Surface Modification Of MoS₂ Nano-lubricant And Its Diffusion Strengthening Mechanism On Hot Rolled Strip

During hot rolling process,the nanoparticles could form protective lubricating films on strips by physical-chemical adsorption.At the same time,they filled in the microcracks and played a surface repair role.The interface gained added energy under the condition which temperature reached 850?1150? and rolling force was very high.The diffusion between strips and the adsorbed nanoparticles were promoted.In this context,nano-lubricants were multifunctional in this paper.They were expected to strengthen surface as well as reduce friction due to the interaction between nanoparticles and strips.For conventional nano-lubrcants used for lubrication and cooling,only tribological and heat transfer properties were paid attention to.The diffusion behavior of nano-lubrcants on hot rolled strip was rarely involved.Therefore,it is necessary to study the diffusion strengthening mechanism of multifunctional nano-lubricants on hot rolled strip surface.To ensure lubrication performance and diffusion strengthening effect of the multifunctional nano-lubricants,diffusion experiment,tribological experiment and other physical-chemical characterization were employed.Qantum chemical calculation was performed using VASP module of Mede A.The lubrication performances of nanoparticles were studied from the perspective of crystal structure by calculating differential charge density,bond population and interlayer interaction energy.It was indicated that MoS2 nanosheets with higher reactivity could adsorb on the strip surface to form a lubrication film with lower shear force.Hence,their diffusion performance and lubrication effect were better,but at the same time,more serious problems of dispersion stability were also faced.To alleviate the agglomeration of MoS2 and improve dispersion stability,MD simulation was used to select surface modification based on the concept of molecular design.The reactivity of the surface modifiers in aqueous solvents and their adsorption capacity on MoS2 were calculated.The TEAS was determined as the main component of desired surface modifiers.The surface modifiers were synthesized based on the reaction of TEA and SA at 60?80 ?.Their preparation procedure was optimized by adjusting the proportion and total dosage of TEA and SA.An organic solvent layer with thickness of 15?17 nm was grafted on MoS2.According to the results of crystal structure analysis,the interlaminar distance of MoS2 sheet was increased because of the adsorption of TEAS.Both interlayer interaction energy and interlayer shear force were reduced.And the interlayer sliping was more likely to happen.MoS2 nano-lubricants were employed in rolling process.The interaction between MoS2 and strips under high pressure were analyzed by XRD,EDS,XPS and theoretical calculation.MoS2 had higher reactivity and adsorption capacity.There were complex physical-chemical reactions between MoS2 and strips.Their lubricating effects were mainly due to pressurized interlayer slip theory and synergistic lubrication of composite film.The interaction energies between atoms in MoS2 were reduced under rolling force and friction,and Mo-S bonds were partially broken.A physical adsorption film with higher adsorbability and interlayer sliding ability was formed on strip surface.Moreover,MoS2 was interacted with the strips and surrounding environment,and generated chemical adsorption of MoO3 and FeSO4.Diffusion experiment,compression test and MD simulation were conducted to study the diffusion behavior.Due to the weak diffusion ability in FeO,MoS2 only passed through Fe2O3 withoutany pressure,and diffused in FeO layer,but did not reach iron matrix.While normal pressure was applied,the diffusion ability was significantly improved,so it diffused into the iron matrix.The diffusion initiation temperature decreased from 800? to 600?.In the matrix,the diffused Mo atoms formed new complexes with the Fe atoms.It was speculated that the diffused MoS2 might affect the metallographic structure of strips during hot rolling.Therefore,hot rolling test and surface characterization were conducted.Surface morphology,oxidized scale and metallographic structure were analyzed and charactered.Wear defects on rolled surface were alleviated.Thickness of oxidized scale was decreased from 30?35 ?m to 16?18 ?m.During hot rolling,Mo diffused into matrix,which promoted the nucleation of cementite.The pearlite growth changed from single to polydirectional.Some carbide precipitates with dispersion strengthening effect also appeared around grain boundary when the concentration of MoS2 was higher than 0.4 wt.%,.In this paper,the multi-function of nano-lubricant not only provided theoretical basis for integration of lubricant and surface strengthening,but also a new path for surface strengthening.