Metallographic Observations Research Articles

Analysis of cracking failure of gast iron brake disc

To investigate the causes of crack initiation and propagation in brake discs, a comprehensive analysis of surface cracks was conducted using macroscopic observation, metallographic observation, scanning electron microscopy, and microhardness testing. The results revealed that the internal structure of the brake disc material consists mainly of pearlite and a small amount of ferrite. Near the friction surface, the internal structure undergoes grain refinement and the formation of a small amount of granular pearlite, with a microhardness range of 350 ∼ 410 HV. Based on metallographic observations, it is evident that there are loose defects within the brake disc. When the brake disc is subjected to external loads and thermal stress, stress concentration occurs around these defects, initiating cracks and their outward propagation, thereby accelerating the crack propagation rate. The crack growth exhibits a combination of transgranular and intergranular characteristics. Analysis of the crack width in the brake disc reveals that the width of the radial primary cracks is approximately three times that of the micro-cracks, and the depth of the micro-cracks is relatively shallow, with a maximum depth of 4 mm. In contrast, the primary crack extends to a depth of 9 mm. This implies that the failure of the brake disc is associated with the extension and deepening of cracks.

Failure investigation of fractured crane crawler track plate

A repetitive failure of crawler track plate made of G22NiMoCr5-6 of heavy-duty crane is observed to be occurring with an average rate of one track plate fractured every 100 working hours, presenting a great problem that may impose hazard on personnel and raising direct and indirect costs required for maintenance, spare parts, and downtime costs. The objective of this research is to investigate the cause of track plate failure. An experimental investigation is carried out including chemical composition, tensile test, impact toughness, hardness test, and metallographic observation along with fractography analysis. Also, working stresses are defined by applying the finite element method. Based on the results of the experimental and computational analysis, the fracture of track plate made of G22NiMoCr5-6 predominantly resulted from deficiency in the track plate geometry design which increases stress concentration within the fracture region, in addition, slight deviation of material properties compared to those prescribed by the standard may have played a role in exacerbating the problem.

The influence of corrosion time on the observation of metallographic structure of 20CrMnMo

20CrMnMo is one of the most widely used alloy steels, and its mechanical properties are closely related to the metallographic structure of the material. Clearly obtaining the distribution pattern of metallographic structure is of great significance for studying the mechanical properties of 20CrMnMo. In this paper, 20CrMnMo samples were subjected to corrosion treatment at different times, and the microstructure of the samples was observed by optical microscope (OM) and Scanning electron microscope (SEM). Through optical microscope observation, the metallographic structure images under different magnification and corrosion time were compared and analyzed, and the best corrosion time interval for metallographic structure observation was obtained; On this basis, by using Scanning electron microscope and EDS, the microscopic images at higher magnification were obtained, and the mechanism of corrosion time on the metallographic structure was further analyzed and explained.

A Study of {10-12} Twinning Activity Associated with Stress State in Mg-3Al-1Zn Alloy during Compression

An eight-sided prism sample, obtained from a hot-rolled AZ31 magnesium alloy sheet, was compressed at room temperature along the transverse direction to investigate the influence of local strain on twinning behavior using electron backscatter diffraction (EBSD) measurements, hardness distribution, and metallographic observations. The octagonal surface of the sample was divided into distinct regions based on hardness distribution and metallographic observations. Combined analysis of the Schmid factor (SF) and the strain compatibility factor (m’) was employed to study twin variant selection. Basal on SF ratio distribution, the Schmid factor criterion, can predict over 75% of observed twin variants in regions A and D (normal stress samples). In contrast, 64% of twin variant selection behavior in region C (shear stress sample) can be effectively explained using a pure shear model. Twin variants with high strain compatibility factors may prefer activation to reduce stress concentration. The strain compatibility factor is more appropriate than the Schmid factor for analyzing the effect of local strain on the selection behavior of twin variants.

Quantitative and Qualitative Evaluation of Non-Metallic Inclusions in High-Silicon Steel after Hot Rolling

This paper presents an analysis of non-metallic inclusions occurring in high-silicon steels containing about 3% Si of terms of their type, volume fraction and morphology. The inclusions were divided into 3 main groups: oxides, sulfides, nitrides which together can also form complex. The work was based on numerous metallographic observations in two sections (longitudinal and transverse to the rolling direction). The study was performed on three casts differing in chemical composition. The analyzed casts were characterized by a different content of non-metallic inclusions, which can be associated with slight differences in chemical composition. The analyzed results showed that the most common inclusions were oxides and nitrides. Sulfides occurred sporadically.

Preload relaxation behavior and its influence on the mechanical performance of bolted carbon fiber‐reinforced thermoplastic sheet molding compound joints

AbstractIn this study, the relaxation of the initial tightening preload of bolted carbon fiber reinforced thermoplastic sheet molding compound (CFRTP‐SMC) joints was experimentally investigated under different temperatures and initial preload conditions. The influence of preload relaxation on the bolted structures was evaluated using static bearing tests, whereas the failure modes during the test were verified based on metallographic observations. The experimental results indicate that the speed of the preload relaxation can be accelerated by increasing the temperature and initial preload. The static bearing strength of the bolted SMC material decreased with a continuous increase in the preload loss. Furthermore, the existence of a lateral preload protected the material around the assembly hole from buckling, resulting in a higher static bearing strength. The shielding effect of the preload was weakened after the relaxation of the initial preload.Highlights Elevated temperature and initial preload can expedite the relaxation process. Preload loss will result in a declined static bearing performance. Initial tightening preload can protect the bolted SMC material from buckling.

Study on failure mechanism of suspension lug elbow in an ethylene cracking pyrolyzer

The cracking of a suspension lug elbow caused a shutdown in a certain petrochemical enterprise. In this study, the authors conducted physical and chemical analysis to investigate the cracking mechanism. Macroscopic observations indicated no signs of corrosion or thinning on the inner and outer surfaces of the head, and the cracks were distributed in the body of the head and the ear. Chemical composition analysis revealed that the main chemical components of the failed elbow met the standard requirements. Metallographic observations showed significant creep damage in the substrate material, and after long-term high-temperature service, both the room temperature and high-temperature mechanical properties of the failed elbow significantly deteriorated. The failure sample exhibit a fracture elongation of 0 %, and the high-temperature creep performance of the head material was only 6.868 h, both lower than the standard requirement of a fracture elongation of 4 % and 120 h of high-temperature creep performance. Fracture surface observation revealed obvious creep voids and fatigue striations, indicating severe creep damage and the influence of alternating loads on the head. Field observations indicated that the head experienced significant shaking inside the furnace. Therefore, simulation analysis suggested that the maximum stress coincided with the crack location, ranging from 121 MPa to 131 MPa, far exceeding the tensile strength at the operating temperature when the elbow was subjected to alternating loads generated by left–right and back-forth swinging. In conclusion, the failure of the suspension lug elbow was caused by creep-fatigue cracking. This study reveals that, even when the internal medium is in single gaseous phase, elbows are still susceptible to cracking under the combined effects of high temperature vibration and creep interaction. To avoid future failures, strengthening the monitoring of the cracking furnace operation, controlling the load appropriately, and preventing severe vibration and shaking of the furnace tube are recommended.

Development of Composite Materials Using Magnesium Matrix with Variations in the Addition of Volume Fractions of Nano-Al2O3 Reinforcement Results of the Stir Casting Method

Magnesium matrix composites were developed as a form of material selection that can save fuel use due to excess magnesium, which has very low specific gravity and still has good mechanical properties. In this study, a magnesium matrix composite with nano-Al2O3 reinforcement was successfully fabricated using the stir casting method. When compared with magnesium monolithic, the addition of nano-Al2O3 particles of 0.05, 0.10, 0.15, 0.20, and 0.25 %Vf in magnesium composite casting was investigated to improve the mechanical properties of Mg/nano-Al2O3 composites. Magnesium composites with 0.20% Vf reinforcement were found to be the best composition of impact price, wear rate, density, and porosity. This is because the more reinforcement given, the more mechanical properties increase, but the agglomeration tendency of nano-Al2O3 particles is higher so that at a composition of 0.25 %Vf, there is a mechanism anomaly because the reinforcement carried out is less homogeneous. In addition to the number of amplifiers, the improvement of mechanical properties is influenced by the fabrication process, i.e. stir casting. This study uses chemical characterization of OES, EDS, and XRD, hard damage, impact, wear, density and porosity testing, and metallographic observations using OM and SEM.

PENGARUH QUENCHING SETELAH PENGELASAN TERHADAP KOROSI DI BAWAH INSULASI MEDIA AIR LAUT PADA BAJA A36

Corrosion in low-carbon steel is a significant issue in the industrial world, particularly in the oil, gas, refining, and chemical industries, as it leads to substantial financial losses. The total losses experienced by companies in Indonesia are estimated to reach 2-5% of the country's GDP. Corrosion arising from insulation damage, known as Corrosion Under Insulation (CUI), is challenging to detect but has a profound impact on industrial processes. Welding quality and corrosion resistance can be improved through post-weld heat treatment (PWHT). This research aims to investigate the influence of rapid cooling after welding low-carbon ASTM A36 steel on corrosion events under insulation using the "Water Immersion" method with seawater from the Muntok area, Bangka Belitung Islands Province, for 7 and 14 days. The welding process is performed using shielded metal arc welding (SMAW). Heat treatment is applied at 880°C for 60 minutes, as determined by the carbon equivalent calculation, followed by rapid cooling in seawater. Testing includes chemical composition analysis, non-destructive testing with dye penetrant on the welds, Brinell hardness testing, corrosion rate calculations, charpy impact testing, and metallography observations. The research results indicate that quenching enhances hardness and toughness while affecting the corrosion rate of the material after corrosion immersion, both with and without insulation. Material immersion exhibits a corrosion rate inhibition on the 14th day due to the formation of an oxide layer that hinders further degradation. Metallography observations reveal that after welding, phases formed include pearlite, acicular ferrite, and widmanstatten structures.

Impact of local plastic deformation on thermo-magnetic instability of high-J c Nb3Sn strand

The future fusion reactor devices built by Institute of Plasma Physics, Chinese Academy of Science will be a compact burning plasma facility to fill the gap between ITER and the China Fusion Engineering Test Reactor, with the mission of studying the deuterium–tritium plasma in steady-state operation. The winding-package (WP) of its toroidal field coil is graded into high-field WP and low-field WP, and the high critical current density (J c) Nb3Sn strand will be applied to the high-field WP based on the current design. The thermo-magnetic instability is the main issue in the application of high-J c Nb3Sn strand, which may induce premature quenching in the low field regions. This issue can be improved by reducing the effective filament diameter (d eff) to suppress flux jumps and increasing the residual resistivity ratio (RRR) to enhance the release of heat generated by flux jumps. However, in the conductor manufacturing process, local plastic deformations (indentation) of strands can impact the sub-element layout and degrade the RRR of the strand, which would increase again the risk on instability. In this study, magnetization measurements and V–I tests were performed on samples with different indentation depths. The hysteresis loss and d eff of the indented sample was obtained from the test results. The impact of local plastic deformation on the thermo-magnetic instability of two types of Nb3Sn strand was confirmed by cross-sectional metallographic observation and quantitative microstructure analysis. It was shown that flux jumps were suppressed at indentation depths below 0.3 mm. Further indentation increase leads to severe flux jumps.

Pengaruh Media Pendingin Proses Laku Panas Terhadap Persebaran Butir Ferrite dan ketangguhan Mild Steel AISI 1020

This research aims to determine the toughness properties and microstructure of AISI 1020 steel material which was previously treated by using a variety of cooling media including air cooling, oil cooling and grease cooling. After being cooled by using several cooling media, it was continued with impact and microstructure testing. The results showed that AISI 1020 steel specimens using air cooling media, had the average impact strength value of 19.1 joules/mm, while those using oil cooling media had an average impact strength of 35.2 joules/mm, and those using grease cooling media had an impact strength of 45 joules/mm. From this data, the one with the highest impact strength value was the grease cooling media at 45 joules/mm and the one with the lowest impact strength was the air cooling media, namely 19.1 joules/mm. The results of metallographic observations were obtained when the grease media was used, the distribution of ferrite was reduced and did not have time to form, whereas in steel that was cooled with oil, the distribution of ferrite was almost the same as the untreated material and for air media, the shape of the ferrite structure spread and formed evenly.

Distribution and Characteristics of Residual Stresses in Super Duplex Stainless Steel Pipe Weld

This paper explores the distribution and features of residual stresses formed by super duplex stainless steel pipe welding. Experimental investigations, which encompass an elevated temperature tensile test and metallographic observation along with a hardness test and residual stress measurement, were first conducted to obtain the mechanical properties at high base metal temperatures and to confirm whether or not the duplex stainless steel undergoes martensitic phase development during the welding process. Finally, experiments were performed to scrutinize the residual stress evolution through the metallurgical phase transformation in the weld region and its vicinity. A sequentially coupled 3D thermal, mechanical and metallurgical finite element (FE) model capable of incorporating the experimental consequences was established next. A 3D FE simulation of the girth welding process was conducted, and the axial and hoop residual stress profiles along the girth were evaluated. The results substantiate that martensitic phase evolution occurs in the process of cooling during the welding of super duplex stainless steel, and they also highlight the significance of taking the metallurgical phase transformation into account in the numerical reproduction of the girth welding process for the accurate expression of weld-induced residual stresses, which is especially important for precisely predicting hoop residual stresses.

Study on Cracking Causes of One 500 kV SSY Type Equipment Clamp

One SSY type equipment clamp serviced in a 500 kV station was found to be cracked. In this paper, the crcaked cause and mechanism is investigated by means of macroscopic morphology observation, fracture surface morphology observation, X-ray digital detection, metallographic observation. The results indicated that the main reason for the fracture of the equipment clamp this time is that the terminal board is a cast part, which contains a large number of casting defects such as porosity and shrinkage, resulting in a decrease in its effective cross-sectional area and load-bearing capacity. In addition, insufficient modification treatment of the terminal board led to insufficient toughness due to needle or rod-shaped eutectic silicon in the organization. Finally, under the combined action of dynamic load and self weight caused by the swinging of the wire in the wind, the terminal board was brittle fractured along the bolt hole with obvious stress concentration effect.

Influence of laser shock peening on the joint surface strength of laser cladding repair of GH4169 superalloy component

Laser cladding is an effective method to repair damaged aeroengine blades. However, the heat affected zone of laser cladding reduces the strength of the repaired component. A solution method that strengthening the joint surface by laser shock peening (LSP) before laser cladding was proposed. The process parameters of LSP, such as energy, spot size, overlap ratio, spot path, etc., were determined based on the theoretical analysis; and the specimens were prepared by laser cladding after LSP. The influence of LSP on the strength, hardness and microstructure of the repaired specimens of GH4169 superalloy were researched based on the axial tensile test, metallographic test and hardness test. The results show that the tensile fracture of the specimens which only treated by laser cladding appears on the joint surface; however, the tensile fracture of the specimens treated by both of LSP and laser cladding does not necessarily appear on the joint surface, which indicates that the LSP can effectively improve the strength of the joint surface. The tensile strength of the specimen treated by both of LSP and laser cladding increased by 52.3%, and the elongation of the specimen increased from 0.8% to 9.2%. The metallographic observation showed that the grains of the specimens treated by LSP were refined obviously, and the grain size decreases by 36.5%, which is beneficial improve the strength of the joint surface. The microhardness of the specimen was more uniform and the maximum difference between the two sides of the joint surface decreased by 19.4% when the LSP was added in the repairing process.

Bronze Age Raw Material Hoard from Greater Poland: Archaeometallurgical Study Based on Material Research, Thermodynamic Analysis, and Experiments.

Hoard finds from the Bronze Age have appeared all over Europe, prompting questions about their functions (either as raw materials for recycling or votive objects). The hoard trove of raw materials from Przybysław in Greater Poland is an interesting example of a discovery that is related to the foundry activities of Late Bronze Age and Early Iron Age communities (c. 600 BC). The deposit consists of fragments of raw materials that were damaged end products intended for smelting. The research included the characterisation of the material in terms of the variety of the raw materials that were used. The individual elements of the hoard were characterised in terms of their chemical compositions, microstructures, and properties. A range of modern instrumental research methods were used: metallographic macroscopic and microscopic observations by optical microscopy (OM), scanning electron microscopy (SEM), chemical-composition analysis by X-ray fluorescence spectroscopy (ED-XRF), X-ray microanalysis (EDS), and detailed crystallisation analysis by electron microscopy with an emphasis on electron backscatter diffraction (EBSD). As part of this study, model alloys were also prepared for two of the selected chemical compositions, (i.e., CuPbSn and CuPb). These alloys were analysed for their mechanical and technological properties. This research of the hoard from Przybysław (Jarocin district, Greater Poland) has contributed to the recognition and interpretation of the function and nature of the hoard by using modern research and modelling methods as a cultic raw material deposit.

ANALISIS PENGARUH VARIASI HOLDING TIME ANNEALING TERHADAP LAJU KOROSI TITANIUM PADA LARUTAN CAIRAN TUBUH SINTETIS

Biomaterials are crucial for bone implants due to their biocompatible and inert nature, ensuring no adverse effects within the human body. Titanium is renowned for its exceptional corrosion resistance. This research aims to analyze the impact of annealing holding time and pH of synthetic body fluid on the hardness and corrosion rate of titanium. The annealing process was performed at 700°C, with holding times of 30, 60, and 90 minutes. As an electrolyte medium, a Hanks' solution with pH variations of 4, 6, and 8 was used and maintained at 37°C. Potentiodynamic corrosion testing demonstrated the lowest corrosion rate in specimens treated with 30 minutes of annealing at pH 8, measuring 0.32 x 10-2 mmpy. The 30-minute annealing exhibited the lowest corrosion rate, which was confirmed by Electrochemical Impedance Spectroscopy (EIS) results showing a higher Rp value, indicating a lower corrosion rate. This is attributed to the presence of a passive Rutile TiO2 layer formed during the annealing process, as confirmed by X-ray Diffraction (XRD) analysis. Metallography observations indicated that the microstructure of untreated specimens consisted of α and β phases. Scanning Electron Microscopy (SEM) analysis of specimens annealed for 30 minutes revealed an oxide layer on the surface without any visible pores. However, an increase in annealing holding time led to the formation of pores, particularly noticeable after 90 minutes of annealing. The presence of pores in the oxide layer resulted in an increased corrosion rate with longer annealing holding times. Conversely, hardness testing demonstrated that longer annealing holding times resulted in higher hardness values.

The effect of a cyclic bending load on the bending resistance of ballooned, ruptured, and oxidized Zircaloy-4 cladding

ABSTRACT The seismic resistance of fuel cladding during the long-term core cooling after loss-of-coolant accidents (LOCAs) was investigated by performing cyclic four-point bending tests (4PBTs) of up to 1000 cycles with fresh fuel cladding samples that experienced integral thermal shock test, simulating LOCA conditions, including ballooning, rupture, oxidation, and quench. 4PBTs were performed on the samples that survived the quenching process. The results showed that up to 1000 cycles and 5.8 Nm of cyclic loading moment, there was no apparent effect on the bending fracture limit of the fuel cladding under the 4PBT. The scatter of the bending fracture limit for a given equivalent cladding reacted (ECR) evaluated by the Baker–Just oxidation rate equation (BJ-ECR) is attributed to two primary factors: first, the difference between the prescribed and the actual oxidation behavior, confirmed by comparing the BJ-ECR and the ECR evaluated based on metallographic observation (M-ECR), and second, the variated shape of the rupture-opening area after the integral thermal shock test. The strength of the α phase-dominant zone near the rupture opening seems to contribute to the bending fracture limit.

Metallographic investigation of first full-size high-Jc Nb3Sn cable-in-conduit conductor after cyclic loading tests

In order to verify the feasibility of applying high-Jc Nb3Sn strand in fusion magnet, a full-size cable-in-conduit conductor (CICC) with short twist pitch (STP) cable pattern was manufactured and tested in SULTAN facility at SPC, Switzerland. Three levels of cyclic electromagnetic (EM) load were applied on the sample stepwise, no visible decrease of current sharing temperature (Tcs) was observed until the EM load increased to 80 kA × 10.8 T, after that the Tcs decreased dramatically with the EM cycles, which suggested that irreversible deformation, causing a change in the strain state, or even damage has occurred in the superconducting strands. For investigating the reason which caused the conductor performance degradation, the tested conductor was dissected for metallographic observation. Eight segments which subjected to different EM loads were extracted from one of the legs, the geometric feature changes of the cable cross-sections were analyzed and compared. A good correlation was found between the decrease of the Tcs and deformation of the cable cross section. A mass of cracks were found on the sub-elements of strands in the segment which subjected to highest EM load, but the amount of crack is much lower in other segments. Combining the analyses, it is speculated that the critical EM load which causes irreversible degradation is between 850 kN/m and 870 kN/m for this conductor. The results could be a reference in high-Jc Nb3Sn CICC design.

A new disposal method for white mud: Replacing limestone in iron ore sintering

The pulp production process generates a CaCO3-rich solid waste known as white mud (WM), and its improper disposal is a cause for global concern. The present study investigates the composition, microstructure, and thermal decomposition characteristics of WM and proposes a strategy for replacing limestone with WM for iron ore sintering. Granulation and sinter pot tests were performed to evaluate the influence of added WM on the granulation and sintering processes. We assess the feasibility of using WM as a flux and discuss the mechanism through which WM affects the mineral phase and strength of the sinter based on metallographic and micropore observations. The results indicate that the sintering rate remains stable after replacing 50% of the limestone with WM via moisture control, and the quality and production indicators of the sinter do not change. Moreover, the mineral phase and microporosity remain similar to the basic case without WM, and the comprehensive index decreased by only 5.5%. Overall, this study demonstrates that it is feasible to replace 50% of limestone with WM in industrial sintering plants, which could significantly increase our WM disposal capacity and bring additional economic benefits.

Study on mechanical properties of Ni-based superalloys coupled with quantified weights of multi-modal microstructure damage evolution

A method for predicting fatigue life using damage variables coupled with multi-modal microstructure damage evolution was proposed after analyzing the weights of the multi-modal microstructure of directionally solidified Ni-based superalloys DZ125 in this paper. Mechanical property tests and metallographic observation tests were carried out, and the microstructure weights of the superalloys were quantified using principal component analysis (PCA) and entropy-based inter-criteria correlation (CRITIC) weight analysis. The relationship between mechanical properties and multi-modal microstructures of the superalloys was analyzed, and fatigue life was predicted using damage variables coupled with multi-modal microstructure damage evolution. The weights of multi-modal microstructures of Ni-based superalloys and the influence of multi-modal microstructural damage evolution on mechanical properties were quantified by taking into account the interactions among the microstructural factors and their combined effects, which were important references for the design and processing of the superalloy as well as the prediction of mechanical properties.