Study On Characteristics And Influence Mechanism Of Structural Steel Surface Morphology In Pre-stress Hardening Grinding

The pre-stress hardening grinding combines with pre-stress grinding and surface hardening,it uses a compound machining approach to substitute conventional grinding process.This topography is thought to be a new technology with development prospects,which can not only simplify working process,improve production efficiency and protect the envrionment,but also control the distribution of residual stress and reduce the surface roughness.Based on the grinding principle,metallography and heat treatment,material science,dislocation and the phase transformation theory as the research foundation,the grinding temperature and residual stress models are built in pre-stress hardening grinding process.Mathematical model of wheel surface and workpiece surface are built.Besides,the dynamic recrystallization(DRX)behavior during pre-stress dry grinding is analysed though simulations and experiments.The characteristics and influencing mechanism of surface microtopography,effect of temperature and pre-stress on surface microtopography and effect of DRX on grain size become the focus of research.The main contents of dissertation are summarized as follows:(1)In order to analysis influence mechanism of process parameters(pre-stress,grinding depth and feed speed)on the surface roughness,the pre-stress hardening grinding experimental work is carried out and specimen surface roughness of different parts is measured.According to the experimental results of hardness distribution and the corresponding relationship between hardness and surface roughness,the general law between the two is analyzed.The inherent relationship between pre-stress and surface roughness is further revealed by the effect of pre-stress on phase transformation,surface microcracks and coating.(2)Study on the grinding temperature field which has important influence on the surface topography though finite element simulated.Heat transfer model and heat distribution ratio in the grinding process are determined and the contact area between grinding wheel and specimen is assumed to be parabolic type moving heat source.The instantaneous temperature distribution curves at different locations and depths were obtained.The relationship between the change of temperature field and the surface microtopography is analyzed by the finite element model.Combined with the result of temperature field distribution,established the residual stress simulation model and studied the influence of the residual stress distribution on the surface microtopography.(3)Based on FFT and Johnson transformation method,the wheel surface topography of the non Gauss distribution is established.It has a skew and kurtosis which differents Gauss distribution is more similar to the actual abrasive grain distribution on the wheel surface.Considering the influence of grinding temperature and pre-stress,a simulation model of workpiece surface micromorphology is established combining the motion equation between abrasive particles and workpiece.The surface micromorphology of the specimens under different prestress shows that it has the same trend with the simulation results,which is the surface roughness decreases with the increase of prestress.(4)Based on dislocation theory in microstructure evolution,presented and studied the dynamic recrystallization behavior in the process of pre-stress hardening grinding which combined with the experiment of pre-stress hardening grinding and temperature characteristics of contact zone.The pre-stress hardening grinding process of 45 steel was simulated on the DEFORM-3D platform,and the CA module was used to simulate the dynamic recrystallization volume fraction,grain size and microstructure evolution of the material.The mathematical model parameters of DRX(dislocation density,dynamic recrystallization nucleation and growth model)were determined by multiple linear regression analysis of the rheological stress data.The nucleation mechanism and microstructure evolution of DRX are studied by experiments,and the intrinsic relationship between the DRX and the surface roughness is discussed.