Research On The Damage Evolution Of Induction Hardened Layer Of Remanufactured Blanks

Printing press is a kind of high-precision equipment in the field of modern machinery.Gears are the key parts and components to ensure the normal operation of printing presses,and they are also the most numerous parts in printing press equipment,which are vital to the quality of printed products.In order to improve the mechanical properties and service life of gear parts,surface treatment technology is generally used in engineering to form a strengthening layer on the surface of the parts,but for the components for remanufacturing,with a history of serving the existence of strengthening layer makes the crack propagation is more complicated,It poses a greater challenge to remanufacturing.Induction hardening is a common surface strengthening technology,this paper,taking 42CrMo steel gear as the research object,through regulating the induction hardening time have different depth of hardening layer,research materials internal microstructure and mechanical properties of evolution,to explore the bending fatigue life and the relationship between the depth of hardening layer,combined with the crack initiation and extension of the remanufacturing process reasonable removal depth to provide the reference.This paper mainly carries out the following studies:1.The UHF GCT-1200 vertical induction quenching machine was used to carry out induction quenching treatment on the samples with different processes,and two kinds of hardened layers of 0.60mm and 1.42mm depth were obtained.The surface of the sample is fine tempered martensite structure.With the increase of depth,fine pearlite structure gradually appears.The transition zone consists of tempered martensite,pearlite and ferrite,and the matrix structure is a mixture of ferrite and pearlite.The surface hardness of the samples containing the hardened layer is increased obviously,and a large residual compressive stress is introduced on the surface of the samples,and the residual compressive stress reaches the maximum on the secondary surface.The relationship between the residual stress relaxation and IgN of the sample containing the hardened layer during service is exponential.After establishing the mathematical model,it is found that the influence of the depth of the hardened layer on the residual stress relaxation is greater than the influence of the load on the residual stress relaxation.2.The GPS-200 high frequency fatigue testing machine was used to carry out three-point bending fatigue tests on quenched and matrix samples.The fatigue life analysis of three kinds of samples showed that the larger the load was applied,the shorter the fatigue life was.and the deeper the hardened layer was.the shorter the life was.The S-N curves of the three samples all show a nonlinear relationship.After processing the data,it is found that the fatigue life has an obvious linear relationship with IgN.3.Scanning electron microscopy(SEM)was used to observe the fracture of the sample.It was found that the crack originated at the corner of the matrix sample,and obvious cracks were observed on the subsurface.With the increasing of the load,the crack sources increased and gradually approached the center area.The sample containing the hardened layer is inductively quenched,forming a strip zone parallel to the surface of the sample,which is both the crack source zone and the crack propagation zone.The crack of the sample containing the hardened layer propagates in two directions,namely transverse propagation along the hardened layer and scattering propagation to the inside.4.When the depth of hardened layer is constant,with the increasing of load,the source zone and propagation zone of crack decrease gradually,and the fatigue life decreases gradually.When the load size is constant,the sample with deeper hardening layer depth has smaller crack source zone and propagation zone,and shorter fatigue life.This is because in the process of induction quenching,the sample with shallower surface quenching speed and cooling speed are faster,the surface grains are finer,and larger residual compressive stress is introduced.Through the analysis,it is found that the relationship between the boundary distance between the extension zone and the transient fault zone and the time can be divided into two stages.The first stage accounts for 7.2%of the total.By fitting the relationship between the distance and time,the mathematical model of how to deal with the depth of strengthening layer is obtained.