Preparation Of Black Film On High Nitrogen Stainless Steel And Research On Its Fricition And Wear Properties

As a key component of the country's major technical equipment,bearings are widely used in many industries such as automotive,machinery manufacturing,rail transportation,aerospace,military,etc.Their performance,accuracy,and longevity all affect the normal operation and safety and reliability of the host.Therefore,it is crucial to ensure the performance and safe use of the bearing steel.High-nitrogen stainless steel has become the best "candidate steel" for high-performance bearing preparation because of its superior strength,toughness,corrosion resistance and high temperature resistance.However,due to the problem that high-nitrogen stainless bearing steels are difficult to meet the design friction performance requirements of the bearing,this project aims to develop a surface treatment process for high-nitrogen martensitic stainless steel bearings to optimize the use of high nitrogen horses for bearing production.On the surface of the stainless steel,a protective film with anti-friction effect is formed.Due to the complex structure of the bearing components,the surface can be chemically converted,and the black oxide film has good abrasion resistance and can improve the friction and wear properties of the stainless steel surface.In this project,the chemical conversion film prepared on the stainless steel substrate by the blackening technique was used to sequentially analyze the composition of the film under different parameters by SEM and XRD,and passed through the nano indenter,scratch tester,friction and wear tester,and friction wear.The experimental machine tested the hardness,bonding strength and friction coefficient of the film under different parameters.Then the relationship between the process parameters and the structure and properties of the film was studied.Firstly,the binding force and substance of phosphate film and black film were compared and analyzed.The method of blackening was used to treat the stainless steel surface.The parameters were optimized by orthogonal test to obtain an optimal formula: H2SO4 300 m L/L,Cr O3 60 g /L,40 m L/L of H3PO4,40g/L of Mn SO4,and 40g/L of NH3NO4.Blackening time 40 min,blackening temperature 90 °C.Through the SEM,it can be seen that the microscopic coating of the blackened film is denser,there are obvious grain boundaries between the grains,and fine second phase particles are dispersedly distributed at the grain boundary.The composition analysis of the coating can be obtained.The second phase is known as a chromi?m carbide and the grain is an iron oxide.The coating thickness is about 10?m.The phase analysis of the coating shows that the coating is mainly composed of Fe O,Fe O/Mn O complexes and Mn O2.The bonding strength between the blackened film and the substrate is good,but the nano-hardness is lower than that of the substrate,and as the time increases,the nano-hardness is reduced.As the temperature rises,the hardness of the coating decreases,and the grain boundary on the surface topography becomes more distinct.The black film on the surface of the coating can significantly reduce the friction coefficient of the substrate surface,mainly because the black film has low hardness,low shear strength and good abrasion resistance.Coating temperature and time have a significant effect on the friction coefficient.When the reaction temperature is 90°C and the time is 50 min,the coating has the lowest friction coefficient and the least amount of wear.At different rotational speeds,the friction coefficient of the coating increases with the increase of the rotating speed,and the wear and oxidation wear occur at the wear marks.under different loads,the friction coefficient of the coating increases with the load in the low load range.Larger and smaller;friction wear increases with time,oxidative wear and abrasive wear,followed by adhesive wear.