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.

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.

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 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.

To investigate and replenish stress corrosion criteria, the axial tensile stress corrosion tests of 2026-T3511 aluminum alloy in the transverse direction were comprehensively analyzed by axial specimen fracture macrostructure observation, metallographic microstructure observation, fracture scanning and blank microstructure verification. It was found that it belonged to stress corrosion failure even if the axial tensile specimen was broken beyond the standard distance. By the short-transverse C ring stress corrosion test, it was found that when conducting axial tensile stress corrosion tests, if the material exhibited transgranular fracture perpendicular to specimen axis and secondary crack parallel to specimen axis, namely intergranular crack, they could also be used as the criterion for stress corrosion failure.In order to verify the influence of specimen length, exposure length and processing parameters on test results, the control variable method was adopted. It was found that the greater the specimen length and exposure length, the lower the finish turning speed, and the less effect on stress corrosion. The surface residual stress caused by rough turning feed in the standard procedure could be ignored.

Boron carbide ceramic is a kind of bullet-resistant material. In order to ensure its protective performance, it is necessary to strictly control its quality through non-destructive testing methods. At present, X-ray method is commonly used for its internal quality inspection.While, the determination of its exposure conditions is lack of corresponding basis during detection by X-ray digital radiography (DR). Under the same transparent tube voltage, X-ray digital radiography of boron carbide bullet-resistant ceramic multistep test blocks and 6063 aluminum alloy multistep test blocks were carried out by equivalent coefficient method, providing a basis for determination of its exposure conditions. The results showed that the equivalent coefficient of boron carbide bullet-resistant ceramic and 6063 aluminum alloy was 0.71-0.86 when the transparent tube voltage was 45-70 kV. The test results had a certain guiding significance for the determination of X-ray digital radiography conditions for boron carbide bullet-resistant ceramic.

The development of preparation method for metallographic samples of thorium dioxide nuclear fuel pellets is of great significance for its microstructure observation and performance study. The influences of five types of chemical etchants, including H₂SO₄, HCl-H₂O, H₂SO₄-HNO₃-HCl-H₂O, H₂SO₄-HCl-H₂O and H₃PO₄ on the preparation of thorium dioxide pellet metallographic sample were investigated to optimize the chemical etching method. The effects of different molding pressure conditions on microscopic pore, cracking and grain size of metallographic samples were discussed. The results demonstrated that the clear grain boundaries could be observed only by preparation with two etchants, i.e., H₂SO₄-HCl-H₂O and H₃PO₄. Considering the relatively weaker irritating odor of H₃PO₄, it was selected for etch preparation of thorium dioxide pellet metallographic sample. Under identical molding pressure, the raw powder with higher specific surface area was more helpful for the reduction of pores and cracks as well as the growth of grains in thorium dioxide pellet due to the superior sintering driving force and sintering activity.

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%.

25Mn hot rolled seamless steel tubes were used to manufacture cold-drawn steel tubes for hydraulic cylinder in a factory. Some steel tubes had transverse fractures in the straightening process, which greatly affected the production organization and resulted in great loss. The on-site investigation and sampling were conducted. The physical and chemical tests, including chemical composition, mechanical properties, metallographic structure, scanning electron microscope fracture analysis, on the fractured steel pipes and hot rolled steel pipes of the same batch were also performed. The reasons for the transverse fracture of 25Mn steel pipes in the straightening process after cold-drawing were analyzed. It was confirmed through the tests that the primary failure mode of transverse fracture of steel pipe in the straightening process was the damage to inner wall of pipe due to poor lubrication in the cold drawing process. The secondary failure mode was poor lubrication due to the poor quality of phosphorization-saponification treatment before cold-drawing, with insufficient and uneven film thickness. The tertiary failure mode was the uncontrolled process of phosphorization-saponification procedure. There were two main reasons for the loss of process control:first, the temperature and time for phosphorization were controlled arbitrarily; second, the amount of steel added is large, resulting in a high degree of contamination of bath.

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.

A certain equipment, equipped with a cast tin bronze pressure reducing valve parts (QSn4-4-2.5), experienced a failure phenomenon of perforation and leakage after being in use for some time. The leakage causes of the pressure reducing valve parts were analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES), optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results showed that the chemical composition of material for the failed pressure reducing valve parts could meet the technical requirements of relevant standards, and no obvious abnormality was found in the metallographic structure. The perforation and leakage of the pressure reducing valve parts were caused by local corrosion inside the valve body. The erosion corrosion by seawater was the main cause of local corrosion leakage, and the presence of micro-porosity in the material could accelerate the generation and expansion of corrosion.