Dual phase weathering (DP-weathering) steels were developed by inter-critical annealing treatments from a commercial hot-rolled weathering steel. The effects of martensite volume fraction (MVF) and microstructural changes accompanied the martensitic transformation on mechanical properties, formability, and corrosion behavior were investigated by metallography, mechanical, and corrosion testing. The investigations revealed that the final microstructures consisted mostly of island-shape martensite particles impeded in a ferrite matrix except for the highest temperature of 840 8C. Depending on MVF and martensite morphology, a wide range of mechanical properties was achieved; yield strength of 370-408 MPa and tensile strength of 580-689 MPa. The coupling of the results from metallography and mechanical testing emphasized the enhanced formability of the developed DP-weathering steels. The optimum combination of strength and formability was achieved for specimens treated at 810 8C and attained a MVF of 26%. Although, the presence of martensite phase raised the corrosion rate of DP-weathering steels during the initial corrosion cycles, it accelerated the nucleation process of the protective FeOOH layer. X-ray diffraction (XRD) investigations demonstrated that the rust layers formed on DP-weathering steels composed mainly of g-FeOOH, a-FeOOH, and Fe x O.
This work aims to investigate the effects of two welding techniques (gas tungsten arc welding (GTAW) with filler metal ER70S-3 and flux cored arc welding (FCAW) with filler metal E71T1C) on the microstructure and mechanical properties (including softening due to the conversion of martensite into tempered martensite) of DP steels with different martensite volume fractions ranging from 9 to 20%. Microstructure features and the constituents of base metals and heat affected zones of all weldments were examined and analyzed using an optical microscope and a scanning electron microscope integrated with energy-dispersive x-ray spectroscopy. Hardness, tensile, and v-notch impact toughness measurements were also carried out. Visual and radiographic inspection showed that both the FCAW and GTAW techniques produced sound weldments. However, DP steel weldments exhibited softening effects, which led to a decrease in joint efficiency. This decrease were related to transformation of the original martensite into tempered martensite. The results also revealed that the DP steel joints efficiencies are ranged from 85.9 to 87.7% using the FCAW process and ranged from 83.3 to 86% using the GTAW process. The impact toughness of the samples welded by FCAW is higher than the impact toughness of those welded by GTAW due to a higher percentage of acicular ferrite. This information should be valuable in the automotive and other industries, where DP steels are valued for their combination of high strength and ductility, which leads to weight savings and thus to reduced fuel consumption.
Improving corrosion resistance of copper is often associated with the presence of cuprous oxide (Cu2O) films on the surface. Many surface modification techniques such as chemical etching, oxidation, inhibitors, electro deposition and sol-gel could be employedIn the present work a film of Cu2O, which is considered to be protective and strongly adherent to the substrate, is formed. Experimental technique includes etching of copper specimens in ammonia solution, calcination, and then modified in ethanol solution of stearic acid for different times was employed Etching of copper for 60 h in 10 wt. % ammonia solution exhibits a contact angle of 135˚ but the formed layer, which is CuO, has poor adhesion.Modifying of etched-calcined copper in 0.1 mol/L ethanol solution of stearic acid for 3 h shows a superhydrophobic film (Cu2O) with a high contact angle of 160˚, good adhesion and lowest corrosion rate. The contact angle was measured at ambient temperature.The surface morphology and chemical compositions of the samples were investigated with a scanning electron microscopy, EDX and an X-ray diffraction. Electrochemical corrosion behavior was conducted in 3 wt. % NaCl aqueous solution at room temperature. The contact angle was measured using Attension Biolin device (Theta Optical Tensiometers) Also Thickness (using Tooke Inspection Guage OG204 according to ASTM D4138) and adhesion (using X-Cut Tape Adhesion test according to ASTM D3359) of formed films were determined
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