| A layer of oxide scale with an extremely complex structure and properties will be produced on the surface of the hot-rolled strip.Its existence not only affects the post-processing and surface quality of the strip but also affects the service performance of the product.Therefore,the removal of the oxide scale（also known as"descaling"）after hot rolling becomes particularly important.Limited to the shortcomings of pickling descaling technology,such as strong pollution and uncontrollable surface quality,the green,pollution-free,acid-free descaling technology,such as slurry blasting and shot blasting,has attracted people’s attention.However,the most critical factor in this kind of technology is to understand and master the cracking behavior and mechanical properties of the oxide scale.In this paper,indentation and scratch tests were used to study the effects of different rates on the failure of oxide scale,and the bonding properties of oxide scale and matrix were analyzed.The effects of different indentation and scratch rates on the mechanical properties and deformation behavior of single crystal Fe/FeO at the nanometer scale were investigated by molecular dynamics simulation,and the effects of porosity on the results of nanoindentation were analyzed.The main studies are as follows:1.The effect of different indentation and scratching rates on the rupture behavior and mechanical properties of 430 stainless steel oxide scale was studied by nanoindentation and micron scratching test methods.The measured hardness values increased from 8.06 GPa to 8.24 GPa and the modulus of elasticity increased from 100 GPa to 109 GPa when the indentation rate increased from 100 to 250μN·s-1.The measured bond strengths of the oxide and the substrate were distributed between 14 and 16 MPa,and the bond strengths increased from 0.5 to 2.0 N/min.The bond strengths were 15.4,15.2and 14.1 MPa when the scratch rate increased from 0.5 to 2.0 N/min,respectively.2.The effect of indentation rate on the deformation behavior and mechanical properties of single crystal FeO/Fe was analyzed based on molecular dynamics.The effect of the indentation rate on the variation of FeO/Fe interface was analyzed by means of load-displacement curve,CSP value,dislocation and phase transformation,hardness value,elastic modulus value,etc.The atomic scale reveals that the increase in the indentation rate does not allow the dislocations to expand in time,leading to the stress concentration phenomenon,resulting in an increase in the hardness value from5.49 to 6.53 GPa and in the elastic modulus value from 202 to 237 GPa.In addition,it is confirmed that the interatomic force at the FeO/Fe interface are weak and have the effect of impeding the atomic motion.The experimental and simulated results are consistent in terms of trends,but there are numerical errors in the indentation force,hardness and elastic modulus due to the scratch rate,scale and the model itself.3.The effects of porosity（0%～5%）on the deformation behavior and mechanical properties of single-crystal Fe/FeO were investigated from two perspectives of pore size（model I）and number of pores（model II）based on molecular dynamics.The trends of load-displacement curves,CSP values,atomic displacements,phase transitions,degree values,elastic modulus values,and hydrostatic stress values and Von Mises stress values were compared for different porosities.The hardness values of models I and II decreased from5.92 GPa in Perfect to 3.28 GPa and 4.66 GPa,respectively.In addition,the average hydrostatic stress value and the average Von Mises stress value decreased in model I with increasing porosity,while the stress change in model II was not obvious,both of which indicated that the pore size had a stronger softening effect on the material compared to the number of pores.4.The deformation behavior of the FeO/Fe structure under the scratching action was simulated from the atomic scale based on molecular dynamics.The effects of scratch rate on FeO/Fe were analyzed from multiple perspectives such as CSP,atomic displacement,temperature,and potential energy.With the increase of the scratching rate,the degree of atomic disorder,energy,temperature,and potential energy all increase,leading to a significantly earlier interface separation,which exactly corresponds to the earlier time point of oxide rupture with the increase of the scratching rate in the scratching test.The bonding properties of FeO/Fe in the oxide scale were analyzed by means of indentation,scratch test and molecular dynamics simulation.The deformation behavior and bonding properties of FeO/Fe in different states were obtained,and the mechanical properties of FeO and other extremely rare parameters were obtained.This is helpful to study the rupture of the oxide scale and the separation of the oxide scale from the matrix,as well as to determine the acid-free descaling process parameters and the promotion of descaling technology. |
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