu katkılar sağlayacaktır. Bu çalışmada, ısıl konforu belirleyen parametreler üzerine incelemeler yapılmış olup, örnek mahal olan sıcak şekillendirme prosesi kullanılarak sac şekillendirme yapan hatta çalışan işçilerin ısıl konfor için çalışma koşulları gözlenmiştir. Isıl konforu sağlamak adına soğuk yelek üretilmiş ve ısı transferi dikkate alınarak iyileştirici faaliyetler belirlenmiştir. People spend most of their activities during the day in closed areas. Therefore, it is extremely critical to design a good ventilation and air-conditioning system in closed spaces for people. Good ventilation is an important criterion for both human health and working efficiencies. Temperature exposure is one of the most frequently encountered problems in the working environment, which significantly affects the physiological and psychological balance of the body and the working efficiency. Thermal comfort means compliance with the temperature of the person's environment and eliminating dissatisfaction. It was observed that the efficiency of the employees who had to work in the environments where the thermal comfort conditions could not be fully decreased, the safety status of the workers had weakened and the frequency of exposure to work accidents increased. Therefore, if the thermal treatment is compulsory and the temperature exposure cannot be eliminated at the source, the improvement of the thermal comfort conditions of the employees will firstly contribute to the health of the employees and then to the production efficiency. In this study, the parameters determining thermal comfort were investigated and the working conditions of the workers who worked on the sheet metal forming even by the hot forming process were observed. In order to provide thermal comfort, cold vests were produced and healing activities were determined considering heat transfer. Beyçelik

Additive manufacturing (AM) brings the possibility to produce tools with a complex design of the cooling channels to achieve desired properties in the working piece. However, AM of tool steels can be challenging due to the residual stresses and crack formation which may be mitigated by optimizing process parameters. In this study, process parameters development in the laser powder bed fusion (L-PBF) of a martensitic hot work tool steel was under investigation. Having power, scanning speed and hatch distance as variables, a design of experiment was performed to map a process window to produce dense components. In addition, the same sets of process parameters were applied at different preheating temperatures to study and discuss the effect of three preheating temperatures on the porosity, microstructure and hardness of the manufactured components. The characterization of the parts was done using optical and scanning electron microscopy, x-ray diffraction and micro-hardness test. The results showed that the martensitic hot work tool steel can be manufactured with L-PBF with high densities above 99.95%. © 2022 The Authors. Published by Elsevier B.V.

In recent years, promising technique of deep cryogenic treatment (DCT) is taking a new step in improving properties of various materials, especially steels. This study is focusing on influence of selected heat treatment process involving deep cryogenic treatment on the microstructure and microstructural evolution of four different steel grades (bearing steel 100Cr6, cold work tool steel X210Cr12, hot work tool steel X38CrMoV5-3 and stainless steel X17CrNi16-2). The study was performed for different heat treatment conditions, focused on effectiveness of DCT when using different austenitizing and tempering temperatures. The evolution of the microstructure was investigated in a sequential manner with various analytical techniques. The study indicates that the microstructure and microstructural evolution and changes are strongly related to the chemical composition of steel and the predefined matrix microstructure. DCT increases precipitation of carbides and induce their more homogenous distribution. The magnitude of increased carbide precipitation after DCT is correlated with the higher carbon content, whereas the content of other alloying elements does not scale with the precipitation behavior. The obtained results indicate that incorporation of DCT with heat treatment with higher austenitizing and lower tempering temperature is the most suitable for improving steels’ properties with DCT, due to the stronger impact of DCT on the carbide precipitation and matrix modification.

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 this study, the microstructure and mechanical properties of martensitic hot-work tool steel AISI H13 produced by laser powder bed fusion (LPBF) under argon atmosphere in different LPBF process t...

In an energy-intensive process, such as high pressure aluminum die casting, reducing the cycle time and scrap rate has a significant influence on the CO2 savings and profitability. By using conformal cooling and state-of-the-art hot work tool steels, the cycle time for molding tools can be reduced and tool life can be increased. This means that not only the component quality in functional areas increases, but also the overall process quality. These innovative solutions can only be realized if the restrictions of additive manufacturing (AM) are understood. Only then can the potential of AM be exploited to develop novel tool concepts from a holistic understanding of component and process requirements. Thermal management then becomes the focus of the entire process chain. In addition to reducing CO2 emissions and increasing component quality, the optimization of thermal management leads to significant cost savings and thus to an increase in the competitiveness of this production process. As a result, the use of additively manufactured die inserts/components in the die casting process brings significant advantages, both economically and ecologically.

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.

This review discusses in detail the process of hot forging and the types of machines involved and explains the die materials used for hot forging of the respective types of machines, such as vertical forging presses (friction presses), drop hammer forging presses and horizontal forging machines. Forging requires forging the metal using compressive forces. It investigates the chemical properties of die materials used in hot forging. The article covers the materials, the properties of the forging die inserts and the master die inserts. The hardness of the materials has been defined on the basis of the chemical composition and the heat treatment process, the heat treatment is widely used for tungsten-based and chromium-based hot work tool steel to achieve microstructure. This article ends with the required die content and uses it on the basis of the hardness of the billet utilized.

The AISI H13 is a chromium based, medium carbon content hot work tool steel which is widely used in hot working as well as cold working applications. These steels are very popular because of their key characteristics such as high hardness, high strength, high fracture toughness and high wear resistance. These steels are continuously subjected to high mechanical stresses and temperature fluctuations, fatigue and wear loss which results in limited die life. It is therefore necessary to improve the properties of these tool steels. One of the methods to improve the properties of these tool steels is with the help of conventional heat treatment. But no significant improvements in the properties were observed. From the literature survey, it is realized that implementation of cryogenic treatment can improve the properties of tool steel. In the present paper, cryogenic treatment on AISI H13 hot work tool steel is studied with the help of characterization techniques such as hardness, wear and microstructure study. One set of specimens were subjected to conventional heat treatment (HTT) viz. hardening at 1020 °C followed by double tempering at 500 °C. Another set of specimens were subjected to conventional heat treatment followed by deep cryogenic treatment at −196 °C and soft tempering at three different temperatures viz. 200 °C, 300 °C and 400 °C (HTTCT). A modified heat treatment cycle (HTCT) is also proposed with varying soft tempering temperatures viz. 200 °C, 300 °C and 400 °C and comparison is made with HTT and HTTCT. The specimens were tested for hardness, wear and microstructure study. The experimental investigation shows that cryogenically treated specimens shows significant improvement in the hardness and carbide density as compared to conventionally treated specimens. It is thus concluded that HTTCT cycle gives two times higher wear resistance than conventional heat treatment cycle (HTT) because of precipitation of fine tertiary carbides.

Friction Stir Welding (FSW) is a nontraditional joining method that is used for the attachment of similar and divergent substances, which are comparatively difficult to be welded by fusion techniques. They are extensively used for joining metals in different applications. Also, this welding is more energy-competent and eco-responsive when contrasted with traditional fusion methods. The FSW has various degrees of prevalence when compared with conventional fusion. Generally, the mechanical properties of heat-treatable alloys are reduced due to thermal cycles and the roughening of the reinforcing expeditions in the FSW, resulting in joint softening. The Underwater Friction Stir Welding (UWFSW) is a preferred methodology to prevail over these problems. This procedure is appropriate for the heat treatable materials which are responsive to thermal activities throughout the fusion cycle. In this work, the UWFSW was carried for welding dissimilar alloys AA7075 and AA6082 with dimensions of 150 × 100 × 6 mm. The Hot work steel H13 was used as a tool material. Also, the influence of the fusion characteristics, including tool rotational speed, tool traverse speed, and tool tilt angle on the micro-arrangement and tensile characteristics of the UWFSW joints of AA7075 and AA6082 alloy, were investigated using Taguchi’s method. The S/N fraction scrutiny revealed that the optimum mechanical rigidity was attained at a tool rotational speed of 1200 rpm, tool fusion speed of 40 mm/min, and tool tilt angle of 1°. In accordance with the ANOVA method, the maximum input of parameters were analyzed for the objective functions, including the UTS (MPa), % of elongation, and micro hardness in the different zones (NZ, TMAZ, HAZ).

In the present study, two different commercial tool steels SKD-61 and SKD-11 were hardened to attain the similar hardness of 50 HRC (5.51 GPa) and nanoindentaion test was performed to obtain the nanomechanical properties of the hardened steels. Furthermore, wear behavior of these steels were investigated using tribo test with different combination of load and sliding velocity. FE-SEM along with EDS was used to examine the surface morphology of the hardened steels before and after the tribo test. Results showed similar wear behavior at low sliding velocity and low applied load for both the steels but with the increase in sliding velocity beyond 0.20 m/s, the specific wear rate of SKD-11 steel also increases. Whereas, wear of SKD-61 tool steel exhibited no sever changes. Microgroove with plastic deformation, micro cracks, adhesion and oxidation was observed as primary wear mechanism. It can be said that at high load and high sliding velocity, SKD-61exhibits better wear performance than SKD-11 tool steel.

CV. Grafika Dua Tujuh is an industry engaged in publishing and printing books and student worksheets located in Klaten. The average output produced daily is 85.400 books and student worksheets, while the company has a production target of 90.000 books and student worksheets. Based on the results of interviews with workers, the level of production that is not maximal is caused by an uncomfortable working environment. Workers in the production room complained about the condition of a hot work environment so that workers feel easily tired and lack of concentration. To overcome the hot workplace, workers often go to the restroom and they work while holding the hand fan. This condition disturbed their concentration and cause work errors. If this condition is carried out continuously, there will be a lot of lost work time which can cause a decrease in productivity. This study aims to analyze the improvement of working temperature conditions in the production room of CV. Grafika Dua Tujuh. This research was conducted by directly measuring thermal conditions in the entire production room of CV. Grafika Dua Tujuh. Determination of the coordinate point of room temperature measurement is based on SNI: 16-7061-2004. Workload assessment is carried out based on SNI 7269: 2009. The results of the measurement of work climate at the content printing workstation are the values of air temperature, humidity, and wind speed i.e 33.32 °C, 39.9%, and 0 m/s. In addition, Wet Bulb Globe Temperature Index (WBGT) value is obtained which is on the verge of a limit, i.e 29.90 °C for the category of the heavy workload with an allocation of working time of 87.5%. The temperature is above the standard set by the Ministry of Health of the Republic of Indonesia No. 1405 / MENKES / 2002 which sets the temperature in an industrial room ranging from 18 °C - 28 °C. Improvement for working temperature is done by engineering control, namely the installation of a turbine ventilator or exhaust fan.

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.

In the pipeline transportation process for crude oil, the most important and popular maintenance method for perforated and ruptured oil pipelines is the replacement of the damaged pipeline segment. However, this method has several disadvantages, including a complex process, large time consumption, and excessively high costs. The present study reported the preparation of a strong cross-linking hydrogel that served as a temporary blocking material during the long-distance oil pipeline partial replacement process. The prepared product was characterized by infrared spectroscopy, X-ray diffraction analysis, and scanning electron microscopy to analyze the microscopic reactions and structures. Orthogonal experiments for shear stress were performed to determine the optimal synthesis condition. The relevant experiments indicated that the proposed product can effectively isolate oil and oil gas, and a 4.5 m long hydrogel can resist the force of a 0.57 MPa overpressure. The blocked pipeline turned to a dredged state on changing the pipeline pressure. The flame resistance experiment showed that the hydrogel exhibited excellent flame resistance and could therefore ensure the safety of the hot work. On the basis of this hydrogel material, a new method for replacing the partially damaged oil pipeline was proposed.

Introduction: Working in a hot work environment has a negative impact on occupational health and safety. The impact on health due to work at temperatures above a comfortable temperature can affect body temperature and blood pressure of workers. The aim of this study was to analyze the differences in body temperature and blood pressure of workers before and after exposure to hot work climates at PT. Pertamina (Persero) Tanjung Wangi. Method: This research was an observational study with cross sectional approach. The population of this study was all workers at PT. Pertamina (Persero) Tanjung Wangi., with the total of 11 people. The sample in this study was obtained by total sampling method with a sample of 11 workers. The dependent variables in this study were body temperature, blood pressure, age, fluid intake, and nutritional status, while the independent variable was work climate. Results: Most of the grass lathe workers at PT. Pertamina (Persero) Tanjung Wangi has an age between 17-25 years, some of the grass lathe workers had a fluid intake with less categories with normal nutritional status. The measurement results showed that the average ISBB value was 28.8°C, this value still exceeded TLV. In addition, the results showed that there were differences in body temperature before and after work, from 36.04° C to 36.8° C. In addition there were differences in systolic and diastolic blood pressure before work which was 112.7 mm Hg 77.3 mm Hg, and the average after work was 121 mm Hg and 83.6 mm Hg. Conclusion: There is a difference between body temperature and blood pressure before and after exposure to hot work climates.Keywords: blood pressure, body temperature, hot work climate

Company XXX is a factory that involving manufacturing of offshore containers in where the hot works are one of the crucial activities in fabrication and structuring the framework of the containers. This study had been conducted at hot work section to conduct initial and advanced ergonomic risk assessment to identify ergonomic risk factors involved among hot-work workers which cause the significant number of reports on ergonomic related health issues at hot works area from the year 2011 to year 2017. The initial and advanced ergonomic risk assessment had been conducted based on DOSH latest release of guideline on ergonomic risk assessment 2017 and all findings had been tabulated and analysed. Based on the intial ergonomic assessment, total score achived is 17.7 with main risk factors identified through the hot work acticties are including awkward postures, repetitive motions, static and sustained work postures, vibration, insufficient ventilation, exposure of noise and working in extreme temperature. Based on Advanced ERA conducted on selected 3 workers, the study shows Muscle Fatigue Assessment (MFA) with average score for risk level shown ‘High’ and ‘Very High’ categories, Rapid Entire Body Assessment (REBA) with average total score more than 10 which categorized as ‘High Risk’ and Quick Exposure Check (QEC) which shown the workers have very high risk for back and shoulder or arm parts with score level are between 29 to 40 for back static and 41 to 56 for shoulder and arm parts. Based on results of the assessment, company XXX recommended had been to conduct further investigation for improvements to determine effective control measure for the work process in order to reduce that risk level towards the hot work workers.

Excessive exposure to heat can lead to injuries, illness, and death among mineworkers. The actual cost of heat-related injuries and illnesses is unknown because of underreporting and lack of symptom recognition. Multi-factorial, evidence-based, and field-ready guidelines for identifying–and predicting–physiological markers of heat strain are currently unavailable. The predicted heat strain (PHS) model, is the latest attempt by mining companies to aid in the evaluation and management of occupational heat exposures. The adopted algorithm relies on worksite environmental measurements and an estimate of individual metabolic rate for mine workers to provide an estimate of the workers’ core temperature during a work shift. There are several known limitations of the PHS model, including the assumption that the subject worker is hydrated and fit. A modified PHS model was presented based on eight physical parameters that are measured at different intervals during a work shift; these parameters are air temperature, relative humidity, air velocity, radiation, metabolic rate, acclimatization, clothing insulation and posture. To validate the results, the predictions from the modified PHS model were compared with direct physiological measurements obtained from ingestible pills and heat stress monitors under different environmental and working conditions.

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.

In this research, the microstructure evolution in the machined subsurface is numerically simulated through a developed multi-physics model applied to H13 hot work die steel. The multi-physics model based on dislocation density evolution is utilized to predict the change of grain size through finite element analysis by varying cutting parameters. In spite of the cutting conditions, the simulated grain size on the top-most machined surface is around 330 nm, and the machining-affected depth with refined grain varies in the range of 25–45 μm. In addition, the appeared periodical fluctuation of dislocation density and grain size in a wavy configuration induced by the generated serrated chip segments is revealed. The efficacy of the proposed finite element model is verified and the probable mechanism of grain refinement is demonstrated with the assistance of TEM observation, which in turn promotes the in-depth understanding of microstructure evolution during metal cutting.

The microstructure and primary carbides in the steel billets produced by an industrial-scale electroslag rapid remelting (ESRR) at different melting rates were studied. The amount and size of primary carbides MC and M2C at the center of the remelted ingots is larger than that at the mid-radius of the remelted ingots. The amount of primary carbides and secondary dendrite arm spacing of the ingot increase with the increase in the melting rates of ESRR, caused by the increase in the local solidification time. The microsegregation of Mo in the remelted ingots after annealing is most serious among the carbide-forming elements. The microsegregation of Mo and Cr increases linearly with increasing the melting rate, and the microsegregation of V keeps nearly constant with further increasing the melting rate from 400 to 500 kg/h. Increasing the melting rate of ESRR do not change the types of primary carbides until 500 kg/h, at which another type of primary carbide M7C3 is formed. The amount of the primary carbides and the microsegregation degree of Mo, V and Cr in the ESRR billets at the melting rate of 400 kg/h is nearly same as that produced by same-scale conventional ESR.

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.

The paper discusses some new technological solutions for producing die inserts for forging on forging machines the parts of a high-pressure tractor engine. In the current solution, the inserts were made of WNL (NiCrMoV6) steel, and then toughened. In the adopted new solution, the inserts made of cast steel with a composition corresponding to WCL (X38CrMoV5-1) steel, after toughening, were subjected to gas nitriding regulated by the NITREG method, or fluidized bed oxynitriding. The conducted tests of immediate resistance, impact strength and service life showed a beneficial effect of nitriding and oxynitriding on the properties and service life of die inserts. Precise casting of inserts by the Shaw method reducing their manufacturing costs, was also an interesting technological innovation.

Until now, additive manufacturing of high-performance materials such as martensitic hardenable tool steels is rarely investigated. This work addresses the introduction of an alternative alloying strategy for hot work tool steel powder, provided for laser powder bed fusion (L-PBF). The focus is on the question whether a powder mixture of spherical iron powder mixed with mechanically crushed ferroalloy particles can be processed by L-PBF, instead of using cost-intensive pre-alloyed gas-atomized powder, and to investigate the material properties associated with it. The particle morphology, packing density and flowability of this L-PBF powder feedstock is compared to gas-atomized spherical pre-alloyed steel powder and the results are correlated to the defect density, the resulting microstructure and the chemical homogeneity. Finally the resulting surface hardness is compared to a conventionally casted material as a reference state. It shows that the L-PBF fabrication of high-dense parts by means of both starting powders is technically feasible. Even though the alternative alloying concept promotes local chemical inhomogeneities within the microstructure, the overall porosity and the appearance of micro cracks are reduced.

Selected thermophysical properties of the hot work tool steel AISI H11 (1.2343) were measured in the temperature range from room temperature to the melting temperature. Thermal diffusivity was measured by the laser-flash method; heat capacity by differential scanning calorimetry; linear thermal expansion by push-rod dilatometry; and density at room temperature by an Archimedean balance. From these experimentally obtained data, thermal conductivity was calculated. Additionally, electrical resistivity of AISI H11 (1.2343) was measured by millisecond pulse-heating in the above mentioned temperature range. The measurement results of electrical resistivity as a function of specific enthalpy was combined with results of specific heat capacity measurements by differential-scanning calorimetry to obtain the relation between resistivity and temperature. Based on measured electrical resistivity and thermal conductivity, a Smith-Palmer-plot for the hot work tool steel AISI H11 (1.2343) is obtained for the ferritic and austenitic phases. No linear behaviour – as expected by the Wiedemann-Franz law – is observed in the ferritic phase region. In the high temperature austenitic region, the thermal conductivity can be computed from electrical resistivity using empirical constants of similar austenitic steels or superalloys.

Metal matrix composite materials are of high interest for their increased stiffness, strength or wear resistance. Wear resistant composites contain hard ceramic particles to reduce microcutting and grooving of the metal matrix surface. In this paper, a gas atomised hot work tool steel X40CrMoV5-1 (1.2344/AISI H13) was combined with fused tungsten carbide (FTC) particles in order to create forging tools with increased abrasive wear resistance. For that purpose, tool components were manufactured by sinter-forging of stacked powder layers to build up a graded hard phase concentration of up to 10 vol.-%. Subsequently, sinter-forged specimens were combined with basic hot work tool steel components and joined by diffusion bonding to assemble the complete tool. In order to evaluate their performance, the tools were examined in a hot backward can extrusion process of low-alloyed steel. Optical geometry measurements, light microscopy and scanning electron microscopy of the worn tool radii indicated a significant decrease in abrasive wear when using FTC-reinforced tools rather than conventional hardened tool steel.

The article discusses the issues of safe operations on the main gas pipelines of the Republic of Kazakhstan, which, as a result of deterioration of pipelines main part and their active susceptibility to stress corrosioncracking, require repair work. Considered new approaches of repair work organization by open fire using. It has beenanalyzed that the application of these measures in practice will ensure proper organizational planning and technicaltraining of personnel, and effective provision of necessary level safety for hot work. It was concluded that it isnecessary to introduce safety increasing measures during fire work on gas pipelines, it will prevent possible disasters,fires, destruction and human losses due to explosions during repair work on gas pipelines, as well as reduce damaging factors affecting workers health. It is shown that introduction of the named above measures helps to preventdisasters, fires, destruction and loss of life as a result of explosions during gas pipelines repair, as well as damagingfactors reduction that affect workers health during these types of work.