Analysis Of Powder Lubrication Properties And Research Of Wear Behavior In Hot Forming Interface Of Ultra-High Strength Steel Plate

With the development of the automotive lightweight requirements,ultra-high strength steel plate used in hot stamping process has been gotten wide applications.The problem about lubrication between red sheet metal and die in hot forming is very important,and the traditional grease lubricant cannot achieve effective lubrication.However,the solid powder lubricant has good adaptability to lubrication of friction interface under high temperature.In order to understand the working mechanism of powder lubrication and the influence on hot-work die steel wear behavior,this paper is based on three high temperature experiments to respectively studied solid powder lubrication mechanism of high temperature interface,hot-work die steel wear behavior with powder lubrication and powder lubrication properties of direct hot stamping interface respectively.Firstly,standard high temperature friction test based on powder lubrication was designed to analyze powder lubrication properties in hot forming interface by change load,sliding velocity and method of lubrication.And friction coefficient,surface microstructure and interface contour curve can be observed.The experimental results are as followed;solid powder lubricant can achieve good lubrication basically and inhibit the oxidation of the metal surface to some extent.Lubrication layer roughness has no direct relation with lubrication effect.Low and high load affect the formation of boundary lubrication layer by different mechanisms,and the stability of the friction coefficient is weaken with the increasing of load and velocity.Uniformity of friction coefficient with multilayer lubrication is low than that with single lubrication.The properties and bond strength of solid powder lubrication have a great influence on high temperature lubrication.Then,hot-work die steel friction and wear test based on powder lubrication was developed to research the influence on hot-work die steel wear behavior deeply by observing the friction coefficient,wear surface microstructure and grinding crack contour curve.The experimental results are as followed,the wear behavior based on powder lubrication includes three stages,which are complete,undermine and completely damage lubrication film stage.Boundary lubrication layer is time-varying.The boundary lubrication layer damaged fast with load increasing,and high speed is not conducive to the stability of boundary lubrication layer.Formation-broken dynamic cycle of local lubricating film and generate-spalling dynamic circulation mechanism of wear debris always exist in wear interface.In a short period of time,die steel under powder lubrication has no abrasion basically,because a plastic accumulation layer is formed on the interface to protect the die.Finally,powder lubrication was tried to apply in industrial hot stamping test by pressing different metal sheets with different lubrication methods,which researched the applicability of powder lubrication in the field of actual thermoforming.The experimental results are as followed;something happens with surface defects under dry friction.Powder lubrication can effectively improve the surface quality,and the lubrication effect of h BN is better than that of graphite.The powder lubrication layer slips with the loading of the die,which will improve the quality of the workpiece.