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).

In corrosion laboratory, the rotameter is usually used to control the constant flow of gas. H₂S bubbling is observed to ensure that H₂S solution is saturated during the whole test. This control method cannot achieve the continuous monitoring of H₂S flow, and may cause test failure. In the digital corrosion test system, the digital mass flowmeter was used to replace the rotameter, which realized the remote real-time monitoring and data traceability of H₂S flow. The digital corrosion test system was used for multiple corrosion tests. H₂S with different constant flow was injected into reaction solution with different volumes to investigate the corresponding relationship between H₂S concentration in the test solution and H₂S flow, so as to ensure the smooth operation of corrosion tests.The test results showed that, in the hydrogen-induced cracking (HIC) resistance test, if the reaction vessel is smaller than 25 L, the constant flow of H₂S introduced should be set to no less than 8.0 mL/min to ensure the stable conduct of corrosion test.

Seamless steel pipe is an important industrial material, and its quality defects directly affect the safety and service life of equipment. In response to the limitations of traditional magnetic flux leakage testing methods in identifying small and oblique defects, a magnetic flux leakage testing system based on array magnetic sensors was proposed in this study. The detection accuracy and efficiency were significantly improved through multi-dimensional signal acquisition and fusion processing. Firstly, the hardware architecture of array magnetic flux leakage(AMFL) testing system was elaborated, including the transverse magnetic flux leakage, the longitudinal magnetic flux leakage, three-roller centering conveyor device, and the host installation platform. The transverse magnetic flux leakage system and the longitudinal magnetic flux leakage system was discussed in detail. Secondly, the detection capability, signal-to-noise ratio, and repeatability of the array magnetic flux leakage testing system were detected by processing comparison sample tubes containing longitudinal, transverse, and oblique artificial defects on the inner and outer surfaces. The experimental results showed that the system had a detection rate of 100% for short longitudinal and transverse defects with length not less than 12 mm as well as oblique defects with length less than 25 mm. The proposed technology provided an innovative solution for the quality monitoring of seamless steel pipes throughout entire lifecycle, and had significant engineering application values.

In the field of modern industrial inspection, water immersion ultrasonic C-scan inspection has become an important method for internal defect detection of materials due to its non-destruction, high accuracy and extensive applicability. Water immersion ultrasonic C-scan inspection system was comprehensively analyzed from the key factors including electronic instrument, ultrasonic transducers, reference block, mechanical scanning devices, and combined system performance verification standards. A set of traceability solution was proposed to ensure the stability and reliability of detection system, thereby ensuring the detection quality and providing solid technical support for industrial inspection.

Nondestructive testing technology is required for the metal structural component of civil aircraft during the stages of raw material selection, production manufacturing and use to ensure that their metallurgical defect equivalent meet the requirements of airworthiness and safety. Reasonably designed reference blocks and well-developed testing methods are important parts for effectively identifying and evaluating the potential defects in aviation equipment, and ensuring the authenticity and reliability of testing results. This article focused on the technical requirements of nondestructive test blocks, and elaborated on the design and quality control methods of reference blocks for metal structural components in civil aircraft from the aspects of material selection, processing, and acceptance. By analyzing the characteristics of raw materials and in-service structural components, the corresponding acceptance and evaluation criteria were proposed to effectively improve the accuracy and reliability of nondestructive testing.

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.

It is often necessary to perform quenching and tempering treatment on large forgings such as forged steel rolls to ensure their comprehensive mechanical properties in use. Due to the high alloy composition, the necks of each roll have deformation to varying degrees after quenching and tempering. Therefore, the straightening treatment is usually necessary. However, the cold rolling rollers have a large tonnage and significant differences in size, making them prone to cracking during straightening. In this study, the causes of cracking failure of 90SiCr6 steel used for cold rolling rollers after quenching and tempering during straightening were analyzed and discussed. The tests showed that the roll neck hardness was 46-48HSD, which was the same to the roll billet with the same material after normal quenching and tempering. The chemical composition in fracture met the composition range of 90SiCr6 steel roll billet. There was no obvious abnormality in waveform of ultrasonic testing (UT) at the fracture site of roll neck, indicating that there were no defects inside the roll neck such as tiny cracks, holes and inclusions. The metallographic structure observation results of blank showed that both network carbide and liquation of original roll billet exceeded the standard. The metallographic structure observation results of roll neck showed that there were severe network carbides and aggregated eutectic carbides inside the roll neck tissue. Based on the comprehensive analysis results above, the presence of severe network carbides and aggregated eutectic carbides inside was the main reason to cause cracking of roll neck. When the roll neck was subjected to the straightening force, the roll underwent plastic deformation. The dislocations accumulated around the network carbides and aggregated eutectic carbides, leading to local stress concentration and ultimately inducing roll neck fracture.

When Cr12 curved rod manufactured by one metal processing factory was polished after heat treatment, some fine cracks were found on the surface of curved rod. The curved rods containing crack defects were dissected for sampling. The causes of surface cracks were analyzed through metallographic examination, scanning electron microscope(SEM), and chemical composition analysis. Metallographic examination revealed the subtle changes in internal structure of the curved rod, while SEM clearly displayed the morphology and distribution of cracks. The results showed that the salt bath medium used in the quenching and heating process had a corrosive effect on the surface of the curved rod under specific dendritic conditions. Small pits were formed, which induced the formation of stress corrosion cracking under the combined action of tissue stress and thermal stress.

At present, the corrosion failure is one of important difficulties in application of austenitic stainless steel pipe. The 06Cr19Ni10 stainless steel seamless pipe pipeline experienced pitting corrosion failure during operation. The failed pipeline was sampled for physical and chemical inspections of defects, including macroscopic observation, microscopic examination, chemical composition analysis, and intergranular corrosion detection. The running medium such as water pH and chloride ion were also detected to analyze the cause of corrosion failure of 06Cr19Ni10 austenite stainless steel. The test results showed that the water in pipeline was at pH 7.9, which was neutral. Moreover, the intergranular corrosion test results of pipes were qualified, thus excluding the possibility of intergranular corrosion failure. The chemical composition analysis and metallographic examination of seamless pipe had no abnormality, which exclude the possibility of microdefect of fluid pipe raw material to cause failure. It was found that the chloride ion content in water within fluid pipe was 62.04 μg/g, which exceeded the water quality requirement in pressure testing. Combining with the influence of silt accumulation, numerous pitting corrosion pits were caused on the stainless steel pipe. The pitting corrosion pits gradually expanded until they penetrated the entire thickness of stainless steel pipe wall, ultimately resulting in failure and leakage. It was recommended to replace with seamless pipe of 316 series austenitic stainless steel or austenitic-ferritic duplex steel, which had higher pitting corrosion equivalent and better pitting corrosion resistance. At the same time, based on the failure cases of 304 series materials, some reasonable suggestions were given for the usage environment of 304 series materials.

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.

After approximately 3 months of use, the 20CrNi2Mo steel heavy-duty gear used in a certain mining machinery broke. The failure cause of these gears was analyzed to reveal the internal mechanism of the gear breakage, and provide a theoretical basis for improving the reliability and service life of the gears. The failure modes of heavy-load gear were analyzed by methods, such as means of macroscopic examination, chemical composition analysis, metallographic examination, scanning electron microscope(SEM), and energy spectrum analysis. The analysis results showed that the oxide slag inclusions were introduced into the failed gear during the smelting process. Under the repeated action of external loads, these slag inclusions acted as fatigue sources, which provided favorable conditions for crack initiation and propagation. The metallographic analysis and SEM observations confirmed that some fatigue cracks originated near the slag inclusions and continuously propagated under sustained loads, eventually leading to fatigue fracture of the gear. To address this issue, the conditions optimization of melting, casting, and solidification, and strengthening the raw material control within the smelting process were suggested to minimize the generation of oxide slag inclusions as possible, thereby improving the reliability and service life of gear.

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.

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.

In the process of product testing, the accuracy of measurement data is the key element to ensure product quality. The metrological status of measuring equipment could directly affect the reliability of test results. Metrological confirmation, as an important part of the quality management system, could effectively ensure that the metrological characteristics of measuring equipment meet the requirements of intended use, thus avoiding the risk of data distortion caused by equipment deviation. In the process of metrological confirmation, the first step is to clarify the measurement requirements of the measuring equipment and formulate a calibration plan; the second step is to carry out metrological calibration; the final step is to compare and analyze the actual metrological characteristics of equipment with the expected requirements through calibration confirmation to determine its applicability. In addition, the calibration confirmation of a hardness tester was used as an example for analysis in this paper, providing a reference path for laboratories to build a standardized and normalized metrological management system.