HRC Hardness Research Articles

Experimental analysis of magnetorheological finishing of blind hole surfaces using permanent magnet designed tools

Permanent mould dies are used for various plastic injection moulding products. Most of the mould cavity is blind and henceforth difficult to finish. In this study, a novel magnetorheological fluid-based finishing process using permanent magnet tools has been developed for nano-finishing of cylindrical blind hole surfaces. Tools to finish the internal and flat-bottomed surfaces of the cylindrical blind hole are developed. The finishing performance of both tools is evaluated for finishing ferromagnetic material used in dies. The material of the die is P20 tool steel having 41 HRC hardness. Response surface methodology using a central composite design technique has been utilized for the plan of experiments and analysis of significant process parameters on the percentage change in surface roughness using newly developed tools. During finishing the internal cylindrical blind hole surface, the process parameters like rotational speed, reciprocation speed and abrasive mesh size are found to be significant. However, during flat-bottomed surface finishing of cylindrical blind hole workpiece, rotational speed, abrasive mesh size and abrasives volume percentage are found to process significant parameters. Experimentation at optimized parameters results in the final surface finish of 83 nm on internal cylindrical surface and 93 nm on the flat-bottomed surface of cylindrical blind hole workpiece.

Comparing tribological effects of various chevron-based surface textures under lubricated unidirectional sliding

Experiments were carried out using a pin-on-disc tribological tester in a flat-on-flat configuration in unidirectional sliding. Both counterparts were made from steel with 50 HRC hardness. The normal load was 20 N, the sliding speed was 0.4 m/s, the number of revolutions was 10,000. Before each test, one drop of L-AN-46 oil (0.08 ml) was supplied to the inlet side of the contact zone. The discs were textured using abrasive jet machining. Tribological effects of eight chevron-based textures were compared with that of the surface having circular oil pockets. All textures had the same pit-area ratios and depths. The untextured assembly was also tested for comparison. It was found that chevron-shaped dimples were sensitive to their angular orientation to the direction of sliding. The best tribological performances were achieved for chevrons inclined to the outer sides of the rotating discs.

An investigation of cutting parameters effect on sound level, surface roughness, and power consumption during machining of hardened AISI 4140

In recent years, the necessity for energy in the manufacturing industry has become an important problem because fossil fuel reserves are decreasing in order to produce energy. Therefore, the efficient use of energy has become an important research topic. In this study, energy efficiency is investigated in detail for sustainable life and manufacturing. AISI 4140 material with high hardness of 50 HRC hardness has been applied cryogenic process to improve mechanical and machinability properties. In this experiment study, the effects of feed rate (0.04, 0.08, 0.12 mm/rev), cutting speed (140, 160, 180 m/min), depth of cut (0.05, 0.10, 0.15 mm) and tool radius (0.4, 0.8) on energy consumption, surface roughness and sound intensity were investigated. Then, a new mathematical model with high accuracy was developed. Total power consumption was calculated by considering the instantaneous current value and machining time. As a result, it is found that good surface quality obtained when the feed rate is low, and the tool radius is high and the machining time is shortened, the energy consumption is reduced due to the increase in cutting speed, depth of cut and feed rate. Also, it is found that the tool radius has a limited effect on energy consumption, but low feed value increases energy consumption.

Experimental investigation of surface characteristics and dynamic effects at micro milling of hardened hot-work tool steel

One of the main trends in modern manufacturing technology is miniaturisation. In this field, micro milling offers the most flexible machining method. Size reduction results in special and unique characteristics with respect to the machining process. The current paper addresses the investigation of the dynamic effects and surface characteristics of micro milled structures. Experiments were carried out on AISI H13 hot-work tool steel with 50 HRC hardness using a five-axis micro milling centre: cutting force components and the vibration signal were recorded and analysed. By means of fast Fourier transform, the dominant frequencies of the process were identified. Time-frequency diagrams were prepared by short-time Fourier transform for studying process changes during cutting time. Also, correlations between surface roughness, burr formation and cutting parameters were investigated. The results of this research provide a deeper understanding of the micro milling process, which ensures well-controlled and reproducible machining of up-to-date materials.

EURAMET supplementary comparison between INRiM and UME in Rockwell hardness scales (HRA - HRBW - HRC) - EURAMET.M.H-S1.a.b.c

This report describes a bilateral EURAMET supplementary comparison on Rockwell hardness scales of two national metrology institutes of Italy and Turkey, INRiM and UME, respectively. The pilot laboratory is INRiM in the comparison where three sets of hardness reference blocks for the Rockwell hardness scales of HRA, HRBW and HRC were used. Each set of blocks consists of four hardness reference blocks for HRA and HRBW and five blocks for HRC hardness scales. The comparison was realized as planned in the Technical Protocol with some delay. The measurement results and uncertainty assessments declared by INRiM and UME are in consistency with each other.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A REPORT OF THE ARTICLE OF THE CANDIDATE OF ENGINEERING SCIENCES

The method of manufacturing gears of embedding engagement with internal tines using cold plastic deformation is described. The method is executed by covering deforming stretching (reduction) on the shapes and mandrel. Material of the matrix (drafts) _ solid alloy ВК 15, mandrels - steel ХВГ, Х 12 МФ, P6M5 at hardness HRC 56-61; modules of internal tines- 05-5 mm, material of gear wheels - plastic metals 1 alloys with relative elongation of more than 3-5% The typical technological process on the basis of reduction with the finishing operation of helpless net nitration in the glow discharge is given.

Effect of machinability, microstructure and hardness of deep cryogenic treatment in hard turning of AISI D2 steel with ceramic cutting

This study examined the hard turning of AISI D2 cold work tool steel subjected to deep cryogenic processing and tempering and investigated the effects on surface roughness and tool wear. In addition, the effects of the deep cryogenic processes on mechanical properties (macro and micro hardness) and microstructure were investigated. Three groups of test samples were evaluated: conventional heat treatment (CHT), deep cryogenic treatment (DCT-36) and deep cryogenic treatment with tempering (DCTT-36). The samples in the first group were subjected to only CHT to 62 HRc hardness. The second group (DCT-36) underwent processing for 36h at −145°C after conventional heat treatment. The latter group (DCTT-36) had been subjected to both conventional heat treatment and deep cryogenic treatment followed by 2h of tempering at 200°C. In the experiments, Al2O3 + TiC matrix-based untreated mixed alumina ceramic (AB30) and Al2O3 + TiC matrix-based TiN-coated ceramic (AB2010) cutting tools were used. The artificial intelligence method known as artificial neural networks (ANNs) was used to estimate the surface roughness based on cutting speed, cutting tool, workpiece, depth of cut and feed rate. For the artificial neural network modeling, the standard back-propagation algorithm was found to be the optimum choice for training the model. Three different cutting speeds (50, 100 and 150m/min), three different feed rates (0.08, 0.16 and 0.24mm/rev) and three different cutting depths (0.25, 0.50 and 0.75mm) were selected. Tool wear experiments were carried out at a cutting speed of 150m/min, a feed rate of 0.08mm/rev and a cutting depth of 0.6mm. As a result of the experiments, the best results for both surface roughness and tool wear were obtained with the DCTT-36 sample. When cutting tools were compared, the best results for surface roughness and tool wear were obtained with the coated ceramic tool (AB2010). The macroscopic and micro hardness values were highest for the DCT-36. From the microstructural point of view, the DCTT-36 sample showed the best results with homogeneous and thinner secondary carbide formations.

The effect of electro-erosion treatment of the surface of hard alloy plates on their phase composition and soldering of nitride ceramics cutting elements

The effect of electroerosive treatment of the surface of carbide plates from superhard nitride ceramics on their phase composition and vacuum soldering of cutting elements is studied. Studies of the surface quality and elemental composition have been carried out. The surface of the plates for soldering is processed by the method of electroerosive cutting with brass wire in water, as well as by the method of electroerosive direct burn-through using copper and graphite electrodes in kerosene. The microstructure and elemental composition of the surfaces of hard-alloy plates were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy before and after their processing. The analysis of the obtained data indicates that the best results at electro-erosion treatment of the hard-alloyed plate and the strongest bonding of brazed materials are achieved using a copper electrode and brass wire, since this ensures maximum wetting of the plate surface with solder based on Cu–Ti–Sn and the absence of pores. The hard-alloy cutter plate and ceramic cutting element were joined by high-temperature brazing in vacuum. Tests of hard-alloy plates with brazed cutting elements showed that the roughness of the machined surface of workpieces made of ХВГ steel with hardness of HRC 47–62 and ШХ15 steel with hardness of HRC 57–58 corresponded to 6–8 purity class at cutting speed of 155–170 m/min. The wear of the cutter along the trailing edge of 0.4 mm served as a criterion for evaluation of the cutting properties of superhard materials according to the results of durability tests.

Experimental and Statistical Investigation of Surface Roughness in Turning of AISI 4140 Steel

In this study, AISI 4140 tempering steel with 48 HRc hardness was machined on CNC lathe with different cutting parameters and cooling environment. The Taguchi L9 test design was developed based on the three-level cutting speed, feed, chip depth and cooling environment parameters. The average surface roughness (Ra) values were measured in experiments made according to the L9 test design. Chip form occurring during turning is photographed. The Signal/Noise (S/N) ratios of the Taguchi experiment design in the Minitab program have been determined. According to the experimental results, the most significant effect on the Ra from the four factors was found in the hand made by the depth of cut. In ANOVA analysis, it was respectively determined that depth of cut, cutting speed, feed rate and cooling environment affected 95% confidence in Ra value. It has been found that the repeat experiments for the optimum parameters yielded about 90% accuracy compared to the Taguchi estimate.

Effect of Heat Treatment Conditions on Retained Austenite and Corrosion Resistance of the X190CrVMo20-4-1 Stainless Steel

In the present work the microstructural characterization of the powder-metallurgy X190CrVMo20-4-1 has been performed and correlated with its corrosion properties. The martensitic stainless steel was hardened at different austenitizing and tempering temperatures. Microstructural analyses were carried out using Scanning Electron Microscopy (SEM–EDS) to define the carbide distribution in the steel matrix. Carbides morphology and retained austenite content were evaluated and correlated to the corrosion behaviour of the different heat-treated steels, investigated by means of electrochemical tests. The results show the presence of M23C6 and M7C3 Cr-V based carbides homogenously dispersed in the matrix in annealed and quenching-and-tempering conditions. The carbides dissolution was evaluated by image analysis in every different heat treatment condition. When low tempering temperature was applied, an increasing in retained austenite content was defined by high austenitizing temperature and elevated carbides solubilization. At high tempering temperature, retained austenite content was not up to 5% nor affected by austenitizing temperature. Contrary to the expectations, HRC hardness was not influenced by the heat treatment conditions and retained austenite content. Corrosion resistance of the different heat-treated samples was found to be mainly influenced by retained austenite volume fraction and the tempering temperature. In particular, high austenitizing temperature and low tempering temperatures allowed the best corrosion resistance among the different heat treatment parameters investigated. The results obtained in the experimentation can provide support to the heat treatment optimization of the steel, widely used in tool and mould applications.

Assessing Effectiveness of Various Wear-Resistant Materials Used as Hard Facings in Mining Applications

Characterizing the abrasiveness of soil/rock and the allowable wear of hard-facing products in various conditions is a critical factor in selection of the best material for certain applications related to drilling and excavation in mining and construction industries. The Soil Abrasion Index test machine at Colorado School of Mines (CSM) is one of the recently developed unique systems capable of testing soil/crushed rock abrasion under various conditions, such as dry, wet, and saturated settings. It is also capable of testing the performance of various types of hard-facing materials in a given geo-material. This paper studies the wear properties of different hard-facing materials in various crushed rocks from a surface mining operation in the iron range region of the USA. The hard-facing materials include regular and hardened steels and six different specialized hard facings, based on chromium carbide. The soil/rock include a standard sand and two rock samples from the surface mine. Fourteen abrasion tests were conducted, where the weight loss of each hard-facing material was measured over timespans up to 1 h of testing. The results show the distinct performance differences between the steels with 17 HRC and 43 HRC hardness and the hard-facing products for this application. The results show the possibility to evaluate the abrasiveness of different rocks at a mine or construction site and the performance of various hard facings in similar working conditions. This is a practical solution for selection of the cutting tool or reinforcement of bucket lips and truck beds for comparison of relative wear life between different wear-resistant materials.

MODELIZACIÓN POR ELEMENTOS FINITOS DEL TORNEADO DE ACEROS EN ESTADO TEMPLADO

The aim of the present paper is to study the capability of modelling by the Finite Element Method (FEM) when modelling behaviour of hard turning of 42CrMoS4 tempered steel, 60 HRC hardness, when machining with a PCBN tool. An analytical and experimental study has been carried out to analyse the effect of cutting parameters on variables such as cutting and feed force, temperature on the cutting zone, contact length and chip morphology. Initially, a flow stress model has been developed by carrying out dynamic and static compression tests at a high temperatures, obtaining the flow stress parameters to be implemented on the FEM model. Then, a 2D orthogonal cutting FEM model has been developed in the commercial software DEFORM. Finally, a series of experimental tests were devoted to the validation of the accurateness of the FEM model. In summary, the tendencies of the predictive model and experiments match in forces and temperatures. Major differences were found for contact length and chip thickness. Key Words: Hard turning, FEM, flow stress model, orthogonal test, machining, 42CrMoS4, PCBN

A Study on the Effects of Milling Strategy on Surface Roughness

In this study, DIN 1.2344 hot work steel which was hardened at 51 HRC hardness value was processed by using high-speed milling technology, and different milling parameters with 6 mm-diameter spherical endmill and the surface qualities which were obtained as a result of milling were examined. Axial and radial feed values, feed value per tooth and depth of cut were changed between the range of 0.05 and 0.1 mm and the rate of cutting was changed between the range of 485 rpm and 4,000 rpm. These millings were carried out on material in the spherical form of which diameter was 21 mm, and the central angle was 150º. Also, milling directions were processed in different ways as climb milling, conventional milling and bidirectional milling in experimental cuttings. Surface roughness was examined in directions with 15º, 45º, 75º, 90º, 105º, 135º and 165º central angles on the material which was processed. The best surface quality was achieved in regions with 15º and 45º angles

Rapid fabrication of TiN/AISI 420 stainless steel composite by selective laser melting additive manufacturing

Although metal matrix composites (MMCs) possess high mechanical properties for wide potential applications, there are limited kinds of ex-situ MMCs fabricated via selective laser melting (SLM) until now. In this study, TiN/AISI 420 stainless steel (SS) MMCs samples were fabricated by SLM. Densification behavior, microstructure, hardness and wear performance were investigated with different TiN contents and laser powers. It was found that the addition of TiN has a strong influence on density, which was mainly attributed to its impact on laser absorptivity of powder and wettability of liquid metal. With a higher laser power, the diffusion behavior of TiN became stronger and the densification of composites was improved with a maximum relative density of 98.2%. Both of the distribution and solid-solution of TiN particles were investigated by SEM, XRD and EDS results. The optimized composites achieved a high hardness of HRC 56.7, which is 11.8% higher than that of SLMed pure AISI 420 SS. The wear performance was enhanced due to the improved hardness and TiN reinforcement particle.

An abrasive wear test for thin and small-sized steel blade specimens

An abrasive wear tester was obtained by equipping a polishing machine with a specimen holding system. The test results for SKD11 and SCM440 steels were consistent with the standard pin on disk test. The main objective of developing this tester was to use it on thin and small-sized specimens. Thermal glue was applied to fix these wear test specimens, instead of using nuts or screws, or embedding them into epoxy resin. Influences of the factors specimen size, test time, load, speed, and environment (dry and wet conditions) on wear in the test were studied with both high speed steel (HSS) and high carbon (High C) steel blades. The results show that larger specimens of both materials had less wear, because at a constant loading force the pressure decreased with area of the specimen. Wear increased with testing time, load, and speed, as expected. In addition, wet conditions gave more wear than dry conditions. The HSS blades with 63 HRC hardness had better wear resistance than the high C steel with 43 HRC hardness. The developed test could distinguish between the wear properties of HSS and high C steel blades for thin and small-sized specimens, for which the ASTM standard wear test cannot be applied.

Modeling and Optimization of the Effect of Sintering Parameters on the Hardness of Copper/Graphene Nanosheet Composites by Response Surface Methodology

Composites obtained by powder metallurgy from a mixture of copper powders and graphene nanosheets are studied. The response surface methodology is used to design the regression dependence of the HRC hardness of the composites on the temperature, the duration of the sintering, and the sintering heating rate. Adequacy of the model for predicting the hardness of the composites is demonstrated. Optimum parameters for sintering copper/graphene nanosheet composites are determined.

Special aspects of thermal treatment of steel for hot forming dies production

Abstract It was found the influence of heat treatment parameters on the structure and properties of perspective die steel for hot working 70Cr3Mn2WTiB. It was specified the optimal mode of heat hardening for hot working hammer die from offered steel including spheroidizing annealing by the temperature of 780 °C with furnace cool up to 550 °C and then in a smooth air to the normal temperature; hardening by 1000 °C with cooling in oil; high-temperature tempering by 550–600 °C with cooling in a smooth air. During the hardening the formation of lath martensite with the high density of dislocation and the hardness HRC 57–62 occurs however it stays 0, 5–0,6% insoluble carbide phase. It’s shown that at the stage of high-temperature tempering by 550–600 °C in steel 70Cr3Mn2WTiB can be seen the process of hardness stabilization through the formation of special complex carbide intermetallic inclusions. The analysis of carbide phase by the temper showed that the combinations of type Me7C3 and Me3C are carbides the composition of which is changing during thermal influence. Thus, some atoms Fe and Cr are changed by titanium and vanadium atoms at different ratio. The simulation of temperature stressed condition of hammer die by thermal treatment was made. It’s shown that the offered mode of thermal treatment of steel 70Cr3Mn2WTiB leads to dispersed ferrite cementite structure with dispersed in it special carbides, high level of mechanical characteristics, provides homogeneous spreading of heat isotherms in extent of the hot deformation stamp and as a consequence insignificant inner residual strength. At the stage of high-temperature soak the temperature difference reduces to 25–30 °C.

Behavior of Nb influence on structure and properties of 30Cr13 cast martensitic stainless steel

The microstructure, mechanical properties and corrosion resistance of 30Cr13 martensitic stainless steel (MSS) with different Nb contents were investigated by using the optical microscope, scanning electron microscope, X-ray diffractometer, HRC hardness measurement apparatus and tensile testing machine. Nb was found to retard the formation of austenite and promote the precipitation of carbides by calculating. The results showed that the addition of 0.2 wt.% Nb elements could improve the strength and corrosion resistance of 30Cr13 martensitic stainless steels while the reduction in toughness was less because of the inhibited effect on Cr-rich carbides precipitation by Nb addition. Specially, M23C6-type carbides almost disappeared in 0.6Nb-MSS. Moreover, the main existent form of Nb element was NbC and the strong carbide-forming ability of Nb element increased the quantity of carbides with the morphology changing from spherical-type to chain-type. 0.2Nb-MSS shows excellent strength, adequate toughness and sufficient corrosion resistance for the application.

Microstructure-property relationships of 420 stainless steel fabricated by laser-powder bed fusion

In this study, we report the mechanical properties, microstructure and corrosion behavior 99+ % dense 420 stainless steel parts fabricated by laser-powder bed fusion (L-PBF). As-printed L-PBF parts exhibited an ultimate tensile strength of 1050 ± 25 MPa, yield strength of 700 ± 15 MPa, an elongation of 2.5 ± 0.2% and a hardness of HRC 55 ± 1. After the heat treatment operation at 315 °C, the ultimate tensile strength improved significantly to 1520 ± 30 MPa, yield strength increased to 950 ± 20 MPa, and elongation increased to 6.3 ± 0.2% respectively whereas hardness remained at HRC 53 ± 1. These properties are higher than previously reported literature values for 420 stainless steel fabricated by L-PBF, metal injection molding and powder metallurgy routes. The microstructure indicated a mixture of martensite and retained austenite phases in the as-printed parts. After heat treatment, the microstructure was richer in tempered martensitic laths that is consistent with the enhancement of ultimate tensile strength, yield strength, and elongation without appreciable change in hardness. The corrosion behavior of the as-printed L-PBF parts exhibited a corrosion current of 2.85 ± 0.4 mA.cm−2, a polarization resistance of 17,100 ± 520 Ω.cm−2 and a corrosion rate of 28 ± 2 μm/year which were comparable to the corrosion properties of wrought 420 stainless steel. A significant increase in pitting potential (170 mV) was obtained after the heat treatment.

THE EFFECT OF SURFACE TEXTURE OF STEEL DISC ON FRICTION AND FRETTING WEAR

Fretting tests were performed using an Optimol SRV5 tribotester in a ball-on-flat scheme. Balls from 100Cr6 steel of 60 HRC hardness and diameters of 10 mm co-acted with discs from 42CrMo4 steel of 47 HRC hardness under dry gross fretting conditions. Tests were performed at 300C and 25–35% relative humidity, and the number of cycles was 18000. During each test, the normal load was kept constant. Six sets of experiments were conducted. Discs had different surface textures as the result of machining. It was found that the lowest coefficients of friction were obtained for anisotropic surfaces when ball movements were perpendicular to main disc texture directions.