Low Carbon Steel Specimens Research Articles

Improved fatigue behavior of low-carbon steel 20GL by applying ultrasonic impact treatment combined with the electric discharge surface alloying

The effects of severe plastic deformation induced by ultrasonic impact treatment (UIT) and the electric discharge surface alloying (EDSA) with chromium on the stress-controlled fatigue response of low-carbon steel 20GL are studied. The surface microrelief and integrity were analyzed using light microscopy and scanning electron microscopy (SEM). The structural formations in the sub-surface layers were characterized by means of X-ray diffraction analysis and transmission electron microscopy (TEM). The steel specimens underwent UIT, and complex UIT+EDSA and UIT+EDSA+UIT processes demonstrate the fatigue strength magnitudes increased respectively by ~15, ~5 and ~30% on the base of 107 cycles in comparison with that for the pristine specimen. SEM analysis of fracture surfaces reveals the subsurface crack nucleation in the UIT-processed specimens instead of superficial crack initiation observed in the pristine and EDSA-processed ones. TEM studies demonstrate that a dislocation-cell structure forms in ferrite grains and partial dissolution of cementite occurs in pearlite grains both at the surface after UIT and in the layer at a depth of 15–25µm after the UIT+EDSA+UIT process. The enhanced fatigue strength and prolonged lifetime of the low-carbon steel specimens after UIT and UIT+EDSA+UIT processes are concluded to be associated with the subsurface crack nucleation achieved by the following factors: (i) minimized surface roughness and improved integrity of the modified layer; (ii) compressive residual stresses; and (iii) surface hardening coupled with the alloying by chromium and with the formation of the dislocation-cell structure containing the cell walls impenetrable to moving dislocations at cyclic loading.

Application of titanium machining chips in welding consumables for wear-resistant hardfacing

Equipment of sugar cane plants and mineral extraction are submitted to severe abrasive wear conditions. Welded hardfacings are usually applied to repair this kind of damage, where commercial chromium/carbon-rich welding consumables have usually been employed. In the present work we investigated the microstructure of experimental hardfacings made by addition of residues (chips) collected from the machining of ASTM F67 (unalloyed Ti, grade 4) alloy. Mixtures with different carbide-formers (Cr/Nb ferro-alloys) were also tested. Two layers of ‘pure’ chips (Ti), chips plus Fe–Cr (Ti–Cr), and chips plus Fe–Nb (Ti–Nb) were applied on low-carbon steel specimens by the GTAW/TIG process. The microstructure of hardfacing layers was observed by optical and scanning electron microscopy (SEM) equipped with EDS microanalysis. The microstructural characterization has determined that carbide distributions change significantly with the chemical nature of the hardfacing. SEM observations coupled with EDS microanalysis have confirmed the formation of complex carbides within the metal weld, whose stoichiometry was determined by X-ray diffraction (XRD) analysis. Mixed carbides of MC type and some cementite have been found. As a result it was suggested that use of ASTM F67 chips as carbide formers for composition of welding consumables can contribute to improved wear resistance of hardfacings, if compared with traditional chromium-based hardfacings.

Effect of hydrogen on plastic strain localization and fracture of steels

The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested specimens of low-carbon steels have been studied using a double exposure speckle photography technique. It is found that the mechanical properties of low-carbon steels are affected adversely by hydrogen embrittlement. The deformation diagrams were examined for the deformed samples of low-carbon steels. These are found to show all the plastic flow stages: the linear, parabolic and pre-failure stages would occur for the respective values of the exponent n from the Ludwik-Holomon equation.

Effect of Nano-oxide addition on corrosion performance of hot dip zinc coating

Corrosion performance of hot dipped zinc coating on low carbon steel was studied at the presence of different nanoand micronsize oxide particles in the liquid zinc bath. Nano-silica, nano-alumina and micro-alumina powders were loaded to the different liquid baths, in the range of 0.05–0.2 wt %. Low carbon steel specimens were immersed in the baths for a constant time of 10s. It was evident that the presence of oxide particles in the liquid bath increased the coating thickness at a constant immersing time; micro-alumina particles provided the thickest coating among the others. Salt spray and potentiodynamic polarization tests were conducted to evaluate corrosion performance of the galvanized coatings, including oxide bearing ones. The results confirmed improvement in corrosion resistance of the nano-oxide bearing zinc coatings; while incorporation of micro-alumina in the bath declined its corrosion resistance. It was shown that incorporation of nano-silica powder in the liquid bath yielded superior corrosion resistance of the zinc layer, in comparison to the other ones. The optimum corrosion performance of zinc coating was achieved via loading 0.1 wt % nanosilica to the liquid zinc bath in this work.

表面応力計測における圧子押込み法とX線回折法の差異について

In this study, the effect of machined surface layer on stress measurement by means of instrumented indentation technique and X-ray diffraction method was comparatively investigated through the use of three weld specimens of low-carbon austenitic stainless steel with different machined surface layers; as-cutout, mechanically-polished and electrolytically-polished specimens. Tensile and compressive stresses exist respectively in the machined surface layer of as-cutout and mechanically-polished specimens. Meanwhile, no stress and no machined surface layer exist in electrolytically-polished specimen. Tungsten Inert Gas (TIG) bead-on-plate welding was performed under the same welding heat input condition to introduce the residual stress into these three specimens. Against these three specimens, firstly the X-ray diffraction method was applied, then the instrumented indentation technique was applied and finally the stress relief technique was applied to measure the distributions of residual stress after welding. Based on a comparison between these stress measurement results, the instrumented indentation technique was in good agreement with the stress relief technique rather than the X-ray diffraction method, even though both machined surface layer and penetration of indenter had almost the same depths. That is why it can be considered that the instrumented indentation technique measures the residual stress in deeper areas of material surface than penetration depth of indenter. A distinction between the instrumented indentation technique and X-ray diffraction method in surface stress measurement was thus clarified from a viewpoint of measurement depth.

The Use of Confocal Laser Scanning Microscopy for the 3D Quantitative Characterization of Fracture Surfaces and Cleavage Facets.

Brittle and ductile fracture surfaces of annealed low-carbon steel specimens having different grain sizes were investigated by means of confocal laser scanning microscopy (CLSM) in conjunction with conventional scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). It is shown that very informative 2- and 3D fractographic CLSM images can be obtained and compared with SEM. The fracture surfaces were quantitatively characterized in terms of the areal surface roughness and characteristic surface area. It was found that the characteristic fracture surface area rather than areal roughness can be used as a measure of fracture surface ductility. The misorientation and diameters of cleavage facets were measured and compared with initial misorientation and size of grains evaluated by EBSD. The excellent agreement was found between characteristics of fracture surface elements and the underlying microstructure. It is concluded that CLSM is the powerful tool for the qualitative and quantitative fracture surfaces analysis.

Cluster analysis of acoustic emission signals in pitting corrosion of low carbon steel

The pitting corrosion characteristics of low carbon steel specimens are studied by acoustic emission (AE) and electrochemical techniques, in a 3.0 wt.% NaCl solution acidified to pH 2.0. The acoustic emission signals generated by pitting corrosion are classified based on multiple acoustic emission parameters using K‐means clustering algorithm, then each classified signals are analyzed by acoustic emission parameters correlation plot and distribution with time. Furthermore, each acoustic source characteristics is extracted using Gabor wavelet transform (WT) in the time and frequency domain. An error back propagation (BP) artificial neural network (ANN) is trained according to the classified signals, so as to successfully identify the acoustic emission signals from parallel experiments. Experimental results show that the hydrogen bubble activation, oxidized film rupture and pit growth are typical acoustic emission sources in pitting corrosion process, which can be effectively classified by cluster analysis and recognized by back propagation neural network. The data gathered from laboratory tests combined with the real data from acoustic emission on‐line storage tank floor inspection can help to evaluate the bottom corrosion severity and interpreter the corrosion source, further to make the on‐site testing more reliable and reduce the risk.

Crystallographic orientation analysis of cleavage facets adjacent to a fracture trigger in low carbon steel

The microstructure and crystallographic orientation under a cleavage crack trigger point, which was detected on a fracture toughness specimen of low carbon steel, were investigated. SEM fractographs of an etched cleavage facet reveal that a flat cleavage facet between facet ridges spreading from the trigger point is divided by a grain boundary between ferrite and pearlite. Even a different phase boundary does not occasionally create any steps and ridges on the cleavage facet: it suggests this phase boundary is not an obstacle to cleavage cracking. Electron diffraction analysis for the thin foil sample milled out from this phase boundary demonstrates that the crystallographic orientation of the ferrite grain is consistent with that of the ferrite in the adjacent pearlite block. It is strictly examined that the ferrite/pearlite boundary does not act as a local resistance to cleavage crack growth when the crystallographic orientation of the ferrite in the pearlite block is aligned with an adjacent ferrite grain.

Study the influence of a new ball burnishing technique on the surface roughness of AISI 1018 low carbon steel

Hard roller burnishing with a ball tool is a surface-finishing where a free-rotating tool rolls over the machined surface under high pressures and flattens the surface roughness peaks by cold work. In the present work, a new burnishing technique has been applied which enables both single and double ball burnishing process in site after turning without releasing the specimen. Sets of experiments are conducted to investigate the influence of burnishing force, feed, speed and number of tool passes on surface roughness of AISI 1018 Low Carbon Steel specimens. Burnishing results showed significant effectiveness of the new burnishing technique in the process. The results revealed that minimum surface roughness are obtained by applying the double ball burnishing process on AISI 1018 Low Carbon Steel specimens. Improvement in surface finish can be achieved in both single and double ball burnishing by increasing the number of burnishing tool passes. The results are presented in this paper.

Bimodal Grain Size Distribution Enhances Strength and Ductility Simultaneously in a Low-Carbon Low-Alloy Steel

Low-carbon low-alloy steel specimens were quenched, then cold rolled, and finally annealed. Electron backscatter diffraction (EBSD) micrographs revealed a bimodal grain structure where ultra-fine grain structures with low-angle grain boundaries are alternating with regions of larger grains. The average total dislocation density was measured by X-ray line profile analysis, whereas the geometrically necessary dislocation density was obtained from the analysis of EBSD data. Using the combination of the Hall–Petch and Taylor equations, a good correlation was found between the total dislocation density and the measured flow stress in the different states of the alloy. The difference in evolutions of the total and the geometrically necessary component of the dislocation densities is discussed in terms of the successive processes of quenching, rolling, and annealing of the alloy.

The effect of microstructure and elemental content on corrosion and corrosion inhibition of mild steel in a 0.5 M H2SO4environment

The effect of composition and surface microstructure on the corrosion behavior of low carbon steel specimens from Nigeria (NCS) and China (CCS) in a 0.5 M H2SO4solution has been studied using electrochemical techniques and surface probe techniques.

Effect of Duty Cycle on Corrosion Resistance and Mechanical Properties of Tertiary Al2O3/ Y2O3/Graphene Pulsed Electrodeposited Ni-based Nano-composite

In recent years exclusive properties of nanoparticle coatings on metal matrix has attracted researchers to study more on synthesis of Ni-based nano-composites by electrodeposition process. In this paper the effects of duty cycle on the microstructure, hardness, wear and corrosion resistance were investigated on an AISI 1005 low carbon steel specimen electroplated in Watt's type bath. The obtained coating was strong and well adherent to the steel substrate. The Ni matrix nano-composite coatings with Al2O3/Y2O3 Graphene uniformly dispersed particles were fabricated by using electroplating technique with the aid of ultrasound condition. Scanning electron microscope (SEM) was used to study cross section profile and thickness measurement of the coatings. Increasing duty cycle in an average current density and constant frequency of 1000 Hz resulted in improvement of the mechanical properties and corrosion resistance of coated samples.

Study on Process and Defect of Arc Welding

This paper welds a layer of austenitic stainless steel (SS316L) on specimen of low carbon steel (C15) with a cylindrical surface using MIG Technology in the experiment. The sample was upsetting experiment, cracks and material forming observation respectively using embossing punch, no lubrication flat punch and lubrication flat punch under the condition of 750 °C, 900 °C and 1050 °C. The paper research on forming mechanism of the specimen under laboratory conditions based on the experimental results, the axial symmetry theory model and Numerical Simulation.

An experimental method for evaluating the critical fields of moving domain boundaries in plastically tension-deformed low-carbon wires

Changes in the magnetization projection on the axis of wire specimens of low-carbon CΤ1ΚΠ steel during their magnetization reversal by a circular field were experimentally determined as a function of the polarizing-field value in a solenoid. Measurements were performed on annealed and plastically tension-deformed specimens. It was shown that the proposed experimental technique allows evaluation of the critical fields of displacements of 90° domain boundaries. The parameter that is related to the induced magnetic-anisotropy field and allows evaluation of the level of residual stresses in the deformed metal is determined.

Aplicação de cavacos de titânio para produção de revestimentos resistentes ao desgaste

Equipamentos usados nas usinas sucroalcooleiras e de extração mineral são submetidos a condições severas de desgaste abrasivo. Revestimentos duros são usualmente aplicados para reparar este tipo de dano, sendo bastante empregados consumíveis de soldagem contendo altos teores de cromo e carbono. No presente trabalho visa investigar a microestrutura de revestimentos duros formados com a fusão de cavacos de titânio puro ASTM F67 grau 4, material usado na fabricação de implantes odontológicos. Misturas com diferentes formadores de carbonetos (Fe-Cr e Fe-Nb como aditivos) também foram testadas. Revestimentos feitos com duas camadas de cavacos "puros" (Ti), cavacos com Fe-Cr (Ti-Cr) e cavacos com Fe-Nb (Ti-Nb) foram depositadas sobre peças de aço-carbono por soldagem TIG/GTAW. A microestrutura das camadas foi observada com microscópio óptico e por microscópio eletrônico de varredura equipado com microanálise. A caracterização microestrutural revelou que a distribuição de carbonetos varia significativamente com a natureza química dos aditivos usados. A microanálise mostrou que houve a formação de carbonetos com composição química complexa no seio do metal de solda, cuja estequiometria foi determinada com análise por difração de raios-X. Carbonetos mistos do tipo MC e cementita foram identificados. Os resultados apresentados indicam que a aplicação de cavacos de titânio ASTM F67, como insumo para formação de carbonetos, pode contribuir para melhorar a resistência ao desgaste em comparação aos tradicionais revestimentos duros com carbonetos de cromo.

Strain measurement based on laser mark automatic tracking line mark on specimen

Conventional video extensometers, using a measurement mark on specimen to obtain material strain, have a problem with deformation of the measurement mark. Therefore, the accurate position of the measurement mark is difficult to evaluate, and measurement accuracy is limited. To solve this problem, a strain measurement method based on a laser mark automatically tracking a line mark on the specimen is proposed. This method is using an undeformed laser mark to replace the line mark to calculate the specimen strain and eliminates the measurement error induced by the deformation of specimen marks. The positions of the laser mark and the line mark are achieved by using digital image processing. Automatic tracking is realized by means of an intelligent motor control. Also, the strain of the specimen is obtained by analyzing the movement trace of the laser mark. A video extensometer experimental setup based on the proposed method is constructed. Two experiments were carried out. The first experiment verified the validity and the repeatability of the method via tensile testing of the specimens of low-carbon steel and cast iron. The second one demonstrated the high measurement accuracy of the method by comparing with a clip-on extensometer.

Measurement of true stress–strain curves and evolution of plastic zone of low carbon steel under uniaxial tension using digital image correlation

Three-dimensional digital image correlation has been utilized widely in many fields due to its advantages of non-contact, full-field measurement and simplicity. Based on 3D-DIC measurement system and electronic universal testing machine, two uniaxial tension tests for low carbon steel specimen were performed to acquire the true stress–strain curves. An assumption was made that specimen’s cross section keeps as a circle in tension test whose diameter could be determined by calculation of the curvature of surface shape. Therefore, true stress of specific cross section was acquired and hence the true stress–strain curves were obtained. In addition, the evolution of plastic zone of specimen under uniaxial tension was studied as well. And experimental results indicate that at certain time instant of expanding process of plastic zone, region that has already entered the plastic zone and that has not entered such zone yet is keeping in a constant deformed state, while region that is entering the plastic zone provides axial plastic deformation, which is almost equal to crosshead movement of testing machine.

Effect of surface lay in the surface roughness evaluation using machine vision

This work explores the influence of orientation of surface lay pattern of the machined components, while quantifying the surface roughness using machine vision approach. The surface images are captured from milled low carbon steel specimens with different roughness values using a vision system with coaxial lighting arrangement at different angular orientations of the work pieces (0°, 30°, 45°, 60°, 90°, 120°, 135°, 150°, and 180°). The captured images are subjected to preprocessing in order to retain the frequency components that attribute to roughness using a Gaussian filter by adapting the filtering procedures specified in ISO 4288. Numerous image based parameters such as gray level average (Ga), gray level co-occurrence matrix based image quantification parameters namely contrast, correlation, energy or uniformity, maximum probability and differential box courting based fractal dimension are computed from the surface images captured at different angular positions of the work piece. The computed vision based parameters are compared and correlated with the roughness average (Ra) obtained using a stylus instrument and the results are analyzed. The results clearly indicated that it is important to consider the orientation of the work piece when the machine vision approach is used to quantify the surface texture parameters.

Effect of the loading frequency on fatigue properties of JIS S15C low carbon steel and some discussions based on micro-plasticity behavior

Ultrasonic testing method has been often used to investigate fatigue properties of various metallic materials. Since ultrasonic fatigue tests are conducted at a very high loading frequency, they are particularly convenient for fatigue tests in the very high cycle regime. Indeed, ultrasonic fatigue method allows us to conduct fatigue tests up to 109–1010cycles in a definite period. However, due to the huge gap of loading frequency between ultrasonic testing method (around 20kHz) and usual testing method (most of the cases in the range 1–100Hz), the frequency effect on the fatigue property is still unclear. Low carbon steel is one of typical metallic materials to provide a significant discrepancy between fatigue strengths obtained under ultrasonic testing frequency and under usual testing frequency range.Thus, by preparing a lot of specimens of JIS S15C low carbon steel (0.15% C), fatigue tests were carried out in a wide range of the loading frequency. The frequency effect on the S–N property was first examined and a useful procedure was proposed to obtain a common S–N property normalized by the lower yield stress. In addition, micro-plasticity behavior such as the stress–strain hysteresis loop and the local misorientation were also measured and the frequency effect on the fatigue property was discussed.

Hardness, Microstructure, and Residual Stresses in Low Carbon Steel Welding with Post-weld Heat Treatment and Temper Bead Welding

This paper investigates the effects of post-weld heat treatment (PWHT) and temper bead welding (TBW) on hardness, microstructure and residual stresses in multi-layer welding on low carbon steel specimens made with two different weld geometries, viz. (1) smooth-contoured and (2) U-shaped. It was found that the PWHT technique gave overall lower hardness than the TBW technique, but the hardness values in both techniques were acceptable. Microscopy analysis showed that the TBW technique was more effective in tempering the heat affected zone as the grain size decreased slightly at the fusion line in spite of the higher temperature at the fusion line. Residual stresses measured using the hole-drilling method showed that the residual stress is not reduced below yield stress near the last bead solidified in TBW. Only PWHT gives low residual stress results in this area. High tensile residual stresses may result in sensitivity to fatigue loading.