Papers by Keyword: Cr-Mo Steel

Abstract: In recent years, the oil and gas well casing is confronted with more complex service environment, and the casing is subjected to higher service load and temperature. In this study, the strength and plasticity of Cr - Mo low alloy casing steel of 80, 90 and 110 steel grades commonly used under high temperature service conditions was studied. The results show that with the increase of temperature, the yield strength and tensile strength of casing steel decreased. The sensitivity of high steel grade to temperature change was higher than that of lower steel grade; with the increase of steel grade, the fracture mechanism of casing steel changed from microporous polymerization fracture induced by large size second phase particles to shear propagation fracture induced by sub grain boundary microporous polymerization. This study has important guiding significance for the service safety and strain design of high grade steel under high temperature conditions.

Abstract: Modified 9Cr-1Mo steel is a heat-resistant steel developed for a steam generator in a FBR (Fast Breeder Reactor) and it has been applied to various thermal power plants. Recently, it was found that the fatigue limits did not appear up to 10⁸ cycles at temperatures higher than 500oC. The reason for the decrease of the fatigue life was attributed to the change of the initially designed microstructure of the alloy. The initially dispersed fine lath martensitic texture disappeared at temperatures higher than 500°C, when the magnitude of the applied stress exceeded a certain critical value. In order to explicate the dominant factors of the change quantitatively, the change of the microstructure and the strength of the alloy were continuously observed by applying an intermittent fatigue and creep tests at elevated temperatures and EBSD analysis. It was found that there was a critical stress which caused the microstructure change at each test temperature higher than 500°C, and the activation energy of the change was determined as a function of temperature and the applied tensile stress. The dominant factor of the micro structure change was the stress-induced acceleration of the atomic diffusion of the component element of the alloy.

Abstract: The aim of this investigation is to study the fracture location as well as mechanical properties of weldments from elevated temperature tensile test in T22/T91 dissimilar joining by GTAW process. Two configurations of welding procedures are used: ER90S-B9 and ER90S-B3. Postweld heat treatment (PWHT) is carried out at 760°C for 30 minutes. The results demonstrate that the higher tested temperature, the lower the strength of welded sample; nevertheless, the greater the ductility of welded sample, except ER90S-B9 welded samples tested at 650°C. The fracture of both configurations tested at 550°C and 750°C occurs at T22 BM and T91 HAZ, respectively. At these temperatures, the fracture surfaces mainly reveal dimple ductile mode corresponding to mechanical properties’ results. On the contrary, the failure tested at 650°C occurs at T22 HAZ (Soft zone) and T91 HAZ of ER90S-B9 and ER90S-B3 welded samples, respectively. The mechanical properties’ results at this temperature are relatively different. The combination of brittle and dimple mode at the edge of samples is observed on the ER90S-B9 welded samples corresponding to low ductility at this temperature. Whereas samples welded by ER90S-B3 show only dimple ductile mode. The results exhibit that the fracture location could be affected by the configuration of T22/T91 dissimilar welding.

Abstract: Metal materials are subjected to innumerable time-dependent degradation mechanisms when operate in power, petrochemical and refinery plant. These materials are subjected to multiaxial stresses, creep, fatigue, corrosion and abrasion. As a result of service especially at high temperatures and high pressures, can lead to forming cracks, damages or failures. In situation of breakdown in such systems there is a need for weld repair on plant components and repair work can be expensive and time-consuming. Most weld repairs of low alloy steels require high-temperature post weld heat treatment (PWHT); but in certain repairs, however, this is not always possible. Expenses of the repair work could be reduced if the weld repairing is performed on site. Application of the nickel based filler metal can be alternative to performing PWHT. These repair welding procedures with Ni based filler metal could be categorized as cold repair welding. Purpose of presented investigation was to compare a repair welding technology with filler austenite material based on Ni and without application of the PWHT, with a classical repair welding procedure with preheating and PWHT and using a filler metal with chemical composition similar to parent metal. Properties comparison of the welded joints obtained by these two repair welding technologies was performed for the Cr-Mo steel (13CrMo4-5) by the metal arc welding procedure with covered electrode (MMA - 111). Weldability analysis by the analytical equations and technological tests for determination of the sensitivity to crack forming for cold and hot cracks by the CTS and Y tests, were performed for both repair welding technologies. Tensile tests, absorbed energies tests, banding tests and hardness measurements were performed on trial joins. Light optical microscopy (LOM) was applied for microstructure analysis. The fracture toughness for both technologies, were estimated by the calculated stress intensity factor KIc and dynamic stress intensity factor KId for weld metal and heat affected zone. All of the obtained results were analyzed and discussed. It was concluded that repair welding technology with Ni base filler material without PWHT, enables welded joints without the appearance of cracks, with a good mechanical properties, slightly higher hardness in the HAZ, but with lower expenses compared to standard repair welding technology. In applying this technology in emergency welding repairing on-site, on the equipment and industrial facilities with high security requirements, inspection using non destructive technique has to be frequently applied compared to standard procedures.

Abstract: The quantification methodology used to predict the residual life of Cr-Mo steel was microstructure/life fraction correlation under creep conditions. Microstructural evolution has been correlated with accelerated creep testing progress during testing at constant load and a temperature of 600°C, as well as with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Experimental results from TEM revealed six distinct stages, which were directly related to the life fraction values obtained. However, in the case of MEV, five stages were found. This difference is likely due to the better analysis possible via TEM of both microstructural evolution and types of carbides formed during the creep process. In addition, an evolution map is proposed to allow for easy interpretation of the relationship between microstructural characteristics and life fraction.

Abstract: The band microstructure has an adverse effect on the comprehensive mechanics performance of Cr-Mo steel used for ball screw. This paper dealt with the different annealing processes combined with the forming mechanism of the banded structure. It shows that the annealing with long time can basically eliminate the band microstructure.

Abstract: With the self-designed system of welding thermal cycle test, low alloy steel of Cr-Mo series was welded through proper welding procedure according to the phenomenon of cold crack and local hardening in weld metal, and in-situ detection of thermal cycle for deposit metal was realized. The results show that self-designed system is reliable within the error range, the maximum peak temperature during thermal process was above 1700°C, it is largely improved than reported formerly.

Abstract: The purpose of this investigation is to develop the nondestructive tools for microstructure assessments in carbon alloyed steels. The role of carbon in steel and its effects on electromagnetic property and also the free electron model have been reviewed. The fundamental electromagnetic principle behind low frequency impedance measurements has been included. The systematic analysis of phonon vibration and ultrasonic resonance spectroscopy for elastic wave perturbation in T22 Cr-Mo steel has been presented. A brief examination of nondestructive microstructure evaluation techniques has been described. The induced microstructure variations in Grade T22 Cr-Mo steel, including the correlations of changes in physical (microstructure) and mechanical (hardness data) properties during annealing have been measured. The explanations of aged carbide precipitates, martensitic and pearlitic nucleation and growth have been illustrated. The possibility of simultaneous use of two nondestructive wave techniques is discussed. The electron model and electron interactions are associated and are shown to support the results of low frequency impedance measurements enhanced elastic wave perturbations.

Abstract: In this paper, based on ctual large-scale ball mill liners working conditions, effects of different quenching temperature and tempering temperature on the Cr-Mo steel performance, optimize the best heat treatment process.The use of sophisticated electronic universal tensile testing machine, and Rockwell hardness testing machine for testing mechanical properties of steel materials were tested; Using the MMS-1G-type high-temperature high-speed Friction and wear tester, the wear properties of steel samples were studied using JSM-5610LV scanning electron microscope study of the tensile test fracture surfaces of steel and the friction and wear morphology. The results show that: For the high carbon alloy steel, of which 870 °C 620 °C tempered quenched specimen extension rate of 7.0% area reduction rate of 9.5%.

Abstract: The hollow circular cylinder specimen of Cr-Mo steel with 0.20 mass% C was carburized in carrier gas and quenched in oil bath. After quenching, the surface residual stress distributions in the radial, axial and hoop directions of the specimen were measured experimentally by x-ray as a function of the distance from the carburized surface. The case depth of the quenched specimen was about 0.8 mm. Diffraction from Fe-211 by Cr-Kα radiation was used to minimize the effect of carbon content gradient on the nonlinearity of 2θ-sin²ψ, because effective x-ray penetration depth was about 5.8 μm at sin²ψ=0. The hardened case layer was gradually removed by electrolytic polishing. X-ray stress measurement was repeated on the polished surface from the carburized surface to the interior. The ψ-splitting was not observed on the carburized surface. The 2θ-sin²ψ diagrams were found to shift from low to high angles in inverse proportion to carbon content. The residual stresses in the hardened case layer were compressive. The maximum compressive residual stresses on the hollow circle and periphery surfaces were about −559 and −544 MPa at the depth of 0.2 and 0.3 mm, respectively. On the other hand, the tensile residual stress was not observed. The full widths at half-maximum intensity of Fe-211 diffraction peaks in the hardened case layer were wider than that of the interior of the specimen. Martensitic transformation of the carbon-rich layer leaded to the broadening of diffraction peaks. Therefore the interior of carburized specimen were deformed elastically to balance the existence of the surface compressive residual stresses.