Changes In Surface Hardness Research Articles

A comparative evaluation of effect of denture cleansers on color stability, surface roughness and hardness of polyamide denture base material.

Different denture cleansers have an effect on color and different surface properties of polyamide denture base material. Thus, selecting a denture cleanser solution for polyamide denture base materials should be based on the properties of the denture cleanser itself. The present in vitro study is aimed to evaluate and compare the effect of different denture base cleansers on color, surface roughness and hardness of polyamide denture base material. Thirty specimens of commercially available polyamide denture base material were fabricated and divided into three groups of 10 each. Specimens from each group were immersed in different denture cleansers (sodium perborate, thyme oil and ozonated water) for 10 mins per day for 180 days. Initial and final color, surface roughness and surface hardness of each specimen were measured and the difference was calculated. Data was tabulated and subjected to statistical analysis using One way ANOVA for pair wise comparison. Polyamide denture base resin exhibited some degree of change in color, surface roughness, and surface hardness in all denture cleansers but was not statistically significant. The choice of denture cleanser for different denture base resins should be based on the chemistry of resin and the cleanser, denture cleanser concentration and duration of immersion.

Surface Hardness Modification of Selective Laser Melted Ti6Al4V Parts by Sliding Friction Diamond Burnishing

Selective laser melting (SLM) is a frequently used additive manufacturing technology for creating metallic, especially Ti6Al4V parts. After the production by SLM usually postprocessing is necessary for several reasons. Here the sliding friction diamond burnishing is applied as postprocessing procedure.In this paper an experimental study of surface hardness improvement of selective laser melted Ti6Al4V ELI cylindrical parts is demonstrated. The surface is modified by sliding friction diamond burnishing as postprocessing machining. The design of experiment method was applied to investigate effect of five factors (two SLM and three machining parameters) on surface hardness modification.It is shown that both SLM and postprocessing factors makes significant effect to the surface hardness improvement, most important ones are laser power, laser scan speed during manufacturing, and the burnishing force as factor of postprocessing. Empirical formulas are fit to measurement data, and visualized by surface plots. Relationship between factors and the surface hardness improvement is strongly nonlinear. In the investigated parameter window burnishing force has always positive effect to surface hardness improvement.Electron microscopic investigations show that change in surface hardness can be related to four main morphological changes: compression of the surface by plastic deformation of protrusions, attenuation of valleys, formation of inner cavities and creation of small protrusions by diamond tool. This paper is an extended paper of a conference paper published in the proceedings book of the XXXI. International Welding Conference (Kecskemét, Hungary).

Hardness and surface roughness of differently processed denture base acrylic resins after immersion in simulated gastric acid

Statement of problemThe effect of gastric acid on the surface properties of denture base acrylic resin is unknown. PurposeThe purpose of this in vitro study was to evaluate changes in the surface roughness and hardness of denture base acrylic resins after immersion in simulated gastric acid. Material and methodsAcrylic resin specimens (n=10) were prepared with 3 different processing techniques (compression-molded, injection-molded, and computer-aided design and computer-aided manufacturing [CAD-CAM] milled) and exposed to either gastric acid or artificial saliva (control). Surface roughness and hardness were measured at baseline (T0) and after 24-hour (T24) and 96-hour (T96) immersion in the solutions. The surface roughness and hardness data were analyzed by 3-way ANOVA and the Tukey HSD test (α=.05). ResultsAt T24, the greatest change in surface hardness was observed for compression-molded specimens in gastric acid (P<.05). At T96, changes in hardness values were higher in compression-molded specimens than those in milled specimens (P<.05). Regarding surface roughness, at T24, compression-molded and injection-molded specimens showed higher values than milled specimens in gastric acid (P<.05). Concerning specimens in artificial saliva, compression-molded specimens showed significantly higher changes in roughness than those of the others (P<.05). At T96, injection-molded specimens had the greatest roughness values (P<.05). Among specimens immersed in artificial saliva, milled specimens showed lower roughness values than the injection-molded or compression-molded specimens (P<.05). ConclusionsGastric acid exposure adversely affected the roughness and hardness of all the acrylic resins evaluated. CAD-CAM milled specimens showed better resistance to acid exposure after 24 and 96 hours in terms of roughness and hardness.

Concentration-dependent effect of carboxymethyl chitosan amorphous calcium phosphate on the surface hardness of primary tooth enamel.

To compare the effects of gels containing 2.5% and 5% carboxymethyl chitosan amorphous calcium phosphate (CMC-ACP) on the microhardness of primary tooth enamel. Twenty-four tooth specimens were demineralized with 37% phosphoric acid and divided into four groups: an untreated control group, a positive control group treated with casein phosphopeptide amorphous calcium phosphate, and two groups treated with 2.5% and 5% CMC-ACP gel, respectively. The enamel surface hardness was then measured with a Vickers hardness tester. In terms of Vickers Hardness Number (VHN), the degree of alteration in tooth surface microhardness was 77.83 ± 13.44 in the 5% CMC-ACP group and 52 ± 6.93 in the 2.5% CMC-ACP group (P = 0.002). The inter-group difference in the surface hardness change was significant (P < 0.05). The 5% CMC-ACP gel increased the hardness of primary tooth enamel to a greater degree than the 2.5% CMC-ACP gel.

Surface roughness and surface hardness changes in composite resin provisional crown before and after brushing with whitening toothpaste

Objective: To determine the surface roughness and surface hardness difference in composite resin provisional crown before and after brushing with whitening toothpaste.&#x0D; Material and Methods: This was a pre- and post-test group design experimental study. In this study, the sample was a composite resin provisional crown based on bis-acryl. The number of samples in this study was 32 samples, 16 for the surface roughness test and the other 16 for the surface hardness test. Each sample was brushed using a V8-Brushing Machine Modified, then tested for surface roughness and hardness using a Profilometer and Vickers Hardness Tester.&#x0D; Result: The paired T test was used to analyze the results statistically. There was a significant difference between the groups before and after brushing with whitening toothpaste. (p&lt;0.05).&#x0D; Conclusion: After simulated brushing with whitening toothpaste, there was a change in the the provisional crown material surface roughness and hardness value.

In vitro surface and color changes of tooth-colored restorative materials after sport and energy drink cyclic immersions.

There has not been any research conducted on surface properties and color changes from sport and energy drinks on bulk-fill resin composite, nanohybrid resin composite and glass ionomer restorative material. The aim of this in vitro study was to investigate the effect of sport and energy drinks on surface hardness, roughness and color changes of bulk-fill resin composite, nanohybrid resin composite and glass ionomer restorative material, and to also evaluate the acidity and titratable acidity of the drinks. One hundred and forty-seven specimens of each tooth-colored restorative material were prepared in a polytetrafluoroethylene mold (10mm. in diameter and 2mm. in thickness). Before immersion, baseline data of hardness, roughness, and color value were recorded. Each material was divided into 3 groups for sport drink, energy drink, and deionized water (serving as a control). The specimens were immersed in a storage agent for 5s, then in artificial saliva for 5s alternately for 24 cycles, and then stored in artificial saliva for 24h. The immersion cycle was repeated for 14days and hardness, roughness and color values were measured at 7 and 14days. After immersion, the glass ionomer restorative material had statistically less hardness, more roughness and more color changes than the others (P < 0.05). Energy drink groups statistically caused more surface and color changes than sport drink groups (P < 0.05). Sport and energy drinks affected hardness, roughness, and color changes in all the tooth-colored restorative materials evaluated.

Coupling Effect of Hydrostatic Pressure and Erosion on Corrosion Behavior of X70 Steel in Simulated Seawater.

The corrosion behavior of X70 steel under the coupling effect of pressure and erosion in simulated seawater was investigated by using corrosion loss, electrochemical tests, SEM, AFM, XPS, and Raman spectroscopy. The coupling effect of pressure and erosion could induce changes in the amounts and compositions of the corrosion products and increase pitting. The rate of the combined corrosion of X70 steel represents a downtrend, which still displays a higher corrosion rate than only immersion at the same pressure. This means that the coupling of pressure and erosion will accelerate corrosion, but the effect of erosion is weakened by pressure. The larger the pressure is, the more erosion is weakened. The pressure reduces the water cutting force by increasing the liquid viscosity and reduces the surface hardness changes under high pressure by generating magnetite, which is closely bound to the substrate.

Effect of Mouthwashes for COVID-19 Prevention on Surface Changes of Resin Composites

ObjectiveTo investigate the effect of various mouthwashes for COVID-19 prevention on surface hardness, roughness and color changes of bulk-fill and conventional resin composites and determine the pH and titratable acidity of mouthwashes.MethodsFour hundred and eighty specimens were fabricated in cylindrical molds (10 mm in diameter and 2 mm in thickness). Before immersion, baseline data of surface hardness, roughness, and color values were recorded. Each product of specimens (Filtek Z350XT, Premise, Filtek One Bulk Fill Restorative, SonicFil 2) were divided into 4 groups for 0.2% povidone iodine, 1% hydrogen peroxide, 0.12% chlorhexidine, and deionized water (serving as a control). The specimens were immersed in mouthwashes for 1 minute and then stored in artificial saliva until 24 hours. This process was repeated for 14 days. After immersion, surface hardness, roughness and color values of specimens were measured at 7 and 14 days. The data were statistically analyzed by two-way repeated ANOVA, Tukey's HSD and a t-test (p<0.05).ResultsAfter immersion, all mouthwashes caused significantly lower surface hardness, greater roughness and color values (p<0.05) on all resin composites tested.ConclusionsMouthwashes had an effect on all resin composites evaluated by a significant decrease of surface hardness, and an increase of roughness and color values (p<0.05).

Study on Thermo-oxidative Aging Mechanism of Air Spring Rubber Cord Composites

To study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, infrared spectrum, quality, hardness, and mechanical properties during the process of thermo-oxidative aging, and analyze the aging mechanism. The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface develops from no cracks to a large number of cracks; at 96-336 h, the rubber surface changes from a cracked state. The size of the crack on the rubber surface affects the rate of change of IRHD hardness. The larger the crack, the greater the hardness growth rate, otherwise the opposite. In the aging process, the rubber is in a state of dynamic development. The increase of cross-linking density causes changes in microscopic The increase of cross-linking density causes changes in microscopic morphology and accessible volume, which affects the IRHD hardness. The aging mechanism is more complicated. Material failure is dominated by the failure of the rubber matrix.

SPECIFIC FEATURES OF MAGNETO-ABRASIVE MACHINING OF CARBIDE TOOLS WITH PROTECTIVE CHAMFERS ON THE CUTTING EDGES

To ensure the durability and working ability of cutting tools, especially carbide, it is promising to form a rational microgeometry of working surfaces, in particular, the shape and geometry of cutting edges, as well as their hardening. For this, it is necessary to carry out additional machining of the tool after its sharpening operation. The magneto-abrasive machining method in conditions of large working gaps with a rational ratio of the impact and frictional interaction of the magneto-abrasive tool with the machined elements makes it possible to form microgeometry and strengthen both the cutting edges and the working surfaces. To ensure effective machining, it is necessary to determine the regularities of forming the microgeometry of the cutting edges with pre-made protective chamfers. The paper presents the results of a complex study of the magneto-abrasive machining process of carbide not sharpened inserts with protective chamfers on the cutting edges made at different angles. It was shown that the process of edge rounding is linearly related to the duration of magneto-abrasive machining. Moreover, the rate of increase in the size of the radius of cutting edges rounding with protective chamfers increases linearly with an increase in the angle of inclination of the chamfers, all other process conditions being equal. The physical description of the hardening mechanism of the surface layer of the working elements of the carbide cutting tool was proposed. It was shown that the hardening process is associated with the rational imposition of forces arising as a result of the frictional and impact interaction of the particles and the formations of the magneto-abrasive tool with the machined surfaces. It was found that the nature of the change in surface hardness obtained after magneto-abrasive machining on the protective chamfers has the wavy shape depending on the time of the process. The greatest increase in surface hardness takes place on chamfers made at angles of 10 ° and 20 ° and is explained by the value of the ratio between the forces of normal and tangential origin arising from the contact of the magneto-abrasive tool with the machined surfaces.

Acid Resistance of CAD/CAM Resin Composites.

Acid resistance of CAD/CAM resin composites. Erosion-related tooth surface loss is closely related to acid exposure, such as contact with acidic beverages or disease-related reflux. As a result, dental restorations in affected patients are also exposed to acids, which indicates that the performance and longevity of a dental restoration is impacted by the acid resistance of the individually employed restorative materials. However, unlike for ceramic materials, the acid resistance of CAD/CAM resin composites is not commonly evaluated by the manufacturers, and no standardised test methods have yet been established. Against this background, the present in vitro study aimed to examine the long-term resistance of CAD/CAM resin composites (Brilliant Crios, Cerasmart, Grandio blocs, Lava Ultimate, Shofu Block HC) against three acidic media (tonic water, acetic acid, hydrochloric acid) as well as demineralized water and to investigate potential damage mechanisms. Changes in surface roughness (Sa) were detected by confocal laser scanning microscopy (CLSM), and changes in surface hardness were measured using Vickers hardness (HV). The damage mechanisms were analysed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and micro X-ray computer tomography (µXCT). For each material, few changes in either Sa or HV were identified for at least one of the different media; for Cerasmart, the sharpest deterioration in surface properties was observed. SEM–EDS revealed leaching of barium, aluminium, and titanium from fillers in a 2 µm zone on the rough but not on the polished surface of the specimen. Within the limitations of the current study, it can be concluded that polished CAD/CAM resin composites can be recommended for clinical use in patients with erosive conditions.

Effect of addition of calcium phosphate nanoparticles to bleaching agents on surface hardness and color change of enamel

Effect of addition of calcium phosphate nanoparticles to bleaching agents on surface hardness and color change of enamel

Effect of different pediatric medications on various tooth colored restorative materials used in pediatric dentistry

Aim: To study and compare the effect of different pediatric medication on tooth-colored restorative materials. Method: One fifty specimens, 50 of each restorative material RMGIC, Compomer and Composite were obtained using circular acrylic mold with a diameter of 5mm and thickness of 2mm and A2 shade for standardization. They were further divided into five subgroups of multivitamin, antiepileptic, anxiolytic, bronchodilator and distilled water as control group. The specimens were immersed in syrup for 2 minutes twice a day for 40 days. The effect of medications on tooth colored restorative material was analysed by evaluation of colour stability using spectrophotometer and surface microhardness using Vikers hardness tester. Two-way analysis of variance (ANOVA) was used for multiple subgroup comparison. Result: All the materials showed statistically significant change in microhardness and color values after immersion in different syrups from baseline to 40th day period (p&lt;0.05). The maximum and minimum change in surface hardness was observed with RMGIC in antiepileptic (14.58) and multivitamin group (8.05) (p=0.000). Also, significant color change was noticed most with RMGIC in anxiolytic group (15.73) and least with composite (7.06) in antiepileptic group (p=0.000).

Effect of denture cleansers on the surface properties and color stability of 3D printed denture base materials

ObjectivesTo evaluate the effect of denture cleansers on surface roughness, hardness and color stability of 3D printed resins compared to heat-polymerized resin. MethodsAcrylic specimens (N = 160) were prepared using one heat-polymerized (HP) and three 3D printed denture base resins. Specimens per material were randomly divided into four groups (n = 10) according to immersion solutions as follows: distilled water (DW), sodium hypochlorite (NaOCl), effervescent tablet 1 or effervescent tablet 2. Color changes (∆E) were measured using a spectrophotometer. Surface roughness (Ra, µm) and microhardness were evaluated. The results were analyzed using one- and three-way ANOVA with Tukey's post hoc test (α = 0.05). ResultsAfter 360 days of cleaning protocols, we observed a significant increase in the surface roughness of tested materials (P<0.001). Hardness values significantly decreased in all groups (P<0.001), except HP and ND specimens, cleaned with effervescent tablet 1 (P>0.05) and AS specimens with effervescent tablet 2 (P = 0.051). According to the National Bureau of Standards (NBS) score, all denture base specimens had ‘perceivable’ to ‘extremely marked’ color change after immersion in NaOCl, while immersion in effervescent tablets 1 and 2 resulted in a ‘slight’ to ‘marked’ color change. Conclusion3D printed denture bases exhibited changes in surface roughness, hardness and color similar to HP denture base material. The use of denture cleansers resulted in a time-dependent increase in surface roughness and a decrease in hardness. The color change was significant with NaOCl, while effervescent denture cleansers produced a minimal color difference. Clinical significanceDenture cleansers seem to influence surface properties over time. The degree of impact is mainly dependent on the type of cleanser selected, regardless of the type of denture base material.

Effect of thermomechanical loads and nanocrystalline layer formation on induced surface hardening during orthogonal cutting of AISI 4140

Strain-hardening, thermal-softening as well as grain refinement may lead to unexpected changes in surface hardness of turned steel parts. Although the relationship between hardness, microstructure and cutting parameters has been investigated in previous research works, the prediction of surface hardness remains still a challenge. In this work, orthogonal turning tests were performed using low carbon steel AISI 4140 and thermomechanical loads, surface hardness and microstructure were measured. The relationship between surface hardness and thermomechanical loads was explored by establishing an empirical model. Moreover, grain size evolution was observed and correlated with micro hardness. Results suggest that cutting conditions can be controlled to achieve desired surface hardness by evaluating functions dependent on in-process measurements.

New insights into the anti-erosive property of a sugarcane-derived cystatin: different vehicle of application and potential mechanism of action.

A new sugarcane-derived cystatin (CaneCPI-5) showed anti-erosive properties when included in solutions and strong binding force to enamel, but the performance of this protein when added to gel formulations and its effect on surface free energy (SFE) requires further studies. Objective 1) to evaluate the protective effect of gels containing different concentrations of CaneCPI-5 against initial enamel erosion (Experiment 1); and 2) to analyze the SFE (γS) after treating the enamel surface with CaneCPI-5 solution (Experiment 2).Methodology In Experiment 1, 75 bovine enamel specimens were divided into five groups according to the gel treatments: placebo (negative control); 0.27%mucin+0.5%casein (positive control); 0.1 mg/mL CaneCPI-5; 1.0 mg/mL CaneCPI-5; or 2.0 mg/mL CaneCPI-5. Specimens were treated with the gels for 1 min, the AP was formed (human saliva) for 2 h and the specimens were incubated in 0.65% citric acid (pH=3.4) for 1 min. The percentage of surface hardness change (%SHC) was estimated. In Experiment 2, measurements were performed by an automatic goniometer using three probing liquids: diiodomethane, water and ethylene glycol. Specimens (n=10/group) remained untreated (control) or were treated with solution containing 0.1 mg/mL CaneCPI-5, air-dried for 45 min, and 0.5 µL of each liquid was dispensed on the surface to measure contact angles.Results Gels containing 0.1 and 1.0 mg/mL CaneCPI-5 significantly reduced %SHC compared to the other treatments (p<0.05). Treated enamel showed significantly lower γS than control, without changes in the apolar component (γSLW), but the polar component (γSAB=Lewis acid-base) became more negative (p<0.01). Moreover, CaneCPI-5 treatment showed higher γS - (electron-donor) values compared to control (p<0.01).Conclusions Gels containing 0.1 mg/mL or 1.0 mg/mL CaneCPI-5 protected enamel against initial dental erosion. CaneCPI-5 increased the number of electron donor sites on the enamel surface, which may affect AP formation and could be a potential mechanism of action to protect from erosion.

Flexural Strength, Elastic Modulus and Remineralizing Abilities of Bioactive Resin-Based Dental Sealants.

Objective: To assess the remineralizing abilities and compare the flexural strength and elastic modulus of different bioactive pit and fissure sealants. Materials and Methods: Human enamel samples were randomly and blindly sealed with one of the following bioactive materials: BioCoat (Bc), ACTIVA KIDS (Av) and BeautiSealant (Bu). Seal-it (Si) was used as a non-bioactive sealant beside a control blank (B) group with no sealant. The sealed samples were subjected to a pH-cycling model (7 days of demineralization–remineralization cycles). The enamel surface hardness change (SHC), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and polarized light microscopy were used to assess the remineralizing abilities of the studied sealants. Flexural strength and elastic modulus were also assessed following the ISO 4049 protocols. One-way analysis of variance (ANOVA) was used to analyze the results. Results: Bc sealant showed the highest FS and EM (p < 0.05). The contact with Bc and Bu sealants showed significantly lower %SHL (p < 0.05) in comparison to the other. These findings were supported by the results of SEM-EDX and polarized imaging by showing higher percentages of calcium and phosphate ions with the former sealants and thinner demineralized enamel bands. Conclusion: In this study, Bc showed the highest flexural strength. Bc and Bu sealants outperformed the other studied sealants in terms of their remineralization abilities.

The structure and prevalence of superficial carious and non-carious lesions of permanent and deciduous enamel in children who presented for routine dental care in various districts of St. Petersburg

Relevance. To increase the effectiveness of prevention and treatment protocols, it is above all necessary to consider the activity of caries, especially at the early enamel lesion stage, in the form of a white spot, to make the correct diagnosis based on a clinical examination, which assesses the location, change in surface hardness, symmetry, contour shape, depth, color and opacity of the lesion. Different causes of superficial enamel discoloration, in the form of white spots, are paramount for the restorative treatment as the quality of the enamel preparation affects the marginal fit and the durability of the restoration. However, poor oral hygiene, disturbance in eating behavior affect the course of non-carious hard-tissue diseases, which caries may complicate. Purpose – to optimize the diagnosis of initial dental enamel lesions to improve the caries prevention quality.Materials and methods. The study examined 460 children living in the Central and Krasnoselsky districts of St. Petersburg. The following indices assessed hard tissue condition: OHI-S, Greene and Vermillion; OHI by O'Leary T., Drake R., Naylor; White spot lesions index, Gorelick L, Geiger A. M, Gwinnett A. J., DMFT and df; caries activity.Results. The total prevalence of superficial (initial) lesions of hard tissues was 37.82%, i.e. 174 people out of 460 examined patients had superficial enamel lesions according to the criteria of I and II categories. The study found enamel changes in the age groups: 5-6 years (130) – 36 people (27.69%); 12 years old (175) – 62 people (35.42%); 15 years old (155) – 76 people (49.03%).Conclusions. Focusing on the caries activity signs rather than a precise differential diagnosis of the lesion nature is necessary to provide well-timed treatment and prevention upon detecting initial enamel lesion at a dental check-up.

Response of silicon nitride ceramics subject to laser shock treatment

A comprehensive and novel investigation on multiple-layer, square-beam laser shock treatment (“laser peening”) of Si 3 N 4 ceramics is reported in this work. Surface topography, hardness, fracture toughness (K Ic ), residual stresses, and microstructural changes were investigated. The evaluation of fracture toughness via the Vickers hardness indentation method revealed a reduction in crack lengths produced by the indenter after laser shock treatment (LST). Upon appropriate calculation, this revealed an increase in K IC of 60%. This being attributed to a near-surface (50 μm depth) compressive residual stress measured at −289 MPa. Multiple layer LST also induced beneficial residual stresses to a maximum measured depth of 512 μm. Oxidation was evident, only on the top surface of the ceramic, post LST (<5 μm depth) and was postulated to be due to hydrolyzation . The surface enhancement in K IC and flaw-size reduction was assigned to an elemental change on the surface, whereby, Si 3 N 4 was transformed to SiO 2 , particularly, with multiple layers of LST. Compressive residual stresses measured in the sub-surface were attributed to mechanical effects (below sub-surface elastic constraint) and corresponding shock-wave response of the Si 3 N 4 . This work has led to a new mechanistic understanding regarding the response of Si 3 N 4 ceramics subject to the LST deployed in this resesrch. The findings are significant because inducing deep compressive residual stresses and corresponding enhancement in surface K IC are important for the enhanced durability in many applications of this ceramic, including cutting tools, hip and knee implants, dental replacements, bullet-proof vests and rocket nozzles in automotive, aerospace, space and biomedical industries.

Redistribution of carbon and residual stress in low-temperature gaseous carburized austenitic stainless steel during thermal and mechanical loading

The effect of thermal annealing and mechanical loading on the redistribution of carbon- and residual stress-depth profiles in low-temperature carburized 316 L austenitic stainless steel was investigated. Gaseously carburized 316 L austenitic stainless steel was strained with a custom-built four-point bending device and isothermally annealed at temperatures in the range 300–500 °C for up to 200 h. Experimental results show that the carburized case is stable at 300 °C and that carbides precipitate only at the highest temperature investigated. At temperatures above 300 °C, the carbon atoms in the carburized case continue to diffuse inwardly, causing an increase of the case depth. Consequently, the surface concentration of carbon, the surface hardness and compressive residual stress change with time. Four-point bending during isothermal annealing accelerates the diffusion-controlled redistribution of carbon over the carburized case for both tensile and compressive side of the strained specimen. Since the carbon-induced volume expansion of austenite during carburizing is accommodated elasto-plastically, a substantial reduction of the carbon content in the surface-near region leads to a change from compressive to tensile residual stresses in the surface region.