Volume 1 Issue 1

Authors: Jihao Cheng; Kaiguang Zhang; Yantang Chen

Abstract: Continuous cooling rate after final rolling is an important parameter which controls the microstructure and mechanical properties of the high strength low alloy (HSLA) steels extensively used in offshore engineering. Continuous cooling transformation (CCT) diagram was drawn using the dilatation-temperature curve of the offshore HSLA steel cooled at rates covered from 0.1℃/s to 100℃/s after austenitized at 950℃ for 15 minutes. 0.5℃/s was a critical cooling rate for bainite formation. When the cooling rate was set to be less than 0.5℃/s, only ferrite and pearlite were formed. 20.0℃/s was a critical cooling rate for martensite formation. When the cooling rate was higher than 100℃/s only martensite was recognized. The mixed microstructure of ferrite, pearlite and bainite was formed while the cooling rate ranged between 0.5℃/s and 20℃/s. Bainite and martensite were formed in the offshore steel cooled at rates from 20℃/s to 50℃/s. The CCT diagram is a significant tool for steel production.

Keywords: CCT Diagram; HSLA Steel; Offshore

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Authors: Norhaslinda Nasuha; Mohamad Syazwan Osman; Rasyidah Alrozi; Nurulhuda Amri

Abstract: The optimal conditions for preparation of guava waste based activated carbon (GWAC) for removal of Methylene Blue (MB) dye from aqueous solution were investigated and the performance of GWAC on adsorption capacity were evaluated. The GWAC was prepared using simple thermo-chemical activation method. Central composite design (CCD) was used to determine the optimum preparation conditions for GWAC with response to the GWAC yield and MB percentage removal. Two quadratic models were developed to correlate the preparation variables for both responses. The significant factors on each experimental design response were identified from the analysis of variance (ANOVA). The optimum GWAC preparation conditions were obtained using 550°C activation temperature, 1.93 hour activation time and 1.00 impregnation ratio resulting in 71.71% of GWAC yield and 54.58% of MB removal. From the analysis, activation temperature was found to have the greatest effect on carbon yield. On the other hand, activation temperature and impregnation ratio were found to have significant effects on MB removal. The adsorption performance of GWAC was then conducted using the batch adsorption study to determine the adsorption capacity. The adsorption study was carried out at different initial concentrations of MB (50 – 500 mg/L) at temperature of 30°C for 5 hours. The equilibrium data were analyzed using Langmuir and Freundlich isotherm models followed by kinetics study. The experimental data for GWAC were fitted well with Langmuir isotherm with a maximum monolayer adsorption capacity of 250.00 mg/g. The kinetic study on adsorption of MB obeyed the peudo-second order kinetics with good correlation. The results demonstrated that GWAC is an effective adsorbent for removal of MB and has potential to replace the commercial activated carbon for removal of dyes from wastewater.

Keywords: Adsorption Isotherms; Guava Waste Activated Carbon; Methylene Blue; Thermo-chemical Activation

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Authors: Uta Klement; Karin Bj?rkeborn; Kumar Babu Surreddi

Abstract: In manufacturing industry, variations in machinability are regularly observed when producing the same part out of different material batches of a case hardening steel. Some batches result in variations in chip breakability which leads to a non-robust production process with unforeseen stops of automatic machining process. The aim of the present study is to investigate the influence of the microstructure on chip formation in case hardening steel. Different microstructures were produced from the same batch of material by varying heat treatment. Chips were collected after machining at different feed rates and depths of cut. The cross sections of the chips have been analyzed with respect to overall deformation pattern, mean thickness, and degree of segmentation. Also, the influence of manganese sulfide on machinability has been investigated. The microstructural investigation of the chips has shown that there is a clear difference in the deformation behavior between a case hardening steel with larger and smaller pearlite nodular structure. Chips from the material with larger pearlite nodular size and lower amount of pro-eutectoid ferrite are by far more segmented as compared to chips from materials with smaller pearlite nodular size.

Keywords: Chip Formation; Chip Breakability; Pearlite Nodular Size; MnS Inclusions; Machinability

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Authors: Shasha Tian; Feng He; Wentao Zhang; Xiaoqing Liu; Junlin Xie

Abstract: The influence of the content of CaO on the crystallization behavior, microstructure and mechanical properties of yellow phosphorous slag (YPS) glass-ceramics was studied. XRD, TEM, SEM and so on were used to analyze the microstructure and properties of glass-ceramics. With the increasing content of CaO, the crystallization of β-wollastonite increased while the aspect ratio and the grain size decreased. The glass-ceramics with fine microstructure showed better mechanical properties. Yellow phosphorous slag waste appears to be well suited for being used as batch material for decorative architectural glass-ceramics.

Keywords: Yellow Phosphorous Slag; Glass-Ceramics; Microstructure; Mechanical Properties

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Authors: Kazunari Fujiyama

Abstract: The methodology was presented for evaluating creep-fatigue damage and for optimizing the shape of stress concentration in high temperature components under start-up cycles and steady state operations. Relatively simplified steam turbine casing models were employed by assigning shape parameters such as wall thickness t, fillet height ts and fillet corner root radius R. Total 27 cases were investigated by FE(finite element) elastic thermal stress and pressure stress analysis for different sets of shape parameters. Elastic stress concentration factors were formulated by the shape parameters and by the reference plate stress under ramp temperature change for thermal stress and also by the internally pressurized cylinder stress under steady state conditions. Neuber’s rule and cyclic stress-strain response were introduced and elastic-plastic strain ranges were obtained numerically. Fatigue life Nf was calculated by the material’s low cycle fatigue properties for the elastic-plastic total strain range and creep rupture life tr was calculated by the material’s creep rupture properties for pressure stresses. The shape optimization was realized to set the corner radius as the object parameter by attaining the optimum sets of fatigue damage as the cycle fraction and creep damage as the time fraction to meet the non-linear creep-fatigue cumulative damage curve. This method was proved to be effective for shape optimization procedure even when non-linear material behaviours were exhibited.

Keywords: Creep-fatigue; Damage; Thermal Stress; Stress Concentration; Steam Turbine; Casing; Shape Optimization

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