The effect of hot stamping parameters on the mechanical properties of 22MnB5 steel sheet with thickness of 1.1mm is studied.The considered parameters are austenization temperature(800-1 000 ℃),austenitizing soaking time(60-540s),initial deformation temperature(560-800 ℃)and tool temperature(20-220 ℃).In order to obtain hot stamped parts with optimal mechanical properties,response surface methodology based on the central composite design has been employed to design the experiment matrix.Tensile strength of hot stamped parts is determined as the relation in the mathematical model.The optimal condition and objective effects of parameters are determined via this relation.The statistical analysis showed that all four factors significantly affect the tensile strength of the hot stamped parts.The optimum austenization temperature is found to be 918.89 ℃ with the austenitizing soaking time,initial deformation temperature and tool temperature of 279.45 s,684.69 ℃ and 21.85 ℃,respectively.These optimal hot stamping parameters prove to have high tensile strength(1 631.84MPa)where deviation between predicted and actual response falls within 2%.
The effect of surface roughness on the oxidation behavior of a directionally solidified Ni-based superalloy was investigated by surface mapping microscope,scanning electron microscope and X-ray diffraction.It was found that specimens with surface roughness of 0.05 urn exhibit the best oxidation resistance,while specimens with surface roughness of 0.14 μm behave worse than specimens with surface roughness of 0.83 μm.The specimens with surface roughness of 0.05 μm have the best oxidation resistance,which is mainly due to the smallest surface area exposed in air and thinnest work-hardening layer.The Al2O3 layer alleviates the oxidation process of the specimens with surface roughness of 0.83 μm,and this is the possible reason for the better oxidation resistance of samples with surface roughness of 0.83 μm than samples with surface roughness of 0.14 μm.
Enukuania huxleyi is marine nanoplanktonic alga with calcify scale called coccolith om its cell surface.This ubiquitous species with the Lafgest biomass in marice forms gigantic blooms covering thousands of
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