The in-service life of ASTM A36 welded steel pipes in power plants is often shortened by ash corrosion. During the heating condition, the ash deposition on the welded steel pipes gradually reduces the thickness of the pipes, thus, reducing the lifetime. Instead of replacing the pipes with new ones, the cost could be significantly reduced if the lifetime could be further extended. Weld cladding was the method selected in this study to temporarily extend the service life of welded pipes. This paper performed the mechanical investigations of A36—A36 welded steel plates after coating the surfaces with 309L stainless steel with a cladding method. The residual stress was also tested to observe the internal stresses developed during the welding processes of A36—A36 specimens. The comparison between the coated and non-coated surfaces of welded steels was performed by using the tensile tests (at room and elevated temperatures), corrosion (pitting corrosion, intergranular corrosion, and weight-loss corrosion) tests, and wear (shot blasting) tests. The life-extension of both coatings was evaluated based on the tensile tests and the corrosion and wear tests provided the qualitative evaluations of the coating performance. The results showed that surfaces coated by cladding could be used to temporarily extend the life of ASTM A36 welded steel under the studied conditions.
The precision and accuracy of the final geometry in micro-parts is crucial, particularly for high-value-added metallic products. Micro-extrusion is one of the most promising processes for delivering high-precision micro-parts. The curving tendency observed in micro-extrusion parts is a major concern, significantly affecting the final part geometry. The purpose of this paper was to investigate the driving mechanism behind the curvature in micro-extrusion at room temperature. A finite element (FE) simulation was carried out to observe the influential primary factors: (1) grain size, (2) grain boundary, (3) grain orientation, and (4) bearing length of a 6063 aluminum alloy. The Extrusion Curvature Index (ECI) was also established to indicate the level of curvature in micro-extruded parts. The results showed that the grain boundary at the high strain and die opening area was the dominant factor for single-grain conditions. The interactive effects of the grain boundary and grain orientation also affected the curvature under single-grain conditions. If the number of grains across the specimen increased up to 2.7 (poly-grains), the curvature effect was dramatically reduced (the pins were straightened). For all conditions, the curvature in micro-extrusion could be eliminated by extending the bearing length up to the exit diameter length.
The paper investigated the effect of localized friction on sheet thinning under lubricated conditions in the deep-drawing process. The Finite Element Analysis (FEA) was used to evaluate the sheet thinning of the AISI 304 sheet under six segmented blank-sheet interfaces. Different values of variable coefficient of friction (VCOF) in each segmented area were investigated, and the sheet thickness values at the considered areas were measured. The regression analysis models (Linear Regression, Response Surface Method, and Polynomial Regression) was used to determine the relationships between VCOF and sheet thinning. The results showed that the Linear Regression showed the best fit. The significant factor analysis was also carried out to determine how the localized friction affected the sheet thinning. The contributions of VCOF from at least two segmented areas affected the sheet thinning at any particular location. The obtained relationships of the VCOF and sheet thinning could be beneficial for the localized friction control for highly complex shapes.
Ultrasonic surface wave have been implemented to measure or predict the existing stress on material. Surface wave velocity shows linearly increase with stress applied in material. However, various applications were coated their surfaces with high corrode resistance material for example paint or aluminum thermal sprays. It may cause the change of the velocity of surface wave and lead to miss prediction. This paper presents the effect of material coating on surface wave velocity and its attenuations. Paint and Aluminum thermal spray coated on low carbon steel graded S420 (EN 10025 Standard) in the range of 100-500 micron. Through transmission ultrasonic surface wave was applied to measure the velocities change. Their frequencies are 2.25 and 5 MHz respectively. It was found that coating thickness show effect on sound velocity and sound wave attenuation. The benefit is to know the effect of coating and to approve the accuracy of stress measurement by ultrasonic wave.
Stress measurement based on the change of ultrasonic surface wave has been accepted to find out residual or existing stress on material. This paper shows the effect of rolling direction and grain size of material on surface wave velocity and energy attenuation. Different grain and rolling direction of material type SS 400, S420 and A516 were selected to test its effect. Three grain sizes of each material were varied by normalizing process at three temperature range (no heating, 850°C, 980°C and 1160°C). Through transmission ultrasonic surface wave, frequencies 2.25 and 5 MHz, were applied and recorded the velocity and attenuation of the response. The results show that rolling direction and grain size slightly effect on attenuation of ultrasonic wave but unaffected on sound velocity. Its outcome was compared with the effect of the material coating.
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