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.

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.

In order to systematically study the recrystallization behavior of Nb-containing high strength IF steel (UF340) during hot rolling and finishing rolling, the rolling process test was conducted in hot rolling line of Shougang Qiangang 2160. The microstructure of rolled material in each frame was characterized by field emission scanning electron microscope. It was found that the recrystallization nucleation and growth in UF340 were finished independently in the first two finishing rolling processes, and the microstructure between the frames was completely recrystallized. Due to the solid solution drag effect of Nb, the recrystallization in UF340 was retarded and partial recrystallization occurred at hot rolling F3-F5. Under cumulative rolling deformation of the final frame, the recrystallization of UF340 was sufficient after F6 rolling, and the microstructure after finish rolling was composed of the uniform equiaxed grains. The main texture was rotated cube texture ({001}<110>). Thermodynamic calculation of recrystallization in hot rolling of UF340 was conducted, and the calculated results were in good agreement with the experimental data. According to the calculation results, the load distribution of each frame in finishing rolling was adjusted to make the recrystallization of UF340 more adequate in hot rolling process, and the microstructure uniformity of edge was obviously improved.

In the process of automatic tape laying, the draping suitability has a significant impact on the draping quality of prepreg. Therefore, it is of great significance to design experiments to evaluate the suitability of prepreg draping. This paper focused on the quantitative characterization method for drapability of prepreg, i.e., three-point bending method. The optimal conditions for testing prepreg drapability were explored through orthogonal experiments. Loading rate, test span, and fixture radius were selected as the influencing factors for the imported prepreg M91 in three-point bending test. The maximum bending force and test dispersion coefficient were used as the evaluation indicators. The range analysis and variance analysis were applied comprehensively to determine the optimal test conditions. The test results indicated that the changes in loading rate had a significant impact on the three-point bending test of prepreg M91, while the changes in test span and fixture radius had little influence on the test results. The optimal test conditions for this three-point bending test of prepreg were obtained as follows: the loading rate was 25 mm/min, the test span was 25 mm, and the fixture radius was 3 mm.

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.

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.

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 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.

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 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.

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.