Severe transverse cracks had appeared on the surface of boron microalloyed steel billets produced by a certain company. The reasons for the formation of cracks in the billet were studied by macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis, and thermoplastic analysis. The results show that factors such as excessive carbon content in the billet, unreasonable secondary cooling system, low casting rate of the casting machine and improper precision control of the casting machine equipment had resulted in transverse cracks on the surface of the billet. Adopting methods such as optimizing the chemical composition of raw materials, improving the casting rate and controlling the accuracy of the casting machine could avoid transverse cracks in the casting billet.

The grain size of high-grade coiled tubing products was relatively small, and traditional metallographic testing methods could not accurately evaluate their grain size. Using a combination of metallographic examination and electron backscatter diffraction technology, the grain size of different grades of coiled tubing products was studied. The results show that using electron backscatter diffraction technology could accurately evaluate the grain size of high-level coiled tubing, and the average grain equicircle diameter of CT90 coiled tubing was 2. 89 μm. The average grain equicircle diameter of CT110 coiled tubing was 1. 37 μm.

An automatic laser cutting technology with the processing ability of cold rolled sheet, hot rolled sheet and pickling sheet sample was developed. The automatic laser cutting process of the whole process of automatic loading, automatic marking, automatic generation of cutting model and cutting sample, automatic sorting and automatic finishing was realized. The technology was compared with the traditional processing technology, and the advantages of automatic laser cutting method for processing plate samples were studied. The research results could provide a theoretical basis for improving the processing efficiency and quality of plate samples in metallurgical industry.

The traditional processing and inspection techniques for finished product samples mainly included turning, milling, planing, grinding and manual sample delivery. Traditional processing and inspection techniques could no longer meet the fast-paced production needs and improved their automation level was beneficial for improved the competitiveness of enterprises. The latest fully automated sample processing and inspection technology were introduced, which integrated various processes such as cutting, rough machining, precision machining, stretching and impact testing of sheets and round bars through robotic arms, automatic guidance devices and centralized control systems, achieved basic automation of the entire process. At the same time, the advantages of fully automated sample processing and inspection technology were analyzed, and future research focuses were prospected.

The methods to maintain the capability of testing laboratories included effective internal and external monitoring of the laboratory, ensured the normal operation of basic factors such as personnel, equipment, methods, and environment, and continuously improving control levels. For abnormal results in daily testing and capability verification, comprehensive analysis and judgment should be conducted on the influencing links of the experimental process, to identify the reasons for abnormal results, and taken timely improvement measures to ensure the long-term maintenance of laboratory capabilities.

The Gleeble3800-GTC thermal simulation testing machine was a comprehensive digital closed-loop thermal and mechanical control testing system, and was one of the most important simulation test systems in the laboratory. It was mainly used for methods such as metallurgical process simulation and thermal deformation behavior simulation of metal materials. The thermal simulation testing machine was used to conduct simulation tests on the samples, and the application of the thermal simulation testing machine to new product development and process optimization was studied. The results could provide a theoretical basis for shortening product development time and reducing research and development costs.

The effect of quenching and tempering times on the microstructure and friction and wear behavior of C110 seamless steel pipe was studied. The results show that with the increased of quenching and tempering times, the grain size of C110 steel was refined, but the refinement effect was becoming less and less obvious, and the second phase in the material continued to aggregate and grow. Under the joint influence of grain size and second phase, the hardness of C110 steel showed a trend of first increasing and then decreasing with the increased of quenching and tempering times. After secondary quenching and tempering treatment, the grain refinement and fine grain strengthening effect of C110 steel were significant, while the growth of the second phase was not significant, indicated the best wear resistance of the material.

The defect structure in forging steel would affect its mechanical properties and subsequent use. The widmanstatten structure, banded structure, bainite and underheated structure encountered in carbon steel and low alloy steel were summarized, and the formation reasons, evaluation methods and improvement methods of these four kinds of defect structures were analyzed. The research results could provide a theoretical basis for improving the mechanical properties of steel products.

The Ni-Al bronze bolt used for the sealing structure of a certain nuclear power plant condenser fractured. The causes of bolt fracture were analyzed by macroscopic observation, chemical composition analysis, scanning electron microscopy analysis, mechanical property testing and metallographic examination. The results show that the bolts experienced stress corrosion cracking in a humid NH₃ environment. During service, fractured bolts were subjected to uneven stress loads, resulted in an increased tendency for surface stress corrosion. Moreover, the bolts were exposed to their own stress corrosion sensitive medium for a long time. Under the coupling effect of the two, stress corrosion cracks initiated on the bolts. The crack propagated inward along the phase boundary area with high residual stress, ultimately led to bolt fracture.

During the production of threaded insulation aluminum alloy building profiles, the polyamide insulation adhesive deformed in the composite part. The causes of deformation of polyamide insulation adhesive were analyzed by component analysis, microscopic analysis, differential scanning calorimetry analysis, mechanical property testing, and infrared spectroscopy analysis. The results show that the binding force between short and fragmented glass fibers and resin was low. The insufficient molding temperature, low crystallinity and low temperature corresponded to the melting peak made the mechanical properties of the material worse, ultimately led to deformation of the polyamide insulation adhesive.

The water wall tube burst accident occurred many times in a thermal power plant. The reasons for the explosion of water wall tube were analyzed by macroscopic observation, chemical composition analysis, mechanical property testing, corrosion product analysis, scanning electron microscopy analysis and metallographic examination. The results show that the positions of the burst pipes were all located on the windward surface of the water wall tube, and there were corrosion grooves on the inner surface of the steel pipes. There were hard and brittle corrosion products in the grooves, and intermediate products such as NaFeO₂ and Na₂FeO₂ were detected in the corrosion products, indicated that the cause of the burst pipes of the water wall tube was stress corrosion cracking caused by alkali corrosion.

During the metallographic examination of a low carbon steel, it was found that the surface of ferrite grains turned gray. The reason for the surface graying of grains was studied by metallographic examination, corrosion test and scratch test. The results show that the reason for the graying of the grains was the residual polishing scratches on the surface of the sample, which increased the surface roughness of the sample and caused diffuse reflection phenomenon. The orientation of each grain was different, and the internal stress caused by polishing scratches was also different, resulting in different degrees of corrosion for each grain, which led to differences in surface morphology and ultimately led to graying of the ferrite grain surface.

The manual high-temperature valve at the outlet of a sulfur incinerator in a certain factory broke after one month of use. The causes of the fracture of the high-temperature valve were analyzed by macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis and finite element analysis. The results show that there were serious non-metallic inclusions and a large amount of carbides in the valve shaft of the high-temperature valve, which reduced the corrosion resistance of the material. In the actual operation process of the incinerator, the working stress of the high-temperature valve had exceeded the yield strength and strength limit of the material, ultimately led to the fracture of the high-temperature valve.

A certain model of elevator safety gear wedge was worn. The reason for wedge wear was analyzed by macroscopic observation, chemical composition analysis, hardness testing, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that during the braking process of the safety caliper, severe friction occurred between the wedge and the guide rail, generated a large amount of heat, which increased the temperature in the middle of the wedge working face, resulted in an over tempering effect. The surface structure of the wedge changed from tempered martensite to tempered sorbite, and the hardness and wear resistance in the middle of the wedge working face decreased, ultimately led to severe adhesive wear and abrasive wear of the wedge.

Cracks were found on the inner surface of a GCr15 steel bearing ring after machining. Macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis were used to analyze the cracked rings. The results show that during the production process of the ring, the piercing plugs broke and foreign particles embedded in the matrix, disrupting the continuity of the matrix and ultimately led to cracking on the inner surface of the ring.

The coating on the shaft sleeve of a certain sliding bearing had fallen off after 2 d of operation. The reasons for the detachment of the shaft sleeve coating were analyzed by macroscopic observation, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that there were large banded structures in the coating of the shaft sleeve, which disrupted the continuity of the coating. During the working process, the shaft sleeve was subjected to frictional force, which caused cracks to initiate at the weak point of the coating, ultimately led to the detachment of the shaft sleeve coating.

During the torsion durability test of a certain type of clutch driven plate assembly, its damping spring fractured. The reasons for the fracture of the spring were studied by macroscopic observation, chemical composition analysis, hardness testing, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that there were original cracks and friction damage on the inner side of the damping spring which caused the spring to bend fatigue fracture under low stress.

The corrosion cause of a water injection pipeline was analyzed using methods such as component content testing, chemical composition analysis, X-ray diffraction analysis, thermogravimetric-mass spectrometry analysis, infrared spectroscopy analysis, gas chromatography-mass spectrometry analysis and sulfate reducing bacteria detection. The results show that the organic components in the water injection pipeline were mainly hydrocarbons, while contained substances such as lipids, amines, alcohols and olefins. The inorganic components were mainly iron oxides, ferrous carbonate and sand. The pipeline contained a large amount of sulfate reducing bacteria. With the assistance of sulfate reducing bacteria, corrosion under scale occurred, ultimately led to corrosion of the water injection pipeline.

When the tool strength and sealing performance of a casing sliding sleeve were tested, the liquid outlet part suddenly broke. The causes of the sleeve fracture were analyzed by macroscopic observation, chemical composition analysis, scanning electron microscope analysis, hardness test, impact performance test and metallographic examination and finite element analysis. The results show that the structure design of the casing sliding sleeve was unreasonable and there was obvious stress concentration at the outlet, resulting in a notch effect. The improper heat treatment process significantly reduced the fracture toughness of the material, which eventually led to the fracture of the outlet of the casing sliding sleeve.

The wire rope of an oil extraction truck suddenly broke during the oil extraction operation in an oil extraction plant. The fracture reasons of wire rope were studied by macroscopic observation, chemical composition analysis, metallographic examination, tensile test, whole rope breaking tensile test and scanning electron microscope analysis. The results show that there were a large number of wear and extrusion damage on the surface of steel wire rope, the fracture surface was characterized by shear failure and torsion-tensile fatigue failure, and the angle between the fracture surface crack and the axial direction was 45°. In the process of use, the initial cracks were initiated at the wear and extrusion of the steel wire surface. Under the action of torsion-tensile load, the loose twist structure of the steel wire rope was destroyed, resulting in stress concentration, which eventually led to the fracture of the steel wire rope.