Hot Working Research Articles

Water-blocking Asphyxia of N95 Medical Respirator During Hot Environment Work Tasks With Whole-body Enclosed Anti-bioaerosol Suit

BackgroundDuring hot environment work tasks with whole-body enclosed anti-bioaerosol suit, the combined effect of heavy sweating and exhaled hot humid air may cause the N95 medical respirator to saturate with water/sweat (i.e., water-blocking). Methods32 young male subjects with different body mass indexes (BMI) in whole-body protection (N95 medical respirator + one-piece protective suit + head covering + protective face screen + gloves + shoe covers) were asked to simulate waste collecting from each isolated room in a seven-story building at 27-28°C, and the weight, inhalation resistance (Rf), and aerosol penetration of the respirator before worn and after water-blocking were analyzed. ResultsAll subjects reported water-blocking asphyxia of the N95 respirators within 36-67 min of the task. When water-blocking occurred, the Rf and 10-200 nm total aerosol penetration (Pt) of the respirators reached up to 1270-1810 Pa and 17.3-23.3%, respectively, which were 10 and 8 times of that before wearing. The most penetration particle size of the respirators increased from 49-65 nm before worn to 115-154 nm under water-blocking condition, and the corresponding maximum size-dependent aerosol penetration increased from 2.5-3.5% to 20-27%. With the increase of BMI, the water-blocking occurrence time firstly increased then reduced, while the Rf, Pt, and absorbed water all increased significantly. ConclusionsThis study reveals respirator water-blocking and its serious negative impacts on respiratory protection. When performing moderate-to-high-load tasks with whole-body protection in a hot environment, it is recommended that respirator be replaced with a new one at least every hour to avoid water-blocking asphyxia.

Constitutive equation and microstructural evolution of one distinctive Al–based hybrid composite reinforced by nano–AlN and micro–TiC particles during hot compression

In this study, an (8.2AlN + 4TiC)/Al–0.3Fe–0.1Mn composite was successfully fabricated for elevated– temperature applications by the liquid–solid reaction method, and the high–temperature performance (hot workability) of the composite was evaluated by unidirectional hot deformation experimentation. The tested temperatures and strain rates were 350–500 °C and 0.001–1 s−1, respectively. The results indicated that the peak stress of the composite was as high as 226 MPa at 350 °C and 1.0 s−1, which was significantly higher than the reported strength values of commercial deformed aluminum alloys or other particle–reinforced Al matrix composites under the same experimental conditions. Although the flow stress of the composite decreased with the increase of deformation temperature and the decrease of strain rate, the peak stress remained at 82 MPa under the experimental conditions of 500 °C and 0.001 s−1. This reflected the excellent high–temperature synergistic strengthening effect of the in–situ nanosized AlN and submicron TiC particles. Based on the true stress–true strain curve, the hot deformation constitutive equation of the composite was established and fitted. The relative microstructural evolution of the composite during hot deformation was characterized by electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the Orowan strengthening and load–transfer strengthening effect of the nanosized AlN and submicron TiC particles were the main reasons for their high–temperature strengthening, and the softening effect of the composite could be attributed to dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), accompanied by partial discontinuous dynamic recrystallization (DDRX). This study provided a new strategy for the design of heat–resistant Al alloys and their high–temperature strengthening and softening mechanism. This study may provide new insights for designing and achieving good workability in Al–based composites for elevated temperature applications.

Hot Work Mold Repaired via Hot Isostatic Pressing towards High Red Hardness

Repairing hot work molds can extend their lifespans and reduce the production costs. This study presents a proposed method for enhancing the red hardness and strength of repaired molds. The method involves utilizing PM23 high-speed steel powder to repair H13 steel molds with two distinct surface states through the process of hot isostatic pressing (HIP). The internal microstructure changes, bonding state, fracture morphology, and crack extension behaviors of the repaired molds are characterized using scanning electron microscopy and electron backscatter diffraction technology. Additionally, the mechanical properties, including red hardness and tensile strength, are quantitatively analyzed. The findings indicate that the repaired area in the sandblasted sample exhibits a rough and uneven structure, demonstrating exceptional toughness. The tensile strength of the repaired region is approximately 1195.42 MPa, while the hardness measures around 672.8 HV. These properties effectively enhance the performance of the molds. The experimental findings indicate that HIP can effectively restore molds, resulting in enhanced red hardness and improved toughness, particularly when combined with sandblasting as a pretreatment method.

Hot workability optimization of W400 non-oriented silicon steel

Isothermal compression tests of W400 non-oriented silicon steel are performed at 0.01 to 10 s−1 and 850 to 1150 °C on a Gleeble thermo-mechanical simulator. Each stress-strain curve shows monotonous but slow increase of flow stress blessed with increasing strain. By introducing temperature into the strain rate exponent in Z parameter and proposing the temperature boundary principle, a revised constitutive pattern is built with a view to quantify flow stress versus temperature and strain rate accurately. Numerous sub-grains and sub-grain boundaries (GBs) are detected in the deformed grains, confirming the distortion energy to be reduced by dynamic recovery and thus slowing down the monotonous increase of flow stresses. Unusual discontinuous dynamic recrystallization is activated when strain rate and temperature is relatively higher, as confirmed by the random orientations of recrystallized grains. Analyses of GB shape and intergranular misorientation prove that local strain due to weak dynamic recovery leads to GB bulging and sub-GB formation, and thus activates the unusual discontinuous dynamic recrystallization. The distribution maps of strain rate sensitivity coefficient are constructed when the strain are 0.2–0.8. Based on high strain rate sensitivity coefficient, low deformation resistance and high GB stability, workability parameters are optimized as: temperature 1000–1150 °C, strain rate 0.01 to 10−0.5 s−1 and strain ≤0.6.

Investigating effects of Lorentz forces and convective heating on ternary hybrid nanofluid flow over a curved surface using homotopy analysis method

Abstract This work investigates the ternary hybrid nanofluid flow over an extending curved surface. The surface is impermeable and convective with hot working fluid water. Additionally, TiO 2 {\text{TiO}}_{\text{2}} , CoFe 2 O 4 {\text{CoFe}}_{\text{2}}{\text{O}}_{\text{4}} , and MgO \text{MgO} nanoparticles are suspended with water to form a tri-hybrid nanofluid. The modeled equations are presented in the partial differential equation form and are then converted to ordinary differential equations with appropriate similarity variables. The semi-analytical solution is determined by homotopy analysis method. The impacts of magnetic field, Joule heating, chemical reaction, Brownian motion, and thermophoresis on flow profiles, Nusselt number, and Sherwood number are determined using tables and figures. The findings of this study demonstrated that as the magnetic parameter upsurges, the velocity distribution shrinkages, while the temperature distribution escalates. The greater curvature factor boots the velocity, thermal, and volumetric fraction distribution. The thermal and volumetric fraction distributions are the increasing functions of thermophoresis factor. The higher magnetic factor, Eckert number, and thermal Biot number increase the Nusselt number, while they reduce the higher Brownian and thermophoretic factors. The higher thermophoresis and Brownian motion factors heighten the Sherwood number. Furthermore, it has been noted that using nanofluid (TiO2-water) and hybrid nanoliquid (TiO2-CoFe2O4/water), the transfer of energy rate increases by up to 17.31 and 31.72% as the nanoparticle parameter increases from 0.01 to 0.04, respectively. However, the energy transference rate in case of ternary hybrid nanoliquid (TiO2-MgO-CoFe2O4/water) is 47.972%.

The effects of climate change on the health and safety of pasta industry workers: assessment of heat stress using wbgt index

Protection of workers from environmental heat stress, especially the risks to which individuals are exposed due to the microclimatic conditions of the summer season characterized by particularly high temperatures, requires a careful assessment of working conditions and the implementation of preventive actions. The sectors most affected by such exposure are related to construction and road works, agriculture, and maritime fishing. This contribution presents the practical assessment and study of some work environments belonging to the pasta production sector, focusing on thermal stress in hot working environments, based on the use of the Wet Bulb Globe Temperature (WBGT) index, easily determinable with the use of simple portable instruments. The impact of climate change on the health and safety of workers in the pasta sector is a topic of growing importance. Climate variations adversely affect the health of workers throughout the entire pasta supply chain. This article explores the tangible effects of global warming on the well-being of sector workers, with a particular focus on heat stress and its related impact on productivity. The challenges faced by workers in the pasta sector due to extreme heat weather conditions and appropriate strategies aimed at mitigating the associated economic impacts were analyzed. Furthermore, precautionary measures were examined to define, prevent, and protect the health and safety of workers, thereby contributing to the long-term sustainability of this vital food industry. This case study delves into the analysis of temperatures in the workplaces of three pasta factories during two distinct periods of the year, using the WBGT index. This index provides a more accurate assessment of the thermal conditions perceived by workers, considering the complexity of the variables involved. The decision to examine three different pasta factories aims to provide a comparative analysis of the thermal conditions, taking into account the specificities of each structure. The chosen investigation period, spanning summer and early autumn, is motivated by the desire to understand seasonal variations and evaluate the impact of climate change on microclimatic conditions in workplaces. The main objective of the study was toidentify any significant differences in thermal conditions between the two periods considered and to analyze how climate change could influence workers’ health.The comparative analysis of the data collected during the months of July and October aims to provide a detailed overview of the thermal conditions in pasta factories, highlighting any trends or fluctuations. Through this investigation, we aimed to outline the potential impacts of climate change on the microclimate of workplaces, contributing to greater awareness and the formulation of adaptation strategies. The information emerging from this study is useful for managing the safety and well-being of workers in the specific pasta factories examined. However, it could also constitute a broader contribution in the context of discussions related to the adaptation of working conditions to climate change. The ultimate objective was to promote safe, comfortable, and resilient working environments capable of facing the challenges imposed by climate variations.

A large strain thermoplasticity model including recovery, recrystallisation and grain size effects

AbstractIn manufacturing, thermomechanical processes such as static annealing and hot working are commonly used to tailor the microstructure of metals to achieve favourable macroscopic material properties that meet specific application requirements. To improve sequential manufacturing processes and to accurately predict the microstructural changes of the material along the process chain, physically motivated constitutive models are required that simultaneously account for the effects of recovery and recrystallisation, as well as grain size dependencies. To this end, Cho et al. [Int. J. Plasticity 112, 123–157 (2019)] proposed a macroscopic hypo‐elasticity based large strain thermoplasticity model that aims at the unification of the effects of static and dynamic recovery and recrystallisation, as well as grain growth and refinement. In the present contribution, the hypo‐elasticity based large strain recrystallisation formulation proposed by Cho et al. is transferred to a hyper‐elasticity based large strain thermoplasticity framework to overcome the limitations typically accompanied with hypo‐elasticity based formulations. For this purpose, an isotropic temperature dependent hyper‐elastic Hencky type formulation defined in logarithmic strains is combined with a temperature dependent von Mises yield criterion. The recrystallisation modelling approach by Cho et al. is adopted, assuming a non‐associated temperature dependent proportional hardening rate in the form of an Armstrong‐Frederick type hardening minus recovery format, wherein the proportional hardening related internal variable is interpreted as a measure of dislocation density. It is shown that the hyper‐elasticity based format results in a thermodynamical consistency condition that effectively constrains the physically motivated evolutions of recrystallised volume fraction and average grain size. To investigate the capability of the model to predict the material response of unified recrystallisation thermodynamically consistently, representative thermomechanical sequential loading conditions including static annealing and hot working are studied.

Hot deformation and microstructural evolution of ultrasonically fabricated as-cast Al-7.3Zn-2.2Mg-2Cu alloy

Al-7.3Zn-2.2 Mg-2Cu alloy is known for its high strength, achieved because of higher alloying concentration. However, the higher alloying concentration presents challenges during the hot deformation process. Nevertheless, hot deformation proves to be an effective method for optimizing the microstructural and mechanical properties of the material. The research presented in the study focuses on investigating the hot working response of an ultrasonically fabricated age-hardening as-cast Al-7.3Zn-2.2 Mg-2Cu alloy. The objective is to observe the attainment of a uniform and dendrite-free microstructure after a single-step hot compression. The flow stress of the deformed specimens showed a notable increase as the temperature and deformation time decreased. This increase in stress was influenced by various factors, including deformation variables and precipitate size. The accurate prediction of the hot deformation behaviour was achieved by combining the constitutive equations and a workability map. The 3-dimensional workability map revealed a gradually increasing power dissipation efficiency (PDE) from 40% to 50% with increasing strain. At the end of 50% compression, four specific optimum working regions (PDE > 40%) were identified. Through detailed microstructural analysis, the best region for hot forging of ultrasonically mixed as-cast alloy for chemical homogeneity and upgraded property is obtained in the range of (350–450 °C) & (0.1–0.001 s−1). The highest extent of recrystallization (73%) was exhibited after deformation at 450 °C-0.001 s−1. The mechanism of dynamic softening during deformation is observed due to DRV, CDRX, and PSN. The microstructural response in 0.1–0.001 s−1 and 350–450 °C indicated dynamic recrystallization, whereas strained and non-working zone was observed at low deformation temperatures (≤350 °C).

Systematic investigation of the microstructure evolution and dynamic recrystallization mechanisms of as-cast Fe–TiB2 composites under different hot deformation parameters

Fe–TiB2 composite shows great potential in lightweight materials for automotive parts due to its lightweight, high strength and high specific modulus etc. However, challenges remain with regard to establishing a fine hot working process of Fe–TiB2 composites. Here, a series of isothermal hot compression tests was conducted to systematically investigate the microstructure evolution and the dynamic recrystallization (DRX) mechanisms of as-cast Fe–TiB2 composites at different sets of hot deformation parameters. The results indicate the true stress drops more significantly after reaching its peak at low temperatures compared to high temperatures, since low temperatures favors the DRX through particle stimulated nucleation (PSN) in Fe–TiB2 composites, as featured by layers of DRXed grains surrounding TiB2 particles. Continuous dynamic recrystallization (CDRX) process gradually dominates as strain rate increase from 0.01 s−1 to 1 s−1 in Fe–TiB2 composites hot compressed to the true strain of 0.69 at 900 °C, as evidenced by the presence of DRXed grains with larger size and uniform distribution in matrix. DRX through PSN is the primary DRX mechanism at low temperature and low strain rate, while CDRX dominates the DRX mechanism at high temperature and high strain rate. Both DRX behaviors deepen with the increase of the strain. Different hot deformation parameters favor different DRX mechanisms. The increase in temperature and strain rate leads to a transition of the dominant recrystallization mechanism from the DRX through PSN to CDRX which is attributed to the competition for stored energy between the DRX through PSN and CDRX process.

Constitutive Modeling of Hot Deformation Behaviors and Processing Maps of Mg–4.83Gd–2.36Nd–0.21Zr Alloy

Accurately assessing the hot workability and flow behavior is crucial in the preparation of high‐performance wrought Mg–rare earth (RE) alloys. The hot deformation behaviors and workability of Mg–4.83Gd–2.36Nd–0.21Zr alloy are examined via Gleeble 3500 thermosimulation tests across a range of deformation temperatures from 350 °C to 450 °C and strain rates ranging from 0.001 to 1 s−1. The experimental results reveal that the flow stress of the experimental alloy decreases as the temperature increases and the strain rate decreases. The activation energies for deformation (Q) of the experiment alloy are calculated by the hyperbolic constitutive equation and range from 186.78 to 234.97 kJ mol−1. Strain compensation is incorporated in constitutive modeling, resulting in the correlation coefficient (R) of 0.9865 and the average absolute relative error (AARE) of 5.4639%. Further, the processing maps are constructed at different strains based on dynamic material models, from which the feasible processing window of the experimental alloy is determined in the areas of deformation temperatures of 425–450 °C and strain rates of 0.01–0.1 s−1.

Influence of process and heat input on the microstructure and mechanical properties in wire arc additive manufacturing of hot work tool steels

The present study demonstrates the suitability of wire arc additive manufacturing (AM) for hot work tool steel processing. Different arc welding techniques and energy inputs were applied and systematically compared to determine the deposition characteristics, microstructure and mechanical properties. All AM deposits show a sound visual appearance and full density without macroscopic imperfections, i.e. cracking. By adhering to a pre-defined interpass strategy, the cold metal transfer process can be used to achieve higher weld beads with lower dilution and faster build-up rates than the metal active gas process. The microstructure of the AM parts is comparable for all process configurations and consists of an α/α′-matrix with a finely dispersed vermicular and polygonal δ-ferrite network; no notable amount of retained austenite could be measured, but it could be observed by transmission electron microscopy embedded within the laths. Intensive precipitation of multiple molybdenum-based precipitates is observed along the interface matrix to δ-ferrite. In contrast, iron-based precipitates are predominantly found inside and at the boundaries of the laths of the matrix. Similarities are also evident in the mechanical properties, resulting in an average hardness of 380–390 HV1 and absorbed impact energy of 10–12 J at room temperature. High yield strength values of 1000–1100 MPa and ultimate tensile strength of 1200–1400 MPa were obtained. No significant differences in the measured mechanical properties could be noted regarding the specimen orientation, indicating the isotropy of the properties.

Influence of B addition on the Mo diffusion-controlled eutectic dissolution process during homogenization of super austenitic stainless steel S31254

The influence of B addition on dissolution behavior of (σ + γ)e eutectics of a 6Mo super austenitic stainless steel S31254 during the homogenization process was investigated by SEM-BSE observations combined with EDS. The results showed that the addition of 0.005 wt% B accelerated the dissolution of the σ phase controlled by Mo diffusion, during homogenization from 30 to 90 min at 1180 °C. TOF-SIMS results showed that B segregated along the σ/γ interface in the as-cast samples. TEM observations combined with EDS investigated the phase interfaces in two as-cast samples in detail to correlate σ phase dissolution. Compared with the B-free sample, the wide transition zone (∼60 nm) with a composition gradient was more clearly observed at the σ/γ interface in the B-containing sample. The transition zone with B had two features: local segregation of B element and precipitation of R phases at the σ/γ interface. R phases owned larger contents of Mo, which was not almost observed in the as-cast S31254. The results indicated that B segregation changed the phase interface, accelerating Mo diffusion at the σ/γ interface. In addition, the results of nanoindentation indicated a more uniform distribution of hardness at the σ/γ interface after homogenization of the B-containing sample, which can be beneficial to improve the deformation compatibility of S31254 during hot working.

Hot workability behaviour of two P92 creep resistant steels: Constitutive analysis

This article reports the flow stress behaviour of two P92 steels at a temperature range of 850–1000°C and a strain rate of 0.1–10 s−1 using the Gleeble® 3500 thermomechanical simulator. A physically-based constitutive model was used to analyse the effects of deformation conditions on the flow stress behaviour during deformation. This model incorporates the influence in the variation of Young’s modulus and the self-diffusion coefficient as affected by temperature. The study developed constitutive equations that predict the flow stress behaviour of the two steels investigated. From the constitutive analysis of the results, the stress exponent n was: 9.8 (steel A) and 10.3 (steel B). The model used the self-diffusion activation energy of steel. The statistical parameters: correlation coefficient of 0.99 (for steel A and B), the absolute average relative error of 2.18% (steel A) and 2.20% (steel B) quantified the applicability of the model. The quantification results show that the constitutive equations developed have high accuracy in predicting the workability of the two P92 steels. The study has shown that this method is applicable in predicting the metal flow pattern of two P92 steels in the metalworking processes.

Some problems related to thermophysical properties of selected barrel steels

The paper discusses selected issues related to the thermophysical properties of selected barrel steels, which the authors have been dealing with over the last few years, i.e. 38HMJ (1.8509), 30HN2MFA, X37CrMoV5-l hot-work tool steel (1.2343), DUPLEX (1.4462) and MARAGING 350 (1.6355). In some of them, i.e. in the X37CrMoV5-1 hot work tool steel, 38HMJ, 30HN2MFA, a ferrite-austenite phase transition occurs, which causes shrinkage of the material. During a series of shots, multiple shrinkage of material degrades the barrel channel and deteriorates the ballistic parameters of the cannon barrel. Another problem concerns the apparent specific heat that we get from the DSC measurement and the dependence of the specific heat on temperature in the form that we use for the numerical simulations. The point is that the phase transition effect should not be taken into account twice, i.e. in the thermal diffusivity characteristics and in the specific heat characteristics. For all selected steels the thermophysical properties, i.e. thermal diffusivity, thermal conductivity, specific heat and thermal expansion, were obtained in a wide range of temperature, so they can be used as input data for numerical simulations.

Optimization-based parameter search of support vector regression for high-temperature compression constitutive modeling of 25CrMo4 steel

An accurate intrinsic structural model is essential to describing the high-temperature deformation behavior of metal materials. Support Vector Regression (SVR) has strong regression analysis capabilities, but its application research in constructing constitutive models of 25CrMo4 steel still needs to be improved. In this study, we use grid search, particle swarm optimization, improved genetic algorithm, and improved gray wolf optimization to optimize SVR parameters. A constitutive relationship model for 25CrMo4 steel under high-temperature compression based on SVR was established through training using experimental data models. The predicted data of SVR constitutive models with different optimization algorithms were compared with experimental data. Statistical values, such as average absolute percentage error (AAPE), mean absolute percentage error (MAPE), and correlation coefficient (R2), were introduced to evaluate the accuracy of each model. The particle swarm optimization-SVR model achieved the best performance, with an AAPE of 0.455 38, MAPE of 0.489 09%, and R2 of 0.999 74. Furthermore, compared to other models, it requires the least time. This model has a higher accuracy than other commonly used instantaneous models. These findings can provide a basis for selecting appropriate deformation parameters and preventing hot working defects of 25CrMo4 steel, thus helping to improve the manufacturing process and material properties.

Study on the in situ strengthening and toughening mechanism of H13 tool steel/WC-12Co composite using laser-based directed energy deposition

To overcome the unworkability of hot work molds in conventional manufacturing, laser additive manufacturing (AM) is widely adopted to print molds/dies with complex internal structures. However, in the AM process, some hot work steels easily crack (e.g., H11 and H13 tool steel) or exhibit dissatisfactory wear resistance (e.g., MS1 maraging steel). To tackle this issue, toughened functionally graded metal matrix/ceramic composite materials can be fabricated on existing molds by laser directed energy deposition (L-DED). Contrary to previous studies that clad Co on WC to avoid the decomposition of ceramic, in this work, we innovatively utilized a type of WC-12Co powder with a substructure to accelerate its decomposition and improve the toughness of composites. It was found that the unmelted tens-micrometer-magnitude WC-12Co powder and in situ synthesized nano WC coexist in the laser-deposited H13 steel/WC-12Co composites to act as the reinforcement phase. Particularly, all the brittle phases (WC and FexWxC) are wrapped by soft γ phases, alleviating the coefficient of thermal expansion (CET) mismatch between materials and the residual stress generated by laser AM. Consequently, defect-free deposits with varied WC contents are manufactured by L-DED and exhibit high hardness and superior wear resistance at both room and elevated temperatures due to the second phase and grain refinement strengthening mechanisms. These findings provide a disparate metal matrix composite design route for laser additive manufacturing to improve the toughness of metal matrix/ceramic composite materials and obtain exceptional performance.

Effect of Mn on Hot Workability and Processing Maps of Al-Mg-Mn 5xxx Alloys

Effect of Mn on Hot Workability and Processing Maps of Al-Mg-Mn 5xxx Alloys

Revealing the Influence of SiC Particle Size on the Hot Workability of SiCp/6013 Aluminum Matrix Composites.

SiC particle (SiCp) size has been found to significantly influence the hot workability of particle-reinforced aluminum matrix composites (AMC). In this work, therefore, three types of SiCp/6013 composites with different SiCp sizes (0.7, 5 and 15 μm) were prepared and then subjected to isothermal hot compression tests. In addition, constitutive analysis, processing maps and microstructural characterizations were used to reveal the influence of SiCp size on the hot workability of SiCp/6013 composite. The results showed that the values of hot deformation activation energy Q increased with decreasing SiCp size. Specifically, at lower temperatures (e.g., 350 and 400 °C), the highest peak stress was shown in the AMC with SiCp size of 0.7 μm (AMC-0.7), while in the AMC with SiCp size of 5 μm (AMC-5) at higher temperatures (e.g., 450 and 500 °C). This is because a finer SiCp size would lead to stronger dislocation pinning and grain refinement strengthening effects, and such effects would be weakened at higher temperatures. Further, dynamic softening mechanisms were found to transform from dynamic recovery to dynamic recrystallization with increasing SiCp size, and the dynamic recrystallization occurred more easily at higher temperatures and lower strain rates. Consequently, the instability zones of the composites are all mainly located in the deformation region with lower temperature and higher strain rate, and smaller SiCp results in larger instability zones.

Usulan Perbaikan Manajemen Risiko Untuk Penerapan Program K3

Risk management in the Occupational Health and Safety (K3) program provides a safe working environment essential to protecting employees. To improve the effectiveness of K3 risk management, the study proposes improvements using Hazard Identification and Risk Assessment methods. (HIRA). The study aims to identify potential hazards and evaluate the risks associated with hot work in the work environment. Using the Hazard Identification and Risk Assessment (HIRA) approach, risks can be identified more effectively and enable companies to take appropriate action to improve the effectiveness of risk management in occupational health and safety programs. (K3). The research methods used include document analysis, field observations, interviews, and surveys. The collected data will be analyzed using HIRA methods that include identifying hazards, assessing risks, and making recommendations for appropriate risk control. The results of this research are expected to enhance our understanding of the potential hazards and risks associated with the workplace. The resulting improvement recommendations will help the company implement appropriate precautions and improve K3 risk management.

Processability and Microstructural Evolution of W360 Hot Work Tool Steel by Directed Energy Deposition

Laser directed energy deposition (L-DED) was used to produce samples of the newly patented W360 hot work tool steel by Böhler. The process parameters were optimized to obtain nearly fully dense samples through the production and analysis of single deposited tracks and single layers. Subsequently, bulk samples underwent a hardening heat treatment, consisting of austenitizing, air quenching, and tempering. The samples were analysed in the as-built condition (AB), after quenching (Q) and following tempering cycles (HT) to observe the microstructural evolution. The microstructure was investigated using optical and scanning electron microscopes, energy dispersive X-ray analysis, and X-ray diffraction analysis. Furthermore, the microstructural evolution was analysed with differential scanning calorimetry, while the mechanical response was evaluated through microhardness test. It was found that the AB samples exhibited a dendritic-cellular microstructure with tempered martensite laths. The thermal history of the AB samples was completely modified by the austenitizing treatment followed by quenching, resulting in a fully martensitic Q sample that did not display the typical dendritic-cellular microstructure of the L-DED process. The completion of the heat treatment with tempering cycles revealed the presence of Mo-rich carbides dispersed in a martensitic matrix. The HT samples exhibited a mean microhardness of 634 HV, remaining constant along the entire building direction from the substrate to the last deposited layer, indicating a homogeneous microstructure. This high value, similar to other hot work tool steels such as H13, makes W360 a very promising candidate for tool build and repair purposes.Graphical