The rating spectrum classification, inclusion classification, and evaluation methods of German standard DIN 50602-1985 of High magnification metallographic examination of nonmetallic inclusions in special steels were analyzed. Moreover, it was compared with GB/T 10561-2023 and ASTM E45-2018a which were widely used in China at present. K method in DIN 50602-1985 was more comprehensive and accurate in reflecting the level of inclusions compared with GB/T 10561 and ASTM E45 due to its more classifications of rating spectra and the use of comprehensive indices to reflect the overall hazard level of inclusions. The analysis of standard was helpful to inspectors for correct rating.

The banded structure is one of the internal defects of materials. It is mainly manifested as the banded single phase or polyphase structure in metal materials, which is roughly parallel and alternately arranged along the direction of thermal deformation. The banded structure has great influence on mechanical property and service performance, so the evaluation of banded structure is relatively important in product acceptance. The methods of China standard and American standard are different in the band rating. Therefore, it has a significant impact on the band rating result when different standards is chosen. In this study, various evaluation standards for the banded structure were compared, and the rating process of standards was demonstrated using examples. The inspection standards of banded structure in steel at home and abroad were analyzed and discussed.

With the development of computer processing technology, the application of software in testing and analysis has become common, and the relevant standards such as API Q1 and ISO/IEC 17025-2017 also put forward requirements for software confirmation. Therefore, how to evaluate the accuracy and reliability of test software is particularly important. In this study, the room temperature electronic stretcher was taken as an example, and the tensile software was confirmed according to the control points in appendix C of GB/T 228.1-2021. The automatic calculation of sampling frequency, yield strength, tensile strength and tensile rate of data acquisition and analysis software was verified. The verification principle, implementation method and steps were described in detail. After verification, the parameters automatically collected by the software could meet the requirements of standard, which indicated that the verification method was reliable.

Total focusing method (TFM) of ultrasonic phased array is a non-destructive testing method which combines phased array probe and total focus imaging technology. As a new non-destructive testing technology, it has attracted much attention in recent years. Total focusing method of ultrasonic phased array is based on the full matrix data acquisition (FMC) technology to obtain the detection data for signal processing. Compared with conventional ultrasonic phased array detection, full focusing method has higher imaging resolution and more accurate defect location. In this paper, the principle, characteristics and function of total focusing method of ultrasonic phased array are described in detail, and the conventional phased array detection and full focusing detection technology are compared and analyzed by using standard test blocks, which has certain significance for further understanding and popularization of total focusing method of ultrasonic phased array.

The edge peeling defect on surface of hot-rolled steel strip is a bottleneck problem to restrict the improvement of its surface quality. Aiming at the edge peeling defect in hot-rolled steel strip, the microstructure and chemical composition of the defect areas were analyzed by scanning electron microscopy(SEM) and energy dispersive spectrometer(EDS). Moreover, the statistical analysis of production data and the rolling test of flame-cleaning slab with prefabricated defect with were conducted in 2 250 mm hot continuous rolling line of Qian'an Iron and Steel Company of Beijing Shougang Co., Ltd., and the causes and evolution process of edge peeling defect in steel strip were clarified. The results showed that the accumulation and residual of slag convergence ridge caused by poor flame cleaning quality of cast slab could not be completely removed after heating in reheating furnace and descaling by descaler. The residual oxide layers from slag convergence ridge were partially embedded into the steel substrate during rough rolling and finish rolling while others remained on the surface of steel strip, ultimately forming edge peeling defect containing numerous oxidized spots with maximum thickness up to 150 μm. An industrial experiment was conducted to investigate the impact of edge convergence ridges removal by flame for slab on the quality of the hot rolled edge. Subsequently, process optimization was carried out and production data were continuously tracked. The results demonstrated that the improvement of flame cleaning quality to reduce the occurrence of intersection edge or the use of narrow-side non-cleaning process could reduce the incidence of edge peeling defect by 87%.

The display and control of original austenitic grain size has important significance for regulating the austenitizing temperature during the solution treatment process of stainless steel. In metallographic test, chemical etching method is commonly used to display the austenitic grain size of carbon steel and alloy steel. Due to the high difficulty of chemically etching stainless steel, it has become a challenge to display the original austenitic grain size in stainless steel. Based on this, a electrolytic polishing device was self-made, and a method for displaying the original austenitic grain size in martensitic stainless steel and martensitic precipitation-hardening stainless steel was proposed by electrolytic etching method with composite electrolyte. The test equipment consisted of direct-current (DC) power supply, 250 mL beaker, stainless steel sample holder made of 420 steel, and 304 stainless steel plate (cathode). The electrolyte was mainly composed of 30%-50%(V/V) deionized water, 50%-70%(V/V) nitric acid, and a small amount of phosphoric acid and sulfuric acid. The area of cathode immersed in the electrolyte was about 2,000 mm² (front and back). Two kinds of steel materials were selected for the optimization of electrolytic etching conditions, i.e., 07Cr16Ni6 steel and 0Cr17Ni4Cu4Nb steel. The results showed that the original austenitic grain size of 07Cr16Ni6 steel could be clearly displayed under the following experimental conditions: the electrolysis voltage was 4.5 V, the electrolysis time was 15 s, and the electrolyte was composed of 100 mL of water, 100 mL of nitric acid, 6 mL of phosphoric acid and 3 mL of sulfuric acid. The original austenitic grain size of 0Cr17Ni4Cu4Nb steel could be clearly displayed under the following experimental conditions: the electrolysis voltage was 0.5 V, the electrolysis time was 40 s, and the electrolyte was composed of 100 mL of water, 100 mL of nitric acid, 8 mL of phosphoric acid and 3 mL of sulfuric acid. The method proposed provided a reference for displaying the austenitic grain size in other stainless steels with matrix of martensite.

G54 steel is a new type of secondary-hardened ultra-high strength steel independently developed by China. It maintains extremely high yield strength while also possessing excellent comprehensive mechanical properties. However, the dynamic mechanical behavior and failure mechanism research of G54 steel under high-temperature and high strain rate conditions are still relatively insufficient. Therefore, it is of great significance to investigate its dynamic mechanical behavior under these conditions. Based on the separated Hopkinson pressure bar (SHPB) device, this paper conducted dynamic compression tests on G54 steel at temperatures of 100, 200, and 300 ℃ and strain rates of 1,000, 2,000, and 3,000 s^-1. The flow stress and plastic response laws of G54 steel were obtained under high strain rate loading. The results showed that G54 steel exhibited strain rate sensitivity and thermal softening effect during dynamic deformation: as the strain rate increased, the flow stress increased, while the load-bearing capacity of the material decreased at high temperatures. Combining the experimental data, the parameters of the Johnson-Cook (J-C) constitutive model were calibrated using the least squares method. The established model could well simulate the mechanical response of G54 steel under high-temperature and high-strain-rate conditions. The research results provided a reliable theoretical basis for revealing the dynamic deformation mechanism of G54 steel and its engineering application under extreme service conditions.

In-situ observation technique of scanning electron microscope (SEM) was used during the in-situ tensile test of TC4 ELI alloy specimen. Microscopic morphology observation and collection of relevant crystallographic information were carried out simultaneously through secondary electron imaging secondary electron (SE) and electron backscatter diffraction (EBSD) imaging techniques of SEM. Consequently, the real-time analysis of the microscopic deformation of the sample was realized during loading, in order to reveal the failure mechanism of TC4 ELI alloy during the tensile process. It indicated that, the fracture form of the specimen was a micro-pore aggregation type fracture from the microstructure evolution law of TC4 ELI alloy specimen during the tensile process and the fracture morphology after fracture. During the deformation process, the internal dislocation density of TC4 ELI alloy increased, the orientation difference increased, and there were differences in the deformation ability of α and β and the crystal grain orientation, which led to the uncoordinated deformation, thereby resulting in tiny holes. As the deformation amount increased, the small pores connected with each other to form cracks and eventually led to failure.

As one of the most fundamental and widely applied methods for evaluating the mechanical properties of metallic materials, hardness testing plays a critical role in material development, process control, and quality assessment. The Sub-committee on Hardness Testing under Technical Committee on Metal Mechanical Testing of the International Organization for Standardization(ISO/TC164/SC3), as the primary body for international hardness testing standardization, has established a complete standard system covering the hardness testing of Brinell, Vickers, Rockwell, Knoop and Leeb, and instrumented indentation testing, while continuously improving international rules on uncertainty evaluation, traceability of reference blocks, and verification of testing machines. In parallel, Working Group of Hardness established by Quality and Related Quantities Advisory Committee under International Bureau of Weights and Measures (BIPM/CCM-WGH) ensures the global uniformity and mutual recognition of hardness values at the level of metrology through international comparisons and uncertainty specifications. In China, the standardization system in this field is mainly composed of Mechanics and Process Performance Test Methods sub-technical committee under National Steel Standardization Technical Committee of Standardization Administration of the People's Republic of China(SAC/TC183/SC4), National Testing Machine Standardization Technical Committee (SAC/TC122), and the National Force Value Hardness Gravity Metrolog Technical Committee (MTC7). It is responsible for the formulation and revision of method standards and equipment standards, as well as undertaking tasks related to metrological traceability and international cooperation. In recent years, Chinese experts have significantly enhanced their voice in international standardization work for hardness tests, leading the formulation and revision of several key ISO standards, making international standards more in line with domestic needs. Overall, the future development trend of hardness test standardization includes further standardization of traditional methods, expansion of new indentation methods, and advancement of extreme environment testing methods, providing a more solid foundation for advanced manufacturing and engineering applications.

The flexible composite pipe has the characteristics of good continuity, high tensile strength, high acid-base corrosion resistance, anti-scaling and waxing. In recent years, it has been rapidly popularized and used in domestic oil and gas fields. Linpan Oilfield Production Factory selected a water injection well to start the downhole test for the first time in October 2013. The test lasted for 8 months. During the test period, all water injection operation indexes were normal. The flexible composite pipe was taken out and its comprehensive performance was evaluated after the downhole test. The results showed that this pipe had a significant anti-scaling effect compared with the traditional metal oil pipes. The bending modulus of its inner and outer spiral armor layers was reduced to 92.66% and 87.14%, respectively. The bending strength was reduced to 84.74% and 69.18%, respectively. The tensile stiffness of the entire pipe was reduced by 9.70%, and the internal pressure stiffness was reduced by 8.39%. However, its overall tensile limit was increased by 2.54%, which could still ensure the safe operation and production of this flexible composite pipe under an internal pressure of 15 MPa and an external pressure of 5 MPa.

The aluminum shell of lithium-ion battery plays the roles of sealing and protection for the positive and negative electrodes, separator, and electrolyte inside the package. Its defects could affect the safety, sealing property, and energy utilization efficiency of the battery. In this study, 53148115-type 3003-H14 aluminum alloy shells were employed to systematically investigate the effects of wall thickness, defect and corrosive environment on the property of tensile, pressure resistance and corrosion. The results showed that the shells with wall thickness of 1.0 mm could satisfy the strength requirements of lithium-ion battery. The location of defects had an important influence on the sealing property. The arc radius depression at the corners of aluminum shell has almost no effect on the blasting pressure, while large depressions or damages on the surface significantly reduce the pressure resistance strength. The crystal structure had no change after exposure to water and 5 g/L NaCl solution for 24 h. However, the surface roughness increased with the corrosion time. NaOH solutions caused pronounced surface corrosion, and new reaction substances were formed within 0.5 min in 50 g/L NaOH solution, accompanied by pitting and powdering.

To clarify the high-cycle fatigue behavior of ZL205A aluminum alloy casing of the main reducer of helicopter and the failure mechanism of micro-porosity, the high-cycle fatigue experiments were carried out with a cycle base of 10⁷ of symmetrical cycles (stress ratio of R=-1) by up-down method. The fracture surface and porosity defects were analyzed by scanning electron microscope (SEM) and optical microscope (OM). The results showed that the median fatigue limit of ZL205A aluminum alloy at room temperature was 81.9 MPa; the fatigue cracks all initiated from the surface micro-porosity, the porosity area percentage (f) increased from 0.14% to 0.32%, the crack propagation life decreased by 52%; the porosity shortened the life through the mechanism of stress concentration-accumulation of plastic strain-rapid propagation. This study provides a key basis for life prediction and process optimization of the casing.

The quenching crack failure of high-speed and heavy-duty bearing ring is the bottleneck problem limiting the service reliability of machinery equipment. Therefore, it is crucial to clarify its failure mechanism for optimizing heat treatment processes and ensuring the performance of key components. This study focused on the cracking phenomenon of 20CrMnTi steel bearing rings during quenching. Through various methods such as macroscopic and microscopic fracture characterization, metallographic examination, and chemical analysis, the multi-scale mechanism of crack initiation and propagation was revealed. The experimental results showed that the cracks initiated from the position with distance of 2-3 mm to surface, and there were aluminum oxide inclusions with diameter of 81 μm at the center of original cracks. The original cracks extended along the hoop in subsequent heat treatment process, and the fracture showed the characteristics of intergranular-quasi-cleavage hybrid brittle fracture. Moreover, there was no plastic deformation trace in the extension area, which proved that the failure mode was the original crack extension dominated by quenching stress. By combining with finite element multi-field coupling simulation, a temperature field-phase transformation field-stress field interactive model was further established. The dynamic evolution law of I-type stress intensity factor (K_IC) of crack tip was quantitatively reveled: when the length of original crack exceeded 1.84 mm, the quenching tensile stress made K_IC reach the critical value (128 MPa·m^1/2) after 14 s of quenching, and the unstable propagation of cracks occurred. At this time, the temperature of crack tip area and the phase transition degree of martensite were consistent with the observation results in experiments. According to fracture mechanics criterion and engineering conservatism principle, it was suggested that the quenching treatment should be avoided in production for 20CrMnTi pieces with internal cracks (the length more than 1.8 mm).

X65 pipeline steel is one of the primary materials used in hydrogen-blended natural gas transmission pipelines. The hydrogen embrittlement susceptibility of thermo-mechanically rolled X65 pipeline steel plate was investigated through slow strain rate tensile tests under in-situ high-pressure hydrogen environment. High-pressure hydrogen significantly degraded the plasticity of X65 pipeline steel with elongation after fracture and reduction of area decreasing by 37.4%-57.7% and 49.9%-86.3%, respectively. While the lower yield strength and tensile strength showed little change. It was revealed by fracture surfaces that the test specimens in high-pressure nitrogen exhibited typical ductile fracture, whereas those under high-pressure hydrogen showed brittle cleavage fracture initiated and propagated from deformed grain bands. These bands acted as fast diffusion channels and strong traps for hydrogen, promoting local hydrogen accumulation and facilitating hydrogen-induced cracking. Thus, it was deemed as a detrimental microstructure for the hydrogen embrittlement resistance of X65 pipeline steel.

Accurately evaluating the service performance of high-strength elastic copper alloys lies in understanding their high-temperature stress relaxation behavior, and the core difficulty in this regard is the precise measurement of bending stress under high temperatures. According to the demands of ASTM E328-21 of Standard tests methods for stress relaxation tests for materials and structures, the testing equipment for bending stress relaxation of copper alloys at elevated temperature had been designed and manufactured. Subsequently, a stress measurement method for stress relaxation of copper alloys had been proposed. The copper alloy specimen was set by fixture and pressure load was applied by a press rod to simulate cantilever bending condition. A tubular furnace was used to provide a high-temperature environment. The bending stress evolution during the stress relaxation process of the copper alloy were measured and recorded by force transducer. The bending stress relaxation tests of Cu-Ti alloys were conducted at 300, 375, and 450 ℃, respectively. The results showed that the stress relaxation rates of Cu-Ti alloy were 15.0% and 28.7% respectively at 300 and 375 ℃ after holding the load for 100 h, and the stress relaxation rate reached 69.7% at 450 ℃ after holding the load for 16 h. The proposed equipment can automatically and accurately measure the stress during the high-temperature stress relaxation process of copper alloys, and has high practicality and promotion value.

Taking the new generation of high-strength and toughness XCrMo series oil casing pipes as an example, the relevant experimental research based on the instrumented indentation technology(IIT) was conducted to solve the technical problem that it was difficult to evaluate their fracture toughness by index of KIC with the in-situ non-destructive analysis method and the latest issued national standards. For the three types of high-strength and toughness oil casing pipes with API grades of 125ksi, 140ksi and 165ksi, the tensile properties and fracture toughness K_JC data converted by J-integral were obtained through conventional tests as references. Meanwhile, the indentation tensile properties (yield strength, tensile strength, etc.) and fracture toughness of the materials were sensed by instrumented indentation technology based on the Oliver-Pharr-Tabor multiple decoupling correction model and Energy Release Rate (ERR) model. The results showed that the overall relative deviations between the tensile properties and fracture toughness sensed by instrumented indentation technology and those from conventional tests could be controlled within 5% and 10% respectively, with high accuracy.This will provide broad application prospects for the non-destructive characterization and service evaluation of ultra-high-strength and toughness steel materials.

To provide numerical solutions for optimizing thermal deformation process parameters, and break through the efficiency bottleneck of traditional trial-and-error method in high temperature plastic forming quality control, thermal simulation testing machine was used to conduct thermal simulation compression tests on 316L austenitic steel at different strain rates. The local mechanical response of grains under different thermal deformation conditions was investigated by nanoindentation test, and the recrystallization process of thermal deformation was analyzed by DEFORM finite element simulation software. A genetic algorithm(GA) back propagation (BP) artificial neural network (ANN) with nonlinear mapping capability was used to predict the mechanical properties of austenitic steel. The results showed that the dynamic recrystallization was the dominant mechanism of microstructure evolution in thermal compression deformation process of 316L austenitic steel, and its progress was significantly affected by strain rate. The tests indicated that the recrystallization nucleation and grain reconstruction could be effectively promoted by high strain rate via accelerating dislocation multiplication and energy accumulation. The numerical simulation study further demonstrated that the dynamic recrystallization volume fraction of materials showed positive growth with the increase of deformation amount, which was accompanied by remarkable grain refinement effect. The high temperature rheological behavior of the material was predicted. The hybrid intelligent algorithm model based on genetic algorithm optimization was proposed. The stability of accuracy of stress prediction was greatly improved by modifying the initial parameter sensitivity of BP neural network, which provided reliable calculation method for numerical simulation of complex thermal deformation process.

Wind turbine gears are prone to fatigue failure under alternating loads, thus the fatigue performance research of its wind turbine gear steel 18CrNiMo7-6 has attracted much attention. The samples from the 18CrNiMo7-6 steel parts of wind turbine gears were selected as the research object in this study. The mechanical properties and microstructures were investigated, and the fatigue properties of were characterized. The main factors influencing the fatigue fracture were revealed, which provided a theoretical basis for the reliability design of key components of wind turbine gearboxes. The tensile tests were conducted to obtain the mechanical properties of the material. The rotating bending fatigue tests were performed to acquire the Smax-lg N(Smaxwas maximum bending stress;N was fatigue life) curve and fatigue limit data. Multi-scale observations of the fatigue fracture morphology were carried out using the characterization methods such as scanning electron microscope (SEM) and optical microscope (OM). Meanwhile, the in-situ detection equipment for inclusions was used for the statistical analysis of the non-metallic inclusions in the material. The results showed that the tensile strength (R_m) of gear steel 18CrNiMo7-6 was 1 180 MPa, the yield strength (Rp0.2) was 930 MPa, the average grain size was 11 μm, and the rotating bending fatigue strength (σ-1) was 473 MPa. It was found that the fatigue cracks mainly initiated from the non-metallic inclusions on the surface, and the main failure mode was mixed fracture of transgranular fracture and intergranular fracture. The average size of non-metallic inclusions in the steel was 23.15 μm, and the main types were sulfides and oxides of Mn and Al.

In order to improve the accuracy and repeatability of J-integral calculations in three-point bending tests, a systematic method that integrated data preprocessing, difference-quotient analysis, and integration with unequal segments was proposed to address the issues of noise sensitivity and integration accuracy in conventional fitting and numerical integration approaches. The study applied the difference-quotient features to the identification of the linear region. Moreover, the unequal-segment integration was used to replace equal-segment assumption, thereby enhancing both applicability and precision of calculations. The original load-displacement data were first processed through point uniquifying, interpolation, and Gaussian filtering to eliminate the repeated points, backward points, and noise, thus ensuring a monotonic and smooth curve. The fitting range was then determined by analyzing the peaks and trends of the first-order central difference quotient. The integral calculation was performed using the unequal-segment integration method, while higher-order difference quotients were employed to estimate the integration error. The results demonstrated that the proposed method significantly improved the integration accuracy and stability while preserving the data authenticity. Moreover, it avoided the error estimation failure caused by non-monotonic data, and provided a reliable and reproducible technical route for the J-integral calculation.

When conducting the test of the critical stress intensity factor for Type Ⅰ cracks(KIC) on metal materials according to the fracture toughness testing standard, the problem that the ligament size or the ratio of the maximum load to the condition load (Pmax/P_Q) fails to meet the determination conditions leads to invalid test results.5083 aluminum alloy plates were selected as the research subject, and the experiments were conducted on plane-sided specimens and side-grooved specimens with different thicknesses. Then,the influence of the side groove on KIC test results was discussed with the finite element calculation method. The results showed that the Pmax/P_Q of the side-grooved specimen was lower than that of the plane-sided specimen, and the valid KIC of the side-grooved specimens with different thickness could be both obtained. For the straight crack the side groove depth with 10% of the specimen thickness could achieve better effect on increasing the consistency of stress distribution at crack tip. Even if the initial crack size met the standard requirements, the decrease of the flatness of crack would still lead to a larger test result of KIC. Processing the side groove for the specimen first could increase the flatness of the initial crack, and was conducive to obtaining more accurate KIC test results.

1J85 Fe-Ni alloy is a soft magnetic material with excellent performance and wide applications. In some cases, it needs to be used as a high-temperature structural component, but there are few reports on the mechanical properties of its high-temperature deformation behavior. For this reason, the high-temperature tensile properties of 1J85 Fe-Ni alloy was investigated, and the structure evolution and fracture mechanism during high-temperature deformation was analyzed. The research results indicated that 1J85 Fe-Ni alloy exhibited low yield ratio, high uniform elongation, and high plasticity at room temperature. Both the strength and plasticity of 1J85 Fe-Ni alloy decreased with the increase of deformation temperature. From room temperature to 400 ℃, the decrease in plasticity was minimal. A significant decline began above 500 ℃, and a sharp drop occurred between 600 ℃ and 700 ℃. With increasing temperature, the fracture morphology changed from dimple fracture to intergranular brittle fracture. From room temperature to high temperature, the mechanical properties of 1J85 Fe-Ni alloy were influenced by both grain boundary strength and high-temperature microstructural softening (facilitated dislocation movement). With the temperature increase, material softening led to a decrease in strength while also promoting plastic deformation capability. On the other hand, grain boundary weakening reduced the plastic deformation capacity of material. During high-temperature deformation, both material softening and grain boundary weakening simultaneously affected the plastic deformation capability.

In order to improve the frequent spalling failure of gearbox bearing in working process of a passenger car, the failure analysis of 42 sets of bearings due to spalling failure was conducted by scanning electron microscope (SEM),energy disperse spectroscopy(EDS) and optical microscope(OM). The results showed that there was no abnormality in SEM morphology for 92.9 % of the bearing spalling products. In addition, the element analysis, microhardness and carbide grade of products could all meet the technical requirements of GB/T 18254-2016 or internal control. The main failure causes for the product were not obviously related to of raw material quality and heat treatment, but were related to product design and lubrication environment. It was necessary to adjust the force design and oil supply mode of gearbox. After improvement according to the analysis results of failure parts, the quantity of bearing failure parts significantly was reduced by about 60%.

The effects of heating temperature and heating time on the grain size of M50 high-temperature bearing steel were investigated by metallographic microscope. The experimental results were discussed and analyzed. The experimental results showed that, when the heating temperature was not higher than 1 100 ℃, both heating temperature and heating time had little influence on the grain size of M50 steel. When the heating temperature was higher than 1 100 ℃, the increase of heating temperature and prolonging of heating time exhibited a positive correlation with the grain size. In other words, the grain size of M50 steel would grow up by increasing the heating temperature or prolonging the heating time. Therefore, the control of heating temperature and heating time is very critical to the control of grain size in actual production process.

The development and application of high-strength automotive structural steels is one of key technologies to promote the vehicle lightweighting. However, the problem of cross-sectional cracking was observed for 700 MPa-grade automotive structural steel sheets during shearing, which significantly influenced the processability and use safety of materials. Regarding this issue, the detection methods, such as X-ray fluorescence spectrometer, tensile testing machine, metallographic microscope, scanning electron microscope and Vickers hardness tester, were employed to systematically investigate the chemical composition, mechanical properties, microstructure, fracture morphology and microhardness of the material. The results showed that the contents of alloying elements such as Mn, Nb, and V were significantly higher in cracked samples plates compared to the normal sample plate in shearing. The segregation of Mn and synergistic effect of Mo in material induced the formation of hard and brittle martensite segregation bands in the core of steel plate during hot rolling, leading to the severe nonuniformity of cross-sectional structure and performance, which was the key factor to cause degraded processability. Under the action of shearing stress, the microcracks were formed due to the stress concentration caused by the property mismatch between martensite segregation bands and other regions. The propagation of microcracks caused cracking along the segregation bands during subsequent processing.

In order to investigate and quantitatively analyze the factors influencing compression creep tests of titanium alloys, TC4 titanium alloy cylindrical specimens with varying specifications and precision levels were machined for compression creep tests. Five groups of comparative experiments were designed to obtain the creep curves of samples. The key creep result parameters were calculated and analyzed. The study revealed that the length-diameter ratio and size effect of the specimens showed no significant correlation with the compression creep behavior of TC4 titanium alloy. It indicated that the specimen size had little influence on the final creep performance results within a reasonable geometric proportion range. The flatness of both ends of the specimen had significant impact on the testing process and final creep results. Excessive flatness deviation would lead to uneven stress distribution, which had severe interference with the accuracy and repeatability of experimental data. In order to ensure the reliability of testing results, the flatness deviation should be controlled within 0.02 mm. In the comparison of platen configurations, it was found that the spherical pressure plate demonstrated better compatibility than flat pressure plate when the end flatness of specimen was not good. The spherical pressure plate could effectively compensate for flatness errors and initial misalignment within a certain range, thus improving the uniformity of stress distribution. This enabled relatively more reliable test results even when the specimen machining precision was limited. Regarding the displacement measurement, the study confirmed that increasing the number of grating scales was more advantageous for enhancing the accuracy of creep displacement measurements as well as the reliability of testing results. A multi-grating-scale layout could help eliminate the interference from minor deflection or tilting of specimens during axial displacement measurement, thereby more accurately reflecting the axial compression creep deformation.

In order to explore the thermal deformation rule of X60 pipeline steel under multiple variable conditions and reveal its microstructural evolution mechanism, the Gleeble3180-GTC thermal simulation test machine was utilized to investigate the thermal deformation behavior of X60 pipeline steel under different deformation conditions (the deformation temperature ranging from 750 to 950 ℃, the strain rate ranging from 1 to 5 s^-1, and the deformation amount ranging from 10% to 30%). The thermal deformation constitutive equation of the material was established. The finite element analysis software of DEFORM-3D was employed for the simulation analysis of thermal deformation process. The evolution of material damage and dynamic recrystallization behavior under different deformation conditions were studied. The results indicated that the selection of a lower strain rate and a higher deformation temperature could avoid generating higher damage values during the thermal processing, and the recrystallization process was significantly suppressed under such conditions. Higher deformation temperature, strain rate, and deformation amount were beneficial for the occurrence and expansion of dynamic recrystallization. The grain refinement could be accelerated, thereby improving the plasticity of the steel.

The surface removal amount of impact specimens is specified in ASTM A 370-2022, and it is in contradiction with ASME B31.3-2022 where the overcooling degree should be considered when the notch width of the notched specimens is less than 80% of material thickness. Based on this, an impact sampling method of thin-walled austenitic stainless steel seamless tubes was discussed. Impact tests were compared on austenitic stainless steel seamless tube specimens in original (solution) state and flattened state respectively, and the results showed that the impact absorbed energy in flattened state was significantly greater than that in original state. Hardness comparison tests were conducted at three different positions on the same flattened state specimens, namely the end, 1/4 (width) W and 1/2 W. The results indicated that the hardness at 1/4 W of specimen was the lowest. The ferrite numbers of specimens in original state and flattened state were determined respectively. The results indicated that the ferrite number in flattened state was significantly higher than that in original state. At 1/4 W of specimen, hardness tests were compared in flattened state and original state under both room temperature and -196 ℃ conditions. The results showed that the hardness of specimen in flattened state at both room temperature and -196 ℃ were higher than those in original state. The strain hardening in flattening process played a dominant role at -196 ℃, which was the main reason for the above phenomena. Therefore, it was considered that the surface removal amount specified in ASTM A370 could be neglected for thin-walled austenitic stainless steel seamless pipes, and the results of impact tests were more representative when the specimens were directly sampled in original state. Meanwhile, it could also meet the requirements for the degree of undercooling specified in ASME B31.3-2022.

Bar materials,as important raw materials for key components such as bearings and chains, their quality directly affects the safety performance of the downstream products. For rods with a diameter not exceeding 50 mm, the magnetic flux leakage non-destructive testing technology is commonly used for defect detection, but it has the disadvantages of high loss and high cost. The application of infrared thermal imaging detection technology in detection of surface defects of small-size bars was investigated. This technology heats the surface of small-size bars in motion by controlling a high-frequency eddy current heat source. The surface temperature field information was collected with infrared camera, and analyzed through image processing technology. The characteristic information of surface defects was obtained by the temperature change rate. The test results showed that when the ratio of defect depth to surface roughness of the bars was greater than 3 ∶1, this detection method could accurately distinguish the defect range from the image. When the motion speed was within the range of 0.5 to 1.5 m/s and the depth of the artificial damage grooves was within the range of 0.1 to 1.1 mm, the defect detection rate was greater than 99.5% and the false alarm rate was less than 0.5%. The feature extraction technology could precisely calculate and obtain the geometric shape features (length, width, etc. of key parameters) and spatial position information of defects. The deviation in the length direction was within ±3 mm and the deviation in the angle direction was within ±5°.

Fatigue life is one of the important indexes for safety assessment of crane, and the existence of average stress is one of important factors to be considered in multi-axial fatigue failure of Q345 steel for metallurgical crane main beam. Uniaxial tension-compression and pure torsion fatigue tests were conducted on the main material Q345 steel for metallurgical crane main beam, and the tensile stress(S)-fatigue life (N) curves and torsional stress S-N curves of the material were obtained. Based on the test results, an appropriate stress was selected as the equivalent stress for multi-axial fatigue loading, and the multi-axial fatigue fatigue tests with different average tensile stresses were carried out under this equivalent stress.The variations of the maximum normal stress and the maximum shear stress under different tensile average stresses and their corresponding planar directions were theoretically deduced. The initiation and propagation of cracks on the surface of fatigue specimen were observed by optical microscope, and the microscopic morphological characteristics of specimen fracture surface were analyzed by scanning electron microscope (SEM) to investigate the failure modes of Q345 steel under different tensile average stresses. The research showed that the multi-axial fatigue life of Q345 steel would be significantly reduced with the influence of tensile average stress. With the increase of tensile average stress, the shear stress gradually played a dominant role in the process of fatigue failure.

A exhaust gas recovery compressor fractured during service. The on-site investigation revealed that all twelve connecting bolts on the cylinder body of compressor had fractured. In addition, compressor piston rod was also fractured. In order to determine the failure cause and prevent such incidents from happening again, the analysis of piston rod and bolts on chemical composition, mechanical properties, metallographic structure, and fracture morphology was conducted through experiments. The fracture cause was identified. The results showed that the failure mode of compressor bolts was the fatigue cracking when the alternating loads exceeded the fatigue limit of material. The main cause of early-stage cracking of bolts was the existence of excessive full decarburization layer on the surface of thread. After the fastening bolt fractured, the compressor run in a state of instability, and the piston rod was abnormally stressed and overloaded, which belonged to the late damage.

This study focused on the mechanical property characterization and inversion of through-silicon via (TSV) copper-filled materials in three-dimensional integrated circuits. The mechanical response of through silicon vias-copper nanoindentation (TSV-Cu) under thermal cycling loading directly affects the reliability of the packaging structure. However, the systematic analysis of its geometric size effect is still relatively lacking in the existing researches. For this purpose, in this paper, the mechanical behavior and microscopic mechanism of TSV-Cu with different diameters after high-temperature annealing were systematically studied by combining the nanoindentation experiments with finite element inversion. The results showed that both the elastic modulus and nanoindentation hardness of TSV-Cu after annealing were positively correlated with the diameter. The simulation inversion results indicated that the yield strength stabilized at 35 MPa after annealing, and the plastic behavior tended to be stable. The medium-diameter TSV-Cu (20 μm) exhibited relatively balanced mechanical properties (nanoindentation hardness of 1.62 GPa and modulus of 133.66 GPa). The microstructure analysis indicated that the medium-diameter TSV-Cu was more prone to grain coarsening and had better thermomechanical reliability. The differences in mechanical properties exhibited by TSV-Cu with different diameters could provide a certain basis for the selection and performance regulation of TSV-Cu in advanced packaging.

To optimize the rolling process parameters of ferrite, dilatometric analysis and metallographic method were combined in this study to construct dynamic continuous cooling transformation (CCT) curve of undercooled austenite for the intermediate billet of SPHC3 steel during the transition from austenite to ferrite. The phase transformation law of SPHC3 steel was further analyzed in continuous cooling process, and the phase transformation points were determined. The experimental results indicated that, under constant deformation conditions, the increase of cooling rate would reduce the initial temperature of ferrite transformation (Ar₃) and the austenite-to-pearlite transformation temperature (Ar₁), while the phase transformation temperature range was widened. Thermal simulation experiments with varying deformation temperatures, deformation amount, and strain rates were conducted, supplemented by lever method of dilatometric curves, to explore the effects of process parameters on dynamic transformation points during austenite-to-ferrite transition. The results demonstrated that, when other deformation conditions were fixed, both Ar₃ and Ar₁ lowered with the increasing of deformation temperature; both Ar₃ and Ar₁ increased with the increasing of deformation amount; both Ar₃ and Ar₁ lowered with the increasing of strain rates. In industrial production, the phase transformation temperatures could be increased by lowering deformation temperature, increasing deformation amount, reducing strain rate, and decreasing cooling rate, thereby ensuring that the finish rolling occurred within ferrite region.

Through analogue simulation, metallographic structure analysis, high-temperature thermoplastic test and fracture morphology analysis of edge crack defects in Q460C angle steel, the formation mechanism of these defects was explored. The results showed that there were oxidation material spots, decarburization and ferrite grain growth in the defective parts of edge cracks in angle steel. The edge cracks in angle steel were caused by the inheritance of cracks in the inner arc angles of casting billet. Q460C continuous casting billet had obvious high-temperature plastic zone and low-temperature brittle zone. The high-temperature plastic zone was in range of 975-1 350 ℃, and the low-temperature brittle zone was in range of 600-950 ℃. When the temperature increased from 950 ℃ to 975 ℃, the section shrinkage rate increased from 34% to 85%. On this basis, the process optimization measures, such as improving the purity of molten steel, stabilizing the drawing speed, controlling the superheat of the middle ladle, adjusting the specific water volume of the secondary cooling, and increasing the temperature before straightening of the continuous casting billet, were proposed for the problem of crack defects at the edge of Q460C angle steel. Then the surface quality at angle of casting billet was significantly improved, and the crack defects on the surface of angle steel were fully controlled.

7N01 aluminum alloy sheets rolled in two different batches were investigated systematacially. Optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM), and electron backscatter diffraction(EBSD) were employed to characterize their microstructural features at different scales. The corrosion resistance of the different sheets were evaluated through exfoliation corrosion and intergranular corrosion tests, while the mechanical properties of the two types of sheets along different orientations were obtained via tensile tests. The correlation between the microstructure and properties of 7N01 aluminum alloy was clarified. The effects of microstructural characteristics (such as phase distribution, grain morphology, and preferred orientation) of the different sheets on tensile properties, exfoliation corrosion performance, and intergranular corrosion performance were investigated. It was found that the distribution of precipitated phases and grain boundary composition were important factors affecting corrosion resistance, and the mechanical properties in different directions were closely related to crystallographic preferred orientation. Furthermore, a comparative analysis was performed on the anisotropy index and yield-strength ratio of the two batches of aluminum alloy, providing guidance for their engineering applications.

The design life of a certain 18CrNiMo7-6 steel gear shaft was 47.2 months, but it broke after 6 months of service. In order to determine the failure cause and prevent such event from happening again, the test piece were carried out by physical and chemical analysis methods, such as scanning electron microscope (SEM), metallographic analysis, hardness test, and chemical composition test. The results showed that the matrix microstructure was tempered sorbite, and there was segregation martensite at the same time. These two kinds of structures had difference in hardness and were distributed alternately in the material. The segregation area had a higher hardness, making it more prone to forming stress concentration points during service. This led to the initiation and propagation of cracks in the gear shaft over a long service period, ultimately resulting in the fracture of the gear shaft.

The microscopic analysis of materials is mainly carried out by means of destruction, such as optical microscope (OM), scanning electron microscope (SEM). Meanwhile, these destruction methods can only analyze the situation of surface, and the situation in whole volume cannot be reflected. How to select and process the analysis surface will directly affect the analysis results. The application of ordinary ultrasonic testing has a long history, but it cannot meet the requirements of material microscopic analysis when it is applied in millimeter defect detection of materials and parts. Scanning acoustic microscope (SAM) is a kind of C-scanning equipment with high precision scanning institutions and special software. The working frequency is high frequency ultrasound which is 100-1 000 times of ordinary ultrasound. The resolution of X/Y axis is up to 0.1 μm, and the resolution of Z axis is up to 5 μm, which can realize the analysis of micrometer-level defect (or tissue structure). It has multiple scanning modes including A, B, C, D, X, G, P and 3D, which can realize three-dimensional defect positioning, size measurement and area proportion analysis. The abnormal internal structure of materials can be accurately reflected, which can be used as the preliminary positioning and screening method for material analysis, or directly used in material analysis.

The macroscopic observation and microstructure analysis of fracture of 45 steel motor shaft were conducted by metallographic microscope, scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The fracture reasons were comprehensively analyzed based on the chemical composition, hardness testing and metallographic morphology. The results showed that the chemical composition of the motor shaft met the composition requirements of 45 steel specified in GB/T 699-2015. Based on hardness test results and analysis of macroscopic structure morphology, it could be concluded that the motor shaft has undergone quenching and tempering in some areas. The short-term fracture was due to the presence of numerous granular non-metallic inclusions and holes within the motor shaft material. At the fracture surface, there was a depression with a diameter of approximately 3.4 mm near the edge. During the operation of the motor, it caused stress concentration, forming a crack source, and then the cracks extended towards the edge. Due to the presence of numerous inclusions and holes within the material, which made it overall loose, the cracks spread rapidly, resulting in the short-term fracture of the motor shaft.

The power supply and communication between instruments were interrupted when a certain drilling adapter fractured, which caused economic loss after drilling. The fracture cause of the adapter was determined by the analysis of macroscopic morphology, microscopic morphology, metallographic structure, chemical composition and hardness testing. The results showed that the adapter belonged to fatigue fracture. The fatigue source was located at the sharp edge defect of the long strip protrusion at the thread root where the cutting groove and thread chamfer were connected. There was a high local stress concentration at this location, and the fatigue cracks initiated and rapidly expanded under the alternating load of drilling work. In addition, the beryllium bronze material under simultaneous action of solid solution and aging treatment was sensitive to notches, weakening the grain boundaries, which was prone to formation of intergranular cracks.

Grass-like wave problem is a common surface wave defect in forged steel cold rolling roller billets. If the traditional tempering and surface hardening processes are adopted, the problem of surface wave defect in the finished rolling roller products cannot be effectively eliminated. The post-forming heat treatment processes such as normalizing and spheroidizing annealing were employed to reduce or eliminate the grass-like wave defects that occured during ultrasonic testing of 70Cr5Mo steel roller billet products. The results showed that a uniform and fine spheroidized pearlite structure could be obtained by adopting a combined pre-treatment process of normalizing with isothermal spheroidizing annealing, effectively improving the microstructure of 70Cr5Mo steel, thereby achieving the goal of reducing or eliminating the grass-like waves.The recommended process was as follows: normalizing (holding at 1 070 ℃ for a certain period and then air cooling) →isothermal spheroidization (holding at 970 ℃)→rapid cooling to 770 ℃ and holding for a certain period→furnace cooling to 500 ℃ and then unloading for air cooling.

The measurement resolution of impact fracture image analyzer is limited by the optical lens, which cannot meet the requirements of metrological characteristics regarding display resolution. In order to improve the display resolution of impact fracture images, the super resolution fracture image analysis was investigated to solve the problem of low resolution of impact fracture images. The original resolution about 0.03 mm was increased to about 0.003 7 mm, which could meet the requirements of relevant standards. In order to meet both the requirements of impact fracture morphology analysis and the display resolution requirements for metrological calibration characteristics, the tower decomposition amplification enhancement method was adopted in this study. Two different types of impact fractures were photographed on the impact fracture image analyzer to obtain the original fracture images, and then the fracture images were subjected to 8 times tower decomposition amplification processing. Through the algorithm evaluation, it was found that the enlarged fracture image maintained good similarity and information content with the original image, which conformed to the measurement principles of geometric quantities. Finally, an uncertainty evaluation was conducted and the results were provided.