HRC Hardness Research Articles

Investigation of the Durability of the Regulating Junction of the Christmas Tree Throttle

Objective: In the research work, the issue of ensuring the stability of its details wasconsidered by studying the voltage distribution mode in the throttle control node. SolidWorks software was used to perform force analysis of the improved throttle. Theoretical Framework: The research draws upon theories and simulations related to regulatory constructions and wear prevention. Methodology: In the research work, the performance criteria of the improved throttle have been studied. The force analysis of the proposed throttle's regulating node was carried out using modern methods and Solidworks simulations. Results and Discussion: The analysis of the wear occurring at the tip of the improved throttle shows that the wear resistance of this equipment is ensured, and the wear of the saddle-cutter pair, which has a hardness of HRC=55-66, amounts to 0.040...0.050 mm after 500 forward-backward cycles intended for the throttle. This is also twice smaller than the allowable limit. The processing of the conducted force analyses has proven that the performance of the improved throttle is ensured. Research Implications: The structural force analysis of the improved throttle shows that its performance is ensured. An analytical expression has been obtained to determine the maximum value of the radial stresses occurring at the tip of the throttle. It has been found that the safety factor for bending stress in the central zone of the throttle tip is equal to 2.5. Originality/Value: Based on simulations and analytical calculations, the radial stresses generated at the tip of the nozzle were investigated, and the longevity of the improved nozzle was enhanced based on new approaches.

Mechanical Properties and Wear Resistance of Biodegradable ZnMgY Alloy

Biodegradable metallic materials are gaining attention for medical applications in short-term implants (15–500 days) because of their good mechanical properties, biocompatibility, and generalized corrosion. Most medical applications involve implant wear processes, particularly for bone fractures. Parallelepipedic specimens (dimensions 50 mm × 10 mm × 3 mm) were obtained by cutting the hot-rolled material processed from cast ingots of ZnMgY. To test the tribological performance of these stationary specimens, they were placed at the upper point of the machine’s tribological contact. The rotating lower disk of the AMSLER machine (AMSLER & Co., Schaffhouse, Switzerland) is manufactured from AISI 52100 bearing steel with a 62–65 HRC hardness and a diameter of 59 mm both radially and axially. Frictional torque is the parameter that is measured. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to analyze the worn areas. The material behavior in the normal and wear states upon immersion in simulated body fluid (SBF) was evaluated.

General investigations on the heat treatment and thermal fatigue behavior of an experimental hot work tool steel tailored for laser powder bed fusion

An experimental hot work tool steel with a leaner chemistry compared to the standard AISI-H13 grade, aimed at enhanced processability, was gas atomized and processed using laser powder bed fusion (L-PBF) to >99.8 % relative density. The lower carbon content (∼0.25 wt% vs. ∼0.4 wt% in H13) resulted in a softer as-built (AB), and quenched martensite (∼485 HV1 vs. 625 HV1 in H13), higher martensite-start temperature (∼360 °C vs. 280–320 °C), and about ∼18 % reduction in dilatation, ascribed to the volume expansive martensitic transformation. Charpy V-notch impact toughness in AB condition (>30 J) was higher than those reported for AB H13. These features account for the improved L-PBF processability. The tempering response in comparison with a wrought H13, was characterized by a larger precipitation of thermally stable Mo- and V-rich secondary hardening alloy carbides at the expense of the easy-to-coarsen Cr-rich ones, attributed to the higher Mo and lower Cr content in experimental alloy. The combination of lower C- and V-contents in experimental alloy, reduced the driving force for the precipitation of coarse vanadium rich carbides during austenitization, as confirmed by electron diffraction spectroscopy (EDS) and synchrotron X ray diffraction. This led to a stronger fine secondary hardening alloy carbide precipitation during tempering, and enhanced temper resistance. As elaborated by isochronal tempering, as well as tempering curves, reduction of the elements Si, and Cr shifted the secondary hardness peak to higher tempering temperatures. Consequently, tempering, and thermomechanical softening resistance was significantly enhanced in the new steel with a maximum hardness of ∼550 HV1 in over-tempered condition (i.e., slightly above secondary hardness peak). Thermal fatigue (TF) tests revealed a denser and finer TF crack network with a larger oxidation in experimental steel. Thereby, the TF crack penetration depth scaling with the local plastic yielding of the matrix was evidently shorter in the new steel compared with wrought H13, thanks to significantly improved hot hardness, thermal conductivity, and enhanced thermomechanical softening resistance. Finally, a proof of concept is demonstrated by processing a relatively large injection molding die (150 mm × 110 mm × 30 mm) with promising tensile and impact toughness properties after direct double tempering to 51 HRC, and 45 HRC hardness levels.

Development of the hardness mathematical model of Ti-alloyed iron for cast parts used in conditions of intensive abrasive friction

The object of research is wear-resistant cast iron, intended for cast parts that work under conditions of intense abrasive friction during operation. Examples of such parts can be mixer blades of various functional purposes, the operational properties of which include stability, which depends on the hardness, determined on the HRC scale. To give such cast parts wear-resistant properties, the cast iron from which they are made is alloyed with elements that contribute to the formation of carbides of different composition: W, V, Mo, Ti, etc. The main problem that prevents the purposeful selection of materials is incomplete knowledge about the effect of chemical composition on properties, in particular, wear resistance, which prevents a justified selection criterion. Using regression analysis methods, a mathematical model was obtained, including a regression equation of the form HRC=f(C; Ceq; Ti), which relates the content of carbon, titanium and carbon equivalent in cast iron and hardness. The resulting model allows for purposeful selection of the chemical composition, which ensures a given value of HRC, on which wear resistance depends. Optimization of the chemical composition, performed according to this model, made it possible to determine that the chemical composition, which provides the maximum hardness of HRC=49, is outside the planning area: C=3.54 %, Ceq=3.95 %, Ti=3.56 %. It was established that the same value of hardness can be obtained inside the considered planning area, which has an arbitrary appearance, provided with available conditions of a passive experiment. According to the available experimental data, the values of the input variables equal to C=3.34 %, Ceq=3.727 %, Ti=0.73 % ensure obtaining hardness at the level of HRC=49. Such alternative options regarding composition and properties may indicate that the HRC=f(C; Ceq; Ti) response surface has a complex appearance that requires additional research.

POSSIBILITY OF INCREASING THE LIFETIME OF THE CHOPPING KNIFE BY APPLICATION OF PVD COATING EVALUATED IN LABORATORY CONDITIONS

A wood is a heterogeneous material and its elements adversely affect the process of its processing. This also significantly affects the service life of tools during its processing. The aim of the contribution was, based on laboratory tests, to assess the suitability of the application of the selected coating on the chopping knife. After the basic analysis of the chopping knife, the CROSAL+ (AlCrN) coating was designed, which is an improved variant of the successfully used first generation CROSAL coating. In the experiment, samples from two knives made of tool steel X48CrMoV8-1-1 were analyzed. One sample was uncoated and the other coated. Based on the results of laboratory analyzes and tests, namely basic macroscopic and microscopic analysis of samples from tools, with semi-quantitative EDX analysis to determine the presence and content of individual chemical elements on the base material - substrate. Furthermore, the samples were tested for resistance to abrasive wear according to GOST 23.208-79. Relative resistance to abrasive wear ψabr was assessed. and hardness coefficient KT. HV and HRC hardness measurements were also carried out to determine the difference in hardness between uncoated and coated knife samples. In conclusion, it can be concluded that from the analysis and results of the measurements, the given coating for the process of processing wood by chopping can ensure the extension of the life of the tool and ensure the sufficient quality of the produced chips.

Application of modern fractal formalism methods for researching the influence of ion-plasma coatings on assessing the wear resistance of volume hydraulic drive components

Problem. The studies on preparation and application of Ti–Cr–N coating on the surface of the 38Х2МЮА steel have been conducted. Goal. The purpose of the work is to investigate the feasibility of using a fractal approach to evaluate the effect of plasma coatings to increase the wear resistance of parts of a volumetric hydraulic drive. Methodology. Cr was chosen as the material for ion bombardment, since it makes it possible to reduce the temperature of the substrate before applying ­the coating and avoid the risk of surface softening. After heat treatment of the 38Х2МЮА steel, its hardness ranges from 40 to 45 HRC. The thickness of the applied coating varied from 3 to 6 microns, which corresponds to good adhesion, a smaller thickness does not significantly affect the properties of the product, and in the case of a thickness of more than 6 microns, peeling is observed due to poor adhesion to the substrate. Results. Five series of experiments with HRC hardness values of 42, 43, 44, 45, 46 were performed. Fractal analysis was used to assess the effect of the Ti–Cr–N coating structure of the working surface of volumetric hydraulic drive parts on its wear indicators. The relative error in calculating wear indicators for fractal models ranged from 0.04 to 8.96. The correlation coefficient of Y(X2) model without using indicators of the surface fractal dimension was only 0.73. Experiments proved that the lowest wear value of 2.11 g*10-3 was obtained at a coating thickness of 6 µm and hardness of 45 HRC. At the same time, a roughness coefficient was 0.16. To confirm this hypothesis, an experiment to determine wear resistance at a hardness of 45, roughness of 0.16, and coating thickness of 6 was conducted. Conclusions. Results of the studies of wear indicators of Ti–Cr–N coated samples at the substrate material hardness values from 42 to 46 HRC, surface roughness and coating thickness showed feasibility of the fractal structure estimation approach.

Effect of austenitizing temperature on isothermal quenching microstructure and mechanical properties of 52100 bearing steel

In general, isothermal quenching heat treatment in salt bath can improve the toughness but sacrifice the strength and hardness of 52100 bearing steel. Many previous studies focusing on the isothermal quenching process have been carried out to balance the strength and toughness. And the optimal mechanical properties are limited to approximately 60–61 HRC hardness and 100 J impact toughness. In this study, in order to further improve the mechanical properties, the influences of austenitizing temperature on microstructural evolution and strengthening-toughening mechanism in isothermal quenched bainite in 52100 bearing steel have been systematically investigated. The increase of austenitizing temperature decreases the volume fraction of undissolved carbides, and increases the carbon concentration in austenite matrix. These changes not only strongly influence the kinetics of bainite phase transformation and bainite microstructure, but also cause the conflict between the coarsening of prior austenite grains, as well as bainite sheaves, and the refining of substructure of lower bainite. Austenitizing at 870 °C can balance this conflict well and obtain a good combination of hardness and toughness. It is found that the carbon content and dislocation density in bainite ferrite reach the peak value at 870 °C austenitized specimens, which effectively strengthens the bearing steels. At the same time, the 870 °C austenitized specimens retain appropriate content of undissolved carbides, which avoids stress concentration and inhibits crack propagation, and finally improve the impact toughness. Therefore, the optimal austenitizing temperature (870 °C) achieves the improvement of mechanical properties with the hardness and toughness of 59.7 HRC and 273 J, respectively.

ОБРАБОТКА РЕЗУЛЬТАТОВ ЭКСПЕРИМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ ИСПОЛЬЗОВАНИЯ ТЕХНОЛОГИЙ КОМПЛЕКСНОГО МИКРОПЛАЗМЕННОГО УПРОЧНЕНИЯ РАБОЧИХ ОРГАНОВ И ДЕТАЛЕЙ СЕЛЬСКОХОЗЯЙСТВЕННЫХ МАШИН

Today, the problem of maintaining the efficiency of complex modern domestic and foreign agricultural machines is quite acute. The working units of agricultural tillage machines operate in an aggressive abrasive environment, which leads to their intensive wear and, as a result, to the loss of geometric shape. This, in turn, leads to a violation of agrotechnical requirements, which significantly affects the yield of cultivated crops. Serial working units of soil-cultivating machines are made of alloy steels of the ST65G type with a working hardness of HRC 55 ... 60. The purpose of the research is to increase the wear resistance of the working bodies of tillage agricultural machines by using the technology of complex microplasma hardening, with the development of a methodology for determining rational modes of processing working surfaces. To evaluate the effectiveness of complex hardening of laboratory samples, studies of the elemental composition of the hardened layer were carried out. Plates made of ST65G steel were used as laboratory samples. Hardening was carried out using various combinations of cermet powders and microplasma hardening modes. Determination of wear resistance was carried out on a friction machine 77 MT-1. The best results were noted after vibro-arc hardening followed by electrospark alloying and the use of a cermet powder consisting of 80% PG-10N-01 matrix powder and 20% B4C boron carbide. Based on the indicators of hardening regimes, Lagrange interpolation polynomials were constructed, which describe the dependence of the amount of sample wear on the current and voltage, an algorithm was developed for determining rational hardening regimes to achieve maximum wear resistance of the studied samples. The microhardness of the surface of products during electrospark hardening increased up to 2 times, and with vibroarc in combination with electrospark alloying and the use of special pastes with cermet powders - more than 3 times. The depth of the hardened surface layer with complex hardening is about 0.3 mm.

Wear and residual stress in high-feed milling of AISI H13 tool steel

Abstract With the new manufacturing technologies, it has been possible to machine hard metals efficiently. During high-speed machining (HSM) of high-strength steel, the poor surface integrity of the workpiece affects the performance of the process. Surface roughness, microstructure, microhardness and residual stress are key performance indices for surface integrity directly controlled by tool wear and cutting parameters. In this study, high-feed milling (HFM) of a pocket on test samples made of DIN 1.2344 ESR mould steel with 55 HRc hardness was carried out on the CNC vertical milling machine. Three different cutting speeds and five different feed rates were used. At the end of the machining, tool wear was measured using a microscope. Subsequently, X-ray diffraction and hole drilling procedures were used to quantify residual stresses on machined test specimens. The results showed that under cutting conditions, the highest tensile residual stress was attained at f z = 0.78 mm·tooth−1, v = 127.58 m·min−1, and the highest compressive residual stress at f z = 0.5 mm·tooth−1, v = 127.58 m·min−1, on the workpiece surface. The most suitable cutting parameters were reported as f z = 0.63 mm·tooth−1 and v = 70 m·min−1 cutting speed when tool wear and residual stresses are considered together.

Improving Grinding Ball Lifespan and Efficiency Through Hardenability Modelling and Optimization

Abstract Grinding balls are spherical or cylindrical components used in grinding and milling operations to reduce the size of particles and achieve a finer product. They are made of high chromium white cast iron (HCWCI) and used in a variety of industrial processes. The efficiency of the grinding process is heavily influenced by the properties of the grinding balls, including their composition, size, and hardness. As such, there is ongoing research and development to improve the performance and durability of grinding balls, with the aim of countering the extreme conditions of wear and impact that cause a reduction in their lifespan. This study involved austenitizing balls with diameters of 50 mm and 70 mm at temperatures of 950°C and 1050°C, followed by quenching using both oil and compressed air. By exploiting the experimental HRC hardness results obtained in this work, the study aims to find a mathematical model relating the response (hardenability) to the main effects (austenitization temperature, quenching medium, and diameter balls) and their interactions. Analysis of variance (ANOVA) was used to establish the statistical significance parameters and an optimization of response by the best sub-models method and by the desirability function is realized in the second part of this work. It seems that the austenitization temperature and the size of the balls have a stronger impact on the hardenability of the balls than the cooling rate (quenching medium) by reducing the hardness difference between the surface and the medium of the ball to minimal values.

Methodology for Determining the Effective Thickness of the Cemented Layer of Steel

Highly loaded transmission gears are cemented and hardened. An important parameter of the hardened cemented layer is its effective thickness hef . Metal banding and the unavoidable instrumental error in hardness measuring have a great influence on the reliability of hef determination. The purpose of this article was to develop a methodology to improve the reliability of determining of the effective thickness hef of the hardened layer in steel after carburizing and quenching.The value of hef is the distance h from the surface of the product to the hardness zone of 50 HRC. The article substantiates that approximation of hardness change from the distance h to the product surface will allow to obtain a more reliable dependence of hardness change in the investigated area when making hardness measurements in a wider range of distance h. Therefore, to increase the reliability of hef determination, results of the HV0.5 hardness measurement in an extended range of changes in h in the vicinity of the analyzed zone were used. The HV0.5 measurement results are converted to HRC hardness values using the formula recommended by the international standard. The HRC(h) distribution of HRC hardness values in the measurement area is interpolated by a second-degree polynomial which physically correctly reflects the change in metal hardness in the analyzed area. The resulting polynomial is used to determine of the distance hef at which the hardness takes on a value of 50 HRC. The methodology was used to determine the hef of an 18KhGT steel gear wheel after carburizing and quenching. It is shown that results of two independent measurements of the hef sample differ from each other by 0.003 mm. This is significantly less than the permissible error of 0.02 mm of the hef determination according to the standard technique. The error of hef determination is reduced by extending the range of variation of h and statistically valid interpolation of the monotonic change in hardness with the distance from the surface of the item in the measurement area. The developed method of determining the effective thickness hef of the hardened steel layer consists in determining the distribution of its hardness in the expanded vicinity of the hef area, approximating the obtained dependence by a polynomial of the second degree and solving the square equation obtained with its use. The technique provides a significant reduction in the influence of the structural banding of the metal and the inevitable error in measuring hardness on the result of determining the hef . Its application will allow to optimize the cementation regimes of gear wheels to increase their service life.

Study of the properties of the metal deposited with flux-cored wire of the Fe‒C‒Si‒Мn‒Сr‒W‒V system.

Alloys of the Fe‒C‒Si‒Мn‒Сr‒W‒V system widely used for hot-rolling roll repairs provide high resistance of the deposited layer against abrasion, but its thermal endurance is relatively low. It is shown that in order to ensure the quality of roll repair, it is necessary to improve the composition of the flux-cored wire charge and the technology of their use. It is proposed to reduce the structural heterogeneity of the deposited metal the use of flux-cored wire of the type PP-Np-35V9X3SF. The influence of the introduction of carbon-fluorinated elements and titanium on hydrogen concentration, microstructure, level of pollution by non-metallic inclusions, grain size, hardness and rate of wear of the deposited metal layer was evaluated. The data on the chemical composition of the deposited layer, the content of non-metallic inclusions in it, the microstructure of the deposited metal, depending on the content of titanium in the flux-cored wire, are presented. It was found that an increase the concentration of titanium increases the hardness of the deposited layer and reduces the rate of wear (abrasion) of samples. The effect on the level of contamination of the studied fused layers with oxide inclusions was not revealed. Increasing the hydrogen content in the deposited layer re-duces its hardness and increases the rate of wear of the deposited layer. Increasing the content of titanium in the depos-ited layer helps to reduce the size of the martensite needles, as well as the size of the former austenite grain. The de-pendencies of HRC hardness and wear resistance on the content of titanium and hydrogen in the deposited layer were established

Investigation on tool wear mechanisms and machining tribology of hardened DC53 steel through modified CBN tooling geometry in hard turning

DC 53 steel has emerged as a possible replacement of AISI D2 steel possessing competitive hardness and better toughness. In the current work, turning of DC 53 steel was conducted via Xcel modified inserts by varying workpiece hardness levels (40 and 60 HRC), cutting speed (130 and 160 m/min), feed rate (0.07 and 0.112 mm/rev), and depth of cut (0.07 and 0.17 mm). A two-level 4-factor full factorial design was employed entailing 16 runs. An analysis of variance (ANOVA) was conducted to statistically analyze the effect and contributions of input parameters on response variables namely tool life, surface roughness, volume of material removed, power consumption, and machining zone temperature. Results show that the tool life, surface roughness, volume of material removed, and machining zone temperature are primarily affected by the hardness of DC53 with PCRs of ~ 96%, ~ 25%, ~ 62%, and ~ 25%, respectively. At a 40 HRC hardness value, true crater wear was observed due to continuous chips sliding at the rake face while for the workpiece having a 60 HRC, discontinuous chip formation produced less prominent crater wear. SEM images revealed complete delamination of the coating from the tool surface with adhesion and attrition wear identified as the main wear mechanisms. The formation of a groove pattern was also noticed on the flank face. The minimum surface roughness was 0.90 µm-Ra for the workpiece having a 40 HRC hardness level, and the same value was obtained for 60 HRC as well. The threshold value of the feed rate for the excellent performance of these inserts was less than 0.20 mm/rev. Additionally, the turning process proved to be productive for this material along with a lower surface roughness value in comparison to the wire EDM process.

EFFECT OF HEAT-TREATMENT TEMPERATURE ON THE MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF AISI 4140 STEEL

Heat treatment is a metallurgical process for removing residual stresses in metals, improving their mechanical properties, reducing surface hardness, and preventing the formation of brittle fractures or cracks. The tempering (age hardening) process, which is a type of heat treatment in tempered steels, affects the mechanical and microstructural properties of the steel more than the other steel types. In this study, the base material test specimens with 13 HRC hardness and 12.5 mm diameter were heat-treated and tempered, and the effect of the heat treatment process on the mechanical and microstructural properties was investigated. AISI 4140 tempered steel was tempered at 600°C for 3 hours after 3 hours of heat treatment at 880°C, 850°C and 820°C and cooled in oil. While the base material has a tensile strength of 654.16 ± 12 MPa, the maximum tensile strengths were determined as 1022.44 ± 10 MPa, 1006.24 ± 9 MPa and 987.454 ± 11 MPa, respectively, after heat treatment at 880°C, 850°C and 820°C. The strength of the material increased by 56.29% by applying heat treatment at 880°C temperature. This increase in strength is associated with the transformation of the existing microstructure from ferritic to martensitic structure. The needle-like structure in the martensitic structure increased and lath martensite structure was formed with the combination of grain boundaries with increasing heat treatment temperature. Strength and hardness increased while the heat treatment temperature is increasing. It was observed that ductility decreased. Hereby, the temperature parameter in the heat treatment process is effective on the strength and the heat treatment has high advantages in terms of material saving in machine designs

Wear Characteristics of 22MnB5 Boron Steel under Friction Micro Pin-On-Disks Test

22MnB5 Boron Steel can be considered as emerged material for high strength and low weight application. This material potentially used in abrasive condition such as cutting tool or brake pad where high friction resistance applies. In this study, the wear characteristics of 22MnB5 was investigated under the frictional tests via micro pin-on-disk. 22MnB5 Boron Steel was prepared the form of round shape within the size of 2.6 mm thickness and 12 mm diameter by using laser cutting. 4 different samples were tested namely blank (sample A), self-hardening heat treatment (sample B), 60 HRC hot stamped (sample C) and 70 HRC hot stamped (sample D). The results show that Coefficient of Friction (COF) increased as the hardness of 22MnB5 decreased. Low COF of 0.2114 recorded for sample D with 70 HRC hardness. The COF increased to 0.24, 0.29 and 0.3 when sample C (60 HRC), sample B (52 HRC) and sample A (45.5 HRC) applied respectively. For pin-on disc test, worn area decreased as the hardness increased. 22MnB5 that prepared with the highest hardness of 70 HRC presented smallest wear area of 700 µm x 2400 µm. It is followed by 800 µm x 2400 µm, 1000 µm x 2400 µm, 1600 µm x 2800 µm, when sample C, B and A were scratched. Observation on the worn surface revealed delamination of 22MnB5 surface in the form of fragmented flaking debris.

Study of manufacturing and material properties of the hybrid composites with metal matrix as tool materials

Composite materials have many applications in industries and using these composites in deep drawing process is a new trend to obtain high quality drawn products. This study aims to prepare the hybrid Metal Matrix Composites (MMC's) iron-based reinforced with 0, 1, 2, 3 and 4% volume fraction of constant mix (80% Al2O3 and 20% ZrO2) by means of powder metallurgy and investigate the mechanical properties of these hybrid Composites. The powders were compacted at 640 MPa and sintered at 1120 °C in the presence of argon gas. The purity, density, average grain size and shape were measured by Dosimeter, particle size analyzer and SEM. The best mechanical properties were obtained at (97% Fe + 3% (80% Al2O3 + 20% ZrO2) among all reinforcement volume fractions and the composites has properties of 61%, 37% and 7% more than the matrix properties for compression strength, hardness HRC and radial crushing strength respectively.

Stiffness-based method to identify the threshold load of low hardness steels using the Incremental step loading test

Hydrogen embrittlement (HE) is one of the main problems related to the use of metallic materials in sour or wet environments. The Incremental Step-Loading (ISL) test used to evaluate the susceptibility to HE of steels has gained more visibility over recent years, thus allowing for the determination of the threshold load (Pth) in H+ enriched environments. However, the ISL standard, ASTM F1624, limits the test to steels with a minimum hardness of 33 HRC. Even for those steels with 33 HRC, the results present some misinterpretations. In addition to this fact, one needs to consider that there are several applications where steels with hardness below 33 HRC are used, as for instance, in fasteners and tool joints under cathodic protection used in the oil and gas industry, for which hardness varies from 26 to 32 HRC. In light of the aforementioned, the standard limitation represents a major disadvantage related to the application of the ISL test. Grounded upon the said, the aim of the present study is to propose a methodology based on the specimen stiffness to be used in the ISL test results, allowing the Pth determination of steels with hardness lower than 33HRC. Conventional and extended ISL tests were performed in two steels (4137-M and 4130-M) with a 32HRC hardness values. Applying the stiffness-based method on the the conventional ISL test results, a threshold load (Pth) of 71.5 %PFFS and 66.0 %PFFS were found for the 4137-M and 4130-M steels, respectively. To validate these results, extended ISL tests were performed on both steels and the results showed a Pth of 73.7 %PFFS for the 4137-M steel and 66.0 %PFFS for the 4130-M steel. The results from the conventional ISL test, using the stiffness-based method proposed in this study, provided values similar or with differences lower than 5 %PFFS, when compared alongside the extended ISL tests. Moreover, ISL tests were performed on the same steels with 40 HRC hardness, and the AISI4137-M presented a Pth of 21.6 %PFFS and for 4130-M the Pth was 22.0 %PFFS. The main conclusion obtained from these tests was that, when large amount of plastic deformation is not present on ISL test, the load drop visual detection is sufficient to determine the Pth. As expected, it was observed that both steels with 40 HRC presented higher HE susceptibility than the 32 HRC ones. This behavior was due to higher stress concentration at the notch root presented by the higher hardness condition. The stiffness-based method proved to be robust and capable of separate yielding from hydrogen induced cracking of low hardness steels and could also be used to identify the Pth values of steels with hardness lower than that specified by the ASTM F1624 standard, and which are tested using the ISL test.

Hard turning of AISI D2 steel with cubic boron nitride cutting inserts

Industries use heat treated steel for various components due to its strength and other mechanical properties. Usually hardening of machining is carried out by energy and cost intensive grinding process. Recently, hard machining has replaced grinding for certain specific applications. In this study, Cubic boron nitride (CBN) of specification CNMG120408is employed to machine AISI D2 steel of 46 HRC hardness. Nine machining experiments established by L9 orthogonal array were conducted. Surface roughness and cutting force were taken as response variables. From the signal to noise ratio analysis, the optimum combination of cutting process parameters for surface roughness is found out to be 80 m/min (Cutting speed) 0.109 mm/rev (Feed) and 0.1 mm (depth of cut). From Analysis of variance (ANOVA), the share made by every process parameter on the machining performance is found out for this CBN tool-work piece combination. Feed rate has the maximum contribution (56 %) for main cutting force while Cutting speed has the maximum contribution (72 %) for surface roughness. Cutting speed exerts greater influence on surface finish compared to feed rate in hard machining.

Performance of Al2O3/TiC mixed ceramic inserts coated with TiAlSiN, WC/C and DLC thin solid films during hard turning of AISI 52100 steel

The present work evaluates the turning performance of alumina (Al2O3) and titanium carbide (TiC) based mixed ceramic cutting inserts with TiAlSiN, WC/C and DLC thin-film depositions during machining of AISI 52100 steel hardened to 55 ± 2 HRC hardness. Based on the generated machining forces, coefficient of friction, geometrical characteristics of the chips, and tool wear, a comparative analysis of the performance of uncoated and coated cutting tools was carried out. The machining outcomes were interpreted in relation to the adhesion strength of coating with the substrate, surface roughness and hardness of the top surface of the coatings. It was observed that the reduction of friction and machining forces accounted to lower localized strain along the shear plane leading to lower deformation of the chips. The TiAlSiN coating exhibited superior wear-resistance at the highest cutting speed when compared to DLC and WC/C coatings owing to its higher hardness and higher coating/substrate adhesion strength. However, the DLC and WC/C coatings, although softer, accounted to significant reduction of machining forces due to their self-lubricating properties.

Influence of grinding parameters on surface roughness and temperature under carbon nanotube assisted MQL

ABSTRACT Conventional flood cooling system has some environmental and economic issues. Minimum quantity lubrication (MQL) has been established as a better strategy to control the machining temperature than conventional flood cooling system. Integrated use of carbon nanotube (CNT) with MQL has been drawing attention in recent times. The purpose was to study the effects of hard grinding with key focus on temperature, surface roughness and chips morphology under the application of CNT-mixed MQL and compressed air. The hardness of work material (AISI 1060 steel) was varied at three values (40, 45 and 50 HRC) with the variation of fluid flow rates and infeed rates to observe the machining behaviour. Experimental plan was established using full factorial design of experiment while mathematical models and optimisation were constructed following response surface methodology (RSM). Optimum output responses were flow rate 75 ml/h, infeed (depth of cut) 10 µm and hardness of material is from 40 to 45 HRC. Fluid flow rate of 75 ml/h resulted in best surface finish while work material of 40 HRC hardness generated lowest temperature while machining. A lower hardness values and a moderate flow rate produced favourable machining outcomes, i.e. lower temperature and improved surface finish.