| In the production process of hot rolling of stainless steel strip,the surface will inevitably produce oxide scale.In order to eliminate the influence of the oxide scale on the deformation of the substrate and reduce its wear on the equipment,the surface oxide scale must be removed before cold rolling or post-processing(referred to as descaling).The traditional descaling method is mainly based on the pickling method,but with the continuous improvement of the country’s environmental protection requirements for industrial production,acid-free descaling technology has attracted wide attention due to its unique advantages of environmental protection and pollution-free.However,due to the wide variety and complex structure of oxide scale,the cracking and peeling performance of oxide scale is not clear enough.As a result,the process parameters in acid-free descaling mainly rely on on-site experience,and the descaling efficiency is low.Therefore,this paper explores the mechanical properties and interlayer and interface bonding properties of 304 L hot-rolled stainless steel oxide scale through molecular dynamics simulation,tensile test and scratch test combined with acoustic emission technology.The main contents include:(1)The fracture process of the oxide scale under the action of tensile stress and compressive stress is analyzed,and the interfacial shear strength model of the oxide scale/substrate under the action of tensile stress is established according to the relevant theory of hard coating.At the same time,the bond strength models between oxide scale layers and oxide scale/substrate interface under the action of scratches are also established.(2)Tensile tests were carried out on 304 L hot-rolled stainless steel.Through the time domain analysis of the acoustic emission signal during the tensile process,it was found that the failure process of the surface oxide scale was roughly divided into three stages: the microcrack initiation stage,the crack propagation caused by the crack propagation.The macroscopic crack stage and the oxide scale exfoliation stage caused by the boundary crack.Through the frequency domain analysis of the acoustic emission signal,it is found that different peak frequencies can characterize the damage mechanism of the oxide scale at different failure stages.Finally,the critical cracking strain for the initiation of oxide scale cracks is calculated to be 0.227%,and the interfacial shear strength of oxide scale/matrix ranges from 126 to 145 MPa.(3)Scratch test and acoustic emission were used to study the properties of the oxide scale on the surface of 304 L stainless steel,analyze the different peeling evolution processes of the scale in the rolling direction and the width direction,and calculate the interlayer and interface bond strength ranges of the oxide scale,respectively: 114～155MPa and 112～121MPa.(4)Perform indentation tests on the Fe O layer of 304 L stainless steel at different pressing rates and positions to measure its mechanical properties,and establish an indentation model with the help of molecular dynamics for simulation analysis to study the indentation force,dislocation,potential energy,stress,The effect of strain variation on mechanical properties of oxide scale.The results show that the grain boundary and trigeminal grain boundary should be avoided as much as possible in the indentation test,and the lower pressing rate should be avoided to promote the plastic deformation of the material.And affected by the size effect,the hardness of Fe O obtained by simulation is quite different from the actual hardness value. |
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