This paper deals with evaluation of the effect of grain size of abrasive particles and number of tool strokes on the roughness values (
Rk
,
Rpk
,
Rvk
,
Mr1
,
Mr2
, and
Rp
/
Rt
ratio) in flexible ...honing. The grain size factor was investigated on two levels (400 and 800 mesh) and the number of tool strokes on three levels (1, 3, and 5) based on a full factorial design 2 × 3. Flexible honing was performed after conventional honing, on 30 crankcase cylinders of hermetic compressors made in gray cast iron. The analysis of variance technique showed that the effect of abrasive grain size on the roughness was more significant than that produced by the number of tool strokes. The abrasive grain size caused statistically significant effects on
Rpk
,
Rk
,
Mr2
, and
Rp
/
Rt
, whereas the number of tool strokes affected
Rpk
only. The interaction between these factors affected
Rk
. The flexible honing process using 800 mesh tool grain size and five tool strokes allowed for the obtainment of surfaces similar to those that resulted from the plateau honing operation. This result can increase the field of application of this process. Flexible honing was not able to remove the waviness present on the crankcase cylinder surfaces, whose amplitude was similar to those presented by the roughness.
Crankcase cylinders of hermetic compressors are produced in large numbers for refrigerators of domestic use. They are, usually, machined by using a three-stage honing process (roughing, ...semi-finishing, and finishing), and for their characterization during the quality control, an evaluation of roughness is carried out. Although the roughness represents a peerless factor to characterize the honed surfaces, its implementation is a challenge for scientists and technicians in general due to the difficulty of detecting the difference between the surface finish on different honing stages. This paper assesses the roughness of parts obtained by flexible honing applied after conventional honing process by using a portable surface roughness tester and an interferometer in white light mode (chromatic length aberration—CLA). An extensive evaluation of roughness was made using several roughness parameters, graphics, and curves that include the following: roughness profile, topographies, amplitude parameters,
Rk
family parameters, volume, and feature parameters. The measurement uncertainty associated with all roughness parameters was estimated by applying the methods proposed in the JCGM 101. The results obtained after flexible honing were compared with those found in parts machined by conventional honing. This experimentation showed that flexible honing process when applied after the conventional honing provided an essential improvement of the surface finish and an increase of the repeatability and the quality of honed parts. The volume and the feature parameters can be used as alternative to appropriately characterizing honed surfaces, because they were able of detecting the changes caused on the surface by different stage of honing process.
Corroded points can act as stress concentrators, usually resulting in the component failure at fewer cycles than was initially projected. Aerators are widely used in waste treatment units for ...chemical and biological control. Due to the chemically aggressive environment to which these components are subjected, they usually fail due to corrosion in one or more components. Cooling towers are one of the most applied equipment for temperature control in industrial processes. Due to generally hostile environments and operating conditions, this equipment is subject to failures which almost always lead to system imbalance followed by the catastrophic failure of the component. This work investigates the synergic effect of corrosion and fatigue in two separate case studies. In the first, the wear of the mixing shaft of an aerator was investigated. It was observed that the root cause of wear was the corrosion of the dissimilar welded joints in the mixing blades, which suffered the sensitization phenomenon. This sensitization led to the formation of accentuated corrosion pits, which concentrated stresses and led to the failure of the welded joint. After the joint failure, the component was left in an unbalanced state, which resulted in severe wear on the mixer shaft of the aerator. In the second, the failure of a cooling tower fan shaft fracture was evaluated, with the fractured component being compared to an intact one. As means of analysis were employed: metallographic tests on macroscopic and microscopic scales, tensile, chemical composition, hardness tests, and fractography. The results indicated the component failure due to fatigue under low amplitude loading, with corrosion pits as stress intensifiers.
This study proposes the use of a loading profile based on a combination of the ISL technique and the continuous multicycle indentation. This combination in our study was named N-ISL loading profile. ...The N-ISL loading profile was used to evaluate the hydrogen effect on nanomechanical properties of a Ni-base superalloy single crystal. For this purpose, nanoindentations were performed on a single crystal Ni-base superalloy. Hydrogen charging was carried out by cathodic protection with the sample immersed in a NaCl 3.5 wt% aqueous solution under a current density of − 1 mA/cm
2
. The results showed that the modified N-ISL profile provided the required time for hydrogen accumulation under the indenter tip, enhancing the hydrogen effect. The load relief in the N-ISL profile was found to be the major indicator of plastic deformation event and consequently strong evidence of dislocation movement. The hydrogen charging accentuated the plastic deformation in all steps, indicating that the hydrogen affected the dislocation mobility.
Graphical abstract
The incremental step loading technique has been widely used for material hydrogen embrittlement characterization. However, due to numerous error sources that can affect the measurement results and to ...the current lack of standardization, users are facing difficulties in the evaluation of measurement uncertainty as well as in the metrological performance evaluation of incremental step loading equipment. The paper deals with evaluation of the metrological performance of equipment used to characterize the susceptibility of materials to hydrogen embrittlement through use of incremental step loading technique. Additionally, a procedure is developed to estimate the measurement uncertainty associated with the results obtained during the test. Two equipment configurations were verified. The first one, with a load cell of 20 kN, was used for test specimens with nominal dimensions of 30 mm, 30 mm and 200 mm in width, thickness and length, respectively; and the second, with a 1 kN load cell was used for test specimens with nominal dimensions of 10 mm × 10 mm × 60 mm. Three measurands were evaluated in each assemblage (force applied on the specimen, equipment arm positioning angle and stress). Several metrological parameters were estimated (bias, accuracy, expanded uncertainty, repeatability, maximum error, hysteresis and nonlinearity). The effectiveness of the proposed procedure for uncertainty assessment was tested by calculation of the uncertainty associated with lower value for fast fracture strength. From the obtained results, it was concluded that the two equipment configurations had excellent metrological properties, in both the loading and unloading phases. It was shown that the proposed procedure can properly estimate the uncertainty associated with measurement on incremental step loading testing. Considering the widely use of the incremental step loading technique, the results here presented can be particularly useful for ensuring the traceability of results to the International System of Units required by the ISO 17025 standard.
•A new method to identify the Pth obtained on the ISL test was proposed.•A stiffness-based method was developed to identify the Pth of low hardness steels tested using ISL.•A revision of the ASTM ...F1624 standard was performed.•Analysis of the influence of step time and strain rate on the ISL results.•Evaluation of the hardness effect on the hydrogen embrittlement susceptibility.
Hydrogen embrittlement (HE) is one of the main problems related to the use of metallic materials in sour or wet environments. The Incremental Step-Loading (ISL) test used to evaluate the susceptibility to HE of steels has gained more visibility over recent years, thus allowing for the determination of the threshold load (Pth) in H+ enriched environments. However, the ISL standard, ASTM F1624, limits the test to steels with a minimum hardness of 33 HRC. Even for those steels with 33 HRC, the results present some misinterpretations. In addition to this fact, one needs to consider that there are several applications where steels with hardness below 33 HRC are used, as for instance, in fasteners and tool joints under cathodic protection used in the oil and gas industry, for which hardness varies from 26 to 32 HRC. In light of the aforementioned, the standard limitation represents a major disadvantage related to the application of the ISL test. Grounded upon the said, the aim of the present study is to propose a methodology based on the specimen stiffness to be used in the ISL test results, allowing the Pth determination of steels with hardness lower than 33HRC. Conventional and extended ISL tests were performed in two steels (4137-M and 4130-M) with a 32HRC hardness values. Applying the stiffness-based method on the the conventional ISL test results, a threshold load (Pth) of 71.5 %PFFS and 66.0 %PFFS were found for the 4137-M and 4130-M steels, respectively. To validate these results, extended ISL tests were performed on both steels and the results showed a Pth of 73.7 %PFFS for the 4137-M steel and 66.0 %PFFS for the 4130-M steel. The results from the conventional ISL test, using the stiffness-based method proposed in this study, provided values similar or with differences lower than 5 %PFFS, when compared alongside the extended ISL tests. Moreover, ISL tests were performed on the same steels with 40 HRC hardness, and the AISI4137-M presented a Pth of 21.6 %PFFS and for 4130-M the Pth was 22.0 %PFFS. The main conclusion obtained from these tests was that, when large amount of plastic deformation is not present on ISL test, the load drop visual detection is sufficient to determine the Pth. As expected, it was observed that both steels with 40 HRC presented higher HE susceptibility than the 32 HRC ones. This behavior was due to higher stress concentration at the notch root presented by the higher hardness condition. The stiffness-based method proved to be robust and capable of separate yielding from hydrogen induced cracking of low hardness steels and could also be used to identify the Pth values of steels with hardness lower than that specified by the ASTM F1624 standard, and which are tested using the ISL test.
The focus of this study is to analyze hydrogen embrittlement susceptibility of a modified AISI 4130 steel by means of incremental step loading tests. Three different microstructures with a hardness ...of 40 HRC were analyzed: martensite with large and small prior austenite grains and dual-phase (martensite/ferrite). According to the results, the dual-phase microstructure presented the lowest hydrogen embrittlement susceptibility and martensite with large prior austenite grains, the highest. This behavior was attributed to the lower fraction of high-angle boundaries presented by the martensite with large prior austenite grains, which led to a higher diffusible hydrogen content. Moreover, the ferrite local deformation in the dual-phase microstructure enhanced its hydrogen embrittlement resistance by lowering the stress concentration. A synergic effect of decohesion and localized plasticity was identified on the hydrogen induced fracture of the tested microstructures leading to an intergranular + quasi-cleavage fracture in the martensite and quasi-cleavage in the dual-phase microstructure.
•Evaluation of the microstructure effect on hydrogen embrittlement by means of ISL test.•Hydrogen embrittlement analysis of martensitic and dual-phase microstructures.•Role of prior austenite grain size on hydrogen embrittlement susceptibility.•Effect of high-angle boundaries on hydrogen diffusion behavior.•Identification of hydrogen induced fracture micromechanisms through SEM and EBSD analysis.
•Hydrogen embrittlement threshold force (Pth) was evaluated using the Small Punch Test.•Small Punch Tests with steps based on ASTM F1624 were carried out.•A methodology for Pth calculation based on ...the specimen stiffness is presented.•The proposed methodology was validated testing notched Small Punch Test specimens.
This study aims at developing a methodology for assessing the hydrogen embrittlement threshold force (Pth) in high strength steels using the Small Punch Test (SPT) technique and the ASTM F1624 standard recommendations. This methodology is based on material specimen stiffness and aims to test steels with hardness lower than 33HRC. In the methodology development phase, non-notched specimens made of four high strength steels (AISI 4137 M − 32HRC and AISI 4130 M − 25, 40, 44HRC), widely used in the oil and gas offshore industry, were tested according to the ASTM F1624 standard. Based on the literature, hold times of 20 min for the first 10 and 40 min for the last 10 steps were adopted. The tests were performed in a cathodic protection environment, consisting of a 3.5 wt% NaCl aqueous solution for hydrogen embrittlement (HE). The threshold force values (Pth-SPT) for the Incremental Small Punch Test (ISPT) were measured based on the specimen stiffness. In order to validate the proposed methodology, the ISPT and the incremental step loading (ISL) techniques were applied to test notched specimens manufactured from AISI 4130 M − 25 HRC and AISI 4137 M − 32HRC. The Pth-SPT values showed a systematic error of -4.0 % and 2.2 %, respectively, in relation to the ISL method, indicating an excellent accuracy. The Pth-SPT values provided by the ISPT under the experimental conditions investigated are adequate and quite promising. These values corroborate that the proposed methodology for the measuring of the Pth-SPT, based on material specimen stiffness, proved to be robust, efficient, and of easy implementation.
•Sigma phase nucleated cracks formed at high temperatures reduced toughness in welds.•Presence of SO2, SO3, O2 accelerates sigma phase corrosion in reduced Cr regions.•Notched specimens revealed ...E308L weld susceptibility, with faster crack formation.•Synergistic stresses, microstructural changes, and corrosion caused weld failure.•Materials with higher resistance to sigma phase formation should be investigated.
This study undertakes a comprehensive examination of crack formation in welded joints of austenitic stainless steel 304, particularly in high-temperature corrosive environments prevalent in sulfuric acid production units. Initially, an investigation was conducted on a steam superheater that had been operational for about 19 years, where a crack formation was discovered. This unit, subjected to a working temperature of approximately 620 °C and exposure to gases composed of SO2, SO3, and O2, allowed for the analysis of corrosion products formed during the crack propagation. Building on the initial findings, a more controlled study was undertaken, focusing on the cracks formed in welded joints using the coated electrode E308L for joining 304H stainless steel plates under similar corrosive conditions. The specimens, constructed using materials typically utilized in sulfuric acid production units, were designed based on the double-beam principle, enabling exposure to both tensile stresses and a corrosive environment at high temperatures. Over a span of 122 days, or roughly 3000 h, microstructural analyses were conducted, revealing that the formation and propagation of cracks preferentially occurred through fragile microconstituents, notably the sigma phase. These findings mirrored the sigma phase formation observed in the initial superheater study and point to a stress corrosion process acting synergistically with sigma phase development, and consequently seen as a probable cause of failure. This comprehensive evaluation, therefore, indicates a significant role of the sigma phase and corrosive environments in influencing crack formation and propagation in welded joints of austenitic stainless steels, which require further studies for preventative strategies in industrial setups.
Characterization of turned surfaces using 3D roughness parameters Arencibia, Rosenda Valdés; Arantes, Luciano José; Franco, Vera Lúcia Donizetti Sousa ...
Journal of the Brazilian Society of Mechanical Sciences and Engineering,
08/2024, Letnik:
46, Številka:
8
Journal Article
In this paper, an extensive study was conducted to identify which 3D roughness parameters best characterize turned surfaces. The investigation took place with samples made of nodular cast iron and ...considering different cutting conditions. For this purpose, a factorial design 2
2
was proposed, where the cutting depth was assumed to be 0.5 mm and 1.0 mm, whereas the feed was 0.1 mm/rev and 0.2 mm/rev. Three-dimensional roughness parameters were collected (area amplitude parameters, functional and feature parameters) and 3D effective topography was also obtained for each condition investigated. The uncertainty associated with the measurement of all evaluated parameters was estimated. The most significant effects were observed for
Sa
,
Sq
,
Vv
,
Vmp
,
Spd
, and
Sda
. Application of the Mann–Whitney
U
tests showed that for
Sq
,
Sa
,
Vv
,
Vmp
,
Spd
and
Sda
there were four combinations (66.6%) that exhibited statistically significant differences. These parameters enable to detect changes caused by different cutting conditions investigated and they can be used to best characterize turned surfaces in conjunction with
Ra
(
Sa
). The most significant percentage differences, in modulus, were observed between values of all parameters obtained in Condition 4 in relation to Condition 1. The most expressive differences were of: 308% (
Sdv
), 288% (
Shv
), 146% (
Ssk
), 118% (
Vmp
), 95% (
Vv
), and 80% (
Sa
). The Shapiro–Wilk test revealed that roughness results of the parameters (
Vv
,
Vmp
,
Vvc
,
Sdv,
and
Shv
) do not follow a Normal distribution, since
p
-value < 0.05 was obtained under the investigated conditions.
