Case Hardening Research Articles

The Role of Case Hardening in the Preservation of the Cavates and Petroglyphs of Bandelier

ABSTRACTBandelier National Monument (BNM) was created to protect an extraordinary inventory of archaeological resources carved in the Tshirege Member of the Bandelier Tuff. These include more than one thousand excavated chambers, called cavates, used for dwelling, storage, and textile production. The glass-rich tuffs at the base of the Tshirege Member are poorly consolidated and susceptible to erosion by wind, rain, and mechanical abrasion, with resultant loss of cultural material. However, rock surfaces develop protective weathering rinds that are resistant to erosion. Using optical microscopy, SEM-EDS, XRD, and electron microprobe analysis, we determined that this rind consists of clay and silt sediments colonized by lichens and other surface biota, accompanied by the precipitation of secondary minerals in the near-surface pore space. Scoping experiments focused on glass-organic acid interactions indicate that oxalic acid excreted by microbial crust constituents catalyzes biogeochemical reactions that lead to the preferential dissolution of Si, Al, and Fe components of the volcanic glass; these cations become available for precipitation of opal, and smectite and sepiolite clays. Enzyme assays that quantify biological activity at outcrop surfaces indicate that microbial populations initially thrive as they derive nutrients from the dissolution reactions of the glass, but activity starts to decline as precipitation of secondary minerals limits access to new sources of nutrients, so that alteration processes are self-limiting. As case hardening progresses, imbibition rates at the surface decrease, and the erosion resistance of the altered surfaces is substantially improved. This article presents summary results of research conducted over a period of five years to characterize the roles of lichens and other microflora in rind formation, and the resulting contributions to tuff stability. The interaction of lichens and other microflora with rock surfaces in archaeological sites and monuments is usually explored in terms of biodeterioration and consequent damage. However, this study shows that, under some circumstances, lichens and microflora provide a level of erosion protection to relatively porous and unconsolidated rock strata that outweighs their biodeteriorative effects.

Model based laser-ultrasound determination of hardness gradients of gas-carburized steel

Gas carburizing is a common industrial process utilized for case hardening of low carbon steels. However, there is a lack of non-destructive evaluation systems for the measurement of hardness-depth profiles. We propose a novel measurement method for the determination of hardness-depth profiles of two-step gas carburized steel specimens. The method is based on the measurement of broadband laser excited Rayleigh waves. Rayleigh waves were generated by a pulsed Nd: YAG laser in the thermoelastic regime and measured with a heterodyne Mach-Zehnder interferometer in the near-field. From two measurements with different source to receiver distances the dispersion diagrams were calculated by means of the phase spectral analysis method. In order to simulate the observed dispersive behavior of the Rayleigh waves, first the two-step gas carburizing process was simulated using solutions of the diffusion equation. The resulting continuous hardness profile was then discretized into up to 100 layers. Thereafter the Rayleigh wave dispersion diagram was calculated from the discretized stack of layers using a delta-matrix formulation of the Thomson-Haskell transfer matrix method. In order to obtain best fitting hardness profiles, the simulated dispersion diagrams were fitted to measurements with a curve fitting algorithm. Comparison of the Rayleigh wave inversion method with destructively obtained Vickers hardness profiles shows good quantitative agreement.

Secrets of Abraham Ganz’s Train Wheels Enlightened by Materials Science Methods

Case hardened, double-walled train wheel, produced in the foundry of Abraham Ganz in 1867 and used for long time on the railroad tracks, was studied and evaluated by modern methods of materials sciences. The investigations indicated the presence of 0.059m% antimony (Sb), distributed uniformly in the material of the wheel. This quantity is several times higher than the average Sb amounts (<0.01m%) of the other components get into the castings. Sb was detected even in the several mm thick crust; except in the outermost surface layer with < 1 µm thickness. Based on the 20th century comprehensive studies, the antimony content, detected in the wheel, was found to be ideal. In grey iron it is a powerful pearlite stabilizer which has favourable effects on its mechanical properties and serviceability.The investigation of the surface structure proved that the excellent hardness (~600 HV) at the crust surface was due to the “nano-composite” structure formed from the pearlite as a consequence of severe plastic deformation during service. This was also promoted by the high amount (4.09m%) of carbon present in the casting. The microstructure refinement during operation most probably contributes to the long service lifetime of the wheels.The secret of the Abraham Ganz’s train wheels is inherently present – besides the novel construction and production technology (case hardening) – in the above mentioned composition and the structure of the material.

Ballistic impact of layered and case-hardened steel plates

We investigated the ballistic resistance of hot-rolled structural steel plates with a nominal yield stress of 355MPa in this study. Ballistic tests were conducted with 7.62mm armor piercing bullets on monolithic and multi-layered configurations both in the as-received (AR) state and in a case-hardened (CH) state. In the CH state we made the surface stronger while preserving a relatively ductile core. This was done to improve the ballistic properties of the plates. Quasi-static uniaxial tension tests and Vickers hardness tests were conducted to calibrate constitutive models for numerical simulations. The ballistic tests revealed that the capacity was highest for a monolithic CH plate, and that case hardening increased the perforation resistance by more than 20%. Plate layering decreased the capacity of the CH plates, while the capacity of the AR plates did not decrease consistently by increasing the number of layers. Finally, we used the hardness measurements to distribute material properties across the thickness of the CH plates. These distributed material properties were used in numerical models. Finite element simulations gave predominantly conservative results within 11% of the experimental values.

Catastrophic Limestone Decay at the Central Sanctuary of Iupiter Dolichenus at Dülük Baba Tepesi in Southern Turkey: Causes and Implications for Future Conservation

Dramatic deterioration of Hellenistic-Roman limestone remains recently excavated at Dülük Baba Tepesi (Southern Turkey) has been observed following the cold, wet winter of 2011/2012. A conceptual model is presented to explain the dramatic deterioration in which case hardening develops and initially strengthens the stone against deterioration, but then makes it more prone to exfoliation and blistering. Data collected using non-destructive techniques (Equotip surface hardness tester and Karsten tube for water uptake) on Fırat and Gaziantep formation limestone time series excavated in 2005, 2007, and 2013 demonstrates the progress of case hardening and deterioration after excavation. In combination with meteorological data from Gaziantep weather station the results are used to test and revise the model taking into account non-linear and threshold effects. Future excavation and conservation efforts should take into account the often-complex interactions between post-excavation case hardening and extreme winter conditions which can cause catastrophic deterioration.

Effects of Beeswax Coating on the Oxidative Stability of Long-Ripened Italian Salami

Beeswax coating of foods put a barrier to oxygen, light, and vapour that can help to prevent oxidation of fat and pigments and water loss. The amounts of 2-thiobarbituric acid reactive substances (TBARS) and water activity (Aw) were assessed in Italian salami coated with beeswax at 55 days of ripening and compared with controls at 5, 6, and 7 months of shelf life. The results were correlated with sensory quality. TBARS levels were below 0.8 mg kg−1 in the beeswax-coated salami until 6 months of aging (median 0.697, max 0.795) and significantly higher in the uncoated salami (median 1.176, max 1.227). A slight correlation between the amount of TBARS and Aw was observed in beeswax-coated salamis, whereas this effect was masked in controls by the large Aw variability observed at 7 months. Beeswax coating prevents case hardening and facilitated the peeling.

Reduction of Burr Formation for Conventional Shear Cutting of Boron-alloyed Sheets through Focused Heat Treatment

Conventional shear cutting is the most commonly used manufacturing process in sheet metal working. Due to its good automation capacity it is high productive and therefore it has a significant economic importance. However, the occurence of burr is still a remaining issue of the conventional shear cutting process. The burr has to be removed as they pose a high risk for functional and ergonomic aspects. Deburring requires additional processing steps in the production line, which are expensive and time-consuming. In the case of automotive industry components, the removal costs make up 15 % to 20 % of production costs. When it comes to precision components, such as engine parts, the cost equals even up to 30 %. Thus, it is worthwhile to aim for the avoidance or at least the reduction of burr formation.In this work, different heat treatment methods were applied to 4 mm thick 22MnB5 sheets, in order to increase the strength of the material and thereby reduce burr formation. For this purpose, the heat treatment methods case hardening, flame hardening, and plasma nitriding were studied. After punching the hardened sheets, the characteristic cutting surfaces were determined by tactile measuring. The results of the different heat treatment methods were compared regarding the resulting burr and evaluated by means of Vickers hardness measurements and microstructural analysis.

Local Residual Stress Depth Distribution in the Inner Gearing of a Case Hardened Sliding Collar

With respect to residual stress analysis the inner gearing of an automotive sliding collar is a component with a challenging, complex geometry. The accessibility of the tooth root does not exist for conventional measuring approaches. However, the process steps like e.g. broaching and case hardening induce characteristic residual stress distributions, which must be known for the valuation of the mechanical integrity of the parts. For lab X-ray stress analysis approaches according to the sin2ψ-method [1] the ring like structure must be sectioned, which affects the process induced residual stress state. The tooth root is rather small, which further leads to shadowing effects during tilting of the sample. Standard mechanical approaches like incremental hole drilling can be excluded due to the narrow tooth root. Local neutron diffraction residual stress analysis in the tooth root by means of neutron through surface strain scanning at the STRESS-SPEC instrument at the research reactor FRM II, Garching (Germany) was successfully carried out for the inner gearing. A measuring and evaluation strategy is proposed, where special attention is paid to the compensation of the surface effect due to the incomplete immersion of the nominal gauge volume during through surface scanning and to the local variation of the D0-value as a consequence of the case hardening process.

Devising Strain Hardening Models Using Kocks–Mecking Plots—A Comparison of Model Development for Titanium Aluminides and Case Hardening Steel

The present study focuses on the development of strain hardening models taking into account the peculiarities of titanium aluminides. In comparison to steels, whose behavior has been studied extensively in the past, titanium aluminides possess a much larger initial work hardening rate, a sharp peak stress and pronounced softening. The work hardening behavior of a TNB-V4 (Ti–44.5Al–6.25Nb–0.8Mo–0.1B) alloy is studied using isothermal hot compression tests conducted on a Gleeble 3500 simulator, and compared to the typical case hardening steel 25MoCrS4. The behavior is analyzed with the help of the Kocks-Mecking plots. In contrast to steel the TNB-V4 alloy shows a non-linear course of θ (i.e., no stage-III hardening) initially and exhibits neither a plateau (stage IV hardening) nor an inflection point at all deformation conditions. The present paper describes the development and application of a methodology for the design of strain hardening models for the TNB-V4 alloy and the 25CrMoS4 steel by taking the course of the Kocks-Mecking plots into account. Both models use different approaches for the hardening and softening mechanisms and accurately predict the flow stress over a wide range of deformation conditions. The methodology may hence assist in further developments of more sophisticated physically-based strain hardening models for TiAl-alloys.

Combined effect of shot peening, subcritical austenitic nitriding, and cryo-treatment on surface modification of AISI 4140 steel

ABSTRACTShot peening is a simple but effective severe plastic deformation process to synthesize ultrafine grains in micro- to nanometer range on metallic surfaces. In this work, shot peening on AISI 4140 steel specimens was done in a novel centrifugal air blast shot peening reactor with shot velocity of 5.8 m/s for 3 h. Characterization of the shot peened surface (XRD, micro-hardness, SEM, and TEM) showed that surface undergoes significant plastic deformation with marked increase in microstrain of lattice, dislocation density, and surface hardness. XRD profiles and TEM analysis confirmed formation of ultrafine grain structure in the nanometer range. These specimens were then subjected to austenitic nitriding at 610°C for 4 h followed by cryo-treatment at − 185°C for 32 h. Characterization of pre-shot peened nitrided and cryo-treated surfaces showed that there was marked improvement in surface hardness (from 695 to 797 HV0.05) and effective case depth (from 19 to 54 µm) in comparison with un-shot peened nitrided and cryo-treated specimens. It was demonstrated that presence of ultrafine grain structure and austenitic phase during nitriding plays synergetic role to improve content and diffusion kinetics of nitrogen in AISI 4140 steel surface.

Coupled process simulation of cold extrusion and heat treatment distortion of steel shafts

A simulation study will be presented regarding effects of cold extrusion – a forming process – on heat treatment distortion of a 20MnCr5 (SAE 5120) steel. Therefore, both cold extrusion and heat treatment simulations with transferring the geometry and the stresses from the cold extrusion to the heat treatment were done. The influence of two degrees of deformation, two friction coefficients, and two heat transfer coefficients between workpiece and tool on the heat treatment distortion was studied. Additionally, heat treatment simulations were done regarding only the geometry without transferring the stress (as machined state). Stress relief annealing and case hardening were applied as heat treatment. Finally, the simulated length changes of the shafts were compared with experimentally determined length changes using different lubricants, degrees of deformation, and heat treatments.

Identification of design related distortion of gear base bodies by experimental investigations

The economic and ecological need for reduced weight of automobiles leads to increasing activities in recent years. One way to achieve this aim is to use modified designs for components with a high weight. Here the gear box and especially the gears have a potential for significant weight reduction. But besides the functional behavior of the components under consideration the manufacturing processes must be able to produce them with high accuracy and without increasing costs. Focussing on manufacturing lines of gears, it is known on the one hand that distortion after final heat treatment can depend on gear geometry, one of the most important carriers of distortion potential. On the other hand no design rules for lightweight gears exist. Therefore in this paper first results of a research project are presented. The manufacturing line was kept constant to continuously cast steel, rolling the square blooms to semi‐finished material, forming of forging blanks with constant dimensions, annealing, turning of different shaped gear base bodies, and case hardening by low pressure carburizing in combination with high pressure gas quenching. The resulting size and shape changes as function of geometry modifications with a maximum weight reduction of 20 % will be shown and discussed.

Distortion after Case Hardening of Steels

Distortion after Case Hardening of Steels

ПОВЫШЕНИЕ ДОЛГОВЕЧНОСТИ ДЕТАЛЕЙ МАШИН КОМБИНИРОВАННОЙ УПРОЧНЯЮЩЕЙ ОБРАБОТКОЙ

The reason of failure of many machine parts is contact fatigue. To increase contact-fatigue wear resistance it is necessary to create a surface layer possessing increased stress-strain properties which are formed by strengthening. The most effective methods of strengthening are those creating a surface layer with simultaneous high hardness and large reserve of plasticity. One of such methods is combined strengthening at which a surface to be strengthened is affected preliminarily by deformation shock waves forming a deep work-hardened layer and then its case hardening is carried out. As a result of this process a strengthened surface layer is formed which consists of hard uniformly strengthened carburized layer and a softer heterogeneously strengthened sublayer alternating hard and soft areas depending on streng-thening modes with shock waves. The operational researches of samples obtained by the offered combined strengthening have shown high efficiency of the method for life increase under conditions of contact cyclic loads which can increase considerably a range of machine parts to be strengthened.

Distortion Control through Synchronized Vacuum Heat Treatment

AbstractControlling distortion is of key importance during the case hardening process for the production of automotive and non-automotive metallic components. By effective control of distortion and the variation of distortion, significant costs in post heat treatment machining processes can be avoided. In some cases it is even possible to eliminate all post-machining. In other cases it may be possible to avoid the press-quenching of individual components, resulting in huge cost-benefits. A recently introduced new vacuum furnace design allows the treatment of small batches in a single layer of parts (“2D-treatment”) which allows for easy automated loading and unloading of the fixture-trays. By using the small batch concept, a continuous flow of parts can be established (“One Piece Flow”). There is no need to wait until enough parts are collected to build a large batch with multiple layers (“3D-batch”). This compact furnace unit can be implemented into the heart of the production chain and provides heat-treatment processes which can be fully synchronized with the green and hard machining-operations. When performing case hardening, the components are Low Pressure Carburized (LPC) at high temperatures (1050 °C) followed by gas quenching. The treatment in single layers offers an optimum in quality regarding: temperature homogeneity, quench homogeneity and distortion control. Typical components for this technology come from the automotive, aerospace and tool industry. The directly following contribution in this Journal (A. Schüler et al., p. 90–98)shows more results achieved with this technology on selected truck-components such as gears and sliding-sleeves.

Fatigue of gears in the finite life regime — Experiments and probabilistic modelling

Fatigue of case hardened gears is investigated experimentally and numerically with focus on the finite fatigue life regime. Pulsating tooth bending fatigue experiments are performed at different load levels on two types of gears of different sizes to determine load–fatigue life relations. The experiments are compared with a probabilistic model for the finite life regime based on weakest-link theory. The stress fields, needed in the evaluations, are obtained by finite element simulations taking residual stresses, both due to case hardening and plastic deformation, into account. The stress history at each element is summarized into two different effective fatigue stress measures; one based on the largest principal stress and the Findley multiaxial fatigue stress. The material parameter needed in the Findley stress is determined by a linear correlation of the parameter with the Vickers hardness of the material using multiaxial fatigue data found in the literature. Both equivalent stress measures show equal behaviour and the probabilistic model shows good agreement with the experimental data in the finite fatigue life regime.

Stress Analysis to Improve Pitting Resistance in Gear Teeth

Helical gears are subjected to contact fatigue loads, which may result in the damage of the gear teeth, for example by pitting-type failure. Microstructural features, mechanical properties and residual stresses have strong influence on the pitting resistance of the material. Case hardening, followed by shot peening processes, are usually carried out to produce a wear-resistant surface with compressive residual stresses established in the gear tooth surface region. This work aims to evaluate, by finite element analyses, the stress distribution through the gear teeth during the gear coupling. The results allow the evaluation of the stress components that may lead to the pitting failure, indicating the design variables that are important to improve the reliability of the gear.

Study the influence of case hardening and sliding wear parameters on carburised AISI 1211 steel

The influence of sliding wear parameters and case hardening parameter on carburised AISI 1211 steel have been investigated using Taguchi technique. The carburising and sliding wear parameters are considered as input parameters and the weight loss is considered as the response for conducting experiments. The signal to noise ratio and analysis of variance are applied to examine the degree of influence of selected parameters on the sliding wear. The experimental results revealed that carburising temperature has a significant effect on wear followed by the applied load. Regression analysis is employed to develop a prediction model for weight loss. The scanning electron microscope (SEM) images exhibit that the case depth varies between 28 microns and 92 microns and it follows the parabolic law. The hardness of the case varies between 613 Hv0.05 and 746 Hv0.05 with increase in temperature. The wear track images and wear coefficient (k) values show that the adhesive wear is the dominant wear mechanism.

Effect of puffing conditions on physical properties and rehydration characteristic of instant rice product

SummaryThe aim of this work was to study the effects of puffing conditions on the properties of instant rice and to obtain optimal processing condition for product with rehydration time within 5 min. Thai jasmine rice was soaked, cooked and dried at 80 °C in a tray dryer before being puffed at different moisture contents (15–20% wb), temperatures (200–220 °C) and time intervals (20–30 s). The rice puffed at higher moisture contents and puffing temperatures for longer time exhibited higher volume expansion ratios and shorter rehydration times. Presumably, case hardening of the grain surface occurred. Instant rice that can be rehydrated in 5 min with more acceptable hardness than the commercial instant rice was obtained. Regression models to predict the quality of instant rice were developed using response surface methodology.

Influence of CO2 Gas in the Electro-Carburisation Process of Mild Steel

In the attempt to develop a clean process, study has been conducted to determine the effect of absorbed CO2 gas as source of carbon to the case hardening of treated mild steels in the recently developed process of electro-carburisation in non-toxic molten carbonate salts. The concentration of CO2 in the process was varied by purging a CO2 and N2 mixture at flow rate ratios of CO2:N2 of 200:0, 150:50, 100:100, 50:150 and 0:200 mL.min -1 . Electro-carburisation was performed in two types of molten salt electrolyte i.e. a mixed anion Na2CO3-NaCl (mole ratio 4:1) and a pure carbonate Li2CO3-K2CO3 (1:1 mole ratio). A voltage of 2.5V was applied between mild steel cathode and an inert SnO2 anode at a carburisation temperature of 800 o C for 60 minutes. The results show that greater CO2 concentration produced samples with greater surface hardness and thicker case-hardening, attributed to the increased availability of the electro-active carbon source which was generated by absorption of CO2. Electro-carburisation in Li2CO3-K2CO3 and Na2CO3-NaCl gave surface hardness of 1075 ± 25 HV, however Li2CO3-K2CO3 (540 thickness) gave thicker case depth compared to Na2CO3-NaCl (500 thickness). This is thought to be due to the amount of carbon deposited in each salt; 12.70 wt.% C in Li2CO3-K2CO3 and 11.10 wt.% C in Na2CO3-NaCl.