| The article mainly researched the influence on microstructure,composition,mechanical properties and corrosion resistance of 35CrMo steel by Subcritical Quenching,Low Temperature Gas Multi-Elements Permeation(LGMEP)process and Sandblasting composite processes.Treated samples were analyzed for ingredients,grain size,microstructure and ferrite content,while,the microhardness,Rockwell hardness,tensile properties,impact properties,fatigue properties were also tested.We also analyzed the neutral salt spray corrosion resistance and electrochemical corrosion resistance.Composition and microstructure on surface of samples after electrochemical corrosion were observed in detail.Comprehensive properties of materials by different composite processes were tested.Results of XRD test and microstructure analysis showed that,subcritical quenching could refine material organization,remain some undissolved ferrite.The surface of samples after subcritical quenching and LGMEP mainly formed Fe3N,Fe3O4,CrN compounds.Samples from outer to inner constituted by oxide layer,compound layer,transition layer and matrix structure.Part of compound layer consisted of columnar crystals,other part of that next to the oxide layer were punctuate loose zone,matrix structure were fine sorbite and dispersed ferrite,which was the same as that of subcritical quenching + tempering organization.Mechanical test results showed that,combination of subcritical quenching and LGMEP process could obviously improve surface hardness,tensile strength and fatigue properties other than impact toughness.Adding sandblasting process between subcritical quenching and LGMEP process could improve both hardness and strength of samples,but decrease toughness.Corrosion test results showed that,corrosion resistance of 35CrMo steel after LGMEP developed a lot,the time to resiste neutral salt spray corrosion could increased a lot.Also electrochemical corrosion resistance developed significantly for improvement of self-corrosion potential,ba and existence of passive zone.We had found the "breakdown point" during electrochemical corrosion,the value of the point,disparity between breakdown point and self-corrosion potential could represent of corrosion resistance of material.Corrosion degree and corrosion morphology were not identical in different areas of specimen after electrochemical test,pitting corrosion rather than homogeneous corrosion occurred in specimen by LGMEP process,and more,pitting did not happen instantaneously,but a gradual process of change.Distribution of elements in different corrosion areas showed some rules.Electrochemical corrosion mechanism of samples changed significantly due to the LGMEP.Both oxide layer,compound layer played roles in protecting materials from corrosion.We also built corrosion model based on corrosion phenomenon.Generally speaking,using LGMEP process instead of tempering to treat 35CrMo steel is entirely feasible,which could significantly improve mechanical properties and corrosion resistance.Adding sandblasting Between LGMEP and subcritical quenching could strengthen 35CrMo steel more.Both the two processes could meet requirments of material in different ways,and have advantages such as saving time,energy and environmental.The composite processes have a broad application prospects,which is also a reference when treat other materials. |
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