Research On The Removal Mechanism And Application Of Bearing Steel Based On The Ferrous Ion Reaction Film Regulated By Tribochemistry

As the core basic parts of high-end equipment such as high-speed railway,wind power and high-end machine tools,bearings determine the operation performance and service life of the host.With the development of the high-end equipment,the running speed,service temperature and load of bearings increase,which puts forward higher requirements for the surface quality of bearings.When the surface roughness of bearings decreases from 24 nm to7 nm,the less the cracks on the bearing surface due to machining are,and the longer the service life of bearings is.However,Chinas high-end manufacturing industry,such as basic core components,has a large gap with developed countries in Europe and the United States,which seriously restricts the independent development of Chinas high-end manufacturing industry.The end manufacturing process of bearing in China is still the traditional process relying on pure mechanical removal,such as high-precision grinding,which is difficult to achieve higher surface quality and almost zero surface and sub surface damage,thus affecting the operation performance and service life of the bearing under more severe service conditions.The essence of ultra-precision surface processing is the material surface migration process in tribological research.Therefore,in view of the shortcomings in the material removal mechanism of traditional bearing process,it is urgent to put forward a new material removal mechanism and process for bearing manufacturing,improve the bearing surface quality,meet the requirements of terminal bearing manufacturing and promote the great leap forward development of bearing manufacturing in China on the basis of enriching the nanotribology theory.In this paper,based on the tribochemical removal mechanism,the chemical mechanical polishing（CMP）process of bearing steel is developed,and the mechanism of Fe²⁺reaction film regulation and its influence on the tribochemical removal behavior of GCr15 bearing steel is deeply studied.The single high carbon chromium-bearing steel（GCr15 steel）with the largest output in bearing steel is selected as the research object.Firstly,the mechanism of reactive oxide film on the micro material removal behavior of iron under pure mechanical action is investigated from the micro point of view.Combined with CMP,the key factors affecting the tribochemical removal of iron-based materials are clarified.On this basis,the mechanism of the complexation of dicarboxylic acid regulating Fe²⁺reaction film and the effect mechanism on the tribochemical removal behavior of GCr15 bearing steel are investigated,and the efficient polishing of GCr15 bearing steel is realized.The mechanism of controlling Fe²⁺reaction film and the effect mechanism on the tribochemical removal behavior of GCr15 bearing steel are investigated,and the high-quality polishing of GCr15 bearing steel is realized.Based on the mechanism of controlling Fe²⁺reaction film by oxidation,complexation and corrosion inhibition,an efficient and high-quality two-step polishing process is proposed.In the first step,high-efficiency polishing is used to obtain nano surface roughness,and in the second step,high-quality polishing is used to obtain sub-nano surface roughness.On this basis,a more efficient one-step polishing process is proposed by acidic p H,high concentration H2O2 and oxalic acid.Finally,the immersion surface CMP method of tapered roller bearing ring raceway is proposed to realize the machining of nano surface roughness of tapered roller bearing ring raceway.The main research contents and innovations are as follows:（1）The change law of micro material removal behavior of iron under loading in vacuum environment is investigated.The structure and properties of reactive oxide film formed after polishing of pure iron are studied.The mechanism of tribochemical removal of pure iron by oxide film under pure mechanical action is revealed.On this basis,combined with CMP results,the key factors affecting the tribochemical removal of iron-based materials are clarified.With the increase of applied load,the scratch depth on the pure iron surface first increases slowly,and then increases sharply.This is mainly because the reactive oxide film formed after polishing is a layered structure with a thickness of about 2.0 nm.It can be roughly divided into outer oxide film and inner oxide film according to mechanical properties.Among them,the outer oxide film is mainly composed of Fe OOH（most likelyα-Fe OOH）and Fe2O3,with high mechanical strength,which is difficult to be removed by silica particles under pure mechanical action.The inner oxide film is mainly composed of Fe3O4,with low mechanical strength and close to that of the pure iron substrate.In pure mechanical removal,the outer reactive oxide film plays a role of hindering material removal.In addition,in CMP,the mechanical strength of the reaction oxide film is much higher than that of colloidal silica.The material removal of pure iron can be realized by adjusting the reactive oxide film through chemical action.In situ chemical corrosion enhanced mechanical wear plays a leading role in the tribochemical removal of pure iron,and the regulation of reaction film is the key of tribochemical removal.（2）The effects of carbon chain length and p H value of dicarboxylic acid on CMP of GCr15 bearing steel are investigated.The mapping relationship between the synergistic effect of oxidation（hydrogen peroxide）,complexation（dicarboxylic acid）and p H in tribochemical reaction and the material removal rate（MRR）and the surface roughness Ra of GCr15 bearing steel is established.The mechanism of the complexation of dicarboxylic acid regulating the Fe²⁺reaction film and the tribochemical removal behavior of GCr15 bearing steel are revealed.An efficient polishing method of GCr15 bearing steel is proposed.The Fe²⁺reaction film is formed rapidly under the conditions of acidic p H and low concentration H2O2.As the carbon chain length of dicarboxylic acid becomes shorter,the MRR of GCr15 bearing steel increases.On the one hand,due to the complexation ability of monohydrogen anions of dicarboxylic acids is greater than that of neutral molecules and dianions,the proportion of monovalent anions gradually increases with the shortening of carbon chain length,which improves the complexation ability.On the other hand,due to the shortening of the carbon chain length of dicarboxylic acid,the complexation ability of anionic or neutral molecules is enhanced,and the Fe²⁺reaction film is more and more easy to dissolve,which promotes the tribochemical removal behavior.In addition,as the p H value decreased from 10.0 to 4.0,the MRR and surface roughness Ra of GCr15 bearing steel gradually increased.This is mainly due to the decrease of p H value and redox potential,resulting in the gradual transformation of insoluble and dense Fe³⁺reaction film into soluble and loose Fe²⁺reaction film.The oxide film changes from dense to porous,which enhances the tribochemical removal behavior.The use of low concentration H2O2,short carbon chain length complexing agent and acidic p H value can promote the rapid formation and dissolution of Fe²⁺reaction film,form soluble complexes that can be easily removed on the surface of GCr15 bearing steel,and then realize the efficient polishing of GCr15 bearing steel.（3）The effects of nitrogen-containing heterocyclic compounds and nitrogen-containing and sulfur-containing heterocyclic compounds on the CMP of GCr15 Bearing Steel under different environments（different concentrations of hydrogen peroxide and p H value）are investigated.The mechanism of 5-methyl-benzotriazole（5-methyl-BTA）and thiazole corrosion inhibition regulating Fe²⁺reaction film and affecting the tribochemical removal behavior of GCr15 bearing steel are revealed.The mechanism of the ternary passive film formed by hydrogen peroxide,5-methyl-BTA and thiazole in the tribochemical removal behavior of GCr15 bearing steel is clarified.A high-quality polishing method of GCr15bearing steel is proposed.With the high concentration H₂O₂,the soluble Fe²⁺is further oxidized to insoluble Fe³⁺,forming a dense oxide layer,isolating the solution from the GCr15 bearing steel substrate,physically hindering the oxidation of soluble Fe²⁺by Fe⁰ and inhibiting the tribochemical removal behavior.Compared with a single inhibitor,the synergistic effect of 5-methyl-BTA and thiazole can achieve lower surface roughness Ra at less dose.This is mainly due to the formation of a triple passive film composed of oxide film and composite corrosion inhibition film on the GCr15 bearing steel surface.5-methyl-BTA is mainly adsorbed on the GCr15bearing steel surface through chemical action to inhibit the oxidation of Fe⁰ to soluble Fe²⁺,and improve the corrosion resistance and corrosion induced wear threshold of Fe²⁺in the recessed area of the asperities of GCr15 bearing steel to protect soluble Fe²⁺.Thiazole is mainly adsorbed on the GCr15 bearing steel surface through physical action as a supplement to 5-methyl-BTA to further improve the corrosion resistance and corrosion induced wear threshold of Fe²⁺in the recessed area of the asperities of GCr15 bearing steel.The dense oxide film and composite corrosion inhibitor film form a triplet passivation film on the GCr15 steel surface,and the concave area on the bearing steel surface forms a complete passivation film under the low-frequency action of low mechanical force,which inhibits corrosion dissolution and improves the energy threshold of surface material removal;The convex area is difficult to form a complete passive film under the high-frequency action of high mechanical force,and is preferentially removed,so as to realize the high-quality polishing of GCr15 bearing steel.（4）Based on the mechanism of controlling Fe²⁺reaction film by oxidation,complexation and corrosion inhibition,a two-step polishing process is proposed.The first step is to obtain nano surface roughness by high-efficiency polishing,and the second step is to obtain sub nano surface roughness by high-quality polishing.On this basis,a surface CMP method for tapered roller bearing ring raceway is proposed.CMP device for curved surface is designed.The raceway of tapered roller bearing ring with surface roughness Ra less than 10 nm is realized.Aiming at the mechanism of oxidation,complexation and corrosion inhibition regulating Fe²⁺reaction film,a two-step polishing process is proposed.In the first step,high-efficiency polishing is used to quickly remove the damaged layer and obtain a smooth surface with nano surface roughness.The MRR of GCr15 bearing steel can reach 219 nm/min.After 15 min,the surface roughness Ra can be reduced from 249.3 nm to 2.7 nm.In the second step,high-quality polishing is used to further improve the surface quality and obtain a super smooth surface with sub nano surface roughness.The MRR of GCr15 bearing steel is about 42 nm/min.After 6min,the surface roughness Ra can be finally reduced to 0.8 nm,and the polished surface becomes smooth,flat and free of fine scratches.In addition,a more efficient one-step polishing process is proposed.Within 14 min,the surface roughness of GCr15 bearing steel can be reduced from 249.3 nm to about 2.0 nm,and the substrate has no damage caused by chemical mechanical polishing.In the end,a CMP method applied to bearing ring raceway is proposed,and the corresponding CMP device is designed.In this method,the tapered roller bearing ring is immersed in the slurry to ensure that the slurry can be in uniform and full contact with each point of the curved surface,solve the problem that the traditional slurry conveying method is difficult to ensure that the slurry can cover each point of the curved surface evenly,and the soft polishing pad is in close contact with the machined surface through the round platform polishing tool.By investigating the influence of mechanical effects such as polishing tool speed and abrasive particle concentration on the surface roughness of tapered roller bearing race,under the protection of complete and solid triplet passivation film,the surface roughness Ra of tapered roller bearing race is finally reduced to 7.8 nm,meeting the design requirements of high-end wind power bearing race for surface roughness Ra≤40 nm.