The surface Rockwell hardness of tinplate could reflect the tinplate hardness of its surface. This feature is very important for the processing and application of tinplate. Therefore, the surface Rockwell hardness measurement is an important step in the inspection process of tinplate. The method for measuring the surface Rockwell hardness is similar to the ordinary Rockwell hardness, but the applied load is different. HR 30T and HR 15T steel balls were used as indenter, and the head diameter was Φ1.587 5 mm. Under the conditions of total load composed of initial test force and main test force, the steel balls were pressed onto the sample surface. The pressure was maintained in the specified time. Then the main test force was removed, while the initial load was still maintained. The indentation residual depth caused by main test force was measured to calculate the surface Rockwell hardness value.

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 technologies for defect assessment of additive manufacturing were investigated. The comprehensive analysis was conducted from the aspects of additive manufacturing process principles, typical defect types, defect detection, and defect assessment progress. The causes of defects and the current main non-destructive detection methods were emphatically discussed. The main defect assessment methods and research status at home and abroad were summarized and sorted out. The existing problems of additive manufacturing defect assessment technology were proposed, which could provide the reference for the assessment research of additive manufacturing defects.

The specific heat capacity of NdFeB material was determined by differential scanning calorimetry (DSC) method. The optimal test conditions were explored from the aspects of crucible selection, standard sample mass and sample weight. Meanwhile, the Curie temperature of NdFeB material was determined by the abnormal turning point of the specific heat capacity near the Curie temperature. The optimal testing conditions were obtained as below: the aluminum (Al) crucible was selected; the mass of sapphire standard sample was 43.3 mg; the sample weight was about 43.3 mg. The results showed that the Curie temperature (T_C) of NdFeB material determined by DSC was consistent with that of typical NdFeB magnetic steel (310 ℃). The Curie temperature of NdFeB materials with different grades was in range of 290-330 ℃, and the Curie temperature of NdFeB magnetic material obtained by this method was in the range of 243-386 ℃ of the third generation of rare earth permanent magnet materials R₂Fe₁₄B series compounds.

The application of LED UV-A lamp is more and more common. Its performance indicators are quite different from the high-pressure mercury vapor arc lamp, and the improper application will directly lead to the missing inspection of defects. Based on the performance index of the UV-A lamp, its use characteristics were discussed so as to facilitate the correct use of the UV-A lamp by technicians. The contents included the production certificate of the UV-A lamp, the integrity and cleanliness of the filter and the inspection method, the radiation intensity of the UV-A lamp, the leakage of the white light of the UV-A lamp, the minimum working distance, the effectiveness of the LED lamp bead work. The requirements and test methods of the UV-A lamp were analyzed in details in order to guide the inspectors to correctly grasp its use characteristics and test requirements. This study was conducive to the correct implementation of the detection, which could ensure the reliability of the defect detection results.

In the practical application of phased array ultrasonic testing technology, the coupling methods of probe and workpieces mainly include contact method and water immersion method. In the contact detection method, the probe is in direct contact with the workpiece, and the detection effect is affected by the workpiece surface roughness and near field region. For the water immersion method, there is a water layer between the probe and the workpiece, which not only has good coupling effect, but also has no near-field influence, so the detection effect is good. This paper analyzed the defect imaging characteristics of the two detection methods, and verified the imaging effect of the same defect through comparative experiments. It showed that the water immersion method of phased array ultrasonic detection had better defect display effect and higher signal-to-noise ratio than the contact method.

This article mainly introduced a high-temperature static Poisson's ratio test method using mechanical axial and transverse extensometers through axial tension. Compared to traditional high-temperature static Poisson's ratio measurement methods, the proposed method had the advantages of more convenient, low-cost, and intuitive displacement measurement. The static Poisson's ratio tests of various materials were conducted at room and high temperatures. Moreover, the data were compared with dynamic Poisson's ratio data under the same conditions. The results showed that for GH49, 316L, GH4720Li, and K6509 materials, there is a certain numerical difference between high-temperature dynamic Poisson's ratio and static Poisson's ratio, and even under temperature changes, the trend of change does not show correlation.

The 40CrNiMoA alloy steel billet produced by a certain forging factory was forged into wear-resistant plate ring billet by forging hammer. After quenching and tempering heat treatment, it was found that there were many crack defects on the surface of the ring forgings. In order to investigate the causes of surface crack defects in 40CrNiMoA ring forgings, samples were dissected and analyzed for chemical composition, metallographic examination and scanning electron microscopy. The analysis results indicate that the crack in the 40CrNiMoA ring forging originates from the end face of the ring forging, and the crack propagation mode is a single transgranular propagation. The formation of the crack belongs to the stress crack of heat treatment quenching.

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.

In order to find out the causes of fine line-like defects at the edges of 20MnB hot rolled fine-blanking steel and propose the effective improvement measures, the micro-cracks were formed by pre-crack and fatigue vibration based on the microstructure analysis of detects in hot rolled plate. The sample with micro-cracks was used for high-temperature oxidation simulation experiments. The oxidation and decarbonization laws of microstructure near the micro-cracks were investigated. The results showed that the depth of oxidation dots was strongly correlated with heating temperature, which was the main basis for judging the formation temperature of defects. The microscopic characteristics in high-temperature oxidation simulation experiments were compared with the defects in hot rolled plate. It was considered that the edge defects in the hot rolled plates occurred in the rough rolling region. The typical microscopic characteristic was that there was an oxidation dot zone with a depth of less than 5 μm near the crack, as well as the slight grain growth and decarbonization or not in metallographic structure. According to the above conclusion, the equipment in rough rolling region was checked up, and it was found that the vertical roller surface was rough and there were adhesive steels on it, which were the main reasons to cause fine line-like defects. The lubrication process and working period of the vertical roller were adjusted. The percentage of the rolled oil was increased from 3‰ to 5‰. Finally, the fine line defects at the edges were significantly reduced.

A rainwater grate in one residential area fractured during use. The intact rainwater grates and fractured ones collected from the site were analyzed and compared by metallographic examination, scanning electron microscopy, and mechanical property testing. By combining with finite element simulation analysis, it was found that the material of the fractured rainwater grate was gray cast iron, which had relatively poor mechanical properties. Additionally, due to the existence of old damage in the fractured rainwater grate, its strength could no longer meet the requirements for pedestrian stepping, posing a safety hazard, and leading to breakage accidents when stepped on by pedestrians.

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 corrosion behavior of Q235B carbon steel for tank in acidic sulfolane solution at two typical temperatures, i.e., 30 ℃ and 50 ℃, was investigated and analyzed by static coupon method,electrochemical impedance spectroscopy and potentiodynamic polarization curve method. The results showed that the corrosion rate was fast at 50 ℃, which was nearly three times of that at 30 ℃. The electrochemical experiments indicated that Nyquist curve showed incomplete capacitive arc in the high-frequency region, and the radius of capacitive arc in the high-frequency region was small at 50 ℃. Due to the greater activation degree of sulfolane degradation at high temperature, the resistance of ions in the solution became smaller, leading to the aggravated corrosion, which was consistent with the result of static coupon method. With the extension of immersion time, the corrosion products of Q235B carbon steel during the immersion in acidic sulfolane solution had no protecting effect on the matrix. The self-corrosion potential shifted negatively, the polarization resistance decreased, and the corrosion resistance gradually decreased.

In the machining process of sleeve parts by one machine manufacturing shop, it was found that the surface of several steel pipe sleeve parts had linear longitudinally stripe defects and the surface quality was unqualified. After scraping the unqualified sleeve parts, the defects were damaged for analysis. Through metallographic detection, scanning electron microscope(SEM) and energy dispersive spectroscopy(EDS) analysis, the causes of defects were finally found out. There were some small skin warping defects on the surface of the tube billet before drawing. These small defects were lengthened longitudinally along the deformation direction during the drawing process, and finally became the folding defects distributed longitudinally in the extension pipe.

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.

By comparing specimen microstructure of the processed surfaces obtained by the three different sample preparation processes,i.e.,wire cutting,punching processing,and laser cutting, as well as the stability of elongation after fracture,the most suitable sample preparation process for ultra-high strength steel was screened out. According to standard requirements, the influences of three different transition arc radii on the detection stability of elongation after fracture for ultra-high strength steel were analyzed. Moreover, the influences of three different rate switching point parameter settings on the stability were also investigated. At the same time, the stabilities of measured elongation after fracture for ultra-high strength steel by laser extensometer and mechanical extensometer were compared. Based on the above research, the suggestions for detection of the elongation after fracture of ultra-high strength steel in the laboratory were put forward: laser cutting was recommended for sample preparation; the transition arc radius was selected as 35 mm; when the rate switching point parameter was set to 0.10 or 0.15, the data were most stable;if the elongation after fracture of ultra-high strength steel was automatically measured, the data obtained by laser extensometer were more stable than those obtained by mechanical extensometer.

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.

The mapping of elements in the non-stick pan inner coating were analyzed using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) under acceleration voltage of 10 kV. The results showed that the overlapping between the K spectrum series of F element and L spectrum series of Fe occurred led to the difficulty to distinguish F and Fe elements in the mapping. By changing the spectrum series of Fe from L to K or employing the TruMap function of EDS software, the true distribution of Fe element could be obtained. By combining the point spectrum fitting with quantitative analysis results, the true position of F element in the mapping was determined.

During the grinding and inspection stage, some surface-initiated turtle-back cracks were observed on the connecting rod neck of φ135 mm 48MnV steel crankshaft after surface induction hardening and tempering. These surface cracks were analyzed by optical microscope, scanning electron microscopy equipped with an energy dispersive spectrometer, and microhardness tester. The results indicated that the observed cracks were grinding cracks. The cracks only existed on the surface layer of the hardened layer, with a depth of about 340-510 μm. The surface layer of the hardened layer had the lowest hardness. Then it firstly increased and then leveled off, and gradually decreased to the hardness of connecting rod journal substrate. The microstructure of the connecting rod journal from the hardened layer to the substrate was: quenched martensite + residual austenite → tempered martensite + tempered troostite → tempered martensite → ferrite + pearlite.

The X80 grade pipeline steel products have been widely used in domestic oil and gas pipeline transportation engineering. The X80M hot-coiled produced by a steel factory had some defects such as edge warping, which led to the unqualified problem of batch flaw detection after pipe manufacturing. The typical defects were selected for macro and micro analysis and energy spectrum analysis, and according to the results of slab nickel nail test, it was found that the defects were mainly caused by the large temperature drop of hot-coiled edge in the rolling process. By adopting various measures, such as corner cutting and grinding of the slab, optimizing the hot rolling secondary model, reducing descaling passes in rough rolling, and modifying the vertical roll pass, the proportion of hot-coiled with scaly skin defects had decreased to less than 5%. The scaly skin defect was also reduced, and the improvement effect was remarkable.

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.

There was abnormal noise for one air conditioning system equipment during commissioning after installation, and it could not continue to run after about 400 h. The dismantling results showed that the threaded part of shaft end of compressor pinion shaft was broken. The pinion shaft was comprehensively analyzed through chemical composition, hardness, mechanical property, microstructure and micromorphology of fracture. The results showed that the carbon content in pinion shaft exceeded the upper limit specified in EN10084-2008. The hardness exceeded the technical requirements of the product. The percentage elongation after fracture and the percentage reduction of area were lower than technical requirements of the product. There was segregation of alloying elements. The cracks were generated at the root of thread in thermal refining. The combined effect of these factors caused the premature failure of pinion 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.

The influences of three kinds of coating, i.e., hot-dip galvanizing coating, hot-dip galvanized iron alloy coating and electroplating galvanizing coating, on the tensile properties of cold-rolled plate were analyzed in this paper. The tensile properties of IF-grade cold-rolled plate with different coatings were measured by 0.5 grade tensile tester, and the tensile properties before and after coating removal were compared. The results showed that there was no obvious difference in tensile properties before and after electroplating galvanized coating removal. The yield strength, strain hardening exponent (n value) and plastic strain ratio (r value) were different before and after hot dip galvanized coating removal. The tensile properties before and after hot-dip galvanized iron alloy coating removal were different, and the difference of r value was most significant, which reached 0.35. The surface and fracture were observed by scanning electron microscope(SEM). It was found that the tiny cracks were produced during the fracture of hot-dip galvanized iron alloy coating, which had a great impact on the measurement of r value.

The leaking of some tubes in heat exchanger was observed in a secondary tower′s top condenser in one certain distillation deisobutanizer. In order to find out the failure cause and prevent the similar incidents from recurring, the chemical composition, mechanical properties, metallographic structure, and microscopic morphology of the tubes were analyzed to identify the reasons for leaking. The results showed that the heat exchanger tubes had a serious uniform corrosion and local point corrosion perforation, leading to the leaking of tubes. Moreover, the corrosion morphology had the characteristics of microbiological corrosion. Meanwhile, the large size nonmetallic inclusions in heat exchanger tubes accelerated the process of point corrosion perforation of tube wall.

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.

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.

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 surface defects in automobile stabilizer rod could lead to the performance deterioration of automobile and even cause the breaking of balance rod, which seriously affect the safety of automobile driving. The 55Cr3 wire rod produced in a certain factory was tested in one automobile parts factory, and it was found that there were some deep decarbonization defects on the surface of the rolled high wire rod. The process of controlled rolling and controlled cooling were optimized, the heating temperature of the billet in heating furnace was reduced, and the control temperature center line of soaking section was reduced from the original 1 080 ℃ to 1 020 ℃. The heating furnace atmosphere was adjusted, and the air-fuel ratio was adjusted from the original 0.75% to 0.55%. The spinning temperature of the wire rod and the running speed of the air-cooled roller were reduced, and the speed of the entrance section was increased from 0.12 m/s to 0.13 m/s. The cascade increase of the roller speed in different proportions was implemented, and the cooling speed in the phase change zone was appropriately increased. Finally, the wire rod without decarbonization defect was obtained, which could meet the product performance requirements for customer.

The unsatisfactory low-temperature impact performance of Q345qD bridge slabs produced by one company was observed successively. The unqualified slabs were mainly concentrated in the thickness of 16 mm. Through a series of analysis and testing on the unqualified samples submitted for inspection, the main reasons for the unqualified low-temperature impact performance of Q345qD steel plate were identified, i.e., the severe segregation in the center of the sample as well as the presence of bainite structure in the segregation zone. At the same time, the nonmetallic inclusions in the sample also affected the low-temperature impact performance of the plate. The corresponding improvement measures were also proposed.

The composition of white unknown substance on the surface of brake pad with new formula which was produced in one brake facing enterprise for automobiles was identified and analyzed by means of X-ray diffraction (XRD), scanning electron microscope(SEM) and energy dispersive spectroscopy (EDS). The results showed that the component of white unknown substance on the surface of brake facing was MgO. The phase analysis of white unknown substance was eventually determined based on X-ray diffraction, and its elemental analysis was conducted by scanning electron microscope(SEM) and energy dispersive spectroscopy (EDS). Then,the composition of the white unknown substance was finally determined. The detection and analysis of unknown substance provided timely and useful information for product innovation, optimization and improvement of production process and quality control, and it had good practical value in the production field.

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.

Monte Carlo method is a distributed propagation method based on random sampling for probability distribution. Monte Carlo method and GUM method were used to evaluate the uncertainty in the determination of elastic modulus of titanium alloy by suspension wire coupled resonance (dynamic method) specified in GB/T 22315-2008 Metallic materials-Determination of modulus of elasticity and Poisson′s ratio. According to the evaluation results of Monte Carlo method, the results of single test could be expressed as (123.6±1.6) GPa with coverage factor of k=2. According to the evaluation results of GUM method, the results of single test could be expressed as (123.6±1.7) GPa,k=2. The deviations of the results, expanded uncertainty, the upper and lower limits of the confidence interval obtained by the above two methods were +0.0, 0.2, +0.2, and 0.1 GPa, respectively. The deviations were less than the numerical tolerance (0.5 GPa). The results of the above two methods were consistent.

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 motorcycle′s frame riser made by 20# seamless steel tube was cracked during use. The cause was investigated through metallographic examination, chemical composition analysis, hardness test and scanning electron microscope. The results showed that the chemical composition of frame riser could meet the requirements of national standards, and there was no abnormality in the hardness and microstructure. Martensite was found in the welding heat affected zone of tested surface. The existence of martensite increased the brittleness and reduced the toughness of riser support. The hardness difference between martensitic structure and matrix structure formed stress concentration. Therefore, the main reason to cause cracking of frame riser was the martensite which was generated during welding.

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).

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.

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 existing high temperature contact angle measuring device could obtain the high temperature wetting behavior by measuring the contact angle. However, the existing devices are only equipped with simple oxide substrates such as aluminum oxide/magnesium oxide, which could not realize the study of high temperature behavior of complex oxides especially the various process problems induced by oxide coalescence behavior in the field of iron and steel metallurgy. A series of interfacial wetting experiments were designed with Al-Si-Ca/Mg-O complex oxides as examples based on the high temperature melt-complex oxides contact angle measuring method which was proposed previously. By obtaining the contact angle of molten steel-Al-Si-Ca/Mg-O complex oxides, their coalescence coefficients were further calculated and their coalescence behaviors were evaluated. The upgrade of equipment function was realized. The results showed that the contact angle between Al-Si-Ca-O oxides and molten steel was the lowest. On the basis of this, the quantitative relationship between the ability of oxide coalescence and molten steel-oxides interface properties was proposed. The coalescence coefficients of various oxides were calculated as below: CaO·2Al₂O₃>Al₂O₃>MgO·Al₂O₃>2CaO·Al₂O₃·SiO₂>CaO·Al₂O₃·2SiO₂. In other words, Al-Si-Ca/Mg-O oxides were difficult to aggregate. This method could be further extended to the study of the coalescence behavior of other oxides. It could help solve the problems of surface and internal defects of steel caused by the agglomeration of oxide inclusions and the formation or coalescence of large-sized inclusions during deoxidation in the field of molten steel metallurgy.