Effects Of Deep Cryogenic Treatment On The Microstructures And Tribological Properties Of Ferrous Materials

The heat treatment,as a kind of technologies,does not change the shape of materials and improves the comprehensive performances by changing the microstructures of materials.And it has played an important role in the mechanical manufacturing process.The cryogenic treatment is an extension of conventional heat treatment,can further explore the potential of internal materials and improve the mechanical properties and service life of materials.And cryogenic treatment has received wide attention all over the world because of its advantages of simple operation,no pollution and low price as well.To obtain the best cryogenic treatment process,the effects of cryogenic treatment on the microstructures and tribological properties of ferrous metal materials of 310S stainless steel,powder metallurgy iron-based self-lubricating materials and CrWMn die steel have been studied in this paper.And the relative tribological mechanism is also discussed.The main contents are as follows:(1)The effects of cryogenic treatment on the microstructure and corrosion resistance of 310S stainless steel in 0.5M H2SO4 solution and 3.5wt%NaCl solution are investigated.The results show that after deep cryogenic treatment,the iron lattice shrinkage,grain refinement,more carbide precipitation will happen in the 310S stainless steel.And corrosion resistance of materials with cryogenic treatment increased first and then decreased and the materials have the best corrosion resistance of acid and salt after 4 h deep cryogenic treatment.The corrosion wear resistance can be improved significantly after deep cryogenic treatment and the 4 h is best cryogenic treatment time.(2)The Fe based self-lubricating materials are prepared by powder metallurgy.The matrix of the material is austenite,and Cu2S is a solid lubricating phase.The effects of cryogenic treatment on the micro-structures and tribological properties of Fe based self-lubricating materials have been studied.After cryogenic treatment,transformation from the austenite to martensite and the precipitation of carbides happens.With the extension of deep cryogenic treatment time,grain size of martensite gets smaller.After cryogenic treatment,the hardness of the materials is improved obviously,and iron-based self-lubricating materials have more excellent lubrication and abrasion resistance than original materials,and materials achieve the best the tribological properties when cryogenic treatment time reaching 8 h.(3)The effects of cryogenic treatment on micro-structures and friction and wear resistance properties of CrWMn steel have been investigated.After deep cryogenic treatment,residual austenite in die steel CrWMn transforms to martensite and the carbides precipitatie in the martensite.With the cryogenic time extension,grain size of martensite gets smaller.Wear resistance of CrWMn die steel achieve the best after deep cryogenic treatment 24 h?...