Hot Working Research Articles

Ti–48Al–2Cr–2Nb alloys prepared by electron beam selective melting additive manufacturing: Microstructural and tensile properties

Here, an electron beam selective melting (EBM) technique was employed to shape Ti–48Al–2Cr–2Nb alloy to combat its intrinsic brittleness and insufficient hot workability. Through process optimization, high-density samples (4.2327 g/cm3) were produced. First, the mechanism of interaction between phase transformation and microstructural evolution of EBM-formed Ti–48Al–2Cr–2Nb alloy was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattering diffraction (EBSD). And then, the mechanism of interaction between tensile properties and microstructural evolution of EBM-formed Ti–48Al–2Cr–2Nb alloy was discussed. Based on the results, the microstructure consists of coarse equiaxed grains and fine lamellar grains, which gradually coarsen from upper to bottom. As the thickness of the layer increases from upper to bottom, the content of the B2 phase increases continuously, with a predominant component of TiAl and a small amount of Ti3Al and B2 phases. The majority of the γ-TiAl phase does not exhibit significant texture, while the α2-Ti3Al phase shows a texture of (0001) with 19.32 times the random intensity, and its c-axis is parallel to the deposition direction. Benefiting from its unique structure features, the maximum room temperature tensile strength of as-deposited Ti–48Al–2Nb–2Cr alloy reaches 854.6 MPa with an elongation of over 2%. And the maximum high-temperature tensile strength of EBM-formed Ti–48Al–2Nb–2Cr alloy reaches 707 MPa at 650 °C with an elongation over 3.5%. According to these results, the mechanical properties of our EBM Ti–48Al–2Cr–2Nb alloy are superior to those previously reported.

Hot deformation behavior and flow stress modeling of coarse-grain nickel-base GH4151 superalloy ingot materials in cogging

Due to the high deformation resistance and poor thermal ductility of the new cast GH4151 alloy ingots, cracks are easy to occur during cogging process. For clarifying the effects of deformation parameters on microstructural evolution and dynamic recrystallization (DRX) nucleation mechanisms. In this work, the causes of crack formation and extension were first investigated using SEM and EBSD. The study revealed that the reasons for crack formation and propagation are the MC carbides at the original grain boundaries, large-size γ′ phase, residual eutectic phases, and tiny pores near the grain boundaries. Subsequently, a series of hot compression tests were performed using a Thermecamastor-Z thermo-mechanical simulator at temperatures ranging from 1080 °C to 1160 °C and a strain rate range of 0.01–10 s−1. The constitutive equation of the Arrhenius model and the hot working map was established, determining activation energy(Q) of 1086.58 kJ·mol−1. Large-size γ′ is coherent with the matrix. For the γ+γ′ dual-phase region, heterogeneous strain-induced dynamic recrystallization (HDRX) occurs, and discontinuous dynamic recrystallization (DDRX) is the main nucleation mechanism for DRX. However, for γ single-phase region, DDRX plays a more significant role. Furthermore, the MC phase (>1 μm) has different crystal orientations with the γ matrix and acts as sites for recrystallization through particle-stimulated nucleation (PSN). Finally, a fine and uniform grain structure can be obtained in the temperature range of 1120–1135 °C and the strain rate range of 0.1 s−1 to 1 s−1.

State‐of‐the‐Art in the Control of Sulfides in Steels

Sulfides like MnS are common phases in resulfurized free‐cutting steels, and are required to be controlled during the hot working process due to its influence on machinability, mechanical, and physical properties of final products. This article extensively reviews published researches on sulfides in resulfurized free‐cutting steels. The formation mechanism and modification of MnS during steelmaking, casting, and heat treatment are discussed based on a number of relevant studies. Measures to control the morphology and number of sulfides are supplied, which are beneficial for the production of resulfurized free‐cutting steels with high quality. Thermodynamic calculation proves to be an effective method to predict and control sulfides.

Hot Working of an Fe-25Al-1.5Ta Alloy Produced by Laser Powder Bed Fusion

In the present work, hot working was used as a post-processing method for Fe-25Al-1.5Ta (at.%) alloy built using laser powder bed fusion (LPBF) to refine the undesirable columnar microstructure with heterogeneous grain sizes and strong textures in the build direction. The hot deformation behavior and workability were investigated using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted up to a true strain of 0.8 at 900 °C, 1000 °C, and 1100 °C with strain rates of 0.0013 s−1, 0.01 s−1, and 0.1 s−1. The constitutive equations were derived to describe the flow stress–strain behavior in relation to the Zener–Hollomon parameter. Processing maps based on a dynamic materials model were plotted to evaluate the hot workability and to determine the optimal processing window as well as the active deformation mechanisms. The microstructure of the deformed specimens was characterized by scanning electron microscopy equipped with an electron backscatter diffraction detector. The results indicated a high degree of hot workability of the LPBF builds without flow instabilities over the entire deformation range tested. The epitaxially elongated grains of the as-built alloys were significantly refined after deformation through dynamic softening processes, and the porosity was reduced due to compressive deformation. The current study revealed a well-suited parameter range of 1000–1080 °C/0.004–0.012 s−1 for the safe and efficient deformation of the LPBF-fabricated Fe-25Al-1.5Ta alloys. The effectiveness of the process combination of LPBF with subsequent hot forming could be verified with regard to microstructure refinement and porosity reduction.

Hot Work Permit at PT Arsitek Arupadatu Karawang

Hot work is a type of work with a high hazard because it has the potential to cause a fire and even an explosion. These events not only cause damage to assets but can also obliterate them. This research aims to find out the program, procedure, and implementation of hot work permit at PT Arsitek Arupadatu. The research method used is descriptive, which tries to describe the conditions currently occurring at PT Arsitek Arupadatu regarding hot work permits. This research was carried out on July 9 - August 9 2021 in the phase 3 development project (Expansion Factory) of PT Akashi Wahana Indonesia Karawang. Collecting data in this study using field observation methods, interviews and study of literature. Data were analyzed with qualitative methods. The data that has been collected is processed by comparing it with the Government Regulation number. 50 of 2012 (concerning the implementation of the Occupational Safety and Health Management System) and the 2019 edition of NFPA 51 B Standard (concerning Standards for fire prevention during welding, cutting and other hot work). The results of this study show that the program implemented at PT Arsitek Arupadatu regarding hot work permits is administrative checking. PT Arsitek Arupadatu has not documented procedures related to hot work. The hot work permit procedure is carried out based on routines that occur in the field, communication is only carried out using the oral method. The hot work permit at PT Arsitek Arupadatu has implemented PP No. 50 of 2012 concerning the application of Occupational Safety and Health Management System attachment II part 6.

Research on Hot Operation of a Petrochemical Plant Based on Compound Edge Operator

In the operation of petrochemical plants, safety operation is the top priority, especially for the control of fire operation. In this paper, based on the real hot work in petrochemical plants, based on the extraction methods of different edge operators, the compound analysis of different edge operators can be carried out to visually detect the hot work of petrochemical workers in petrochemical plants, and based on the neural network algorithm, the convolution operation of edge data is carried out, and the data is input into the hot work database to build the hot work database and identify the flame. Remind the hot operation, according to the size of the flame to make a preliminary judgment on whether the danger, combined with the characteristics of the petrochemical device itself to add smoke identification. This method is of great significance to improve the thermal safety monitoring level of petrochemical plant.

Characterization of hot workability of IN617B alloy using activation energy, Zener-Hollomon parameter and hot processing maps

In order to predict the hot workability of the material more accurately, this paper takes the hot deformation of IN617B as the example. The activation energy (Q) map, Zener-Hollomon parameter (Z) map, and hot processing map were established based on the hot compression tests conducted at 950–1200 °C and 0.01–5 s−1. It was found that the area with high power dissipation values (denoted by η) in the hot processing map did not match the complete dynamic recrystallization (DRX) region completely. However, the microstructure corresponding to the high η area and low Z and Q area exhibited higher DRX. Therefore, the optimal hot processing region for this alloy was determined to be 1200 °C/0.1 s−1/0.8. Under this parameter, the DRX mechanism of IN617B alloy was dominated by discontinuous dynamic recrystallization (DDRX), supplemented by small amounts of continuous dynamic recrystallization (CDRX) and twinning dynamic recrystallization (TDRX).

Evolutions of the microstructures and mechanical properties of TC18 titanium alloy processed by hot-rolling in β single-phase region

In this study, hot rolling treatment followed by water quenching was conducted on a TC18 titanium alloy in β single-phase region with varying reductions. Experimental evidences from X-ray diffraction and transmission electron microscopy indicate the formation of α phase, induced by sufficient stress and assisted by ω phase. In addition, the existence of α" phase and diffuse streaks were also observed during the hot working processing. Furthermore, dynamic recrystallization (DRX) including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) was proved to exist in the hot rolling process. During the whole DRX process, with increasing the deformation degree, recrystallized grains nucleated preferentially at high-energy areas such as grain boundaries and shear bands, then accumulated and grew until achieving a complete recrystallization state. It should be noted that DDRX mainly occurred at the grain boundaries, while CDRX grains nucleated within the shear bands. The elongation gradually decreased and tensile strength gradually increased with the increment of the deformation degree.

Physical constitutive modelling of hot deformation of titanium matrix composites

Second-phase particles have complex effects on the micro- and macro-deformation behaviours of titanium matrix composites (TMCs). Therefore, it is difficult to accurately predict the microstructure evolution and flow stress during their hot working. To address this issue, this paper presents a physical unified constitutive model for TMCs. In the model, the dislocation evolution is modelled by considering the geometrically necessary dislocations introduced by the mismatches of the elastic modulus and thermal expansion coefficient between the second-phase particles and matrix material, and the dynamic recrystallization (DRX) is modelled by considering the role of second-phase particles in promoting DRX grain nucleation and inhibiting DRX grain growth. Subsequently, the constitutive equation is developed considering the contributions of thermal activation stress, hardening by dislocation multiplication, DRX softening, second-phase particles dispersion strengthening, and Hall–Petch strengthening. The developed unified constitutive model is used to quantitatively investigate the effects of second-phase particles on the flow behaviour and microstructure evolution during the hot working of the (TiC+TiB)/Ti–6Al–4V alloy. This study is of great significance for optimising the hot-working parameters of TMCs.

Flow stress and dynamic recrystallization behavior and modeling of GH4738 superalloy during hot compression

GH4738 superalloy is a key material for gas turbine engines, yet its relatively poor thermoplasticity and narrow temperature range for hot working deteriorate grain structure uniformity and thereafter service performance. Employing hot compression experiments and finite element analysis (FEA), the present study examined the thermoplasticity of the GH4738 alloy and proposed a fast approach to establishing its dynamic recrystallization (DRX) model. The hot working conditions were considered in the 1000–1160 °C temperature range under strain rates of 2–26 s−1 up to a true compressive strain of 0.69. Friction- and temperature-corrected stress-strain curves were obtained, based on which the efficiency of power dissipation and constitutive equations were constructed. It reveals that DRX is the dominant softening mechanism in the GH4738 alloy, where the sensitivity of flow softening positively correlates with lower temperatures and higher strain rates. The appropriate hot working condition for the alloy is temperatures around 1040–1080 °C and a strain rate larger than 8 s−1. The final grain sizes (d) and fractions of DRX (Xdyn) were minimized using the stochastic gradient descent algorithm based on 120 sets of data within the framework of the Avrami equation. It is shown that the formulated model and its integration into the FEA not only yield satisfactory agreement with the experiment but effectively avoid the complexity involved in the traditional method. The study provides key inputs for predicting the flow behavior and grain structure of the GH4738 superalloy, which shall be critical for process development and optimization of industrial manufacturing processes.

Deformation behavior and microstructure evolution of TZM alloy with 1.0 wt%ZrO2 under high temperature compression

The hot deformation behavior of TZM-1.0 wt% ZrO2 alloy in the temperature range of 1000–1600 °C and strain rate range of 0.005–1 s−1 was studied by hot compression method. The constitutive equation and hot working diagram were established, and the microstructure evolution was emphatically analyzed by SEM and EBSD. The results indicate that the flow stress decreases with the increase of temperature and the decrease of strain rate, and ZrO2 particles can improve the stability of TZM alloy in rate-control during hot deformation. The constitutive equation accurately predicted the correlation coefficient as high as 0.9685, calculated the average activation energy Q = 426 kJ mol−1, and obtained the best process parameters of 1150 °C–1250 °C /0.01–0.05 s−1 under 0.7 strain. The unstable zone was mainly composed of a small number of coarse grains and a large number of fine grains. The main reason for flow instability was the disharmonious deformation between coarse and fine grains during compression. The optimum hot working zone consists of more uniform equiaxed grains. However, EBSD observed that at a strain rate of 1 s−1, the recrystallization fraction at 1600 °C was lower than 1200 °C, and the dynamic recrystallization (DRX) and texture evolution trends at 1200 °C and 1600 °C were completely different. The abnormal changes in recrystallization fraction and texture evolution at 1600 °C were due to the competition between deformed grain growth and DRX on energy storage consumption, and the effect of deformed grain growth on energy storage consumption was greater than that of DRX. At 1600 °C/1 s−1, the growth of deformed grains was dominant, exhibiting strong texture components in the [001] direction, with〈100〉fibers as the main component and the highest peak texture strength. As the strain rate decreases, DRX dominates and weakens the texture strength, resulting in a significant decrease in<100>fibers.

Dynamic competition between coarsening mechanisms of Ti2Cu phase during thermal cycling

The dynamic competition between the coarsening mechanisms activates various coarsening behavior of the precipitate in multi-phase metallic materials, leading to different mechanical performances of alloys. In this work, the morphological evolution and coarsening kinetic of Ti2Cu phase in Ti–14Cu alloy were investigated comprehensively during thermal cycling at 200–600 °C. Our results suggest that the coarsening kinetic showed a gradual transition from the Lifshitz-Slyozov-Wagner (LSW) mechanism to the trans-interface diffusion-controlled (TIDC) mechanism. Ti2Cu phases precipitated at the triple junctions of α-Ti matrix by discontinuous precipitation under the control of LSW mechanism at lower temperatures (200–400 °C), and grew into lamellae along the high-energy grain boundaries. While the low-angle grain boundaries within Ti2Cu phase accelerated solute atom diffusion during the coarsening governed by TIDC mechanism at higher temperatures (400–600 °C), which leads to the boundary splitting of lamellae. In addition, it was also found that the blocky Ti2Cu phase improved the yield strength of the alloy as its high solid solution strengthening. This work provides a clear understanding for the coarsening of Ti2Cu phase, it could provide theoretical evidence for the hot working process design to improve the damage tolerance of Ti–Cu alloys.

Development of a Laboratory-Scale Test Methodology for Performance Evaluation of Lubricants for Hot Stamping of an Aluminium Alloy

In hot stamping of aluminium, the need for efficient methods to evaluate, compare, and rank lubricants based on their tribological performance is critical in the early stages of selection. Pilot and simulative testing can be costly, time-consuming, and complex, making it inefficient for initial benchmarking. This work aims to develop a test methodology to assess lubricant performance for hot stamping under key operating conditions without fully simulating the forming process. The proposed method distinguishes the impact of temperature on lubricant degradation, friction, wear response, and cleanability. The tests utilised a conventional hot work tool steel and a 6010S aluminium alloy with two commercially available lubricants: a polymeric lubricant and a lubricant containing graphite. The tribological tests involved a reciprocating, sliding flat-on-flat configuration at two temperatures (100 °C and 300 °C). The methodology showed that the graphite-containing lubricant exhibited over a four times lower friction coefficient than the polymer-based lubricant at 10 wt.% concentration and 300 °C. At 100 °C, both lubricants provide lubrication and can be cleaned, but increasing temperature led to a significant decline of both aspects. The observed temperature range where the lubricants degrade was between 120 °C and 170 °C.

Prediction of Grain Size in a High Cobalt Nickel-Based Superalloy.

With the advancement in computational approaches and experimental, simulation, and modeling tools in recent decades, a trial-and-validation method is attracting more attention in the materials community. The development of powder metallurgy Ni-based superalloys is a vivid example that relies on simulation and experiments to produce desired microstructure and properties in a tightly controlled manner. In this research, we show an integrated approach to predicting the grain size of industrial forgings starting from lab-scale cylindrical compression by employing modeling and experimental validation. (a) Cylindrical compression tests to obtain accurate flow stress data and the hot working processing window; (b) double-cone tests of laboratory scale validation; (c) sub-scale forgings for further validation under production conditions; and (d) application and validation on full-scale industrial forgings. The procedure uses modeling and simulation to predict metal flow, strain, strain rate, temperature, and the resulting grain size as a function of thermo-mechanical processing conditions. The models are calibrated with experimental data until the accuracy of the modeling predictions is at an acceptable level, which is defined as the accuracy at which the results can be used to design and evaluate industrial forgings.

Hot deformation behaviors and dynamic softening mechanism of 6%Si high-silicon austenitic stainless steel

The hot deformation behaviors and softening mechanism of 6%Si high-silicon austenitic stainless steel were investigated under deformation conditions of 1000–1200 °C/0.01–10 s−1. The constitutive equation was established based on the stress-strain curves, and the processing maps were drawn based on the Dynamic Material Model (DMM) at different strain levels. The results show that the activation energy(Q) of hot deformation is 368.555 kJ/mol. The peak region of the hot processing maps is 1130–1170 °C/0.01–0.03 s−1 at the strain of 0.7, the η value is 0.47, indicating that the best hot workability can be achieved in this region. At high strain rates (1000–1200 °C/0.66–10 s−1), the material is easily destabilized, while in the non-destabilized zone, η values are greater than 0.3, excluding the processing danger zone, and a better microstructure can be obtained. The accuracy of the processing maps established in this paper was verified by combining the microstructural morphology of different regions with the processing maps. Under the deformation conditions of 1200 °C/0.01 s−1, the χ phase and a small amount of δ ferrite are precipitated. The second phases induce the occurrence of a fracture along the grain while refining the grain size. Therefore, processing should be avoided in the range of second-phase precipitation. Crystallographic information analyses showed that the softening mechanism of high-silicon austenitic stainless steel is mainly discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) occurs in the softening mechanism between 1100 and 1150 °C.

Statistical investigation on the characteristics of hazardous chemical accidents in special work in China from 2008 to 2021

AbstractSpecial work involves hot work, confined space, blinding‐pipeline operation with stop plate, work at height, lifting work, temporary electricity, excavation work, work for road breaking, and other work, which may cause harm or damage to the operators themselves, surrounding buildings, equipment, and facilities. In this article, we conducted a statistical investigation on 154 large and above hazardous chemical accidents that occurred between 2008 and 2021 in China, and found that there were 58 accidents that occurred in special work alone, accounting for 37.7% of the total number of accidents. However, at present, no statistical analysis has been conducted on the characteristics of special work accidents in China. Therefore, this paper analyzes the special work accidents in terms of six aspects: categories of special work, industry distribution, enterprise scales, provincial location distribution, time‐volatility characteristics, and accident causes. Moreover, this article puts forward countermeasures and suggestions, aiming to provide useful information for the prevention of special work accidents in China.

Microstructural evolution of cast super austenitic stainless steel during hot compression

In the present paper, the effect of strain on the microstructure evolution of 7Mo-0.42N contained cast super austenitic stainless steel (SASS) during compression deformation at 1200 °C was systematically studied to optimize the hot working process. The dynamic recrystallization (DRX) grains size, recrystallization mechanism, annealing twin characteristics, and dislocation evolution during high-temperature deformation at varied strains were examined. Results show that the recrystallization behavior of the SASS during high-temperature compression can be divided into three stages. In stage I, the parent grain boundaries were gradually replaced by recrystallized grains, and observed both cyclic grain refinement and coarsening of grains. In stage II, the recrystallized grains elongated into the parent grain interior from the boundaries until the parent grain was completely covered. Meanwhile, the DRX and abnormal grain growth occurred simultaneously and developed rapidly at this stage. At stage III, the recrystallized grains abnormally grew to ∼76 μm and was deformed again because of the increased strain. The nucleation mechanism also changed during deformation. The discontinuous dynamic recrystallization (DDRX) dominated at stage I and II (ε = 0.1–0.6) with relatively low deformation strain. While in the high strain range of stage III (ε = 0.7–1.0), the continuous dynamic recrystallization (CDRX) took over. These quantitative statistics and analyses of data were carried out in terms of recrystallization grain size and nucleation mechanism under different strain variables, providing experimental basis and theoretical guidance for the production of SASS.

Evolution Behavior and Fracture Criterion of Carbides in D2 Cold‐Work Die Steel During Hot Working Process

Investigating the fracture mechanisms of carbides is of paramount importance for optimizing hot working processes in die steels. This work establishes a comprehensive criterion equation to predict the behavior of carbide fracture in D2 cold‐work die steel during hot working process. High‐temperature laser confocal microscope is employed to prepare samples with varying solidification rates. Subsequently, these samples are subjected to a range of heating temperatures spanning from 1000 °C and 1100 °C. The samples are analyzed utilizing scanning electron microscopy energy spectrum analysis and X‐ray diffraction. The activation energy of M7C3 carbides is calculated through the utilization of kinetic equations and the Arrhenius law. Additionally, a criterion model for the fracture behavior of M7C3 carbides in D2 cold‐work die steel is established. The results reveal that thin hollow rod‐shaped carbide is easy to fracture. Moreover, the activation energy for phase transition of M7C3 carbides in D2 cold‐work die steels is determined to be 226.974 KJ mol−1. Furthermore, the fracture behavior of carbides in D2 cold‐work steel is found to be influenced by various factors such as heating temperature, deformation rate, and peak stress. Finally, the criterion model demonstrates substantial agreement with the experimental observations gathered, affirming its reliability and accuracy.

Hot Deformation Behavior and Dynamic Softening Mechanism in 7B50 Aluminum Alloy.

The hot deformation behavior and dynamic softening mechanism of 7B50 aluminum alloy were studied via isothermal compression experiments in the range of 320-460 °C/0.001-1.0 s-1. According to the flow curves obtained from the experiments, the flow behavior of this alloy was analyzed, and the Zener-Hollomon (Z) parameter equation was established. The hot processing maps of this alloy were developed based on the dynamic material model, and the optimal hot working region was determined to be 410-460 °C/0.01-0.001 s-1. The electron backscattered diffraction (EBSD) microstructure analysis of the deformed sample shows that the dynamic softening mechanism and microstructure evolution strongly depend on the Z parameter. Meanwhile, a correlation between the dynamic softening mechanism and the lnZ value was established. Dynamic recovery (DRV) was the only softening mechanism during isothermal compression with lnZ ≥ 20. Discontinuous dynamic recrystallization (DDRX) becomes the dominant dynamic recrystallization (DRX) mechanism under deformation conditions of 15 < lnZ < 20. Meanwhile, the size and percentage of DDRXed grains increased with decreasing lnZ values. The geometric dynamic recrystallization (GDRX) mechanism and continuous dynamic recrystallization (CDRX) mechanism coexist under deformation conditions with lnZ ≤ 15.

Hot Deformation Behavior and Dynamic Recrystallization of a Medium Carbon Cr–Mo Steel for Class 16.8 Bolts

AbstractThis study investigates the hot workability of medium carbon Cr–Mo steels for manufacturing ultra-high strength bolts. The main purpose of this research is to establish a constitutive equation and a kinetic model of dynamic recrystallization of the material for industrial applications. Hot torsion tests were conducted at temperatures of 1173, 1273, and 1373 K and strain rates of 0.1, 0.5, 1.0, and 2.0/s. Strain rate sensitivities and work-hardening coefficients of the material were calculated at various strain rates and temperatures using the Fields–Backofen equation. Results indicated that the material’s strain rate sensitivities and work-hardening coefficients generally increased with temperature. Stress–strain curves showed a general variation depending on the strain rates and the deformation temperatures, with higher strain rates and lower temperatures resulting in increased flow stresses. However, peak stresses were not clearly observed due to the presence of Nb in the material. A constitutive equation for flow stresses was derived, with a thermal activation energy for deformation of 238.57 kJ/mol. Zener–Hollomon parameter was used to analyze the relationship between peak strains and critical strains, finding that the critical strains being about 0.17 times the peak strains. The volume fractions of dynamic recrystallization were estimated using an Avrami form of the kinetic equation, and the Avrami constants $$k$$ k and $$m$$ m were 0.84 and 6.89, respectively. The kinetic model of dynamic recrystallization that we developed can be applied to arbitrary deformation conditions, enabling the optimization of the hot rolling process for this material. Graphic Abstract