Improving mechanical properties and high-temperature oxidation of press hardened steel by adding Cr and Si

This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel.Results indicated that the microstructure of the Cr-Si micro-alloyed press hardened steel consisted of lath martensite,M_(23)C_(6)carbides,and retained austenite.The retained austenite and carbides are responsible for the increase in elongation of the micro-alloyed steel.In addition,after oxidation at 930℃for 5 min,the thickness of the oxide scales on the Cr-Si micro-alloyed press hardened steel is less than 5μm,much thinner than 45.50μm-thick oxide scales on 22MnB5.The oxide scales of the Cr-Si micro-alloyed steel are composed of Fe_(2)O_(3),Fe_(3)O_(4),mixed spinel oxide(FeCr_(2)O_(4)and Fe_(2)SiO_(4)),and amorphous SiO_(2).Adding Cr and Si significantly reduces the thickness of the oxide scales and prevents the generation of the FeO phase.Due to the increase of spinel FeCr_(2)O_(4)and Fe_(2)SiO_(4)phase in the inner oxide scale and the amorphous SiO_(2)close to the substrate,the oxidation resistance of the Cr-Si micro-alloyed press hardened steel is improved.

Modulating planarity of cyanine dye to construct highly stable Haggregates for enhanced photothermal therapy

Self-assembly of dyes has become a flexible strategy to modulate their photophysical properties.H-aggregates show great potential to increase heat generation,while the precise designing of H-aggregates as efficient photothermal agents is still challenging.Herein,a quinoline cyanine(QCy)is developed for constructing stable H-aggregated nanoparticles(NPs)to significantly enhance photostability and photothermal conversion efficiency(PCE).With symmetrical rigid planar quinoline structures,QCy has a small and symmetrical dihedral angle(11.9°),which ensures excellent molecular planarity.In aqueous solution,the planar QCy can form closeπ–πmolecular stacking,and fast self-assemble into stable H-aggregates even at low concentrations(1×10−7 M).QCy H-aggregates are sphere-like NPs(QCy NPs)with an average diameter of 120 nm and exhibit high stability.H-aggregation of QCy significantly enhances PCE from 20.1%(non-H-aggregated QCy)to 63.8%(QCy NPs).In addition,the positive charge of quaternarized quinoline provides mitochondrial anchoring ability,which further enhances the photothermal effect.With high PCE and tumor accumulation,QCy NPs in low-doses have been successfully used in photoacoustic imaging-guided tumor photothermal therapy.

Texture and Microstructure Evolution During Tensile Testing of TWIP Steels with Diverse Stacking Fault Energy

Texture and microstructure evolution in two kinds of the twinning induced plasticity （TWIP） steels （Fe-Mn- Si-AI and Fe-Mn-C） with diverse stacking fault energies during tensile testing were investigated by interrupted testing. The strain-hardening rate curves of the two steels were quite similar, but the texture characterization curves （maximum of pole density measured by X-ray diffraction） were varied. According to the curvature of max pole density curves, the evolution of the texture and the microstructure can be divided into three stages： low strain stage, medium stage and high stage. In low strain stage the difference of the microstructure came from the intensity of dislocation, which was much smaller in Fe-Mn-Si-AI. The main difference of the microstructure in medium and high strain stages originated from the numbers of activated twin systems. There were more than one twin systems activated in Fe-Mn-C, while only a single twin system activated in Fe-Mn-Si-AI. Texture showed various differences in the whole tensile process because it was affected by their micromechanism, such as concentration of the dislocation and the activation of twin systems. Texture in low strain stage was connected with annealing twin; the evolution ofthe texture was mainly induced by deformation twin generation. More than one activated twin systems in medium and high stages may counteract each other in the view of concentration of the grain orientations.