Bulk Hardening Research Articles

The influence of confining stress and pore pressure on effective stress coefficient for permeability: A novel Discretized Clay Shell Model for clayey sandstone

The effective stress coefficient α determines the effective stress and dominates the permeability of rocks. This study proposes a novel theoretical model called the Discretized Clay Shell Model (DCSM) that modifies the Clay Shell Model (CSM) by incorporating the stress-dependent elastic modulus of clay into a discretized multi-layer clay domain to depict the relationship between α, pore pressure, and confining stress. The proposed model was successfully used to provide insights into the stress-dependent α of clayey sandstones. We found that α always decreased with increasing pore pressure and could decrease or increase with increasing confining stress. The modelling trends, which are also observed in the previous laboratory tests, can be well explained using two effects due to the heterogeneity of radial stress within clay domain, that is, the bulk and differential clay hardening effects. The bulk clay hardening effect generates a decreasing trend in α with increasing pore pressure, while the differential clay hardening effect competes with the bulk clay hardening effect and yields a reverse trend, that is, α first decreases with increasing confining stress and then decreases when the confining stress reaches a certain critical value. This study provides synthetic cases to quantify the influence of stress-dependent α evaluated by the DCSM on the evaluation of the permeability-depth relation. Based on the laboratory testing data, the calibrated parameters of the stress-dependent permeability model assuming α=1 are significantly overestimated, and the prediction model yields overestimated permeability up to three to four orders of magnitude. Meanwhile, the synthetic in-situ case shows that the predicted permeability could be underestimated by up to one third, and the errors due to laboratory analysis that neglect the stress dependency of α will propagate to and amplify the errors of prediction for the in-situ permeability-depth relation.

EFFECT OF THE STRUCTURE FORMED AFTER BULKAND SURFACE HARDENING ON THE HARDNESSAND WEAR RESISTANCE OF 20Cr2Ni4A STEEL

The article presents the results of a comparative study of the effect of bulk and surface hardening on the structure and properties of 20Cr2Ni4A steel. Surface hardening was carried out by the electrolytic plasma method. Bulk quenching was carried out by heating to a temperature of 870 °C, followed by cooling in water and oil. The structural-phase states of20Cr2Ni4A steel samples were studied by metallographic and X-ray structural analysis. Tribological tests of the samples were carried out according to the ball-disk scheme, and the microhardness of the samples was also determined. It has been determined that after volumetric and surface hardening, the hardness and wear resistance of 20Cr2Ni4A steel increase. In this case, the most significant change is observed in samples that have undergone electrolytic plasma hardening. It has been established that high values of hardness and wear resistance of 20Cr2Ni4A steel after electrolytic plasma hardening are associated with the formation of fine-needle martensite

Gaseous nitriding of additively manufactured maraging steel; nitriding kinetics and microstructure evolution

The nitriding response of additively manufactured M300 maraging tool steel was investigated through a series of nitriding treatments at different temperatures in the range 360–480 °C for a duration of 40 h. The interaction between nitrogen and alloying element nitrides (Ti and Mo) and intermetallics (Ni 3 Ti and Ni 3 Mo) was studied by comparing nitriding responses of as-solution treated and subsequently aged specimens. The nitriding behavior was found to depend strongly on the initial condition of the material and the nitriding temperature applied. Ultra-low temperature nitriding at 360 °C was found to be feasible as it resulted in a nitrided case, albeit with incomplete precipitation hardening of the bulk structure, thus resulting in a softer core. The application of a post-ageing treatment resulted in full bulk hardening and distinctly changed the appearance of the hardness profile. • Nitriding of solution treated and not aged maraging steel creates deeper case. • Nitride and intermetallic formation competes at increased nitriding temperatures. • Ultra-low temperature nitriding of maraging steel is feasible. • Post-ageing of ultra-low temperature nitriding creates promising hardness profile.

ВЗАИМОСВЯЗИ СКОРОСТЕЙ ИЗНАШИВАНИЯ ЗУБЬЕВ МЕЖДУ ВЕДУЩЕЙ И ВЕДОМОЙ ШЕСТЕРЕН

The article reviews interrelation of wear speeds of the accelerating and decelerating gears’ teeth heads and legs, at an account of the ratio of a relative wear of the teeth depending on the number of gear teeth participating in meshing and gear ratio. Regularities of wear rate changes between gear teeth head and foot, hardened by bulk hardening, hardening by high frequency current, cementation and nitriding, in the presence and absence of abrasive particles in the working environment, when the gear ratio has increasing (accelerating) or decreasing (reducing) tendency, have been established. Hardness laws of the friction surfaces of the driven gear wheel teeth friction surfaces of the accelerating and reducing gears have been determined.

BORONIZING MITIGATE FAILURE MECHANISMS WITH EXTENDED LIFE IN OIL/GAS STEEL PIPING UNDER ACOUSTIC INDUCED VIBRATION (AIV)

Oil and gas piping systems suffer from acoustically induced vibration, AIV, that end with hearing losses and consuming personnel’s lives. However, Leak-Before-Break (LBB) methodology was developed to mitigate failure, the primary piping systems exhibit an extremely low probability of rupture (xLPR). For understanding of piping failure mechanisms under AIV, 3-point bending tests are conducted to study structural integrity in oil/gas piping (ASTM A333 Carbon Steel GR.6 Seamless). Besides, for ultra-fast surface hardening and strengthening, a non-traditional powder pack boronizing technique is introduced at 950oC for 10 and 30 minutes. Mechanical characterization as well as microstructural analysis are conducted for continuous and incremental bending tests. In addition, FE modeling, ANSYS, is conducted on actual “case study” of oil/gas piping to study the changes in dynamic characteristics for both as-received (AR) and boronized steel Under AIV(173 dB). Failure mechanisms is established in AR sample with clear banding and early localized micro-plasticity at 0.2 flexural stress (sf). Void coalescence induce crack initiation at 0.3 sf. Crack propagation (at 0.5 sf), crack evolution (at 0.7sf) and catastrophic failure are captured. Boronizing with the diffusion of Boron into the outer surface dominate functional-graded materials (FGM), with surface and bulk hardening. Surface hardening via boronizing mitigate fracture mechanisms with no clear micro-plasticity, but with clear twinning and banding elimination. In addition, to investigate the sustainability of piping and the effect of boronizing, under AIV, FE modeling is introduced with two different steel piping systems (AR with strength 580 MPa, and boronized steel with strength 1390 MPa). Failure mitigation is introduced with the increase of endurance limit as well as increase of piping life. تعاني أنظمة أنابيب النفط والغاز من الاهتزازات الناتجة عن الصوت ، AIV ، والتي تنتهي بفقدان السمع واستهلاک حياة العاملين. ومع ذلک ، تم تطوير منهجية التسرب قبل الکسر (LBB) للتخفيف من الفشل ، حيث تظهر أنظمة الأنابيب الأولية احتمالية منخفضة للغاية للتمزق . (xLPR) لفهم آليات فشل الأنابيب بموجب AIV ، تم إجراء اختبارات الانحناء من 3 نقاط لدراسة السلامة الهيکلية في أنابيب النفط / الغاز المستخدمة (ASTM A333 Carbon Steel GR.6 Seamless) . إلى جانب ذلک ، من أجل تغطية وتقوية السطح بسرعة فائقة ، تم تقديم تقنية التغطية بالبورون غير التقليدية عند درجة حرارة 950 درجة مئوية لمدة 10 و 30 دقيقة. تم إجراء التوصيف الميکانيکي وکذلک تحليل البنية المجهرية لاختبارات الأنابيب –الإنحناءات المستمرة والمتقطعة. بالإضافة إلى ذلک ، يتم إجراء نمذجة FE ،بإستخدام ANSYS ، على حالة فعلية لأنابيب النفط / الغاز لدراسة التغيرات في الخصائص الديناميکية لکل من الفولاذ المغطي بالبورون المستلم (AR) والفولاذ البورونى تحت AIV (173 ديسيبل). تم دراسة آليات الإنهيار في عينة AR مع النطاقات الواضحة واللدونة الدقيقة الموضعية المبکرة عند 0.2% إجهاد الانحناء . (sf) يؤدي الاندماج الفارغ إلى بدء الشروخ عند %0.3 . sfتم التقاط انتشار الشروخ (عند %0.5 sf) ، وتم إکتشاف تطور الشقوق (عند %0.7 sf) ثم الفشل الکارثي المفاجئ. تؤدي التغطية بالبورون إلى انتشار البورون علي السطح الخارجي تدريجيا ويؤدي إلى تکوين مواد مرکبة- المواد المتدرجة الوظيفية (FGM) ، مع تصلب السطح والکتل. تصلب السطح الخارجي يؤدي إلى تخفيف آليات الکسر وزيادة التصلد بالبورون مع عدم وجود لدونة دقيقة واضحة ، ولکن مع إزالة التوأمة والنطاقات الواضحة (Banding). بالإضافة إلى ذلک ، للتحقق من استدامة الأنابيب وتأثير البورون ، في إطار AIV ، تم تقديم نمذجة FE مع نظامين مختلفين للأنابيب الفولاذية (AR) بقوة 580 ميجا باسکال ، والفولاذ بالبورون بقوة 1390 ميجا باسکال). يتم تقديم تخفيف الأعطال من خلال زيادة حد التحمل بالإضافة إلى زيادة عمر الأنابيب) .

Single layer graphene controlled surface and bulk indentation plasticity in copper

The impact of graphene reinforcement on the mechanical properties of metals has been a subject of intense investigation over the last decade in surface applications to mitigate the impact of tribological loadings or for strengthening purposes when dispersed into a bulk material. Here, the effect on the plastic indentation response of a single graphene layer grown on copper is analyzed for two configurations: one with graphene at the surface, the other with graphene sandwiched under a 100 nm thick copper cap layer. Nanoindentation under both displacement and load control conditions show both earlier and shorter pop-in excursions compared to systems without graphene. Atomic force microscopy reveals much smoother pile-ups with no slip traces in the presence of a surface graphene layer. The configuration with the intercalated graphene layer appears as an ideal elementary system to address bulk hardening mechanisms by indentation testing. Transmission electron microscopy (TEM) cross-sections below indents show more diffuse and homogeneous dislocation activity in the presence of graphene. 3D dislocation dynamics simulations allow unraveling of the origin of these 3D complex phenomena and prove that the collective dislocation mechanisms are dominantly controlled by the strong back stress caused by the graphene barrier. These results provide a quantitative understanding of the impact of graphene on dislocation mechanisms for both surface and bulk applications, but with an impact that is not as large as anticipated from other studies or general literature claims.

Tailoring the electrical conductivity and hardening in BiFeO3 ceramics

In this report, the influence of cobalt doping and annealing atmosphere on the electrical conductivity and polarization switching of BiFeO3 (BFO) ceramics was studied. Electrical conductivity as well as hardening behavior has been found to increase with introduction of acceptor CoFe' sites. BFO ceramics doped with Co exhibit p-type conductivity, dominated by Fe4+ defects, which can be successfully reduced during high-temperature annealing in N2. However, indications of local reduction were found, presumably on domain walls and grain boundaries. A mechanism of hardening is proposed, which assumes two types of pinning centers: i) VBi''' and FeFe• related and ii) CoFe' and VO•• related, most probably bound into complexes, which are shown to play the key role in the hardening behavior and hysteresis loop pinching and biasing. The results of this study could further promote designing local and bulk conductivity and hardening properties of BFO-based materials.

Effect of Explosion on the Mechanical Properties of 110G13L Steel

Shock loading is an effective method of bulk hardening of materials. This study of the structure and mechanical properties of 110G13L steel before and after explosion loading showed that the mechanical characteristics reached maximum values at the surface of the explosively treated material: Vickers hardness HV =480, yield strength of 850 MPa, and tensile strength of 1240 MPa. The thickness of the hardened layer was ≈40 mm. For steel without shock loading, the above parameters had the following values: HV =240, yield strength of 355 MPa, and tensile strength of 840 MPa. Metallographic studies revealed that the number of slip lines in grains decreased with distance from the explosive loading surface.

INVESTIGATION OF BIAXIAL STRESS STATE IN R65 RAILS BY ACOUSTOELASTICITY METHOD

Исследованы коэффициенты упругоакустической связи и двухосное напряженное состояние в отрезках рельсов Р65 с помощью измерений скорости поперечных и продольной волн. Измерения с помощью структуроскопа СЭМА и дефектоскопа DIO 1000 проведены на девяти рельсах, один из которых изготовлен по технологии объемной закалки, остальные дифференцированно упрочненные. Измерения проведены с использованием электромагнитно-акустического (ЭМА) и пьезоэлектрического (ПЭП) преобразователей для ввода и приема соответственно поперечных и продольной волн. Преобразователи устанавливались на поверхность катания головки и на боковую поверхность шейки рельса. ЭМА-преобразователь возбуждает две поперечные волны, поляризованные в продольном и поперечном направлении рельса. Волны, отраженные от противоположной стороны образца, принимаются тем же самым преобразователем. Точно такой путь проходит продольная волна, возбуждаемая ПЭП. Полученные значения остаточных напряжений в нескольких сечениях отрезков рельсов оказались неодинаковыми как в каждом отрезке по его длине, так и существенно неодинаковыми в разных образцах, включая образцы, полученные по одной технологии. Для исследования коэффициентов упругоакустической связи k1, k2, k3 из рельса вырезаны головка и подошва, которые сжимали в продольном направлении на машине «INSTRON» с нагрузкой до 240 кН. До начала испытаний по сжатию были измерены начальные значения временных задержек акустических волн. Расчет коэффициентов упругоакустической связи производился по вторым донным отражениям. Коэффициенты акустоупругой связи K1, K2 рассчитывались при нагружении на торцы элементов от 0 до 240 кН. QUOTE Обнаружено, что продольные напряжения QUOTE в рельсах QUOTE выше на два порядка поперечных. Таким образом, наиболее информативным методом акустической тензометрии для определения остаточных напряжений является метод, основанный на регистрации изменения скорости распространения упругих волн, зависящих от напряженного состояния, с использованием электромагнитно-акустического (ЭМА) и пьезоэлектрического (ПЭП) преобразователей для ввода и приема соответственно поперечных и продольной волн.

Measuring wear-resistance of AISI 1.7225 steel under various heat treatments: Hydraulic spool valve

Abstract Producing mechanical components with long time functioning is a vital issue in the advanced industries. Wear is one of serious difficulties which prevents from achieving desires. The objective of present study is how wear-resistance of a spool valve, which is an important part of hydraulic valves, can be improved. Hence, different heat treatment methods were implemented to harden the surface layer of this component which is an AISI 1.7225 steel. Wear-resistance measurement test coupled with roughness and distortion tests have been performed to run this analysis. Furthermore, a vision measuring microscope was used to investigate the quality of surfaces that impaired by the wear test. As a result of this work, it was revealed that surface hardening methods generally outperformed the bulk hardening process. In particular, carburizing surface hardening method generates the surfaces with ability of high wear-resistance and better surface quality compared to the other heat treatment processes used in this study. Moreover, highest distortion occurred in the spool valve when gas carburizing heat treatment method has been carried out.

Properties and Commercial Application of Manual Plasma Hardening

A new method and a device for plasma hardening of various parts are considered. Installation of the new device does not require too much investment (the active mechanical productions are appropriate for its accommodation) and special choice of personnel (welders train to use it without difficulty). Plasma hardening does not deform and worsen the smoothness of the surface, which makes it possible to employ many hardened parts without finishing mechanical treatment required after bulk or induction hardening. The hardened layer (about 1 mm) produced by plasma hardening exhibits better wear resistance than after bulk hardening with tempering, which prolongs the service life of the parts.

Filler-immobilization assisted designing of hydroxyapatite and silica/ hydroxyapatite filled acrylate based dental restorative composites: Comparative evaluation of quasi-static and dynamic mechanical properties

The comparative effect of filler combinations on the quasi-static and thermo-mechanical properties of light cured acrylate based restorative composites is addressed in the study. Two series of acrylate based restorative composites filled with hydroxyapatite (Hap) and silica/Hap combination were prepared. FTIR spectroscopy showed the filler-assisted functional interference with the chemical structure of the resin, whereas SEM–EDX revealed the state of micro-dispersion/distribution morphology of the filled composites. The silica/Hap combination filled (micro-hybrid) composites with 30 wt.-% filler showed highest compressive strength (CS) and composites with 20 wt.-% filler showed highest diametral tensile strength (DTS) as well as flexural strength (FS). Dynamic mechanical properties revealed reinforcement effectiveness correlated to extent of filler immobilization effects estimated from Kerner equation. Our study conceptually establishes the possibility of manipulating the mechanical and thermo-mechanical strength requirements, by catering to the extent of filler induced bulk hardening contributions, as characterized by immobilized volume fraction of the polymer chains. It was imperatively deduced that at very high amount of overall filler content (e.g. > 50 wt.-%) the reinforcement effectiveness is filler-controlled whereas the same extent of effectiveness may be obtained by manipulating the filler induced immobilization effects (e.g. < 20 wt. - %).

Comparative Analysis of the Structure and Phase States and Defect Substructure of Bulk and Differentially Quenched Rails

Optical and transmission electron microscopy (TEM) methods are used for layer by layer comparative analysis of low-temperature reliability rails with increased wear resistance and contact-fatigue strength of the highest quality after bulk quenching and differential hardening by different regimes. Quantitative relationships are established for changes in structural parameters, phase composition, and dislocation substructure over the central axis and fillet at different distances from the running surface. The degree of structure and phase composition inhomogeneity and defective substructure is revealed. It is shown that with respect to structural component content and interlamellar distance the structure after bulk hardening compared with differential hardening is more uniform in a layer 2 mm thick and less uniform at a distance of 10 mm from the running surface. With respect to stress concentration density, the rail structure after bulk hardening (compared with differential hardening) is less uniform in a layer 2 mm thick and more uniform in a layer at a distance of 10 mm from the running surface.

Optimization of modes of plasma treatment crane rails

Crane operation is accompanied with wear and tear of rails and crane wheels. Actual direction is the renovation and improvement of efficiency of these parts. Modern technologies of restoration of wheels and rails provide surface deposition or treatment with high-frequency currents. A promising direction is a surface treatment of highly concentrated streams of energy: with a laser beam, plasma jet. It is proposed to increase the efficiency of crane rails of surface plasma treatment. The work was carried out on the selection of treatment regimens. Simulation of the thermal impact of the plasma jet on a solid body of a complex shape was performed. Defined were multiple ranges of plasma hardening regimes that meet the requirements of production. The structural transformation of the material in the crane rails plasma treatment was investigated. It is concluded that in carbon and low alloy crane steels plasma exposure zone is characterized by a high degree of dispersion hardened structure and higher toughness as compared to the quenching with high-frequency current. Both shift (within the upper zone of plasma influence) are realized, and fluctuation (in the lower zone of the plasma effect) mechanisms of phase transformations. With high-speed plasma heating is a major transformation of granular or lamellar pearlite into austenite. The level of operational properties of hardened steel, which is achieved in this case is determined by the kinetics of the completeness and pearlite → austenite transformation. For carbon and low alloy rail steels plasma hardening of achievable properties can effectively replace the bulk hardening, hardening by high-frequency, or surface deposition. The range of conditions for plasma treatment was determined which allows to obtain a surface layer with a certain performance properties.

Influence of Microstructure and Process Conditions on Simultaneous Low-Temperature Surface Hardening and Bulk Precipitation Hardening of Nanoflex®

Precipitation hardening martensitic stainless steel Nanoflex was low-temperature nitrided or nitrocarburized. In these treatments, simultaneous hardening of the bulk, by precipitation hardening, and the surface by dissolving nitrogen/carbon can be obtained because the treatment temperatures and times for these essentially different hardening mechanisms are compatible. The effect of the processing history of the steel on the nitrided/nitrocarburized case was investigated by varying the amounts of austenite and martensite through variation of the degree of plastic deformation by tensile strain, deep cooling, and deliberate manipulation of the austenite stability. The nitrided/nitrocarburized case was investigated with reflected light microscopy, hardness-depth profiling, X-ray diffraction analysis, and glow discharge optical emission spectroscopy. The results demonstrate that a microstructure consisting of martensite results in the deepest nitrided case, while a shallow case develops on a microstructure consisting of austenite. For an initial microstructure consisting of both martensite and austenite a non-uniform case depth is achieved. Simultaneous bulk and surface hardening is only possible for martensite because the precipitation hardening does not occur in an austenite matrix.

Fatigue-induced reversible/irreversible structural-transformations in a Ni-based superalloy

Cyclic loading and the subsequent fatigue-induced structural transformations have been investigated with in-situ neutron diffraction and thermal characterization for a single-phase, polycrystal nickel-based alloy. The lattice-strain evolution is compared with bulk parameters, such as the applied stress and thermal response as a function of the fatigue cycles. In-situ neutron-diffraction and temperature-evolution measurements identify the development of different stages in the fatigue-induced structural transformations, such as bulk hardening, softening, and eventual saturation. An increase in the dislocation density and the formation of planar-patterned dislocation structures are responsible for hardening during the early cycles. With further cyclic loading, the rearrangement of the dislocations results in cyclic softening. A transition is observed during the saturation cycles, which is characterized by the emergence of lattice-strain asymmetry in the loading and transverse directions. The dislocation density and dislocations-wall spacing are determined with diffraction-profile analyses and complemented by transmission-electron microscopy. The thermal behavior of the sample during deformation correlates with corresponding in-situ observation of the time-dependent dislocation structure. An anomaly during saturation cycles is believed to arise from dislocation self-organization – possibly during the formation of microcracks.

Solar hardening of steels with a new small scale solar concentrator

Concentrated solar energy has been widely used in heat treatments for more than 20 years. In this work a new concentrating system and the first experimental results in heat treatments are presented. The concentrator, named as “Double Reflection Fresnel Lens” is a low cost, small scale facility with a concentration factor of 1000×. It has very good features for making heat treatments, e.g. on steel samples. Surface and bulk hardening can be easily achieved with this new concentrator.

Features of electromagnetic methods for testing the wear resistance of medium-carbon structural steel subjected to laser or bulk hardening and tempering

Features of applying attachable eddy-current transducers of two types (with a flat end surface and a protruding ferrite rod core with localities 5–6 and 3–4 mm in diameter, respectively) for testing the structural state, hardness, and abrasive wear resistance of structural steel 45X (0.45 mass % C and 0.85% Cr), which was hardened under the action of continuous laser radiation, have been studied. The feasibilities of the eddy-current and coercimetric techniques for evaluating the wear resistance of a medium-carbon steel subjected to laser or bulk hardening and tempering in the temperature range 75–600°C have been studied.

Simultaneous surface engineering and bulk hardening of precipitation hardening stainless steel

This article addresses simultaneous bulk precipitation hardening and low temperature surface engineering of two commercial precipitation hardening stainless steels: Sandvik Nanoflex® and Uddeholm Corrax®. Surface engineering comprised gaseous nitriding or gaseous carburising. Microstructural characterisation of the cases developed included X-ray diffraction analysis, reflected light microscopy and micro-hardness testing. It was found that the incorporation of nitrogen or carbon resulted in a hardened case consisting of a combination of (tetragonal) martensite and expanded (cubic) austenite. The duration and temperature of the nitriding/carburising surface hardening treatment can be chosen in agreement with the thermal treatment for obtaining optimal bulk hardness in the precipitation hardening stainless steel.

Simultaneous surface and bulk hardening of HSS steels

A method of simultaneous surface and bulk hardening in a single operation is presented in which samples of an annealed HSS steel coated previously with thin carbide-forming metal layer are submitted to a unique heat treatment (in vacuum or in a nitrogen atmosphere). As a result, the bulk hardness of the samples increases to a value of 62–66 HRC and that of the surface increases to a value of 2500–3600 VHN (the latter due to the solid state reactions Me ⇒ MeC or Me ⇒ MeCN). At the same time, the impact toughness of the steel substrate is greater than that after conventional heat treatment of the relevant steel. Single carbide coatings (4 μm thick) of transition metal carbides of groups IV b and V b (Ti, Zr, Hf, V, Nb and Ta) with a dense, fine-grained microstructure, excellent adhesion to M2, 3-2Si, ASP23, ASP30 and ASP60 HSS substrates and approximately the same smoothness of the coatings as that of the substrates before deposition have been obtained using this method. The performance tests of numerous HSS tools (in particular of those for cold working of metals) as well as of some machine parts coated with a TiC layer according to the method have proved that the tool life increased 1.7–176 times in comparison with that for the same tools without any coating.