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In this study, the DED-LB/M process of AISI H11 tool steel powder blends modified by adding WC nanoparticles (WC-np) in concentrations of 1, 2.5 and 5 wt.-% was the object of scientific investigations. For this, 30-layer cuboid specimens were manufactured. The overall scientific aim was to examine how the WC-np interact with the steel melt and in the end, influence the processability, microstructure and mechanical properties of produced specimens. The examinations were carried out on both as-built and thermally post-processed specimens. An advanced microstructural analysis (SEM, EDS, EBSD and XRD) revealed that due to the high solubility of WC-np in the molten steel, most of the WC-np appear to have dissolved during the ongoing laser process. Furthermore, the WC-np favor a stronger distortion and finer grain size of martensite in the manufactured specimens. An increase in hardness from about 650 HV1 for the H11 specimen to 780 HV1 for the one manufactured using the powder blend containing 5 wt.-% of WC-np was observed in as-built conditions. In the same way, the compression yield strength enhanced from 1839 MPA to 2188 MPA. The hardness and strength increasing effect of WC-np remained unchanged even after heat treatments similar to those used in industry. [ABSTRACT FROM AUTHOR]

In this investigation, the method of minimum quantity lubrication (MQL) is utilized in the procedure of finishing milling of AISI H11 steel instead of the conventional lubrication method. The variants are three three-level experimental cutting parameters, including V c -cutting speed, f z -feed per tooth, and a p -depth of cut. The responses are production rate (MRR, in mm3/min), cutting force ( F c , in N), and surface roughness ( R a , in μ m). The purpose of this study is to generate the mathematical regression models for the responses ( R a , F c , and MRR), and solve the multi-objective optimization problem to estimate the appropriate input parameters respecting the defined criteria for F c , R a , and MRR. Experimental research was conducted with an experimental matrix designed by Box–Behnken Design (BBD). The experimental runs were executed on a 5-axis CNC machine tool, model DMU50. The desirability function (DF) method is used to resolve the problem of multi-attribute optimization. The results show that the optimum process variables include V c = 2 1 0 m/min, f z = 0. 0 5 9 mm/tooth, a p = 0. 1 9 6 mm, corresponding to R a = 1. 8 1 9 μ m, F c = 1 5 2 , 3 2 6 N, and MRR = 1 2 9 9. 1 7 7 mm3/min. [ABSTRACT FROM AUTHOR]

Hot forming processes of complex parts with small cavities demand high-performance tools made of hardened steels. Their surface can be tribologically modified in order to control the material flow for improving the mold filling of functional elements. Surface structuring here offers great potential for adjusting the frictional properties and thus controlling the material flow in forming processes. In this study, high-feed milling (HFM) of surface structures in hot work tool steel (HWS) components is investigated. The process performance was determined by cutting force measurements and tool life tests. The achievable surface topography was measured and evaluated in terms of structure quality and roughness parameters, and friction properties were derived based on the results. In a hot ring compression test, the influence of certain structure variants on the material flow was analyzed. The results conclude that HFM is a suitable process for structuring HWS components with constant structure quality and low tool wear. In addition, a variety of structures showed significant influence on the hot ring compression test. This indicates a relevant potential of HFM for the modification of hardened tool surfaces to improve the performance of hot forming processes and increase the manufactural quality and productivity. [ABSTRACT FROM AUTHOR]

In this study, the DED-LB/M process of AISI H11 tool steel powder blends modified by adding WC nanoparticles (WC-np) in concentrations of 1, 2.5 and 5 wt.-% was the object of scientific investigations. For this, 30-layer cuboid specimens were manufactured. The overall scientific aim was to examine how the WC-np interact with the steel melt and in the end, influence the processability, microstructure and mechanical properties of produced specimens. The examinations were carried out on both as-built and thermally post-processed specimens. An advanced microstructural analysis (SEM, EDS, EBSD and XRD) revealed that due to the high solubility of WC-np in the molten steel, most of the WC-np appear to have dissolved during the ongoing laser process. Furthermore, the WC-np favor a stronger distortion and finer grain size of martensite in the manufactured specimens. An increase in hardness from about 650 HV1 for the H11 specimen to 780 HV1 for the one manufactured using the powder blend containing 5 wt.-% of WC-np was observed in as-built conditions. In the same way, the compression yield strength enhanced from 1839 MPA to 2188 MPA. The hardness and strength increasing effect of WC-np remained unchanged even after heat treatments similar to those used in industry.

• ANSYS static structural module is used to predict the contact stresses. • Bilayer coated steels exhibit higher load carrying capacity compared to monolayer. • Nitriding improves the not only load carrying capacity but also wear performance. • Model-based examinations are in agreement with the wear analysis. In this study, AlTiN (monolayer) and CrN/AlTiN (bilayer) coatings are deposited on the surface of conventional heat-treated AISI H11 steel which is then nitrided by cathodic arc physical vapor deposition (CAPVD). Structural analyses of the coatings reveal that homogeneous, continuous, and defect-free coatings are obtained with a good adhesion on the diffusion layer of the substrate material. Considering the surface hardness, the CrN/AlTiN coating (1718 HV 0.01) deposited on the surface of the heat-treated tool steel has a higher value than that of AlTiN coating (1658 HV 0.01), and this hardness value is increased even more (1932 HV 0.01) with the application of the nitriding process. With a contact model in which the ANSYS static structural module is operated, it is shown that CrN/AlTiN coating contributes to lower tensile stress distribution on the surface during indentation. Analysis has also revealed that bilayer coating, CrN/AlTiN, exhibits reduced deformation compared to monolayer coating, indicating enhanced mechanical strength under contact conditions. Additionally, nitriding is found to increase stress distribution, emphasizing its role in improving coating performance. It is determined that wear losses can be reduced by the high load carrying capacity provided by nitriding and the high surface hardness provided by CrN/AlTiN coating under dry friction test conditions performed against alumina as counterpart material at room temperature. [ABSTRACT FROM AUTHOR]

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In this experimental study, vibration, energy consumption, power consumption and surface roughness values that occur in the machining of AISI H11 tool steel under CO2, coolant and dry cutting conditions were investigated. The effects of different cutting parameters and cooling systems on machinability were investigated. Analysis of variance was done. Regression equations were obtained. Relationships between power consumption, vibration and surface roughness are explained with mathematical equations. Finally, the optimum CC were determined by the multiple optimization methods. According to the test results, while the instantaneous power consumption increases by increasing cutting parameters, energy consumption decreases as the processing time is shortened. Vibration value increases by increasing cutting parameters. The highest vibration value occurs in cutting with CO2. Compared to dry and CO2 cutting, the vibration is lowest in coolant cutting. The friction decreases with the coolant and the vibration value decreases. There is a similar relationship between vibration and surface roughness value. The most effective parameter on the surface roughness value is the feed rate. It was seen that the most suitable CC for the most efficient cutting, the lowest energy consumption, vibration and surface roughness value, under coolant cutting, 0.2 mm depth of cut, 175 m/min cutting speed and 0.119 mm/rev feed rate. With optimum CC, the vibration value was reduced by 5.18%, the surface roughness value by 37.12%, energy consumption by 36.19% and the machine efficiency was increased by 7.16%. [ABSTRACT FROM AUTHOR]

This study investigated the effects of the cryogenic treatment on cutting tool performance in the turning of AISI H11 steel. In the experiments, TiCN/Al2O3/TiN-coated tungsten carbide tools were used. Shallow cryogenic treatment was applied for 6 h at −80 °C (SCT6), deep cryogenic treatment at −196 °C for 6 h (DCT6), and deep cryogenic treatment at −196 °C for 24 h (DCT24). Turning tests were conducted at three cutting speeds (200, 240, and 280 m/min), three feed rates (0.15, 0.18 and 0.21 mm/rev), and a 0.6-mm depth of cut under dry cutting conditions. Experimental results showed that the cryogenic treatment increased the abrasion resistance of the cutting tool. The best cutting tool wear and surface roughness performance was obtained with the DCT24 tool. As a result of the tool life test, DCT24 tool wore 14.5% less than U tool. In terms of surface roughness, DCT24 tool improved up to 16.5% compared to the U tool. Moreover, it was determined that the cryogenic treatment provided an increase in the hardness of the cutting tools. The highest hardness increase also occurred in the DCT24 tool (10.87%). In addition, cryogenic treatment types were optimized for flank wear and surface roughness using the Taguchi method, and the effect levels of the cutting tools and cutting parameters were determined via analysis of variance. According to ANOVA results, for flank wear, the parameter having the most effect was the cutting speed, with an ratio of 56.811%, while for surface roughness it was the feed rate, with 95.827%.

Bu çalışmada, AISI H11 sıcak iş takım çeliğinin tornalanmasında kriyojenik işlemin kesici takım performansı üzerine etkileri araştırılmıştır. Deneylerde TiAlN+TiN kaplı tungsten karbür takımlar kullanılmıştır. Kesici takımlar üzerine 6 saat süre ile -80 °C’de sığ kriyojenik işlem (SCT6), 6 saat süre ile -196 °C’de derin kriyojenik işlem (DCT6) ve 24 saat süre ile -196 °C’de derin kriyojenik işlem (DCT24) uygulanmıştır. Tornalama deneyleri 0,6 mm kesme derinliği, 0,18 mm/dev ilerleme hızı ve 320, 360, 400 ve 440 m/dak olmak üzere dört farklı kesme hızında gerçekleştirilmiştir. Deneysel sonuçlar kriyojenik işlemin kesici takımın aşınma direncini artırdığını göstermiştir. En düşük kesici takım aşınması ve yüzey pürüzlülüğü değerleri DCT24 takımla elde edilmiştir. Yanak aşınmasında %13-28 oranlarda, yüzey pürüzlülüğünde ise %7-14 oranlarda iyileşmeler gözlenmiştir. Diğer yandan kriyojenik işlemin kesici takımların sertliğinde %4,4-8,7 oranlarda artış sağladığı tespit edilmiştir. En yüksek sertlik artışı da DCT24 takımda meydana gelmiştir.

This work investigates the influence of multi-step laser polishing on microstructural properties of the remelted surface layer of tool steel H11. Four different sets of process parameters were selected for laser polishing of initially annealed samples made from tool steel H11. In a sequential, multi-step process using continuous and pulsed laser radiation (Nd:YAG) a significant reduction of surface roughness was achieved.. The remelted layers were analyzed using roughness measurements, white light interferometry, X-ray diffractometry, electron backscatter diffraction, glow discharge emission spectroscopy, and nanoindentation hardness measurements. Laser polishing leads to a grain refinement and a significant increase in hardness. A minimal surface roughness of Ra = 50 nm was achieved in an Argon process atmosphere with an additional 6 vol% CO2. In particular the carbon concentration was significantly reduced within the remelted layer. The lower carbon concentration is correlated with a decreased maximal surface hardness down to 366 HV. High residual tensile stresses of up to 926 MPa can be introduced by laser polishing. Overall, high temperature gradients and, in particular, decarburization due to carbon diffusion processes were identified to be the major driving force for significant changes in surface roughness and microstructural properties.

Tool & Die is one of the important department in the manufacturing industries that takes care of proper designing and fabrication of tools and dies required for the production. In this sector, tool steels are used as the primary source of materials. These tool steels belongs to the family of carbon and alloy steels. Mostly used alloying elements are chromium, tungsten, molybdenum and vanadium and are heat-treated. The objective of the work involves machinability study of AISI H11 chromium hot-worked steel extensively used for tool & die making. It deals with the analysis of machining parameters and its influences on the responses considered. Here the controlling parameters considered are cutting speed (C _s ), feed rate (F _r ) and depth of cut (D _c ) and responses as surface roughness (R _a ) and material removal rate (M _rr ). Each controlling parameters are assigned with 3 levels and experimental runs were executed as per taguchi robust design. To determine multi-objective optimal solution, grey relational analysis (GRA) is employed. GRA is used as it provides a feasible platform for converting a multi-objective function into single-objective function. The experimental runs were performed as per L27 orthogonal array sequence in CNC end-milling. The responses recorded are then analyzed using analysis of variance (ANOVA) and optimal solutions are validated through confirmatory runs. The entire machinability study of AISI H11 is performed in two conditions involving rough machining and finish machining. This has been addressed based on the machining scenario followed in industries taking up job orders. The confirmatory results for rough machining recorded was found to be 0.7871 microns against predicted value of 0.7654 microns resulting with a deviation error of 2.88%. Similarly, for finish machining, confirmatory runs recorded 0.8579 microns against predicted value of 0.8357 microns resulting with a deviation error of 2.66%. The deviation level indicated above between predicted and observed values are minimum, which shows the reliability of the optimal solutions arrived in.

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

Abstract The duplex treatment, consisting of plasma nitriding and the deposition of a DLC coating, was carried out on the hot-work tool steel AISI H11. The coating structure, composed of Cr-based interlayers and a hydrogenated carbon layer, was sputtered on non-nitrided, nitrided, as well as nitrided-repolished AISI H11 steel with an either annealed or quenched and tempered base condition to examine the influence of the pretreatment condition on the tribo-mechanical properties of the DLC coating. Besides the graded hardness profile, plasma nitriding leads to a roughness increase, which affects the microstructure as well as the mechanical properties of the DLC coating. The rougher surface favors a film growth of a carbon layer with larger cluster-like structures. As a result, these DLC coatings exhibit hardness values below 22 GPa, while the coating systems sputtered on substrates with smoother surfaces reach values of approximately 26 GPa and showed a good adherence. The heat treatment condition influences the load-bearing capacity of the nitrided substrate as the higher core hardness enhances the mechanical support of the coating and reaches the highest adhesion class HF1 in the Rockwell C tests. Due to the lower film adhesion and the low hardness of the DLC coatings sputtered on nitrided non-repolished AISI H11, high coefficients of frictions and wear coefficients of up to 0.59 and 3.19 ∗ 10−5 mm3/N∗m were determined in tribometer tests against WC/Co counterparts. In contrast, the nitrided repolished steel exhibits a low coefficient of friction of 0.12 as well as a low wear coefficient of 0.06 ∗ 10−5 mm3/N∗m. Therefore, a repolishing of the nitrided AISI H11 with quenched and tempered base condition ensures the highest load-bearing capability of the substrate as well as an improved friction and wear behavior of the DLC coating. Highlights • Well-adjusted pretreatments enhance the tribo-mechanical properties. • The surface condition of the nitrided AISI H11 has an impact on the DLC coating. • A surface finish of the nitrided steel improves the tribo-mechanical properties. • The core hardness of the nitrided AISI H11 affects the load-bearing capacity. [ABSTRACT FROM AUTHOR]

Abstract: Hot extrusion is one of the most commonly used manufacturing methods for metal plastic deformation, and the consumption of extrusion tooling is considerably high due to its fatigue damage under cyclic serving condition. Hot‐work tool steel AISI H11 is one of these typical materials employed in extrusion tooling. This work is dedicated to calculating the stress/strain state of AISI H11 and predicting its lifetime at high temperature 500°C by building a unified constitutive model coupled with Lemaitre's damage law. Tensile tests and strain/stress reversed cycling tests have been conducted at 500°C to investigate mechanical properties and damage evolution. A unified constitutive model with Armstrong‐Fredrick/Ohno‐Wang kinematic hardening rule and a new proposed isotropic hardening rule is built; Lemaitre's damage law is employed as well. Parameters are determined based on tests and are temperature dependent. Finite element simulation of the deformation behaviour and fatigue lifetime is implemented into commercial software ABAQUS Standard v6.14‐2 with user material subroutine to validate the proposed method. The comparison shows good agreement with experimental results, and this part of work is essential and crucial to subsequent structure analysis. [ABSTRACT FROM AUTHOR]

In the present research, an innovative testing method, specifically developed to characterize the tool steels under creep-fatigue conditions, was carried out on a TQ1 (X36CrMoV5-2) hot-work tool steel in cooperation with Constellium R&D center. The experimental campaign consisted of different testing conditions, and most of the specimens were nitrided to account for the specific surface state of the tools. Tests were performed on a 100 kN MTS fatigue machine equipped with a heating furnace. A creep-fatigue loading type was applied to the specimens, i.e., a cyclic load with a dwell time, in order to properly reproduce the conditions acting on extrusion tools and dies. Under a constant temperature of 520 °C, the effects of four different load levels and two different values of dwell times were evaluated. In addition, selected test conditions were replicated with specimens not nitrided with the aim to evaluate and quantify the influence of the superficial treatment. Final results were presented in terms of fatigue diagram of the TQ1 steel and compared to the performances of the H11 tool steel tested in a previous research by the same authors. [ABSTRACT FROM AUTHOR]

The surface finish of machined parts is known to have considerable effect on some properties such as wear resistance and fatigue strength. Thus, the quality of the surface has a significant importance for evaluating the productivity of machine tools, and mechanical parts. In this paper, the effects of cutting speed, feed rate, depth of cut and workpiece hardness on surface roughness, cutting pressure, and cutting power in the hard turning of hardened AISI H11 (X38CrMoV5-1) using CBN7020 tools were experimentally investigated. The response surface methodology (RSM) and analysis of variance (ANOVA) were used to check the validity of quadratic regression model and to determine the significant parameter affecting the output responses. The mathematical models for output parameters have been developed using Box-Behnken design with 29 runs. The results indicated that the surface roughness parameters are influenced principally by the feed rate and workpiece hardness while the depth of cut has no significant influence. In addition, cutting speed is the main influencing factor on the cutting power. Also, the results show that the tool life is influenced principally by the cutting speed and in the second level by the feed rate. [ABSTRACT FROM AUTHOR]

The aim of this experimental study is to evaluate the tool life of each cutting material used in dry hard turning of AISI H11, treated at 50 HRC. This steel is intended for hot work, is free from tungsten on CrMoV basis, insensitive to temperature changes and has a high wear resistance. It is employed for the manufacture of the moulds and inserts, module matrices of car doors and helicopter rotor blades. The tests of straight turning were carried out using the following cutting materials: carbides (H13A and GC3015), ceramics (mixed CC650 and reinforced CC670) and cermets (CT5015 and GC 1525). Experimental results enable us to study the influence of machining time on flank wear VB of these cutting materials and to determine their lifespan for this cutting regime (depth of cut ap = 0.15 ram, feed rate f= 0.08 mm/rev and cutting speed Vc = 120 m/min). It arises that mixed ceramic (insert CC650) is more resistant to wear than cutting materials. Its tool life is 49 min and consequently, it is the most powerful. [ABSTRACT FROM AUTHOR]

This experimental study is conducted to determine statistical models of cutting forces in hard turning of AISI H11 hot work tool steel (∼ 50 HRC). This steel is free from tungsten on Cr-Mo-V basis, insensitive to temperature changes and having a high wear resistance. It is employed for the manufacture of highly stressed diecasting moulds and inserts with high tool life expectancy, plastic moulds subject to high stress, helicopter rotor blades and forging dies. The workpiece is machined by a mixed ceramic tool (insert CC650 of chemical composition 70%AlO+30%TiC) under dry conditions. Based on 3 full factorial design, a total of 27 tests were carried out. The range of each parameter is set at three different levels, namely low, medium and high. Mathematical models were deduced by software Minitab (multiple linear regression and response surface methodology) in order to express the influence degree of the main cutting variables such as cutting speed, feed rate and depth of cut on cutting force components. These models would be helpful in selecting cutting variables for optimization of hard cutting process. The results indicate that the depth of cut is the dominant factor affecting cutting force components. The feed rate influences tangential cutting force more than radial and axial forces. The cutting speed affects radial force more than tangential and axial forces. [ABSTRACT FROM AUTHOR]

Hot work tool steels (HWS) are widely used for high performance components as dies and molds in hot forging processes, where extreme process-related mechanical and thermal loads limit tool life. With the functionalizing and modification of tool surfaces with tailored surfaces, a promising approach is given to provide material flow control resulting in the efficient die filling of cavities while reducing the process forces. In terms of fatigue properties, the influence of surface modifications on surface integrity is insufficiently studied. Therefore, the potential of the machining processes of high-feed milling, micromilling and grinding with regard to the implications on the fatigue strength of components made of HWS (AISI H11) hardened to 50 ± 1 HRC was investigated. For this purpose, the machined surfaces were characterized in terms of surface topography and residual stress state to determine the surface integrity. In order to analyze the resulting fatigue behavior as a result of the machining processes, a rotating bending test was performed. The fracture surfaces were investigated using fractographic analysis to define the initiation area and to identify the source of failure. The investigations showed a significant influence of the machining-induced surface integrity and, in particular, the induced residual stress state on the fatigue properties of components made of HWS.

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

This work investigates the influence of multi-step laser polishing on microstructural properties of the remelted surface layer of tool steel H11. Four different sets of process parameters were selected for laser polishing of initially annealed samples made from tool steel H11. In a sequential, multi-step process using continuous and pulsed laser radiation (Nd:YAG) a significant reduction of surface roughness was achieved.. The remelted layers were analyzed using roughness measurements, white light interferometry, X-ray diffractometry, electron backscatter diffraction, glow discharge emission spectroscopy, and nanoindentation hardness measurements. Laser polishing leads to a grain refinement and a significant increase in hardness. A minimal surface roughness of Ra = 50 nm was achieved in an Argon process atmosphere with an additional 6 vol% CO 2. In particular the carbon concentration was significantly reduced within the remelted layer. The lower carbon concentration is correlated with a decreased maximal surface hardness down to 366 HV. High residual tensile stresses of up to 926 MPa can be introduced by laser polishing. Overall, high temperature gradients and, in particular, decarburization due to carbon diffusion processes were identified to be the major driving force for significant changes in surface roughness and microstructural properties. Unlabelled Image • Multi-step laser polishing of tool steel H11 leads to a minimal surface roughness of Ra = 0.05 μm • High temperature gradients, small interaction times, and multiple tempering cycles result in a fine-grained microstructure • Each laser polishing step results in a characteristic decarburization of the surface boundary layer (carbon fingerprint) • Decarburization due to CO 2 and O 2 correlates with less martensite formation, lower hardness and smaller surface roughness • Laser polishing can introduce high residual tensile stresses of up to 926 MPa [ABSTRACT FROM AUTHOR]