Degree Of Work Hardening Research Articles

Evaluation of the depth and degree of work hardening during rough turning of high-manganese steel

Evaluation of the depth and degree of work hardening during rough turning of high-manganese steel

Effects of surface hardening by laser shock peening and shot peening on a nickel-based single-crystal superalloy CMSX-4

Improving the expected life of nickel-based single-crystal superalloy turbine components by surface hardening treatments including laser shock peening (LSP) and mechanical shot peening (MSP) are of particular interest for mitigation of life limiting damage such as environmental assisted cracking in hot section components of gas turbines. In the present study the effects of LSP and MSP on the surface roughness, microhardness and work hardening of a nickel-based single crystal superalloy CMSX-4® have been assessed. Surface roughness was measured using laser profilometry. The degree of work hardening was measured using electron backscattered diffraction with local misorientation analysis. The analysis showed evidence for a work hardening layer in the MSP sample to a depth of approximately 70 μm. Sets of slip bands extending far into the bulk of the sample were observed in the LSP-treated sample, without any evidence of a work hardening layer. Microhardness measurements used to gauge the depth of residual stress showed that LSP produced a much deeper hardness profile than MSP, with compressive residual stress depths of 1000 μm and 200 μm in LSP and MSP respectively. The retention of hardness after a heat treatment of 50 h at 700 °C was more prominent in the LSP sample than in the MSP sample. LSP and MSP have therefore been shown to be at the opposite ends of the spectrum of surface hardening treatments of CMSX-4, with LSP giving milder hardening, but to a greater depth.

Study on Surface Characteristics and Work Hardening of SiCp/Al Composites by SCCO2-MQL Combined with Ultrasonic Vibration Milling

This study investigated the milling of SiCp/Al composite materials using Polycrystalline Diamond (PCD) tools under various machining conditions, including dry cutting conditions, supercritical carbon dioxide (SCCO2) conditions, supercritical carbon dioxide cooling with minimum quantity lubrication (SCCO2-MQL) conditions, ultrasonic vibration conditions, and supercritical carbon dioxide cooling with minimum quantity lubrication combined with ultrasonic vibration conditions. The objective was to compare the surface roughness and morphology of the materials under different machining conditions. Furthermore, under dry cutting conditions and SCCO2-MQL combined with ultrasonic vibration, the effects of different milling parameters on the surface roughness and morphology of SiCp/Al composite materials were investigated through a univariate experiment. Microhardness tests were carried out on the machined workpieces to explore the influence of process conditions and milling parameters on work hardening. The experimental results indicate that among all the tested machining conditions, the SCCO2-MQL in combination with the ultrasonic vibration process significantly reduced the surface roughness of the material. When the milling speed was increased from 40 m/min to 120 m/min, both the surface roughness and the degree of work hardening first increased and then decreased. As the feed rate or cutting depth increased, the degree of work hardening also increased. Therefore, under SCCO2-MQL combined with ultrasonic vibration conditions, it is recommended to use a milling speed of more than 60 m/min and avoid using high feed rates and cutting depths in order to optimize the machining performance.

Optimization of modes of pendular surface plastic deformation for intensification of the stress-strain state of carbon steel parts

The results of modeling on the influence of the main parameters and modes of the pendulum SPD process on the stress-strain state (SSS) of the surface layer are presented. It has been established that the obtained dependences of the SSS indicators on the technological parameters of the pendulum RPM process are not linear, for the solution of which polynomial equations are used as input data in the Statictiska 10.1 software package. Using the software package Statictiska 10.1, the optimal modes of the pendulum RPM process were determined. It has been established that the optimal modes of the pendulum SPD, which allow simultaneously obtaining the maximum intensity values of temporary (560–580 MPa) and residual compressive stresses (340–350 MPa) of the surface layer of hardened parts, are quite close. To optimize the value of work hardening (h), a significant increase in the value of the radial interference and a decrease in the value of the longitudinal feed are required, which lead to the approach of the intensity of temporary stresses to the u l timate strength of the material (600 MPa), and the intensity of residual stresses to the yield strength of the material (360 MPa). Such regimes lead to a decrease, and perhaps even to a complete removal of the residual stresses of the hardened layer, as well as to a decrease in the degree of work hardening. Thus, the rational maximum value of the hardened layer with pendulum RPM is 2.45 mm.

Acoustic and thermal energy evolution of AZ31B magnesium alloy under static tensile deformation

Based on the complexity of material damage and fracture behavior, the tensile deformation process of AZ31B magnesium alloy is characterized by infrared thermography (IR) and acoustic emission (AE) these two non-destructive technologies, and using in-situ EBSD technology to explore microstructure evolution under different tensile strains simultaneously. The results show that in the process of tensile deformation, the degree of strain hardening increases continuously with the deformation, and the deformation mechanism of the material changes from basal slip to pyramidal slip and {10–12} tensile twinning. The tensile deformation stage presents different signal characteristics. Using fracture mechanics and the energy release law of materials, combined with temperature and AE signal fluctuations, the transformation of the deformation mechanism, the degree of work hardening, and the dangerous zone during the entire tensile process can be effectively captured.

Analysis of microhardness and degree of work hardening (DWH) while turning Inconel 718 with high pressure coolant environment

Inconel is considered as one the difficult to cut metal and to find out causes of why Inconel 718 is difficult to machine is a topic of research for many researcher since past many years. The availability of high-pressure cooling (HPC) of cutting tools can be very effective when machining the difficult to cut metal like Inconel 718. With high-pressure coolant, it is possible to improve machinability of Inconel 718. Analysis of Microhardness and Degree of Work Hardening (DWH) is presented in this paper while Turning Inconel 718 with High Pressure Coolant Environment. There is a sudden change in micro hardness values in region between 30 and 120 μm depths from the machined surface. After this depth the microhardness of the machine affected zone slowly approaches the bulk microhardness. The bulk microhardness is found at a depth of about 270–300 μm below the machined surface for all samples. The microhardness close to the machined surface is found in the order of 1.11 times the bulk microhardness.

Cryogenic Deformation Behavior and Microstructural Characteristics of 2195 Alloy

Cryogenic deformation can improve the strength and plasticity of Al–Li alloy, although the underlying mechanism is still not yet well understood. The effects of cryogenic temperature on the tensile properties and microstructure of an Al–Cu–Li alloy were investigated by means of tensile property test, roughness measurement, scanning electron microscope (SEM), optical microscope (OM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The results indicated that the strength and elongation of the as-annealed (O-state) and solution-treated (W-state) alloys increased with the decrease in deformation temperature, where the increasing trend of elongation of the W-state alloy was more significant than that of the O-state alloy. In addition, a temperature range was observed at approximately 178 K that caused the strength of the W-state alloy to slightly decrease. The decrease in temperature inhibited the dynamic recovery of the Al–Cu–Li alloy, which increased the dislocation density and the degree of work hardening, thus improving the strength of the alloy. At cryogenic temperatures, the internal grain structure was more involved in the deformation and the overall deformation was more uniform, which caused the alloy to have higher plasticity. This study provides a theoretical basis for the cryogenic forming of Al–Li alloy.

Effects of Sequential Operation with Heat Treatment and Mechanical Milling on Work Hardening for Superalloy GH4169

Engineering components are usually manufactured with sequential production processes. Work hardening due to previous production processes affects the machinability of the workpiece in subsequent operations. In this research, the surface work hardening of a workpiece manufactured by two sequential processes with heat treatment/milling (HT + M) and milling/heat treatment (M + HT) of superalloy GH4169 was investigated. First, the surface microstructure characteristics, including plastic deformation and grain size of the machined workpiece surface processed by the two sequential processes, were quantitatively presented. Then, the microhardness on the machined workpiece surface and its cross-section was measured and analyzed. Finally, a surface microhardness calculation model considering twin boundary deformation was proposed. Here, we also present the microstructure evolution principle of the machined workpiece surface by the two sequential processes. It was found that the degree of work hardening of HT + M machining was 179%, whereas that of M + HT was only 101%. The research results can be applied to the optimized selection of process sequence for manufacturing superalloy GH4169.

Surface hardening analysis for shot peened GH4720Li superalloy using a DEM-FEM coupling RV simulation method

A systematic study was performed to analyze the surface hardening of shot-peened GH4720Li superalloy by combining experiments and numerical simulations. Firstly, it was proved that fine grain strengthening (FGS) and work hardening (WH) are two main strengthening mechanisms of the hardened layer for the plate specimen after shot peening (SP). Then, in order to improve the simulation efficiency, a coupled discrete element method-finite element method model (DEM-FEM) was integrated into the representative volume model to obtain strength distribution quantitatively. The simulation of grain refinement was realized through the dislocation density evolution equation and the degree of WH was characterized by the equivalent plastic strain. Motived by the Vickers hardness test principle, a novel expression between strength and hardness was finally deduced considering both WH and FGS mechanisms, based on which the hardness distribution was evaluated after SP treatment. The hardness by the numerical framework revealed a good agreement with the experimental observations.

Оценка уровня упрочнения стружки из алюминиевого сплава, предназначенной для последующей обработки давлением

Introduction. It is noted that the chip is an undesirable type of metal scrap, because it has a developed surface, which creates conditions for more intense interaction with the surrounding atmosphere. This creates conditions for oxidation and gas saturation, especially at elevated temperatures typical of remelting processes. Therefore, the process of chip utilizing is considered, bypassing the remelting stage. The aim of the work is to establish the level of work hardening of chips during the processing of aluminum alloys and to predict its effect on the subsequent processing process. Research methods: to assess the deformed state, the finite element method was applied, implemented in the RAPID-2D software package. The sequence of actions included the creation of the initial shape of the deformation region and the configuration of the tool. The mutual displacement of the tool and the deformable material is specified using the corresponding boundary conditions. The deformable medium is a viscous-plastic material with power-law hardening, the physical and mechanical properties correspond to an aluminum-magnesium alloy. Results and discussion: the solution obtained shows that the degree of shear deformation in the chips can reach a value of more than 2. In this case, a higher level of deformation is localized on the side of the convex part of the chip. The comparison of the solution with those obtained earlier by other authors is carried out and its similarity is shown. In the considered solution, the difference in the degree of work-hardening of the chips along its thickness is 36 %. A variant of the sequence of processing the workpiece first by cold deformation, and then by cutting is considered. The field of application of the results of the work is the development of methods for the processing of technogenic formations. Conclusions. During the cutting process, the plastic deformation of the chips reaches significant values. In this paper, the difference in the degree of shear deformation in the chip thickness is established, depending on the proximity of the cut layer to the surface of the cutting tool. It is proposed to take this difference into account at the subsequent stages of chip processing. The presence of the marked inhomogeneity of mechanical properties leads to consequences in the form of an inhomogeneous distribution of the temperature of the beginning of recrystallization during subsequent operations of heat treatment or hot deformation treatment. The principle of additivity of the degree of deformation obtained by the metal at the stage of plastic shaping of the workpiece and the shaping of the chip itself is introduced.

Surface integrity evolution of machined NiTi shape memory alloys after turning process

Owing to their shape memory effect and pseudoelasticity, NiTi shape memory alloys (SMAs) are widely used as functional materials. Mechanical processes particularly influence the final formation of the product owing to thermal softening and work-hardening effects. Surface integrity is an intermediate bridge between the machining parameter and performance of the product. In this study, experiments were carried out on turning NiTi SMAs at different cutting speeds, where surface integrity characteristics were analyzed. The results show that a higher cutting speed of 125 m/min is required to turn NiTi SMAs based on the evaluation of surface integrity. The degree of work hardening is higher at 15 m/min. Consequently, as a primary effect, work hardening appears on the plastic deformation of the machined samples, leading to dislocations and defects. As the cutting speed increases, the thermal softening effect exceeds work hardening and creates a smoother surface. A stress-induced martensitic transformation is considered during the turning process, but this transformation is reversed to an austenite from the X-ray diffraction (XRD) results. According to the differential scanning calorimetry (DSC) curves, the phase state and phase transformation are less influenced by machining. Subsequently, the functional properties of NiTi-SMAs are less affected by machining.

Influences of particle collision treatments on surface characteristics and fatigue strength of Ti-6Al-4V alloy

In this study, the particle collision treatments (fine particle bombarding (FPB) and conventional shot peening (SP)) were performed for Ti–6Al–4V alloy in order to comprehensively investigate the influences of their treatment conditions on the surface conditions, microstructures, hardness distributions and residual stress. Moreover, we examined the relationship between the surface characteristics of the treated materials and their mechanical properties including fatigue strength in detail. According to the obtained experimental results, the values of the maximum height waviness increased with increasing in the size of collision particles and injection pressure. Among all the treated materials, the differences in hardness distribution were relatively small because the work hardening exponent of Ti–6Al–4V alloy is low and the degree of work hardening is insensitive to the amount of plastic deformation. The absolute values of compressive residual stress generated at the surfaces became higher when finer particles were used as collision particles. The increase in injection pressure increased the surface temperature and released the introduced residual stress. As the particle collision treatments affected only the surface regions, the mechanical properties of the treated materials were almost the same as those of the annealed one. In the range of the conditions examined in this study, the most effective treatment to improve the fatigue strength of Ti–6Al–4V alloy was FPB under a relatively low injection pressure. This was because the value of the maximum height waviness was the smallest and the highest compressive residual stress was introduced at the same time.

An Investigation of the Work Hardening Behavior in Interrupted Cutting Inconel 718 under Cryogenic Conditions

The severe work hardening phenomenon generated in the machining of Inconel 718 is harmful to continue cutting processes, while being good for the component’s service performance. This paper investigates the performance of cryogenic assisted machining used in the cutting processes, which can reduce the waste of fluids. The influence of dry and cryogenic machining conditions with different cutting speeds on the work hardening layer is investigated based on the interrupted cutting of Inconel 718. Cutting temperature distribution obtained from simulations under different conditions is used to discuss the potential mechanism of work hardening. Then, the depth of work hardening and degree of work hardening (DWH) are investigated to analyze the surface deformation behavior, which strengthens the machined surface during metal cutting processes. From the cutting experiments, the depth of the work hardening layer can reach more than 60 μm under the given cutting conditions. In addition, a deeper zone can be obtained by the cooling of liquid nitrogen, which may potentially enhance the wear performance of the component. The results obtained from this work can be utilized to effectively control the work hardening layer beneath the surface, which can be applied to improve the service performance.

Influence of Guillotine Clearance on Cut-Edge Damage to Nonoriented Electrical Steel

Nonoriented electrical steel of 0.65 mm thickness was sheared to investigate the influence of guillotine clearance on cut-edge damage. The result shows that all the burr, work hardening, and magnetic property damage present an increasing trend initially, then a decrease, followed by an increase with increasing guillotine clearance. In particular, when the relative guillotine clearance (c/t) is within 4.6-6.2%, the burr is small and the cut edge is only slightly damaged. Damage to the burr, work hardening, and magnetic properties are influenced and inter-correlated. The plastic deformation of the microstructure at different c/t ratios is the decisive factor affecting burr forms and cut-edge damage. On the one hand, it leads to different degrees of work hardening and then results in a diversity of crack propagation patterns, forming burr and cross-sectional morphologies with different shapes. On the other hand, the stress distribution and grain orientation also change, which further influences the magnetic properties. Moreover, the relationship between microstructure deformation and grain orientation was established by analyzing texture occupancy and orientation distribution function diagrams. It is clarified that both nucleation position evolution and edge stresses generated by different clearances contribute to the evolution of grain orientation and texture.

Effect of pre-strain on the fatigue behavior of SAPH440 steel

The present research envisages the effects of different uniaxial tensile pre-strain levels on the fatigue properties of the SAPH440 steel. The S-N curves of different pre-strain levels (0%, 6%, 12%, 18%) were drawn using different load levels, with a stress ratio R = –1. The test results show that the fatigue strength of the SAPH440 steel increased with an increasement in the uniaxial tensile pre-strain levels. The static tensile test was carried out on different uniaxial tensile and different pre-strain levels specimens. The results show that with an increase in the uniaxial tensile pre-strain levels, the degree of work hardening of the SAPH440 steel and the static strength increased. Additionally, the hardening index and the elongation at break reduced, while the tensile strength and yield strength increased. TEM (Transmission Electron Microscopy) observation of the test samples with different pre-strain levels showed that the dislocation density of different pre-strain levels specimens increased with an increasement in the pre-strain levels. This resulted in an increasement in the fatigue strength of the SAPH440 steel, the degree of work hardening, and the static strength. However, compared with fatigue strength, the increase of dislocation density has a more significant effect on static strength.

Effect of electrochemical polishing on surface quality of nickel-titanium shape memory alloy after milling

Nickel-titanium shape memory alloys have been widely used in medical fields due to their unique shape memory effect, superelasticity, corrosion resistance and biocompatibility. However, there are still many processing difficulties to achieve required machined surface quality due to their high toughness and low elasticity. This paper proposes a sequential processing operations including milling, burnishing and electrochemical polishing. The effects of electrochemical parameters on surface quality, such as surface roughness, work hardening and surface grain size, are investigated in detail using orthogonal experiment. It is found that the electrochemical polishing parameters have the most significant effect on improving the surface roughness. With adjusting electrochemical polishing parameters, the surface roughness can be reduced to one tenth of the original value obtained by milling operations. Moreover, the current density in electrochemical polishing has more important influence on the surface quality than the distance and polishing time does, respectively. The conditions of 1.5A/cm2 current density, 7cm electrode distance and 20s polishing time can obtain the lower surface roughness, hardening degree and the larger grain size. The effects of electrochemical parameters on surface roughness, work hardening and grain size are related to each other. The degree of work hardening can be qualitatively estimated by surface roughness and grain size to avoid damage to the machined surface.

Strength response of 1200 MPa grade martensite-ferrite dual-phase steel under high strain rates

A commercial 1200 MPa grade martensite-ferrite dual-phase steel (martensite volume fraction is 61.3%) was studied by dynamic tensile tests and Nano-indentation tests. Results indicate that the strain rate sensitivity of this DP1200 steel is mainly owing to the increase of martensitic strength. Both (yield strength) Rp0.2 and (ultimate tensile strength) Rm increase with the increase of strain rate. But the degree of work hardening is decreased when strain rate exceeds the critical value (about 600 s−1). The above result is mainly caused by the two facts: i) ferrite loses strain rate sensitivity; ii) softening effect of adiabatic heating on martensite.

Influence of a multi-step process on the thickness reduction error of sheet metal in a flexible rolling process

Flexible rolling is a forming process based on thickness reduction, and the precision of thickness reduction is the key factor affecting bending deformation. The major purpose of the present work is to solve the problem of bending deformation error caused by insufficient thickness reduction. Under the condition of different rolling reductions with the same sheet thickness and the same thickness reduction with different sheet thicknesses, the thickness reduction error of sheet metal is analyzed. In addition, the bending deformation of sheet metal under the same conditions is discussed and the influence of the multi-step forming process on the thickness reduction error is studied. The results show that, under the condition of the same sheet thickness, the thickness reduction error increases with increasing rolling reduction because of an increase in work hardening. As rolling reduction increases, the longitudinal bending deformation decreases because of the decrease of the maximum thickness difference. Under the condition with the same thickness reduction, the thickness reduction error increases because of the decrease of the rolling force with increasing sheet thickness. As the sheet thickness increases, the longitudinal bending deformation increases because of the increase in the maximum thickness difference. A larger bending deformation is divided into a number of small bending deformations in a multi-step forming process, avoiding a sharp increase in the degree of work hardening; the thickness reduction error is effectively reduced in the multi-step forming process. Numerical simulation results agree with the results of the forming experiments.

DEVELOPMENT OF WEAR- AND IMPACT-RESISTANT COATINGS BASED ON FE-TI-MN-C SYSTEM FOR OIL AND GAS EQUIPMENT

The paper presents the results of research on the development of wear-resistant coatings on the working surfaces of equipment and tools operating in conditions of intense abrasive wear. Titanium carbide alloyed high-manganese steel with a high strain hardening capacity served as the basis for coatings. The coating was made by electric arc surfacing with powder electrodes, the charge of which consisted of ferrosilicomanganese, titanium powder, graphite, and components that protect the arc from the atmosphere. The coatings consiss of manganese austenite and dispersed inclusions of titanium carbide with dimensions of ~ 1 micron. Rockwell hardness was measured my means of TK-2 hardness testers (GOST 3882-74) by indentation of a diamond cone under a load of ~ 150 N (scale C). Before measuring the hardness, the surface deposited layer was deformed using the TS-2 hardness gage. At the same time, a carbide ball with a diameter of 10 mm manufactured according to GOST 3722-81 was used as an indenter. The indentation effort was 3,000 kg. Hardness was measured both in the well and in the undeformed zones. By the difference in hardness, the degree of work hardening was calculated. The developed coatings are characterized by the capacity for strain hardening under plastic deformation conditions. It was found that the hardness of the deformed coatings exceeds the hardness of the coatings in the initial state by 57% higher. Experimental studies of abrasive wear resistance under friction conditions on a fixed abrasive were carried out by comparing the developed coatings and serial materials for surfacing. The results of the comparison of abrasive wear resistance showed that the developed coatings are characterized by wear resistance higher compared to serial high-chromium alloys for surfacing almost 2 times. The wear resistance of coatings under conditions of aero-abrasive erosion was carried out using a Kleis centrifugal accelerator in an environment of quartz sand at angles of attack of 30 °, 60 ° and 90 °. The test results showed that the highest wear resistance of the developed coatings was determined at an angle of attack of 90 °. Analysis of the surface of the coatings carried out by electron microscopy showed no signs of brittle fracture. The developed coatings can be applied to increase the durability of the working surfaces of oil and gas equipment operating in abrasive conditions.

Microstructure and mechanical properties of thin varying thickness strips with different transition zones produced by micro flexible rolling

In order to better understand transition zones with a variety of structural features that affect thin varying thickness strips, 6061 aluminium alloy thin strips were flexibly rolled into different thickness ratios and transition zone lengths, using an innovative micro rolling mill. The microstructure and mechanical properties of the thin varying thickness strips produced by micro flexible rolling were systematically investigated and the mechanisms were analysed. The results indicate that a thin varying thickness strip with either a larger thickness ratio or a shorter transition zone length will present a relatively high slope of the transition zone during micro flexible rolling. After tensile tests, a thin varying thickness strip with the highest thickness ratio achieved the largest yield strength and ultimate tensile strength. In comparison, transition zone length can have a greater influence on the strain of the transition zone than on the thickness ratio because of the variation in β. The measured hardness is greater in the thinner zone than in the thicker zone. Values in the thinner zone are about 7%–21% greater than those in the thicker zone for strips with different thickness ratios due to the increased strain level which causes different degrees of work hardening.